BR112019013173B1 - MONITORING, DOWNWELL DEVICE OPERATION, COMMUNICATION REPEATER, AND DOWNWELL ENERGY COLLECTION SYSTEMS HAVING METALLIC STRUCTURE CONDUCTING ELECTRICAL ENERGY - Google Patents

Abstract

The present invention relates to the collection of electrical energy and downhole communication in systems for well installations having a metallic structure conducting electrical current, for example, CP current. In some cases, there is a collection module (4) electrically connected to the metallic structure (2) at a first location and at a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to the electric current flowing in the structure (2); and the collection module (4) being arranged to collect electrical energy from the electrical current. In addition or alternatively, there may be a communication apparatus (4, 5, 6) for communication via current modulation, for example CP current, in the metallic structure (2).

Description

[0001] The present invention relates to downhole energy collection. In a particular case it refers to methods and systems for powering a downhole device in a well installation having a metallic structure provided with cathodic protection. The invention also relates to methods and systems incorporating energy harvesting methods and systems as well as apparatus for use in such methods and systems.

[0002] There is a general desire to be able to extract data from oil and/or gas wells as well as control devices in oil and/or gas wells such as valves - for example, subsurface safety valves.

[0003] However, providing power to such downhole devices represents a challenge. There are some circumstances where power can be provided directly from the surface via a cable or devices can be powered directly from the surface using hydraulic power. However, in other circumstances these power distribution methods are not appropriate. In some circumstances the use of batteries becomes an option. However, this in itself poses challenges particularly in the downhole environment where relatively high temperatures tend to lead to shorter battery life.

[0004] In this way it is desirable to provide alternative power sources for downhole devices that can be used in circumstances where distribution of power from the surface via a cable or hydraulically is difficult, impossible or undesirable while avoiding the limitations that are encountered if relying on battery power. It is also desirable to provide alternative methods for communication between downhole locations and other downhole and/or surface locations.

[0005] In the present report the expression surface comprises the land surface in a land well where a wellhead will be located, the sea floor in a subsea well and a wellhead deck on a platform. It also comprises locations above these locations where appropriate. In general, “surface” is used to refer to any place convenient for application and/or capture of energy/signals, for example, that is outside the wellbore.

[0006] According to a first aspect of the invention, a downhole electrical energy collection system is provided for collecting electrical energy in a well installation having a metallic structure conducting electrical energy, the system comprising: a connected collection module electrically to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to an electrical current flowing in the structure; and the collection module being arranged to collect electrical energy from the electrical current.

[0007] The well installation can be one with cathodic protection so that the electrical current is cathodic protection current. Although the present technique can be used in a system where current is specifically applied to the downhole structure for use in power distribution, it has been understood that it is possible to harvest power from cathodic protection systems and that it is particularly preferred if the power can be collected from currents that are already present.

[0008] The second location will generally be a downhole location.

[0009] In some cases the connection to the second location may be a connection to the formation via an electrode. More typically, however, the collection module will be connected to the metal structure at the first and second spaced locations.

[0010] Such systems and methods are advantageous because power can be provided to a downhole device without having to provide a separate power source. Furthermore, power can be supplied without having to rely on local batteries which will tend to have a limited life and can be supplied without having to provide a cable that penetrates through the wellhead. Similarly, these techniques can be implemented without using toroids to inject or extract signals. This can reduce the complexity and technical issues that will incur when implementing a system.

[0011] The collection module may be arranged to collect electrical energy from dc currents.

[0012] Preferably the current flow within the portions of the metallic structure in regions between the first location and the second location is in the same longitudinal direction.

[0013] Preferably there is an uninterrupted current flow path between the first location and the second location that is at least partially through the metallic structure.

[0014] These represent characteristics that will generally be present in an installation unless modification is made to the configuration. The present ideas generally do not require modifications to the standard configuration of the well installation as a whole, that is, they are intended to work alongside a standard installation.

[0015] The collection module can be electrically connected to the metal structure at the second location.

[0016] Each or every connection to the metal structure can be made to a course of metal elongated members/a course of metal tube.

[0017] In a set of embodiments the spaced locations may be axially spaced. Connections may be made to a common course of metallic elongated members, for example, a common course of metallic pipe that is part of the metallic structure. The highest surface of the two spaced locations may be adjacent to the location of a casing support provided in the wellbore. Often this will represent the highest practical location for the highest location. In some cases the upper connection can be made to a riser.

[0018] In this way, for example, the connections can both be made to the production piping provided in the well, or both made to a first course of well casing pipe separated by a first ring, “A”, from the production piping. , or both made to a second course of well casing pipe separated by a second ring, “B”, from the first course of well casing pipe, or so on.

[0019] In other cases, axially separate connections can be made to different courses of metallic elongated members, for example, different courses of metallic tube with similar results, but it is generally more convenient to make the connections to the same course of metallic elongated members/tube metallic if there is no reason to do otherwise.

[0020] Where spaced locations are axially spaced and there is dependence on this for there to be a potential difference between them, the spacing between locations is likely to be considerable - typically 100 m or more. More preferably 300 m to 500 m.

[0021] The electrical connection to the metal structure in the first location may be a galvanic connection.

[0022] The electrical connection to the metal structure at the second location may be a galvanic connection.

[0023] The collection module can be positioned in one or more of external to the elongated well members, inside a well ring and inside an internal wellbore.

[0024] Connection to at least one of the first and second locations may be via a cable running along the metal structure.

[0025] Preferably if the second spaced contact is made with the at least one course of metallic elongated members then the electric current flowing in the at least one course of metallic elongated members where the first contact is made flows in the same longitudinal direction as the electric current flowing in at least one course of metallic elongated members where the second contact is made.

[0026] Preferably if the first spaced contact and the second spaced contact are both made with the same course of metallic elongated members, this course of metallic elongated members is continuously conductive between the first and second locations.

[0027] At least one connection between the at least one of the electrical contacts and the collection module can be provided by an insulated cable.

[0028] The cable can be selected to have a conductor with a relatively large cross-sectional area. When selecting a cable the objective is to choose a cross-sectional area that is large enough to allow the desired level of collection - one that provides low enough resistance in the cable.

[0029] Preferably the insulated cable has a conductive area of at least 10 mmA2, preferably at least 20 mmA2, more preferably at least 80 mmA2.

[0030] The cable can be a conductor encapsulated in tubing.

[0031] One of the connections can be made without an external cable. One of the connections can be made through a conductor housing or surrounding the collection module.

[0032] Typically there will be an optimal spacing between connections. The greater the spacing, the greater the potential change between the contact locations, but also the greater the resistance of the cable. The method may comprise determining an optimal spacing between the spaced locations. This can be determined by modeling a particular installation.

[0033] The spacing between locations can be at least 100 m.

[0034] In another set of embodiments the spaced locations may be radially spaced. A first of the connections may be made to a first course of metallic elongate members, for example, a first course of metallic tube that is part of the metallic structure, and a second of the connections may be made to a second, distinct course of metallic elongated members. , for example, a second, distinct course of metal tube that is part of the metal structure. In this way, the connection can be through a ring defined by two courses of metal tube.

[0035] For example, a connection may be made to the production piping provided in the well and one to a first course of well casing pipe separated by a ring, “A”, from the production piping, or a connection may be made to a first course of well casing pipe provided in the well and to a second course of well casing pipe separated by a second ring, “B”, from the first course of well casing pipe, and so on.

[0036] In some cases the spaced locations may be both axially spaced and radially spaced.

[0037] Connections can be made to a common course of metallic elongated members that is part of the metallic structure.

[0038] In some embodiments, a first of the connections is made to a first course of metallic elongated members that is part of the metallic structure and a second of the connections is made to a second, distinct course of metallic elongated members that is part of the metallic structure. .

[0039] Insulating means may be provided for electrical isolation of the first course of metallic elongated members from the second course of metallic elongated members in the connection region.

[0040] Insulating means may be provided for electrical isolation of the first course of elongated members/metallic tube from the second course of elongated members/metallic tube in the region of at least one of the connections. This can help ensure that there is a potential difference between the lengths of elongated members/metallic tube at the locations where connections are made. This being due to the different path to land seen from each limb/tube course.

[0041] Note that in the present techniques the currents from which energy is collected will generally be flowing in the same direction in the first and second courses of elongated metal members/tubes. In this way the isolation is not provided to form a separate return path, but rather to alter the path to land for one of the courses in relation to the other.

[0042] The insulation means may comprise an insulation layer or coating provided on at least one of the courses of elongated members/metal tube. The isolation means may comprise at least one isolation centralizer for keeping the courses of elongated members/metallic tube separate from each other.

[0043] Insulating means may be provided to prevent electrical contact between the two courses of elongated members/metallic tube for a distance of at least 100 m, preferably at least 300 m.

[0044] At least one of the connections may be located within the isolation region. Both connections can be located within the isolation region. At least one of the connections may be located toward a midpoint of the isolation region. The location of at least one of the connections can be determined by modeling a particular installation to determine an optimal location which is then selected.

[0045] The collection module may be provided in the hole of a central course of tubing, in a ring or outside the well casing tube - between the well casing tube and the formation. In this way, among other possible locations, the collection module can be provided in the “A” ring, the “B” ring, the “C” ring, the “D” ring or any other ring.

[0046] This gives rise to the possibility of providing power in locations where it is generally not possible and/or desirable to provide cables from the surface. This is particularly useful for subsea wells. Yet this is possible without relying on the use of primary batteries or other local energy sources, and so there is a possibility of “well life” energy provision in such locations.

[0047] The collection module may comprise a variable impedance means for varying the load seen between the two connections. The variable impedance medium can be controlled by microprocessor.

[0048] The variable impedance means can be used to vary the load in order to optimize energy collection.

[0049] The variable impedance means can be used to modulate the charge in order to communicate data from the collection module towards the surface.

[0050] Downhole communication means can be provided for transmitting data from the bottom of the well towards the surface. The downhole communication means may also be arranged to receive data, for example, from the surface.

[0051] The collection module may comprise downhole communication means. In other cases the downhole communication means may be provided separately. A downhole device that is powered by the collection module may comprise the downhole communication means.

[0052] The downhole communication means may comprise variable impedance means.

[0053] Superior communication means can be provided at a location external to the hole including a detector for detecting changes in current, that is, the cathodic protection current, flowing in the metallic structure and in this way allowing extraction of coded data by modulation of the load on the collection module. For example, the detector may be arranged to detect the potential of the metallic structure relative to a reference or to detect the potential seen through; or current seen by a power source used to apply an impressed cathodic protection current to the metallic structure.

[0054] In other embodiments, instead of communication towards the surface through charge modulation, other communication techniques can be used. In general, for example, acoustic and/or EM (Electromagnetic) signaling can be used. Charge modulation is an example of EM signaling, but another, more direct means of EM signaling can be used.

[0055] The downhole communication means can be arranged to apply signals carrying acoustic data to the metallic structure and the upper communication means can be arranged to receive signals carrying acoustic data.

[0056] The downhole communication means can be arranged to apply signals carrying EM (Electromagnetic) data to the metallic structure and the upper communication means can be arranged to receive signals carrying EM data.

[0057] The upper communication means can be arranged to apply signals carrying acoustic and/or EM (Electromagnetic) data to the metallic structure, and the downhole communication means can be arranged to receive signals carrying acoustic and/or EM data .

[0058] In some cases the upper communication means and the downhole communication means may be arranged to communicate using acoustic and EM signals. This creates useful redundancy in that if one communication channel fails, the other can remain operational.

[0059] The collection module may be disposed at a selected location downhole for energy collection and a cable may be provided for supplying electrical energy further downhole to a downhole device. The cross-sectional area of the cable used to supply the electrical power downhole will typically be smaller than that of any cable used in collecting energy, and typically the power will be supplied downhole at a voltage greater than the voltage developed across closely spaced contacts due to current flowing in the metal structure, due, for example, to cathodic protection currents.

[0060] In some embodiments, the current flowing in the elongated members is supplied from the well surface.

[0061] In some embodiments the current flowing in the elongated member is supplied from one or more sacrificial anodes.

[0062] In some embodiments the current flowing in the elongated members is a current impressed from an external energy source.

[0063] In some embodiments the well surface voltage is, in use, limited to a range minus 0.7 volt to minus 2 volts with respect to a silver/silver chloride reference cell.

[0064] Preferably the potential difference between the spaced contacts is less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

[0065] Optionally the resistance of the well structure between the contacts is less than 0.1 ohm, preferably less than 0.01 ohm.

[0066] The optional location for energy collection will typically be close to the location at which currents, for example cathodic protection currents, are injected into the metallic structure.

[0067] Where the spaced locations are axially spaced, preferably the upper location is adjacent to the location at which currents, for example cathodic protection currents, are injected into the metallic structure. Note that where there is a platform structure, current, for example cathodic protection currents, can reach the downhole metal structure through a galvanic connection to the platform structure. In some cases the present techniques may include controlling the location of this connection.

[0068] The optimal location for energy collection will often be close to the wellhead where there is the greatest rate of potential change as progress is made down the well. On the other hand, a downhole device to be powered may be further down the well. In this way the collection module and the downhole device can be in different locations, in particular, different depths in the well.

[0069] In other situations, the collection module and the downhole device may be located together. The system may comprise a downhole unit comprising the collection module and the downhole device.

[0070] The upper spaced contact may be: where the well is an earth well, within 100 m, preferably within 50 m, of the earth's surface; and where the well is a subsea well, within 100 m, preferably within 50 m, of the sea floor.

[0071] The upper spaced contact may be located adjacent to a location that corresponds to a maximum in potential magnitude caused by the electrical current flowing in the structure.

[0072] The system may also comprise downhole communication means for transmitting and/or receiving data.

[0073] The downhole communication means can be arranged for data transmission by varying the load seen between the connections at the spaced locations.

[0074] According to another aspect of the invention there is provided a downhole device operating system comprising a downhole electrical energy collection system as defined above and a downhole device, the collection module being electrically connected to and arranged to supply power to the downhole device.

[0075] The downhole device may comprise a downhole sensor, for example, a pressure and/or temperature sensor. The sensor can be installed, for example, on ring “A”, “B”, “C” or “D”.

[0076] A sensor disposed in a ring or hole may be arranged to monitor a parameter in an adjacent ring or hole as well as or instead of the ring or hole in which it is located. A port may be provided through a metal frame course to permit detection in an adjacent ring or hole.

[0077] A sensor can be provided for detecting a leak in a cemented ring.

[0078] A sensor may comprise an array of sensors.

[0079] The downhole device may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0080] The communications module may comprise a downhole communications repeater. This can be a repeater for acoustic communication or EM communication including wireless EM communication and cable EM communication or for a hybrid communication system. For example, the repeater can receive acoustic signals from the bottom of the well and signal toward the surface using EM communication or vice versa. Similarly both acoustic and EM communications can be used in one or both directions. EM signaling can be achieved by applying electrical signals to the bottom of the well or modulating the load on the collection module as described above. EM signaling can be at least partially along cables as mentioned above.

[0081] Where the downhole device is a repeater or a transceiver, the system can be pre-installed in a well installation to make the well “wireless ready”. That is, the system may be installed to provide a wireless communication backbone although the communication ability may not be used initially. Here again wireless refers to at least one leg being wireless in the communication channel, other legs can be via cable.

[0082] In other situations the system can be retrofitted.

[0083] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0084] Note that each device may be a remotely controlled device which may be a wireless controlled device, for example, in the sense that where controlled from the surface there is at least one wireless leg in the communications channel. Other legs may be via cable, for example between a sensor location and the collection location.

[0085] EM signaling can be using dc or ac signals and appropriate modulation schemes. The collection module may comprise a dc to dc converter for collecting energy from the cathodic protection currents or other current present. The collection module may comprise an energy storage device for storing collected energy. The energy storage device may comprise a charge storage device which may comprise at least one capacitor and/or at least one rechargeable battery. Where there is an energy storage medium, the collection module may be arranged to selectively supply energy from the storage device or directly from the collected energy. This selection can be made based on predetermined conditions. Alternatively there may be no energy storage device and the collection module may be arranged to supply energy continuously when required.

[0086] A primary battery may also be provided in the collection module for selective use.

[0087] The dc to dc converter may comprise a Field Effect Transistor arranged to form a resonant scaling oscillator. The dc to dc converter may include a stepping transformer and may include a coupling capacitor.

[0088] The collection module may be arranged to control the turns ratio of the stepping transformer to modify the load generated by the dc-dc converter. A secondary winding of the scaling transformer may comprise a plurality of taps and/or the scaling transformer may comprise a plurality of secondary windings and the pickup module may be arranged to select windings and/or taps to provide a ratio of laps desired. A microprocessor controlled switch can be used to select taps and/or windings.

[0089] According to another aspect, a downhole unit is provided comprising a collection module as defined above and at least one device arranged to be powered by the collection module.

[0090] One or more of the sensor module, the communication module and the collection module may be provided in the ring - for example, in the “B” ring or the “C” ring or another ring. The sensor module and the collection module may be provided as part of a common downhole unit, however more typically they will be separated so that the sensor may be located deeper than the collection module.

[0091] The downhole device may be provided in a location other than the location of the collection module in the well.

[0092] The collection module may be arranged at a selected location downhole for energy collection and a cable may be provided for supplying electrical power deeper in the wellbore to the downhole device at a different location in the wellbore .

[0093] The cross-sectional area of the conductive core, or cores, of the cable used to supply the electrical energy deeper in the well may be smaller than that of the cable used to connect the collection module to the downhole structure for collection of energy.

[0094] According to another aspect of the invention, a downhole well monitoring system is provided for monitoring at least one parameter in a well installation having a metallic structure conducting electrical current, the system comprising: a collection system of electrical energy as defined above; a sensor module for capturing at least one parameter; and a communication module for sending data encoding readings from the sensor module to the surface, the electrical energy collection system being arranged to provide electrical energy to at least one of the sensor module and the communication module.

[0095] According to another aspect of the invention, a downhole well monitoring system is provided for monitoring at least one parameter in a well installation having a metallic structure conducting electrical energy, the system comprising: a sensor module to capture at least one parameter; a communication module for sending data encoding readings from the sensor module toward the surface; and an electrical energy collection system comprising a collection module electrically connected to the metallic structure at a first location and a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a difference in potential between them due to an electric current flowing in the structure; and the collection module being arranged to collect electrical energy from the electrical current, the electrical energy collection system being arranged to supply electrical energy to at least one of the sensor module and the communication module.

[0096] The system may comprise at least a first length of cable for connecting the collection module to one of the spaced locations.

[0097] The system may comprise at least a second length of cable for supplying power from the collection module to the sensor module.

[0098] The cross-sectional area of the conduction portion of the first cable length may be greater than the cross-sectional area of the conduction portion of the second cable length.

[0099] The communication module may be arranged to modulate the electrical current flowing in the metal structure at a signaling location so as to encode data to allow extraction of the data at a reception location remote from the signaling location by detecting the effect of said modulation on the electrical current at said reception location.

[0100] The well monitoring system may comprise a detector for detecting the effect of said modulation on the electrical current at said reception location to extract the encoded data.

[0101] The communication module can be arranged to control the charge generated by the collection module to cause said modulation of the electrical current in the metallic structure at the signaling location.

[0102] The sensor module may comprise a pressure sensor.

[0103] The pressure sensor can be arranged to monitor the well reservoir pressure.

[0104] The pressure sensor can be arranged for monitoring the pressure in a well ring.

[0105] The pressure sensor can be arranged to monitor the pressure in a closed well ring.

[0106] According to another aspect of the invention there is provided a downhole communication repeater system for use in a well installation having a metallic structure conducting electrical current, the system comprising: an electrical energy collection system as defined above ; and a communications repeater disposed at the bottom of the wellbore and arranged for communication with a first device beyond the wellhead using a communication channel that is at least through the wellhead and arranged for communication with a second device located at the wellhead. well and then below the wellhead so that the communications repeater can act as a repeater between the first and second devices, the electrical energy collection system being arranged to supply electrical energy to the communications repeater.

[0107] According to another aspect of the invention, a downhole communication repeater system is provided for use in a well installation having a metallic structure conducting electrical current, the system comprising: a communications repeater arranged at the bottom of the well in the wellhead and arranged for communication with a first device beyond the wellhead using a communication channel that is wireless at least through the wellhead and arranged for communication with second device located in the wellhead and then below the wellhead so that the communications repeater may act as a repeater between the first and second devices; and an electrical energy collection system comprising a collection module electrically connected to the metallic structure at a first location and a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a difference in potential between them due to the electric current flowing in the structure; and the collection module being arranged to collect electrical energy from the electrical current, the electrical energy collection system being arranged to supply electrical energy to the communications repeater.

[0108] It will be understood that reference herein to a first device beyond the wellhead refers to one on the other side of the wellhead other than the second device that is in the wellhead such that communication through the wellhead is desired. . Finally, the first device should be located almost anywhere, whether near the wellhead or in a remote location, as long as appropriate communications are provided.

[0109] The communications repeater may be arranged to modulate the electrical current flowing in the metal structure at a signaling location so as to encode data to enable extraction of the data at a reception location remote from the signaling location by detecting the effect of the said modulation on the electrical current at said reception location.

[0110] The communications repeater and/or collection module may be provided in a ring - for example, the “B” ring and the “C” ring or another ring.

[0111] The communications repeater and collection module may be provided as part of a common downhole unit.

[0112] The system may comprise at least a first length of cable for connecting the collection module to one of the spaced locations.

[0113] The system may comprise at least a second length of cable for supplying power from the collection module to the communications repeater.

[0114] The cross-sectional area of the conduction portion of the first cable length may be greater than the cross-sectional area of the conduction portion of the second cable length.

[0115] The downhole communication repeater system may comprise a detector for detecting the effect of said modulation on the electrical current at said reception location to extract the encoded data.

[0116] The communications repeater can be arranged to control the charge generated by the collection module to cause said modulation of the electrical current in the metallic structure at the signaling location.

[0117] According to another aspect of the present invention there is provided a downhole device operation system for operating a downhole device in a well installation having a metal structure conducting electrical energy, the system comprising: a downhole device; an electrical energy collection system comprising a collection module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to the electric current flowing in the structure; and the collection module being arranged to collect electrical energy from the electrical current, the electrical energy collection system being arranged to supply electrical energy to the downhole device.

[0118] The downhole device may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0119] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0120] Energy may be supplied to control the valve, with energy to move the valve coming from another source (e.g., spring loading, differential pressure), or supplied to move the valve or for control and movement of the valve. The valve may comprise a trigger mechanism, for example, a pilot valve, which is operated using energy from the power distribution system.

[0121] The device operating system may be arranged to provide variable power levels. In this way a first energy level can be provided other than at times when a second, higher energy level is required. The applied currents, for example the cathodic protection currents, can be increased when a higher power level is required by switching to more anodes or applying a higher impressed current.

[0122] This would be at a level that is undesirable in the long term due to the potentially damaging effects of a very high potential difference caused by cathodic protection currents - hydrogen embrittlement - but acceptable in the short term. In this way the system, apparatus, method can be arranged to temporarily increase the applied current, for example, the cathodic protection current. The higher energy level can be used, for example, to move a valve from one state to another, with the lower level used at other times, for example, monitoring and/or control signals.

[0123] The downhole device may be provided in a location other than the location of the collection module in the well.

[0124] The collection module may be disposed at a selected location downhole for energy collection and a cable may be provided for supplying electrical power further downhole to the downhole device at a different location in the wellbore. pit.

[0125] The cross-sectional area of the conductive core, or cores, of the cable used to provide the electrical power further downhole may be smaller than that of the cable used to connect the collection module to the downhole structure for energy collection.

[0126] An additional power source may be available to the downhole device in addition to the electrical power provided by the electrical energy collection module.

[0127] In each of the above apparatus, the collection module may comprise variable impedance means for varying the load seen between the two connections. The variable impedance medium can be controlled by microprocessor.

[0128] The variable impedance means can be used to vary the load to optimize energy collection.

[0129] The variable impedance means can be used to modulate the charge in order to communicate data from the collection module towards the surface.

[0130] Impedance modulation can also be used in communication from a higher location toward the collection module in order to modulate the applied current (e.g., cathodic protection). One possibility is to switch an anode in and out of operation that will modulate the potential seen at the bottom of the well. Then data can be encoded by switching the anode in and out of operation. For example, the connection between the anode and the structure can be selectively made and broken with switching means. In this way the upper communication unit may comprise a switching means for switching an anode in operation and out of operation. In a printed current system the applied signals can be modulated to encode data.

[0131] According to another aspect of the present invention, there is provided a method of powering a downhole device in a well installation having a metal structure conducting electrical current, the method comprising the steps of: electrically connecting a collection unit to the metallic structure to a first location and to a second location spaced from the first location, the first and second locations being chosen so that there is a potential difference between them due to the electrical current flowing in the structure and the collection unit being arranged to collecting electrical energy from electrical current when connected between locations having a potential difference between them; collecting electrical energy from electrical current in the collection unit; and supplying electrical energy from the collection unit to the downhole device.

[0132] The method may comprise the steps of: determining a location where there is a maximum in potential magnitude caused by the electric current flowing in the structure, and choosing the first location, while the collection unit is connected to the metallic structure, depending on the place of said maxim.

[0133] According to another aspect of the present invention there is provided a downhole electrical energy collection system for use in a well installation having a metallic structure comprising at least one course of elongated metallic members conducting electrical current, the system collection device comprising: an energy collection module comprising an electrical circuit connected between spaced contacts to collect energy from a potential difference between the spaced contacts, wherein a first of the spaced contacts is made with the at least one course of elongated members metallic at a first location and a second of the spaced contacts is made with the at least one course of metallic elongated members at a second location and the potential difference is caused by the current flowing in the at least one course of elongated members, and at least in part, the impedance of the at least one course of elongated members.

[0134] The electrical current flowing in the at least one course of metallic elongated members where the first contact is made may flow in the same longitudinal direction as the electrical current flowing in the at least one course of metallic elongated members where the second contact is made .

[0135] Preferably if the first spaced contact and the second spaced contact are both made with the same course of metallic elongated members, this course of metallic elongated members is continuously conductive between the first and second locations.

[0136] Preferably the metallic structure provides an uninterrupted current flow path between the first location and the second location.

[0137] Preferably the current flow within portions of the metallic structure in regions between the first location and the second location is in the same longitudinal direction.

[0138] Preferably the collection module is arranged to collect electrical energy from dc currents.

[0139] The electrical connection to the metal structure in the first location may be a galvanic connection.

[0140] The electrical connection to the metal structure at the second location may be a galvanic connection.

[0141] The electrical connection to the metal structure in the first location can be made with one of: well casing tube, casing, tubing, coiled tubing, sucker rod.

[0142] The electrical connection to the metal structure at the second location can be made with one of: well casing pipe, casing, tubing, coiled tubing, sucker rod.

[0143] The spaced locations may be axially spaced.

[0144] The spaced locations may be radially spaced.

[0145] At least one connection between the at least one of the electrical contacts and the electrical circuit may be provided by an insulated cable.

[0146] Preferably the insulated cable has a conductive area of at least 10 mmA2, preferably at least 20 mmA2, more preferably at least 80 mmA2.

[0147] The cable may be a conductor encapsulated by tubing.

[0148] The spacing between locations can be at least 100 m.

[0149] Connections can be made with a common course of elongated metallic members that is part of the metallic structure.

[0150] In some embodiments, a first of the connections is made with a first course of metallic elongated members that is part of the metallic structure and a second of the connections is made with a second, distinct course of metallic elongated members that is part of the metallic structure. .

[0151] Insulating means may be provided to electrically isolate the first course of metallic elongated members from the second course of metallic elongated members in the connection region.

[0152] The insulation means may comprise an insulation layer or coating provided on at least one of the courses of metallic elongated members.

[0153] The isolation means may comprise at least one isolation centralizer for keeping the courses of metallic elongated members separated from each other.

[0154] Insulating means may be provided to prevent electrical contact between the two courses of metallic elongated members for a distance of at least 100 m.

[0155] The current flowing in the elongated members can be supplied from the well surface.

[0156] The current flowing in the elongated member may be supplied from one or more sacrificial anodes.

[0157] The current flowing in the elongated members may be an impressed current from an external power source.

[0158] The well surface voltage may be, in use, limited to the range minus 0.7 volt to minus 2 volts with respect to a silver/silver chloride reference cell.

[0159] The potential difference between the closely spaced contacts may be less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

[0160] The resistance of the well structure between the contacts may be less than 0.1 ohm, preferably less than 0.01 ohm.

[0161] The upper spaced contact may be: where the well is an earth well, within 100 m, preferably within 50 m, of the earth's surface; and where the well is a subsea well, within 100 m, preferably within 50 m, of the sea floor.

[0162] The upper spaced contact may be located adjacent to a location that corresponds to a maximum in potential magnitude caused by the electrical current flowing in the structure.

[0163] The system may comprise downhole communication means for transmitting and/or receiving data.

[0164] The downhole communication means can be arranged for data transmission by varying the load seen between the connections at the spaced locations.

[0165] According to another aspect of the invention there is provided a downhole device operating system comprising a downhole electrical energy collection system as defined above and a downhole device, the collection module being electrically connected to and arranged to supply power to the downhole device.

[0166] The downhole device may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0167] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0168] The downhole device may be provided at a different location in the well from the location of the collection module.

[0169] The collection module may be arranged at a selected location downhole for energy collection and a cable may be provided for supplying electrical power further downhole to the downhole device at a different location in the wellbore. pit.

[0170] The cross-sectional area of the conductive core, or cores, of the cable used to supply the electrical power further downhole may be smaller than that of the cable used to connect the collection module to the downhole structure for energy harvesting.

[0171] According to another aspect of the present invention, there is provided a method of powering a downhole device in a well installation having a metal structure conducting electrical current, the method comprising the steps of: electrically connecting a collection unit to the metallic structure at a first location and to the metallic structure at a second location spaced from the first location, the first and second locations being chosen so that there is a potential difference between them due to the electrical current flowing in the structure and the collection unit being arranged to collect electrical energy from the electrical current when connected between locations having a potential difference between them; collecting electrical energy from the electrical current in the collection unit; and supplying electrical energy from the collection unit to the downhole device.

[0172] The method may comprise the additional steps of: determining a location where there is a maximum in magnitude of potential caused by the electrical current flowing in the structure, and choosing the first location, where the collection unit is connected to the metallic structure, depending from the place of said maxim.

[0173] According to another aspect of the present invention, a downhole electrical energy collection system is provided for collecting electrical energy in a well installation having a metallic structure provided with cathodic protection, the system comprising: a collection electrically connected to the metal structure at a first location and a second location spaced from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to cathodic protection currents flowing in the structure ; and the collection module being arranged to collect electrical energy from the cathodic protection currents.

[0174] The collection module may be arranged to collect electrical energy from dc currents.

[0175] The current flow within portions of the metallic structure in regions between the first location and the second location may be in the same longitudinal direction.

[0176] There may be an uninterrupted current flow path between the first location and the second location that is at least partially through the metallic structure.

[0177] The collection module may be electrically connected to the metal structure at the second location.

[0178] The spaced locations may be axially spaced.

[0179] The spaced locations may be radially spaced.

[0180] At least one connection between the at least one of the electrical contacts and the collection module may be provided by an insulated cable.

[0181] The insulated cable may be a conductive area of at least 10 mmA2, preferably at least 20 mmA2, more preferably at least 80 mmA2.

[0182] The cable may be a conductor encapsulated by tubing.

[0183] The spacing between locations can be at least 100 m.

[0184] Connections can be made with a common course of metallic elongated members that is part of the metallic structure.

[0185] A first of the connections can be made with a first course of metallic elongated members that is part of the metallic structure and a second of the connections can be made with a second, distinct course of metallic elongated members that is part of the metallic structure.

[0186] Insulating means may be provided to electrically isolate the first course of metallic elongated members from the second course of metallic elongated members in the connection region.

[0187] The insulation means may comprise an insulation layer or coating provided on at least one of the courses of metallic elongated members.

[0188] The isolation means may comprise at least one isolation centralizer for keeping the courses of metallic elongated members separated from each other.

[0189] Insulating means may be provided to prevent electrical contact between the two courses of metallic elongated members for a distance of at least 100 m.

[0190] The current flowing in the elongated members can be supplied from the well surface.

[0191] The current flowing in the elongated member is supplied from one or more sacrificial anodes.

[0192] The current flowing in the elongated members may be an impressed current from an external power source.

[0193] The well surface voltage may be, in use, limited to the range minus 0.7 volt to minus 2 volts with respect to a silver/silver chloride reference cell.

[0194] The potential difference between the closely spaced contacts may be less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

[0195] The resistance of the well structure between the contacts may be less than 0.1 ohm, preferably less than 0.01 ohm.

[0196] The upper spaced contact may be: where the well is an earth well, within 100 m, preferably within 50 m, of the earth's surface; and where the well is a subsea well, within 100 m, preferably within 50 m, of the sea floor.

[0197] The upper spaced contact may be located adjacent to a location that corresponds to a maximum in potential magnitude caused by the electrical current flowing in the structure.

[0198] The system may further comprise downhole communication means for transmitting and/or receiving data.

[0199] The downhole communication means can be arranged for data transmission by varying the load seen between the connections at the spaced locations.

[0200] According to another aspect of the invention there is provided a downhole device operating system comprising a downhole electrical energy collection system as defined above and a downhole device, the collection module being electrically connected to and arranged to supply power to the downhole device.

[0201] The downhole device may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0202] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0203] The downhole device may be provided at a different location in the well from the location of the collection module.

[0204] The collection module may be disposed at a selected location downhole for energy collection and a cable may be provided for supplying electrical power further downhole to the downhole device at a different location in the wellbore. pit.

[0205] The cross-sectional area of the conductive core, or cores, of the cable used to provide the electrical power deeper in the well may be smaller than that of the cable used to connect the collection module to the downhole structure for collection of energy.

[0206] According to another aspect of the present invention there is provided a downhole data communication apparatus for use in a well installation having a metallic structure provided with a cathodic protection system so that there is an electrical circuit comprising the metallic structure and a return to earth around which an electrical current flows as a result of the cathodic protection system, the downhole data communication apparatus comprising: a first communication module for location at a first location and comprising modulating means for modulating the electrical current at a first location so as to encode data; and a second communication module for location at a second location, spaced from the first location, and comprising a detector for detecting the effect of modulation of the electrical current at the first location so as to extract said data.

[0207] The modulating means may be arranged for at least one of: i) where the cathodic protection system is a printed cathodic protection system, controlling a signal source of the printed cathodic protection system to directly modulate the protection current cathodic applied to the metallic structure; ii) modify the connection between at least one anode of the cathodic protection system and the metallic structure; and iii) change the impedance of the electrical circuit.

[0208] The first communication module may be arranged for location at the bottom of the well.

[0209] The second communication module may be arranged for location at the bottom of the well.

[0210] The apparatus may comprise a sensor module for capturing at least one parameter, where the first communication module is arranged to send data encoding readings from the sensor module towards the second communication module.

[0211] The sensor module may comprise a pressure sensor.

[0212] The second communication module may be arranged to provide data to a downhole device in dependence on data received by the second communication module from the first communication module.

[0213] The downhole device may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0214] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0215] At least one of the first and second communication modules may comprise a communications repeater for downhole location in a well and arranged to communicate with a first device beyond the wellhead using a communication channel that is wireless. at least through the wellhead and arranged for communication with second device located in the wellhead and then below the wellhead so that the communications repeater can act as a repeater between the first and second devices.

[0216] The apparatus may comprise a downhole electrical energy collection module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for collecting electrical energy, in use, from a potential difference between the spaced locations, used for collection, which acts as an input voltage, the collection module being arranged to supply power to at least one component of the communication apparatus.

[0217] The first communication module may be arranged to control the charge generated by the collection module to cause said modulation of the electrical current in the metallic structure at the signaling location.

[0218] The collection module may be arranged to collect electrical energy from dc currents.

[0219] According to another aspect of the present invention there is provided a downhole data communication system comprising downhole data communication apparatus as defined above located in a well installation having a metallic structure provided with cathodic protection .

[0220] According to another aspect of the present invention there is provided a downhole data communication system for use in a well installation having a metallic structure provided with a cathodic protection system so that there is an electrical circuit comprising the metallic structure and a return to earth around which an electrical current flows as a result of the cathodic protection system, the system comprising a downhole data communication apparatus comprising: a first communication module located at a first location and comprising modulating means for modulating the electrical current at the first location so as to encode data; and a second communication module located at a second location, spaced from the first location, and comprising a detector for detecting the effect of modulation of the electrical current at the first location so as to extract said data.

[0221] The apparatus may comprise a downhole electrical energy collection module electrically connected between two spaced locations in the well installation and comprising an electrical circuit arranged for collecting electrical energy, in use, from a potential difference between the spaced locations, used for collection, which acts as an input voltage, the collection module being arranged to supply power to at least one component of the communication apparatus.

[0222] The current flow within portions of the metallic structure in regions between the closely spaced locations used for collection may be in the same longitudinal direction.

[0223] There may be an uninterrupted current flow path between the closely spaced locations used for collection that is at least partially through the metallic structure.

[0224] At least one of the first communication module and the second communication module may be located in a closed ring of the well.

[0225] The system or apparatus may comprise a pressure sensor arranged for monitoring the well reservoir pressure.

[0226] The system or apparatus may comprise a pressure sensor arranged for monitoring pressure in a well ring.

[0227] The system or apparatus may comprise a pressure sensor arranged for monitoring the pressure in a closed ring of the well.

[0228] According to another aspect of the present invention there is provided a downhole electrical energy collection module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for collecting electrical energy, in use, from a potential difference between the closely spaced locations that acts as an input voltage.

[0229] The collection module may be arranged to collect electrical energy from dc currents.

[0230] The collection module may comprise control means for modifying the input impedance of the electrical circuit to match the impedance of the electrical circuit to optimize power conversion efficiency.

[0231] The electrical circuit may comprise a dc-dc converter.

[0232] The dc-dc converter may be arranged to operate with input voltages above a minimum threshold, where the minimum threshold is not greater than 0.5 volts, preferably the minimum threshold is not more than 0.25 volts and most preferably the minimum threshold is not more than 0.05 volt.

[0233] The dc-dc converter may comprise self-starting means to allow initiation of energy harvesting when the available input voltage is below a band gap voltage of components in the dc-dc converter.

[0234] The dc-dc converter may comprise self-starting means to allow initiation of energy harvesting when the available input voltage is below 0.5 volts.

[0235] The dc to dc converter may comprise a stepping transformer.

[0236] The self-starting means may comprise a Field Effect Transistor arranged together with the stepping transformer to form a resonant scaling oscillator.

[0237] The dc-dc converter may comprise a transistor H-bridge disposed under the control of control means for providing an input to the stepping transformer and the self-starting device may comprise an auxiliary power source for the control means to allow departure.

[0238] The collection module may comprise control means arranged to control the turns ratio of the stepping transformer to modify the load generated by the dc-dc converter.

[0239] A secondary winding of the stepping transformer may comprise a plurality of taps and/or the stepping transformer may comprise a plurality of secondary windings and the control means may be arranged to select windings and/or taps for a desired turns ratio. The collection module may comprise at least one pair of terminals from which connection to the two spaced locations may be made.

[0240] The collection module may have more than two terminals, where each of the terminals is to permit connection to a respective location and the collection module may further comprise switching means for selectively electrically connecting two of the terminals in the electrical circuit thereby allowing selection of which of the respective locations the electrical circuit is connected.

[0241] This allows a configuration where multiple contacts with the metal structure can be made during installation and after installation a selection is made of which contacts should be used. In this way, for example, the configuration may include one lower connection and two upper connections in different locations. Once installed it can be determined that more energy can be collected if a first of the upper connections is used, then this first connection can be used. In another case the second upper connection may be better.

[0242] The switch would also be used dynamically in use to switch between connections.

[0243] In another case there would be two lower connections as well as or instead of the two upper connections, or there may be other numbers of upper and/or lower connections.

[0244] The collection module may comprise an energy storage device for storing collected energy. The energy storage device may comprise a charge storage device which may comprise at least one capacitor and/or rechargeable battery. The collection module may comprise variable impedance means for varying the load seen between the two connections.

[0245] The variable impedance medium can be controlled by a microprocessor.

[0246] The collection module may be arranged to use variable impedance means to vary loads in order to optimize energy collection.

[0247] The collection module may be arranged to use the variable impedance means to modulate the load so as to communicate data distant from the collection module.

[0248] The collection module may comprise a primary battery so that in use energy may be selectively drawn from the energy collected by the circuit and the primary battery.

[0249] In accordance with another aspect of the present invention there is provided a downhole apparatus comprising a collection module as defined above and a downhole device for accepting energy from the collection module.

[0250] The downhole apparatus may comprise charge storage means and power control means for controlling power to the downhole device when sufficient power is available to power the device.

[0251] The downhole apparatus may comprise impedance modulation means for varying the input impedance of the collection module to modulate the load so as to transmit data from at least one of the electrical energy collection unit and the downhole device.

[0252] The downhole apparatus may comprise modulation means for applying a modulated voltage across the spaced connections so as to transmit data.

[0253] The downhole apparatus may comprise a primary battery so that in use energy may be selectively withdrawn from the collected energy and the primary battery.

[0254] The downhole device of the downhole apparatus may comprise at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or a packer element; a valve; a downhole communications module, for example, a transceiver or repeater.

[0255] The valve may comprise at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve.

[0256] According to another aspect of the present invention, a downhole electrical energy collection system is provided for collecting electrical energy in a well installation having a metallic structure conducting electrical current, the system comprising: a collection module as defined above electrically connected to the metallic structure at a first location and a second location spaced apart from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to electrical current flowing in the structure ; and the collection module being arranged to collect electrical energy from the electrical current.

[0257] According to another aspect of the invention, a downhole power distribution system is provided for powering a downhole device in a well installation having a metal structure conducting electrical current, the system comprising: a module collection device as defined above electrically connected to the metallic structure at a first location and a second location spaced apart from the first location, the first and second locations being chosen so that, in use, there is a difference in potential between them due to electrical current flowing in the structure; and the collection module being arranged to collect electrical energy from the electrical current and supply electrical energy to the downhole device.

[0258] According to yet another aspect of the invention there is provided a downhole power distribution system for powering a downhole device in a well installation having a metallic structure provided with cathodic protection, the system comprising: a collection module as defined above electrically connected to the metallic structure at two spaced locations chosen so that, in use, there is a potential difference between them due to cathodic protection currents flowing in the structure; and the collection module being arranged to collect electrical energy from the cathodic protection currents and supply electrical energy to the downhole device.

[0259] According to a further aspect of the invention there is provided a method of data communication in a well installation having a metallic structure provided with a cathodic protection system so that there is an electrical circuit comprising the metallic structure and a return to the earth around which electrical current flows as a result of the cathodic protection system, the method comprising the steps of: modulating the electrical current at a first location so as to encode data; and detecting at a second location, spaced from the first, the effect of the modulation of the electrical current at the first location in order to extract said data.

[0260] One of the locations may be outside the well site, that is, on the surface, another of the locations may be at the bottom of the well.

[0261] The current modulation step may, among other things, comprise and the modulation devices may, among other things, be arranged to: iv) where the cathodic protection system is a printed cathodic protection system, control a source printed cathodic protection system signal to directly modulate the cathodic protection signals applied to the metallic structure; or v) ) modify the connection between at least one anode and the metallic structure - in this way at least one anode can, for example, be switched to be in connection and out of connection with the metallic structure to modulate the electrical signals or impedance between the anode and the structure can be varied; or vi) ) change the impedance of the electrical circuit - this may, for example, be achieved by using a variable impedance medium or by switching components in and out of connection with the circuit.

[0262] Techniques i) and ii) are likely to only be available at a higher location, while technique iii) is likely to be available at the bottom of the well and at a higher location. Communication using this general idea can be used for one-way communication, that is, from the surface to the bottom of the well, one-way, that is, communication from the bottom of the well to the surface, and two-way communication.

[0263] These techniques allow communication as part of a hybrid communication system - that is, some parts of the signal channel are provided by modulation of cathodic protection signals and some by other techniques, such as wireless techniques including other EM techniques and acoustic techniques.

[0264] In each case above, cathodic protection where present may be provided by a passive cathodic protection system where sacrificial anodes are connected to the metal structure of the well installation or by a printed cathodic protection system where a protective current is applied to the metal structure of the well installation.

[0265] In the present methods and systems the objective is to make use of existing cathodic protection systems (or other current sources if available), in particular to make use of existing anodes where present, for example in marine installations, and without requiring modification ourselves. In this way, anodes where present will be outside, that is, above, the well and located in the water. Furthermore, the anodes will typically be far from the location where power and/or signaling is required.

[0266] In this way the above system may include one or more of: at least one existing anode; at least one anode provided in water, that is, the body of water in which a subsea well installation is provided; at least one anode that is distant from the location at which power and/or signaling is to be obtained using current developed by this anode.

[0267] Further any of the above systems may be arranged to permit the transmission of power from a location at which current, e.g., CP current, is applied to the structure to a collection and/or signaling location. This is true whether the current is a passive CP current, an impressed CP current or another applied current. That is, typically, the source of the CP current or other current is far from the collection and/or signaling location.

[0268] Furthermore, the metallic structure may be uninterrupted in the region of at least one anode and/or in the region of the collection module.

[0269] Where mention is made above of optimization through modeling, for example in relation to spacing of connections, use of insulation, choice of only radial or axial spacing, and the selection of at least one preset collection load one of the following parameters can be used in the model: 1. Attenuation rate at the top of the well derived from well casing pipe and tubular dimensions, weights and material type (resistivity) and the resistivity of the overburden (medium surrounding the well ); 2. Top connection location; 3. Bottom connection location; 4. Cross-sectional area and type of material (resistivity) of the upper cable used in supplies to the collector; 5. Number, location, material (electropotential) and surface area of wellhead anodes; 6. Effective resistance of the well as seen from the seafloor/wellhead, again derived from well casing pipe and tubular dimensions, weights and material type (resistivity) and overburden resistivity (medium surrounding the well), but this time for full completion.

[0270] In each case above the systems may comprise a primary battery for supplying power independently of collected energy. The collection module may comprise the primary battery. Where a primary battery is provided this can preferably be used whilst it has power. It would be used, for example, to allow use of a higher data rate at an early stage, this being allowed to drop when only harvested energy is available.

[0271] According to another aspect of the invention there is provided a well installation comprising a metal structure conducting electrical current and any of the above systems or apparatus, for example, at least one of: an apparatus or system for collecting electrical energy from well bottom; a downhole device operating apparatus or system; a downhole communication repeater device or system; a power distribution apparatus or system; or a collection module; or a downhole well monitoring apparatus or system; or downhole communication apparatus or system, as defined above. Such an installation may also have a cathodic protection system to protect the metallic structure.

[0272] Note that in general each of the optional features following each of the above aspects of the invention is equally applicable as an optional feature in relation to each of the other aspects of the invention and could be rewritten after each aspect with any necessary changes in wording . Not all such optional features are rewritten after each aspect just for the sake of brevity.

[0273] For example, it will be understood that any of the systems, methods, apparatus and installations mentioned above may make use of a collection module having any combination or subcombination of the characteristics defined above, and so on.

[0274] The well mentioned in any of the above methods, systems, apparatus or installations may be a subsea well.

[0275] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 schematically shows a well installation including well monitoring apparatus including a bottom-end energy management system pit; Figure 2A schematically shows a collection module of the energy management system of Figure 1 and Figure 2B shows an alternative downhole unit; Figure 2C is a schematic circuit diagram of a dc to dc converter that can be used in a collection module; Figure 2D is a schematic circuit diagram of a dc to dc converter that can be used in a collection module; Figure 3 schematically shows a downhole installation including downhole communications apparatus comprising a downhole communications repeater and a downhole power distribution system for powering the downhole communications repeater; Figure 4 schematically shows a well installation including valve operating apparatus comprising a remotely controlled downhole valve and a power distribution system for powering the remotely controlled downhole valve; Figure 5 schematically shows a well installation including an alternative well monitoring system comprising a downhole pressure gauge and a downhole power distribution system for powering the downhole pressure gauge; Figure 6 schematically shows an alternative well installation; Figure 7 shows a graph of energy capable of optimal collection against depth of a lower connection for an arrangement of the type shown in Fig. 1; Figure 8 shows an energy harvesting optimization flowchart; Figure 9 shows an operation flowchart of a downhole unit; and Figure 10 schematically shows a well installation including a platform.

[0276] Figure 1 shows a well installation of an oil and/or gas well. As is well understood, such an oil and/or gas well may be an onshore well or a subsea well (meaning a well below any body of water) where the wellhead is underwater on the floor of the sea, river, lake , etc. or on a platform. Well installations are often provided with a cathodic protection system. In the case of onshore wells this will most likely be in the form of an impressed current cathodic protection system where a protective current is applied to the metal structure of the well. On the other hand, for a subsea well, the cathodic protection will most likely be a passive cathodic protection system where a plurality of anodes of a relatively reactive metal, such as a magnesium alloy, are connected to the metal structure and exposed to the water in which well installation is located.

[0277] Note that the present techniques are also relevant to water injection wells - that is, wells used to inject water into a reservoir to aid in the recovery of oil and/or gas from other wells in the field. Thus, a “well installation” in the present application may be a water injection well. Such a well will have a similar construction to the installations shown in more detail in the present application. Similarly the present techniques can be used while drilling a well as during production and following abandonment. This way the well installation can be a partially complete installation where drilling is taking place. Most commonly the present techniques can be used during any period of the life cycle of a well installation.

[0278] Furthermore, although the present description is made in relation to installations where cathodic protection is present and this is particularly preferred, many of the present systems and techniques also function in other situations where electrical current is flowing in the metallic structure and energy can be harvested. from the same.

[0279] The well installation shown in Figure 1 comprises a wellhead 1 and downhole metal structure 2 in the downward direction of the wellbore from the surface S. The well installation is provided with a cathodic protection system 3A, 3B. As mentioned above, this will be a 3A impressed cathodic current protection system or a passive cathodic protection comprising a plurality of 3B anodes connected to the metallic structure of the well installation, i.e. to the wellhead 1 or other metallic components connected thereto. .

[0280] The downhole metal structure 2 comprises a first course of metal tube 21, that is, production tubing, descending to the wellbore. Surrounding this is a first well casing tube 22. Outside this layer is a second well casing tube 23 and then a third well casing tube 24. As will be understood there is a respective ring between each course of metal tube. In this way there is a first ring between the production tubing 21 and the first well casing tube 22 commonly referred to as the “A” ring in the oil and gas industry and indicated by the reference numeral A in the drawings. A second ring exists between the first well casing tube 22 and the second well casing tube 23 commonly known as the “B” ring and so indicated in the drawings and a third ring exists between the second well casing tube 23 and the third well casing tube 24 commonly known as the “C” ring and also indicated in the drawings. Wells can also typically have an additional “D” ring, and sometimes even more rings.

[0281] In other situations, the metallic structure may comprise other elongated members, specifically, one or more well casing tube, casing, tubing, coiled tubing, pump rod.

[0282] Monitoring apparatus provided in the well installation comprises an electrical energy collection module 4 provided, in the present embodiment, in ring A. The collection module 4 is electrically connected via cables 41 to a pair of spaced locations 41a, 41b in production piping 21. In an alternative the collection module 4 may be electrically connected to one of the locations via a cable, but may be electrically connected to the other location without a cable. The collection module 4 may be electrically connected through a conductive housing of (or surrounding) the collection module at one of the locations. This way only one cable of this type may need to leave the housing.

[0283] Note that there is a galvanic connection between the collection module 4 and the metallic structure 21 at spaced locations 41a, 41b. In particular, there is a galvanic connection with the metallic structure 21, instead of, for example, an inductive coupling. This simplifies construction and removes engineering difficulties. In the present case there is a galvanic connection all the way from the metal structure to the inputs of the circuit included in the collection module for energy collection.

[0284] It will also be noted that the metal structure of the well is generally not affected by the installation of this system. Any isolation joints have been introduced into any of the metal tube courses in order to make the system effective and the normal flow of cathodic protection current in the structure has not been altered - other than, of course, the collection that is taking place. In this way, for example, between the spaced locations the course of metal structure to which connections are made is continuous, more generally all courses of metal structure are continuous in these regions. This is not essential for operation, but is possible and is the normal prevailing situation in a well installation - that is, the standard metal structure of the installation has been left unmodified. Similarly, current can and does flow in the same direction in the metal structure in the region of connections and between connections. Again this is the normal prevailing situation in a well installation, modification in the well installation was avoided. The flow of current would be in a single course of metallic structure to which connections are made or change from one course to another or flow in parallel in several courses - the point is that an artificial arrangement of metallic structure in the well does not have to be configured to allow the system to function, and in this way there is an uninterrupted current flow path provided by the metallic structure and current flow is in the same longitudinal direction in the metallic structure.

[0285] Note that the “A” ring is often accessible by cable through wellhead 1. However, it is still advantageous to use the present arrangements as they minimize the number of penetrators at the wellhead, reducing risk and expense. and/or freeing the penetrator for other use.

[0286] The monitoring apparatus further comprises a downhole pressure gauge 5 which is provided deeper in the well than the collection module 4 and is connected thereto via a cable 42. In this embodiment the downhole pressure gauge 5 is provided slightly above the packer P. Typically the cables 41 connecting the collection module 4 to the production unit 21 will be tubing enclosed conductors (TEC) as typically used in the oil and gas industry and the cable 42 connecting the collection module 4 to the downhole pressure gauge 5 will also be a pipe-enclosed conductor (TEC). More typically the cross-sectional area of the conductor in the lengths of cable 41 connecting the collection module 4 to the production piping 21 will have a greater cross-sectional area than that of the cable 42 connecting the collection module 4 to the downhole pressure gauge. 5.

[0287] Where cathodic protection is provided in a well installation, the potential of the well metal structure is brought to a sufficiently negative potential at the injection point, i.e., wellhead 1, so as to suppress corrosion at the wellhead. well and at other points along the metal downhole structure 2 as it descends into the well. However, the magnitude of this negative potential will decrease as it descends further into the well due to losses in the system. In this way, the potential of the metallic structure 2 close to the wellhead will be more negative than in deeper locations in the well. In this way when the cathodic protection currents are flowing in the well installation there will be a potential difference between the location 41a where the first of the cables 41 from the collection module is connected to the production piping 21 and the location 41b where the other of the cables 41 of the collection module 4 is connected to the production pipe 21. In this way the collection module 4 will see a potential difference across it and in this way can extract energy from the cathodic protection currents.

[0288] It will be noted that energy extraction will use energy from the cathodic protection system, however the impact on the effectiveness of the cathodic protection system or any acceleration of anose corrosion will be negligible. Typically cathodic protection currents will be on the order of 10 Amps, while the present systems would draw, for example, 10-100 milli Amps. In this way, the amount of current extracted is well within the tolerance generally permitted when developing cathodic protection systems. If desired, an increased level of impressed current could be provided or the number of anodes provided could be increased beyond normal. This would increase the cathodic protection current and thus improve collection.

[0289] Electrical energy can be collected from the system at the downhole location of collection module 4 and this collected energy can be used for other purposes.

[0290] In the arrangement of Figure 1 this collected energy is used to power the downhole pressure gauge 5 and allow extraction of readings from it and communication of these readings to the surface S.

[0291] In the present embodiment an upper communication unit 6 is provided for communication with the collection module 4 and downhole pressure gauge 5. In this case the upper communication unit 6 is provided on the surface S - in this case the earth's surface.

[0292] It will be understood that arrangements such as the present can be used in place of a conventionally installed permanent downhole pressure gauge (PDG) with the advantage that use of a penetrator through the wellhead can be avoided, while the life of Well monitoring will be possible in many cases. Monitoring can be of reservoir pressure where desired or similarly of pressure in a closed loop to, for example, help detect any leaks, discharges or failures in the system. The sensor and collection module may be located in the closed ring in such a case.

[0293] All of these options are possible, for example, in a subsea well installation where there will typically be a ready source of current to be collected, i.e. CP current, typically generated by sacrificial anodes located in the water in which the subsea installation is provided, and where other power and signaling options are more problematic.

[0294] In a well with a subsea wellhead, it is conventionally not generally possible (practically/cost effective) to provide hydraulic or electrical connectivity with the outer rings (B, C, etc.). Particularly where these rings are sealed at their base it is useful to monitor and optionally control the pressure in these rings, for example to reduce the risk of high pressures causing collapse of the well casing pipe.

[0295] In particular flow, or well drilling, can increase the temperature of the sealed outer ring and therefore increase the pressure therein. The ability to monitor pressure in such a case and optionally control pressure in such a case (such as with an inter-ring vent valve, as mentioned elsewhere) is beneficial. In particular, monitoring pressure in a closed loop may allow production at rates greater than those that can be achieved if modeling of the expected pressure increase alone is used since use of modeled pressure would require larger safety margins and potentially higher production rates. correspondingly reduced. As will be understood, the present techniques can facilitate such monitoring and/or control.

[0296] Another particular implementation of the present techniques will include a sensor module located in the same location as is more common for a conventional permanent downhole pressure gauge and provided for the same purpose as is more common for a permanent downhole pressure gauge. conventional.

[0297] In this way, the sensor module can be arranged in ring A and arranged to monitor the reservoir pressure by capturing the pressure in the piping through a pressure communication port through the piping, thus allowing inference of the reservoir pressure with based on captured pressure and taking into account static pressure and flow effects. As is the case with a conventionally used PDG, reservoir pressure will generally be inferred in this manner rather than directly measured - positioning a sensor directly in the reservoir is generally not possible - as will also be understood “monitoring reservoir pressure” comprises usage of such measurement techniques.

[0298] A collection module may also be provided at the location of the sensor module.

[0299] Different techniques can be used to allow data extraction from the downhole pressure gauge 5 towards the surface.

[0300] In the present embodiment, the collection module 4 is arranged to accept a signal from the downhole pressure gauge that is indicative of the parameter to be measured, for example, pressure and/or temperature, and transmit this data towards the surface due to load modulation that the collection module 4 creates between the spaced connections 41a and 41b. In turn this change in load will change the amount of current drawn from the cathodic protection currents applied to the system. This in turn is detectable at the surface or other convenient location by virtue of a change in potential of the metallic structure at the surface or other convenient location. It can be detected by detecting, for example, the change in potential at the wellhead 1 or by detecting the voltage across, or a current seen by, a power source used in a 3A printed cathodic protection system. In the present embodiment, the modulation effect is detected by the upper communications unit 6, monitoring the wellhead potential in relation to a reference ground, to extract pressure and/or temperature measurement data.

[0301] Preferably the spacing between the spaced connections 41a, 41b is at least 100 meters and more likely in the range of 300 to 500 meters. The optimal spacing for spaced connections 41a, 41b can be determined through modeling for a given installation. As the distance between these connections is increased, this tends to increase the potential difference between the connections (although the rate of potential difference increase decreases as the depth of the bottom connection is increased). On the other hand, as the spacing increases the total length and then resistance of the cables 41 increases. This way in most systems there will be optimal spacing.

[0302] Fig. 2A shows the collection module 4 of the apparatus shown in Figure 1 in more detail. In this embodiment the collection module 4 has a pair of terminals 43a, 43b to which the respective cables 41 are connected. There is a galvanic connection between the metallic structure and terminals 43a, 43b. Connected between these terminals 43a, 43b is a dc to dc voltage converter for collecting electrical energy where potential difference is seen across terminals 43a, 43b. The dc to dc converter 44 is connected to a charge storage means 45 including at least one low leakage capacitor and connected to and controlled by a microprocessor-driven central unit 46. The charge storage means 45 and the central unit 46 are also connected via a respective terminal 43c to the length of cable 42 leading to the downhole pressure gauge 5. In an alternative, the charge storage means 45 would be dispensed with - that is: sufficient energy would be collected to allow continuous operation as and when necessary.

[0303] In operation, the central unit 46 controls the operation of the dc to dc converter 44 so as to optimize the charge that is present for the current seen by the collection module 4 due to cathodic protection currents in order to maximize the energy that can be collected and used or stored in the charge storage medium 45. Note that the central unit can be arranged to selectively use and/or distribute directly collected energy when appropriate, and store energy and extract stored energy when appropriate.

[0304] Note that in an alternative the microprocessor-driven central unit 46 may be replaced by alternative electronic devices including, for example, an analog feedback circuit, or a state machine, or even a fixed collection load based on modeling. for private installation.

[0305] When stored energy is to be used, energy from the charge storage medium 45 is fed through the cable 42 to the downhole pressure gauge 5 and readings from the downhole pressure gauge 5 are acquired by the central unit 46 through of the cable 42. The central unit 46 also controls operation of the dc to dc converter 44 to modulate the charge that is introduced between terminals 43a and 43b in order to send signals back to the surface carrying readings from the downhole pressure gauge 5 as described above.

[0306] Note that in the present embodiment the dc to dc converter 44 and the central unit 46 together act as a variable impedance medium by virtue of the central unit 46 controlling the operation of the dc to dc converter 44 to introduce variable impedance between the terminals 43a and 43b.

[0307] Note that in alternatives, instead of a sensor being provided in a separate downhole pressure gauge 5, an appropriate sensor may be provided in the same location as the collection module 4.

[0308] In particular, a downhole unit 4a as shown in Figure 2B can be provided, which comprises both a collection module 4 and at least one downhole device to be powered. In this case the downhole unit 4a includes a pressure sensor 47 and a communication unit 48.

[0309] In such a case there may be no secondary cable 42 running away from the downhole unit 4a. On the other hand in some other cases the downhole unit 4a would still be used to power an external device even if including its own sensor 47 and/or communications unit 48 and then there would be a secondary cable 42.

[0310] In alternatives, instead of communicating with the surface using the load modulation technique as discussed above, the downhole unit 4a could use its own communications unit 48 to communicate back with the surface. Such communication would be in the form of EM communication signals which can be applied back to the downhole metal structure 21 via cables 41. In other cases the communications unit 48 provided in the downhole unit 4a would be a acoustic communications for applying acoustic signals to the metallic structure 21 for transmission back to the surface. In such a case then an upper communications unit would be arranged to receive acoustic signals. It will be understood that two-way communication can be provided as and when desired on any or all parts of the communications channels. Yet two communication techniques can be used in parallel on either leg of the communication channels - this way EM signals and acoustic signal would be used side by side.

[0311] In additional alternatives the collection module 4 or downhole unit 4a may comprise at least one power converter for controlling the voltage at which energy is collected for administration to the charge storage means 45 and/or other components such as the central unit 46. It may be desirable to store energy at a voltage different from that at which it is collected and/or different from that at which it is used by the central unit 46 or other components. For example, it may be desirable to store energy at a higher voltage than that at which it is collected and/or consumed. This can be useful, for example, if there is a large withdrawal in stored energy during, for example, transmission.

[0312] One possible implementation for a dc to dc converter is to use a commercially available integrated circuit. An alternative is to produce a similar circuit using different components. To provide effective performance a dc to dc converter that can handle low input voltages is desirable. One way to achieve this is to use a Field Effect Transistor, such as JFET switch, to form a resonant scaling oscillator using a scaling transformer and a coupling capacitor. In order to help optimize energy harvesting the transformer turns ratio can be selected, preferably dynamically selected during operation. A plurality of taps may be provided on the secondary of the transformer which may be used selectively to provide respective feedback ratios.

[0313] A processor, such as that of the central unit, may be arranged to control a switch to dynamically select respective taps and then control the load generated by the dc-dc converter.

[0314] Fig. 2C shows a schematic circuit diagram for a possible implementation of a resonant scaling oscillator of the type described above. The available input potential difference can be connected across the input terminals as Vin and the output Vout is seen through the output terminals. The circuit comprises a Field Effect Transistor 201, a stepping transformer 202 which together act as an oscillator and a rectification output arrangement 203 comprising a pair of crossed diodes 206 and respective coupling capacitors 205. A primary winding 202a of the transformer 202 is connected in series with FET 201 and the Vin input is applied across these. The FET gate 201 is connected to the secondary winding 202b of the transformer 202. The Vout output is seen through the coupling capacitors 205 which are connected across the secondary winding 202b through the respective diodes 204.

[0315] The secondary winding 202b of the transformer 202 comprises a plurality of taps 202c that can be selected using the switch 206 in this way allowing adjustment of the turns ratio. The switch 206 may be controlled by a microprocessor, in this case the central unit 4b.

[0316] This type of dc to dc converter arrangement is capable of functioning even when the potential difference seen across the terminals (input voltage) is low, i.e., 0.5 V or below. In practical examples the input voltage may be less than 0.25 V and perhaps even less than 0.05 V. Since this is very low compared to semiconductor band gap voltages (e.g. 0.7 ) many types of dc to dc converters will not work to allow energy harvesting at such input voltages. However, dc to dc converters based on the above principles can work even at such low voltages. Such a dc to dc converter may be considered to include starting means arranged to permit operation when input voltage is 0.5 V or below as well as at higher voltages.

[0317] An alternative approach is to provide a circuit with a separate power source to act as part of the starting medium. In this way, for example, a primary battery can be provided to start the system after installation. Furthermore, energy stored in an energy storage would be used to restart the system if energy collection temporarily stops.

[0318] Figure 2D shows a schematic circuit diagram for a possible implementation of a dc to dc converter operating on such a basis. The dc to dc converter of Figure 2D comprises an H bridge 207 of transistors 207a through which the input voltage is connected. The gates of the transistors 207a are connected to a control unit 208 which is arranged to control the switching of the transistors 207a to generate an ac output. The ac output of the H bridge 207 is connected through a primary winding 202a of a stepping transformer 202. The secondary winding 202b of the transformer 202 is connected to a rectifier 209. An output of the rectifier 209 is connected through a diode 204 to the input of a power supply unit 210 and the other output is connected to ground. Also connected to the input of the power supply unit 210 via another diode 204 is a battery 211.

[0319] The power supply unit 210 is arranged to power the control unit 208. In order to initiate operation the power supply unit 210 may use energy from the battery 211. Once the energy is collected by the dc to dc converter then the power supply unit 210 can use energy received from the rectifier 209 - that is, collected energy.

[0320] Although in the present embodiment energy is used directly as collected, in alternatives collected energy can also be stored in a storage medium and used from the storage medium. As described elsewhere in the present application, the storage medium may, for example, include at least one low leakage capacitor and/or at least one rechargeable cell. Where energy is stored this allows a mechanism to reset the system if collection is stopped at any point after the battery 211 has discharged.

[0321] Battery 211 may be a primary (single shot) battery or may be a rechargeable battery as long as it is charged at the time of installation. Where the battery is a rechargeable battery, in some implementations the power supply unit 210 may be arranged to store energy therein when available, alternatively it may be more convenient to provide a separate energy storage means (which would include a rechargeable battery).

[0322] Note also that in an additional alternative a dc to dc converter of the type shown in Figure 2D can be arranged to allow control of the load generated by the dc to dc converter. In this way, for example, an arrangement similar to that shown in Figure 2C can be used where the secondary winding 202b has multiple taps and a switch is provided to allow selection of the multiple taps. The commutator could be between the windings and the input of the rectifier 209. In another alternative embodiment separate secondary windings could be provided instead of multiple taps, to obtain a similar result. The switch can be controlled by a control unit as in the case of the arrangement in Figure 2C.

[0323] Note also that in other embodiments the collection module 4 and the downhole pressure gauge 5 (or downhole unit 4a) may be provided in other rings within the well installation instead of ring A. Still the manometer can be arranged to capture a parameter on a ring different from that to which it is located.

[0324] For example, these components may be provided in ring B or C and a pressure gauge located in said ring B may be arranged to capture one or more parameters in ring A, ring B, ring C or any combination thereof. It is noted that these are locations where it is generally not possible, or at least undesirable, to attempt to provide direct cable connections from the surface. In this way the present techniques give rise to the possibility of monitoring, for example, the pressure in the B or C rings during the life of a well installation where this would be difficult and/or expensive using conventional power distribution methods. The present techniques avoid the use of penetrators through the wellhead, which can reduce risk and costs. They also provide relatively simple, clear and easy installation solutions.

[0325] Figure 3 shows a well installation similar to that in Figure 1, but including a downhole communications repeater 7 instead of a downhole pressure gauge. The repeater 7 is provided in ring B together with a collection module 4 of the same type described above in relation to Figures 1, 2A to 2D. Here again the collection module 4 collects energy from the cathodic protection currents in the metallic structure 2 and provides this energy to the downhole communications repeater 7.

[0326] The structure and operation of the well installation, cathodic protection system and power distribution system in the arrangement of Figure 3 are substantially the same as those in the system described with reference to Figures 1, 2A to 2D.

[0327] The only difference lies in the fact that the power distributed by the downhole component by the power distribution system is a communications repeater 7 instead of a downhole pressure gauge 5.

[0328] Therefore, detailed description of the well installation and energy management system is omitted here for the sake of brevity. Where components referred to with respect to the present embodiment are the same as those in Figures 1 and 2A to 2D, the same reference numerals are used.

[0329] The downhole communications repeater 7 is arranged to capture signals from the downhole metal structure 2 in the region of the repeater 7 and transmit the relevant data further towards the surface. In this embodiment the signals are applied to the downhole metal structure 2 as EM signals by a transmission tool 71 located further down the well, for example in the production pipe 21. Correspondingly the repeater 7 is arranged to capture EM signals.

[0330] In alternatives a different type of transmission tool may be provided to send signals that are captured by the repeater. Such a tool can, for example, be arranged outside the pipeline.

[0331] In alternatives, the communications repeater 7 can be arranged to capture acoustic signals from the downhole metal structure 2 that have been applied further down the well.

[0332] Similarly, the downhole communications repeater 7 may be arranged to apply acoustic signals to the downhole structure 2 for transmission toward the surface or arranged to apply EM signals to the downhole metal structure 2 for transmission to the surface or make use of the impedance modulation signaling technique described above.

[0333] In this way, for example, the communications repeater 7 can capture signals at its location and transmit these along the cable 42 to the collection module 4 by applying signals to it or by modulating the load it places. into the power source in the collection module 4. Similarly, the collection module 4 may be arranged to apply signals to the metallic structure 2 for transmission towards the surface or be arranged to modulate the charge it generates between the closely spaced connections 41a, 41b for detection on the surface by the upper communication unit 6.

[0334] Note that in the case of the provision of a downhole communications repeater 7, EM signals may, for example, be captured and/or applied by the repeater 7 using spaced contacts made with the metallic structure or using an inductive coupling comprising a toroid or signaling through an isolation joint that must be made available and so on. Similarly conventional acoustic signal collection and application techniques can be used.

[0335] In alternatives there may be communication from the surface downwards to locations at the bottom of the well and in general two-way communications. In this way repeater 7 can act as a repeater in both directions. Again two communication techniques can be used in parallel on at least one leg of the channel to provide redundancy.

[0336] Note also that the downhole communications repeater 7 can be provided in a location so as not to be in the product flow yet allowing well operating life.

[0337] Two specific examples in relation to Figure 3 are: 1. Repeater 7 comprises a continuously powered EM receiver at 3-500 m depth that either receives and decodes messages or simply continuously retransmits using load impedance modulation at a frequency larger raw data/signals to decode on the surface. 2. Repeater 7 comprises a continuously powered acoustic receiver at 3-500 m depth that receives and decodes messages and then retransmits data to the surface using load impedance modulation.

[0338] Note that in both these cases the repeater 7 can be provided in a downhole unit with the collection module or be separate from it. Again the repeater can be a two-way repeater.

[0339] In any of the systems described in the present application devices can be arranged to manage the energy budget, that is, use less energy in total, using intermittent operation of components such as EM or acoustic receivers and/or transmitters.

[0340] Figure 4 schematically shows a well installation including a remotely controlled valve and a power distribution system of the same general type as described above.

[0341] The general structure and operation of the well installation and power distribution system are again substantially the same as those described above in relation to the arrangements shown in Figures 1, 2A through 2D. Therefore, detailed description of these common elements is omitted here for the sake of brevity and the same reference numerals are used to indicate those characteristics that are common between the two modalities.

[0342] In this embodiment the well installation comprises a first hydraulically operated subsurface safety valve SSSV provided in the production pipeline 21 as is conventional.

[0343] However, here an additional subsurface safety valve 8 is also provided within the production pipeline 21, but deeper in the well. Thus in the present case the second subsurface safety valve 8 is provided as an additional safety or recoil measure. However, in alternatives it could be that the hydraulically operated subsurface safety valve SSSV could be dispensed with.

[0344] The second subsurface safety valve 8 is powered and operated using a power distribution system. In particular a collection module 4 is connected to the second subsurface safety valve 8 via a cable 42 and the collection module is arranged to output power and control signals to the second subsurface safety valve 8 via the cable 42. In this way energy is collected from the cathodic protection currents running through the downhole structure 2 and this is used to both control and operate the second subsurface safety valve 8.

[0345] Such a subsurface safety valve 8 may be located deeper in the wellbore than a traditional SSSV hydraulically operated subsurface safety valve. This is because it is not subject to the same range limits as hydraulically driven systems - there is no requirement to direct hydraulic fluid into it. It will be noted that here control signals for the second subsurface safety valve 8 may be transmitted by the upper communications unit 6 through the metal well structure 1, 2 for detection by the collection module 4 and transmission onwards to the subsurface safety valve 8. subsurface 8. In some circumstances the valve 8 may be made to operate in a fail-safe mode such that the valve will close in the absence of power and/or control signals. Note that certainly in an alternative the valve 8 and the collection module would be provided as part of a common downhole tool 4a. Still in some cases energy for closing the valve may come from another source, with the downhole energy distribution system providing energy for control operation and/or operating a trip mechanism.

[0346] Figure 5 shows an alternative well installation including well monitoring apparatus. Here again there are similarities with the arrangement shown in and described with reference to Figures 1, 2A to 2D. Again there is a collection module 4 provided within the downhole metal structure 2 and connected to spaced locations in the downhole structure 2 and in addition there is a downhole pressure gauge 5 connected to the collection module 4. In this case the collection module 4 and downhole pressure gauge 5 are both provided in ring B to provide condition monitoring in this ring. The downhole pressure gauge 5 may, for example, comprise a pressure and/or temperature sensor.

[0347] In this case the spaced locations 41a, 41b are provided in different courses of the downhole metal structure 2. In particular in this embodiment, a first of the connections 41a is made with the second casing tube 23 while the other of the connections 41b is made with the first well casing tube 22. The system works on a similar principle as discussed above and is thus based on a potential difference existing between these two connections 41a, 41b. In the present embodiment, this potential difference is obtained by isolating the two courses of metallic structure 22, 23 from each other at least in the region of these two connections. This means that there is a different passage to earth for the cathodic protection currents for the two metal structure courses 22, 23. In the present embodiment the means of insulating the two metal structure courses 22, 23 from each other comprises a coating of insulation 91 provided on the outer surface of the first well casing tube 22 and a plurality of isolation centralizers 92 provided on the first well casing tube 22 to keep it separate from the second well casing tube 23.

[0348] Preferably this insulation 91 and these centralizers 91 will be provided on a length of the first well casing pipe 22 of at least 100 meters and more likely 300 to 500 meters. Where desirable and practical, insulation spacers may be fitted to the outer course of metal framing forming the ring. In this way, for example, mounted on the second well casing tube 23 in the above example. Note that isolation does not need to be completely continuous to provide a useful effect. Creating a different path to earth is the goal. So although, for example, isolation may be provided for 100 m, it may not be continuous, or provide continuous isolation over this distance.

[0349] The benefit of the arrangement shown in Figure 5 is that the long lengths of cable 41 between the collection module 4 and the metal structure 2 required in the arrangement shown in Figure 1 can be dispensed with. This means the system can be easier to install. For example, the system may be implemented by virtue of a housing for the collection module 4 being mounted on a piece of metal pipe and provided with a sliding contact for contacting another piece of pipe through the ring. For simplicity, the position of the downhole pressure gauge 5 can be dispensed with and a sensor provided along the collection module 4 in a downhole unit 4. Such an arrangement can reduce the equipment time required for installation.

[0350] Thus in some circumstances the provision of insulation means 91, 92 may be preferred to the provision of cables 41. Which system is preferred for a given installation may be determined by external factors with respect to the installation or perhaps by modeling the installation particular.

[0351] In a typical case, however, the arrangement of Figure 1 is likely to provide better performance than that of Figure 5, where it is possible to use this system.

[0352] In an arrangement of the type shown in Figure 5 relatively larger current but relatively smaller potential difference is likely to be seen by the collection module. Thus, in an arrangement in Figure 5 the potential difference would be, for example, 10-20 mV and the current, for example, 1 Amp. On the other hand, in an arrangement in Figure 1, the potential difference would be, for example, 100200 mV and the current, for example, 100-150 mAmps. Greater potential difference is obtained by the greater spacing given by the cable(s) 41 in the arrangement of Figure 1, but the smaller current is caused by the resistance of the cable(s).

[0353] Except for this difference in how connections are made and a potential difference is obtained, and the different benefits and advantages observed, the structure and operation of the system as shown in Figure 5 are similar to those shown in Figure 1. Hence Thus, the different alternatives that are explained above in relation to Figures 1 to 4 are also applicable where a system such as that shown in Figure 5 is used.

[0354] This means that an isolation and connection arrangement as shown in Figure 5 can be used in each of the implementations shown in Figures 1, 3 and 4 and similarly the different shapes of the collection module 4 and downhole unit 4a discussed above can be used in an arrangement such as that shown in Figure 5.

[0355] Note that in some circumstances it may be desirable to use the present power distribution systems to provide a wireless-ready well installation even if there is no intention to use the wireless technology capabilities when the well is first installed. .

[0356] In this way the arrangement shown in Figure 3 where a communications repeater 7 and associated power distribution system are included in ring B can be provided when a well is first installed to make the well ready for wireless technology. This will facilitate communication to the surface if at a later time it is decided to use, for example, a wireless downhole signaling tool 71 to signal to the surface. Note here again that there is reference to “wireless” between downhole and outside - that is, no cables/wires running through the wellhead.

[0357] In other circumstances, the present systems may be retrofitted. For example, a system such as that shown in Figure 1 installed in ring A can be retrofitted when production piping is replaced. In another case, a system could be installed in the main bore of the production pipe. Note that importantly each of the arrangements and techniques described herein in the present application avoids the need for a cable to penetrate through the wellhead 1. In this way these systems can be used where no penetrator is available or the use of one is unattractive.

[0358] Although the arrangement in Figure 4 shows the provision of an additional subsurface safety valve 8, in other circumstances a different type of (possibly remotely operated) valve or component may be provided. For example, an arrangement of the type shown in Figure 4 may be used with a ring vent valve in a well to allow fluid communication or controlled ventilation between the ring and another or between a ring and the borehole. The valve could comprise a gas injection valve to allow gas to pass into the production piping bore from the A-ring. Similarly the valve may be a packer, a through-packer valve or a packer bypass valve. Again to allow ventilation of a particular ring under control from the surface. In another example the valve may comprise a flow control valve for either controlling input from a zone or providing a means for enabling improved pressure buildup data capture by removing the effect of wellbore storage. Note that the valve in each case may be a flow control device that may not allow complete closure of flow, but, for example, act as a variable choke.

[0359] The valve or component in each case may be a wireless control valve or component.

[0360] In another alternative, the present techniques can be used to communicate with and/or control a tool supported by a single-wire cable/wire or attached to coiled tubing in production piping 21. That is, such a tool can be arranged to apply signals to and/or capture signals from the pipeline, signals passing through the repeater 7.

[0361] With systems of the present type it might be possible to extract energy at the level of perhaps 50 mW. In this way the amount of energy that would be extracted is not particularly large, but what is of interest is the fact that this energy can be available for the entire life of the well and is sufficient to carry out useful functions such as controlling bottom devices. well, perform important measurements and allow transmission of these measurements to the surface.

[0362] Note that in general in embodiments of the general type shown in Figures 1 to 4 collection efficiency will be dominated by the cross-sectional area of the cable(s) 41 and the source impedance provided by connections 41a and 41b is low . This means that if multiple collection systems are included in a well installation there is little reduction in performance of any one collection module 4. Note that in general any additional collection system would have its own cables 41 where appropriate. This is on the basis that cable losses mean that typically little would be gained by having more than one collection system sharing a cable.

[0363] In general a plurality of collection modules of any of the types described above may be provided in a well installation. In this way, for example, a pressure gauge may be provided to monitor conditions in production piping, a pressure gauge may be provided to monitor a ring, and a valve may be provided, all of which have power supplied from a respective separate collection module. Similarly any one of the collection module can be used to power a plurality of devices. In some cases, each device may have a dedicated cable from the collection module. In other cases there may be a multipoint system where a collection module cable is used to connect to a plurality of downhole devices. The multipoint system may be arranged to permit power distribution and communications with the plurality of downhole devices. In this way, the cable can carry power signals, communication data and addressing data. Correspondingly the collection module can be arranged to manage the multipoint system.

[0364] Note that although in the above embodiments the cables 41, 42 run within unobstructed rings, in other cases one or more of the cables 41, 42 may pass through a packer (including an expansion packer), cement or other sealing device ring.

[0365] It will also be understood that in at least some cases features of the present systems and apparatus may be distributed in form. This means, for example, the collection module can be provided in a plurality of separate parts, components or submodules that can be located differently.

[0366] Figure 6 shows an alternative well installation that has similarity to the installation shown in Figure 1 and the same reference numerals are used to indicate the features in common with the embodiment of Figure 1 and detailed description of these common features is omitted .

[0367] The well installation shown in Figure 6 helps to illustrate in more detail some of the alternatives described above in relation to each of the well installations shown in and described with reference to Figures 1 to 5.

[0368] The well installation includes monitoring apparatus in the same manner as in Figure 1. In this way there is a collection module 4 connected via cables 41 to a pair of spaced locations 41a and 41b. However, in this case, a first of the locations 41a is in the production piping 21 and then a first of the cables 41 is connected to the production piping while the second of the spaced locations 41b is in the well casing pipe 22. In this way there are both axial and radial spacing between connections 41a, 41b in this embodiment and then the collection module 4 is connected through ring “A”. Furthermore, insulation 91 is provided in the production pipe 21 in the region of the second connection 41b and extends axially on either side thereof. Note that in another alternative, a connection would be with the formation instead of with the metallic structure. In some cases all of the energy management system apparatus could be provided outside the well casing tube - that is, between the well casing tube and the formation. This will generally be undesirable from an installation risk/difficulty standpoint, but it is a possibility.

[0369] Furthermore, in the present embodiment there are second and third collection modules 4' and 4" (which are part of respective downhole units) provided in the "A" ring. In this embodiment each of these other collection modules 4', 4" makes use of the same first cable 41 and in this way a terminal of each of the collection modules 4', 4" is connected to the first connection point 41a. Note that in other embodiments separate cables could be used to make these connections with the first connection point and this would be preferable leading to improved performance. A single top handle as shown, although possible, is unlikely to be used, but helps to simplify the design. In some cases a plurality of collection modules may be provided, which are distributed across different rings.

[0370] In the present embodiment the first collection module 4 is connected via a secondary cable 41 to a downhole pressure gauge 5 similarly to the embodiments shown in Figure 1. However, here the downhole pressure gauge 5 is located below of a P packer and cable 42 passes through it. The pressure gauge 5 in this case is arranged to make pressure and/or temperature measurements of conditions within the production pipeline 21 through a port 21a provided in the wall of the production pipeline 21. This means that although the downhole pressure gauge 5 is provided in the “A” ring, it is arranged for measuring parameters within the production pipe 21.

[0371] Furthermore, in this embodiment second and third downhole pressure gauges 5' and 5" are provided. In this embodiment each of the downhole pressure gauges 5, 5', 5” is connected to the collection module 4 via the same secondary cable 42. In this way this is a multipoint system and the cable 42 is used to carry power signals , control signals, parameter data and addressing data to allow power supply to each of the 5, 5', 5” pressure gauges as well as extracting readings from them.

[0372] Note that in alternative embodiments multiple downhole pressure gauges or other downhole devices may be powered from a collection module 4 via individual dedicated cables 42 rather than a single cable as in the present embodiment. Further, as alluded to above, while in the present embodiment there are a plurality of pressure gauges that are powered by a collection module, in other embodiments a collection module may be used to power different types of downhole device. In this way, a collection module, for example, would be used to power a downhole pressure gauge, a downhole repeater and a downhole valve.

[0373] In the present embodiment the second collection module 4' is part of a downhole tool comprising both a collection module and a sensor. In the present case the sensor is arranged for measuring parameters in the “B” ring through a port 22a provided in the first well casing tube 22. In this way, for example, the sensor in the second collection module 4' can be arranged to starting from measuring the pressure and/or temperature in ring “B”.

[0374] Furthermore, in the present embodiment the third collection module 4” is again part of a downhole tool comprising, in this case, the collection module and a communication unit for communicating with sensors 605 provided in the “B” ring. and in the “C” ring. Here, communication between the sensors 605 and the second collection module 4” is via wireless means. In this way, for example, there may be inductive signaling or acoustic signaling between the sensors 605 and the collection module 4”. The sensors 605 can be placed physically as close as possible to the collection module 4”.

[0375] It will be understood that once the data is in the upper communications unit 6, it can be transmitted further to any desired location using standard communications techniques such as mobile communications techniques, the internet and the like to a table location D to additional processing and/or review. Of course, wired connections would also be provided between the desktop location and the upper communication unit 6.

[0376] Furthermore, data may also be sent from the table location D to the upper communication unit 6 for transmission to the bottom of the well. In this way, for example, control signals can be transmitted from a table location D via the upper communication unit 6 to the bottom of the well to control operation of a collection module or sensor or downhole valve or repeater. or other and similarly any desired data can be sent in this manner to the bottom of the well.

[0377] In an alternative embodiment, insulation may be provided on the exterior of the outermost well casing tube, for example, the third well casing tube 24 in the embodiment shown in Figure 6 in the region near the wellhead 1. This can help direct the maximum negative potential caused by cathodic protection currents further down the well. This is due to minimizing leakage in this region close to the wellhead. In this way, provision of insulation on the outermost well casing pipe can help to allow the higher connection 41a to be positioned lower in the well without significantly reducing the effectiveness of the system. If the potential drop curve is considered, then through the provision of insulation in the outermost well casing tube 24, the negative potential will fall very slowly in the isolated region near the wellhead and then begin to fall more rapidly once the non-isolated region having been reached.

[0378] Figure 7 is a graph showing an example of how the optimal energy available for collection in a well installation varies with depth in the well. As mentioned above, due to the increase in potential difference that is available as connection spacing increases on the one hand and cable resistance on the other hand, there tends to be an optimum depth for the bottom connection 41b, or speaking of a otherwise an optimal spacing between the two connections 41a and 41b. The graph shown in Figure 7 refers to a position where the upper connection 41a is approximately 5 meters below the wellhead and then in the region of the casing support. In this example it can be seen that the optimum depth at the bottom connection is on the order of 550 meters down the shaft. However, it can also be seen that a significant proportion of the optimum energy can be obtained at depths between, for example, 300 and 950 meters. In general terms it would be desirable to minimize cable length while obtaining optimal energy harvesting suggesting minimization of the depth of the second connection. However there may be some circumstances where advantage of the fact that the collection module can be placed deeper in the well can be obtained.

[0379] The optimal location for the top connection may depend on where the CP current (or other current) is injected and where the current is a maximum or the potential caused by the current is a maximum. The present methods and systems may include steps of first determining where the applied current (or potential) has maximum magnitude and choosing the location for the upper connection depending on this.

[0380] Where the well is an onshore well the upper connection may be within 100 m of the surface, preferably within 50 m.

[0381] Where the well is a subsea well the upper connection may be within 100 m of the sea floor, preferably within 50 m.

[0382] As mentioned above, although the above description makes reference to collection from cathodic protection currents and this is preferred, if other currents are present in the metallic structure, they can equally be used.

[0383] It will be understood that although particular examples are given above, in general any of the components of the system can be provided in any available rings.

[0384] Where mention is made above of optimization through modeling, for example in relation to connection spacing, use of insulation, choice of radial only or axial spacing, and the selection of a preset collection load at least one of the following parameters can be used in the model: 3. Attenuation rate at the top of the well derived from well casing pipe and tubular dimensions, weights and material type (resistivity) and the resistivity of the overburden (medium surrounding the well ). 4. Top connection location. 5. Lower connection location. 6. Cross-sectional area and type of material (resistivity) of the upper cable used in inputs to the collector. 7. Number, location, material (electrical potential) and surface area of wellhead anodes. 8. Well effective resistance as seen from the seafloor/wellhead, again derived from well casing pipe and tubular dimensions, weights and material type (resistivity) and overburden resistivity (medium surrounding the wellbore) but this time for full completion.

[0385] In particular examples of the above systems, the cable or cables 41 used in connecting the collection module to the structure/surroundings may have a cross-sectional area of, for example, 10 mm2 to 140 mm2, 10 mm2 would be considered a low limit of a desired operating cable size. Larger cross-sectional area would normally be preferred. A 140 mm2 cable would be a Kerite Flat Type (RMT) LTF3 cable. This represents the upper end of what is currently commercially available, but if available, larger sizes can be used.

[0386] Figure 8 is a flowchart showing a process for optimizing energy collection from a collection module of the type described above.

[0387] In step 801 the dc to dc converter 44 starts using initial settings/configuration and distributes available energy to the charge storage medium 45.

[0388] In step 802 a determination is made as to whether there is sufficient voltage to power the microprocessor in the central unit 46. If not, this step 802 repeats until the answer is yes and when the answer is yes, the process proceeds to step 803 where the microprocessor in the central unit 46 is powered.

[0389] Then in step 804 the microprocessor measures the power output from the energy harvester and in step 805 the microprocessor modifies the settings of the dc to dc converter 44 to slightly increase the load. Subsequently in step 806 a determination is made whether this leads to an increase in collector output. If the answer is yes then the process returns to before step 850 so that the dc to dc converter settings 44 can be changed again to slightly increase the load.

[0390] On the other hand, if the determination is made in step 806 that output has not been increased, then the process proceeds to step 807 where the microprocessor modifies the settings of the dc to dc converter 44 to slightly decrease the load and the process returns stops before step 806 so that it can be determined whether this resulted in an increase in output.

[0391] Thereafter, steps 805, 806 and 807 are iteratively repeated during energy harvesting so that the load is successively increased and decreased based on the result in step 806. In this way this leads to dynamic optimization of energy harvesting .

[0392] As mentioned above, where the dc to dc converter 44 makes use of a Field Effect Transistor and an accompanying transformer, the step of changing the settings of the dc to dc converter in steps 805 and 807 may comprise the step of changing taps used on the secondary transformer in order to modify the load appropriately. This will also be true where such a variable transformer is provided with an H-bridge as shown in Figure 2D. Alternatively in such a case the duty cycle of the transistors in the H-bridge can be adjusted to vary the load.

[0393] Figure 9 shows a flowchart illustrating operation of a downhole unit 4a of the type described above.

[0394] In step 901 it is determined whether there is sufficient energy to power the processor in the central unit 46. If not, the process remains in this step until there is sufficient energy.

[0395] When there is sufficient power, the process proceeds to step 902 where it is determined whether a command has been received or there is a request to send a programmed data set. If not, then the process remains in this state of determining whether any action is required until action is required.

[0396] When action is required, the process proceeds to step 903 where data is retrieved from a sensor or memory as required and the charge presented by the energy harvesting module between connections 41a is modulated to encode data.

[0397] Separately at the wellhead, in step 904, the voltage potential of the wellhead is monitored and the data is decoded in a second microprocessor. Then in step 905 the extracted data can be exported or retransmitted to a client, for example, via a seawater acoustic link or an umbilical link.

[0398] Figure 10 shows a well installation including a platform 1000. The wellhead 1 is provided on a deck 1001 of the platform 1000. In this case the metallic structure includes a riser 1002 between the sea floor and the deck 1001 The production pipe 21 runs within the riser 1002 as well as to the bottom of the well. The well casing tube 22, 23 is provided at the bottom of the well. The innermost well casing tube 22 is a continuation of the riser tube 1002. Cathodic protection anodes 3B are provided in the platform structure 1000. Electrical connection will exist between the platform and the downhole structure 2 (casing tube well and production piping). This can be through a 1003 drill template and/or through the wellhead, riser pipe and other components such as riser guides. In such cases it may be difficult to know where to make the top connection of a collection arrangement of the type shown in Figures 1, 3, 4 and 6 to obtain best performance. It will not always be known where the cathodic protection current will be injected into the conductor tube (the courses of elongated members) running down to the wellbore. As mentioned above it may be desirable to make the upper connection adjacent to the location where the CP current is injected. If optimization is being sought, one option is to control this injection point - that is, ensure galvanic connection at a known point. Another option is to provide the system with a plurality of alternative upper connection points for the collection module and allow selection of the most effective connection point after installation. Typically in such a case, the power distribution system will be installed with a plurality of cable connections superior to the metallic structure and the best performing one selected through, for example, operation of a switch under control of the central unit.

Signal, device and sensor options

[0399] Several particular signaling techniques are described above. For the avoidance of doubt it should be noted that a wide range of signaling techniques can be used alone or in combination on various parts of the signal channel in current-type systems. In this manner wireless signals may be transmitted in at least one of the following forms: electromagnetic, acoustic, inductively coupled tubular and coded pressure pulsation and references herein to “wireless” refer to said forms unless otherwise noted. declared.

[0400] Signals, unless otherwise stated, may include control and data signals. Control signals can control downhole devices including sensors. Sensor data can be transmitted in response to a control signal. Furthermore, data acquisition and/or transmission parameters, such as acquisition and/or transmission rate or resolution, can be varied using suitable control signals.

[0401] Pressure pulses include methods of communicating to/from the well/hole, to/from at least one additional location within the well/hole, and the surface of the well/hole, using positive pressure changes and/or or negative, and/or changes in the flow rate of a fluid in a tubular and/or annular space.

[0402] Coded pressure pulses are such pressure pulses where a modulation scheme has been used to encode commands and/or data within variations in pressure or flow rate and a transducer is used within the well/borehole to detect and/or generate the variations, and/or an electronic system is used within the well/hole to encode and/or decode commands and/or data. In this way, pressure pulses used with a well/borehole electronics interface are defined here as coded pressure pulses. An advantage of coded pressure pulses, as defined herein, is that they can be sent to electronic interfaces and can provide greater transmission rate and/or bandwidth than pressure pulses sent to mechanical interfaces.

[0403] Where coded pressure pulses are used to transmit control signals, various modulation schemes can be used to encode control signals such as a pressure change or rate of pressure change, on/off (OOK), pulse position (PPM), pulse width modulation (PWM), frequency shift keying (FSK), pressure shift keying (PSK), amplitude shift keying (ASK), combinations of modulation schemes can also be used, for example, OOK-PPM-PWM. Transmission rates for pressure coded modulation schemes are generally low, typically less than 10 bps, and may be less than 0.1 bps. Coded pressure pulses can be induced in static or flowing fluids and can be detected by directly or indirectly measuring changes in pressure and/or flow rate. Fluids include liquids, gases and multiphase fluids and may be static control fluids and/or fluids being produced from or injected into the well.

[0404] Wireless signals may be such that they are capable of passing through a barrier, such as a plug or said annular sealing device, when fixed in place. In this way wireless signals can be transmitted in at least one of the following ways: electromagnetic, acoustic and inductively coupled tubular.

[0405] EM/Acoustics and coded pressure pulsation use the well, borehole or formation as the transmission medium. The EM/acoustic or pressure signal can be sent from the well or from the surface. If provided in the well, an EM/acoustic signal may be able to travel through any annular sealing device, although for certain embodiments, it may travel indirectly, for example, around any annular sealing device.

[0406] Electromagnetic and acoustic signals are useful since they can transmit through an annular sealing device without special inductively coupled tubular infrastructure, and for data transmission, the amount of information that can be transmitted is typically greater compared to with encoded pressure pulsation, especially receiving data from the well.

[0407] Where inductively coupled tubulars are used, there are typically at least ten, usually many more, individual lengths of inductively coupled tubulars that are brought together in use, to form a string of inductively coupled tubulars. They have an integral thread and can be formed from tubulars such as tubing, drill pipe or well casing pipe. At each connection between adjacent lengths there is an inductive coupling. Inductively coupled tubulars that can be used can be provided by N O V under the brand name Intellipipe®.

[0408] In this way, wireless EM/acoustic or pressure signals can be transmitted a relatively long distance as wireless signals, sent over at least 200 m, optionally more than 400 m or more which is a clear benefit over other short range signals. Inductively coupled tubulars provide this advantage/effect by combining the integral wire and inductive couplings. The distance traveled can be much longer depending on the length of the well.

[0409] Data and commands within signals may be retransmitted or transmitted by other means. In this way, wireless signals could be converted into other types of wireless or wired signals, and optionally retransmitted, via the same or other means, such as hydraulic, electrical or fiber optic lines. For example, signals may be transmitted via a cable for a first distance, such as over 400 m, and then transmitted via acoustic or EM communications for a shorter distance, such as 200 m. In another example they can be transmitted 500 m using coded pressure pulsation and then 100 m using a hydraulic line.

[0410] Non-wireless medium can be used to transmit the signal in addition to the wireless medium. The distance traveled by signals is dependent on the depth of the well, often the wireless signal, including repeats but not including any non-wireless transmission, travels more than 1000 m or more than 2000 m.

[0411] Different wireless signals can be used in the same well for communications going from the well toward the surface and for communications going from the surface to the well.

[0412] Wireless signals can be sent to a communication device, directly or indirectly, for example, by making use of relays within the well and/or below any annular sealing device. A wireless signal can be sent from the surface or from a probe descending into the cable/coiled tubing (or tractor) at any point in the well optionally above any annular sealing device.

[0413] Acoustic signals and communication may include transmission through vibration of the well structure including tubulars, well casing tube, casing, drill pipe, drill collars, tubing, coiled tubing, sucker rod, downhole tools; transmission through fluid (including through gas), including transmission through fluids in uncased sections of the well, within tubulars, and within annular spaces; transmission through static or flowing fluids; mechanical transmission via cable, single-strand wire or coiled rod; transmission through land; transmission through wellhead equipment. Communication through the structure and/or through the fluid is preferred.

[0414] Acoustic transmission can be at subsonic (< 20 Hz), sonic (20 Hz - 20 kHz) and ultrasonic (20 kHz - 2 mHz) frequencies. Preferably the acoustic transmission is sonic (20 Hz - 20 kHz).

[0415] Acoustic signals and communications may include Frequency Shift Keying (FSK) and/or Phase Shift Keying (PSK) modulation methods and/or more advanced derivatives of these methods, such as Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM), and preferably incorporating Spread Spectrum Techniques. Typically they are adapted to automatically tune acoustic signaling frequencies and methods to suit conditions.

[0416] Acoustic signals and communications can be unidirectional or bidirectional. Piezoelectric transducer, moving coil transducer or magnetostrictive transducers can be used to send and/or receive the signal.

[0417] Electromagnetic (EM) wireless communication (sometimes referred to as Quasi-Static (QS)) is typically in the frequency ranges of: (selected based on propagation characteristics) sub-ELF (extremely low frequency) < 3 Hz (normally above 0.01 Hz); ELF 3Hz to 30Hz; SLF (super low frequency) 30 Hz to 300 Hz; ULF (ultra-low frequency) 300 Hz to 3 kHz; and VLF (very low frequency) 3 kHz to 30 kHz.

[0418] An exception to the above frequencies is EM communication using the tube as a waveguide, particularly, but not exclusively, when the tube is filled with gas, in which case frequencies from 30 kHz to 30 GHz may be typically used depending on the size of the pipe, the fluid in the pipe and the communication range. The fluid in the tube is preferably non-conductive. US 5,831,549 describes a telemetry system involving gigahertz transmission in a gas-filled tubular waveguide.

[0419] Sub-ELF and/or ELF are useful for communications from a well to the surface (e.g., over a distance of more than 100 m). For more local communications, e.g. less than 10 m, VLF is useful. The nomenclature used for these bands is defined by the International Telecommunication Union (ITU). EM communications may include transmitting communications through one or more of the following: imposing a modulated current on an elongated member and using earth as feedback; transmitting current in one tubular and providing a return path in a second tubular; use of a second well as part of a current path; near-field or far-field transmission; creating a current loop within a machining portion of the well in order to create a potential difference between the machining and ground; use of closely spaced contacts to create an electrical dipole transmitter; use of a toroidal transformer to impose current in the well machining; use of an isolation sub; a spiral antenna for creating a modulated time-varying magnetic field for local or full formation transmission; transmission within the well casing pipe of the well; use of the elongated member and ground as a coaxial transmission line; use of a tubular as a waveguide; transmission out of the wellbore casing pipe.

[0420] Especially useful is imposing a modulated current on an elongated member and using earth as a return; creating a current loop within a portion of the metalwork of the well in order to create a potential difference between the metalwork and ground; use of closely spaced contacts to create an electrical dipole transmitter; and use of a toroidal transformer to impose current to the well metal machining.

[0421] To control and direct current advantageously, any number of several different techniques can be used. For example, one or more of: use of a casing or insulation spacers on well tubulars; selection of well control fluids or cements inside or outside tubulars to conduct electrically with or insulate tubulars; use of a high magnetic permeability toroid to create inductance and then an impedance; use of an insulated wire, insulating cable, or elongated conductor for part of the transmission path or antenna; use of a tubular as a circular waveguide, use of frequency bands of SHF (3 GHz to 30 GHz) and UHF (300 MHz to 3 GHz).

[0422] Various means for receiving a transmitted signal may be used, these may include detecting a flow of current; detection of a potential difference; use of a dipole antenna; use of a spiral antenna; use of a toroidal transformer; use of a Hall effect or similar magnetic field detector; use of sections of the pit metal machining as part of a dipole antenna.

[0423] Where the expression “elongated member” is used, for the purposes of EM transmission, it could also mean any elongated electrical conductor including: cladding; well casing pipe; pipe or tubular; coiled tubing; pump rod; cable; drill pipe; single strand wire or coiled rod.

[0424] Pressure gauges may comprise one or more of several different sensor types. The or each sensor may be coupled (physically or wirelessly) to a wireless transmitter and data may be transmitted from the wireless transmitter above the annular sealing device or otherwise toward the surface. Data can be transmitted in at least one of the following ways: electromagnetic, acoustic and inductively coupled tubulars, especially acoustic and/or electromagnetic as described here above.

[0425] Such short range wireless coupling can be facilitated by EM communication in the VLF range.

[0426] The sensors provided can capture any parameter and therefore be any type of sensor including, but not necessarily limited to, such as temperature, acceleration, vibration, torque, displacement, movement, cement integrity, pressure, direction and inclination, load , various angles of tubular/well casing tube, corrosion and erosion, radiation, noise, magnetism, seismic movements, stresses and strains in tubular/well casing tubes including coiling, shearing, compressions, expansion, bending and any other form deformation; chemical or radioactive trace detection; fluid identification such as gas detection; water detection, carbon dioxide detection, hydrate, wax and sand production; and fluid properties such as (but not limited to) flow, density, water cut, resistivity, pH, viscosity, bubble point, gas/oil ratio, hydrocarbon composition, fluid color or fluorescence. Sensors may be imaging, mapping and/or scanning devices such as, but not limited to, camera, video, infrared, magnetic resonance, acoustic, ultrasound, electrical, optical, impedance and capacitance. Sensors can also monitor equipment in the well, for example valve position or engine speed. Furthermore, sensors can be adapted to induce the detected signal or parameter through the incorporation of suitable transmitters and mechanisms.

[0427] The apparatus, especially the sensors, may comprise a memory device that may store data for retrieval at a later time. The memory device can, under certain circumstances, be rescued and data recovered after rescue. The memory device may be configured to store information for at least one minute, optionally at least one hour, more optionally at least one week, preferably at least one month, more preferably at least one year or more than five years.

Claims (38)

1. Downhole electrical energy collection system for collecting electrical energy in a well installation having a metallic structure provided with cathodic protection, in order to conduct cathodic protection electrical current, in use, characterized by the fact that it comprises : a collection module electrically connected to the metallic structure at a first location and electrically connected to the metallic structure at a second location spaced apart from the first location, the first and second locations being chosen so that, in use, there is a potential difference between them due to the cathodic protection electrical current flowing in the structure; and the collection module arranged to collect electrical energy from the cathodic protection electrical current, wherein the collection module is arranged to collect electrical energy from dc currents. 2. Downhole electrical energy collection system according to claim 1, characterized by the fact that the current flow within the portions of the metallic structure in regions between the first location and the second location is in the same longitudinal direction . 3. Downhole electrical energy collection system according to claim 1, characterized by the fact that there is an uninterrupted current flow path between the first location and the second location that is at least partially through the structure metallic. 4. Downhole electrical energy collection system according to any one of the preceding claims, characterized in that the spaced locations are axially spaced. 5. Downhole electrical energy collection system according to any one of the preceding claims, characterized in that the spaced locations are radially spaced. 6. Downhole electrical energy collection system according to any one of the preceding claims, characterized by the fact that at least one connection between the at least one of the electrical contacts and the collection module is provided by an insulated cable . 7. Downhole electrical energy collection system, according to any of the preceding claims, characterized by the fact that the spacing between the locations is at least 100 m. 8. Downhole electrical energy collection system according to any one of the preceding claims, characterized in that the connections are made with a common course of elongated metallic members that is part of the metallic structure. 9. Downhole electrical energy collection system according to any one of claims 1 to 7, characterized in that a first of the connections is made with a first course of elongated metallic members that is part of the metallic structure and a second of the connections is made with a second, distinct course of elongated metallic members that is part of the metallic structure. 10. Downhole electrical energy collection system according to claim 9, characterized by the fact that insulation means is provided for electrical isolation of the first course of metallic elongated members from the second course of metallic elongated members in the region of connections. 11. Downhole electrical energy collection system according to claim 10, characterized by the fact that isolation means are provided to prevent electrical contact between the two courses of elongated metallic members for a distance of at least 100 m. 12. Downhole electrical energy collection system according to any one of the preceding claims, characterized in that the current flowing in the elongated members is supplied from the surface of the well. 13. Downhole electrical energy collection system according to any one of the preceding claims, characterized by the fact that the current flowing in the elongated member is supplied from one or more sacrificial anodes. 14. Downhole electrical energy collection system according to claim 12, characterized in that the current flowing in the elongated members is a current impressed from an external energy source. 15. Downhole electrical energy collection system according to any one of the preceding claims, characterized in that the well surface voltage is, in use, limited to a range minus 0.7 volts to minus 2 volts with respect to a silver/silver chloride reference cell. 16. Downhole electrical energy collection system according to any one of the preceding claims, characterized by the fact that the potential difference between the spaced contacts is less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt. 17. Downhole electrical energy collection system, according to any of the preceding claims, characterized by the fact that the metallic structure is provided with cathodic protection. 18. Downhole electrical energy collection system according to any one of the preceding claims, characterized by the fact that the upper spaced contact is: where the well is an earth well, within 100 m, preferably within 50 m of the earth's surface; and where the well is a subsea well, within 100m, preferably within 50m of the sea floor. 19. Downhole electrical energy collection system according to any one of the preceding claims, characterized by the fact that the upper spaced contact is located adjacent to a location that corresponds to a maximum in magnitude of potential caused by the electrical current that flows in the structure. 20. Downhole electrical energy collection system, according to any of the preceding claims, characterized by the fact that it further comprises downhole communication means for transmitting and/or receiving data. 21. Downhole electrical energy collection system, according to claim 20, characterized by the fact that the downhole communication means is arranged for data transmission through the variation of the load seen between the connections at the locations spaced. 22. Downhole device operating system characterized by the fact that it comprises a downhole electrical energy collection system as defined in any one of the preceding claims and a downhole device, the collection module being electrically connected to and arranged to provide power to the downhole device. 23. Downhole device operating system according to claim 22, characterized in that the downhole device comprises at least one of: a downhole sensor; a downhole actuator; an annular sealing device, for example a packer or packer element; a valve; a downhole communications module, for example, a transceiver or repeater. 24. Downhole device operating system according to claim 23, characterized in that the valve comprises at least one of: a subsurface safety valve; a borehole flow control valve; a hole-to-ring valve; a ring-to-ring valve; a bore valve for pressure compensation chamber; a ring valve for pressure compensation chamber; a through packer or packer bypass valve. 25. Downhole device operating system according to any one of claims 22 to 24, characterized in that the downhole device is provided in a location other than the collection module in the well. 26. Downhole device operating system according to claim 25, characterized in that the collection module is disposed at a selected location in the bottom of the well for collecting energy and a cable is provided for supplying electrical power further downhole to the downhole device at a different location in the well. 27. Downhole monitoring system for monitoring at least one parameter in a well installation having a metallic structure conducting electrical energy current characterized by the fact that it comprises: an electrical energy collection system as defined in any one of the claims 1 to 22; a sensor module for capturing at least one parameter; and a communications module for capturing data by encoding readings from the sensor module towards the surface, the electrical energy collection system being arranged to provide electrical energy to at least one of the sensor module and the communications module. 28. Downhole well monitoring system for monitoring at least one parameter in a well installation having a metallic structure provided with cathodic protection so as to conduct cathodic protection electrical current, in use, characterized by the fact that it comprises : a sensor module for capturing at least one parameter; a communication module for sending data encoding readings from the sensor module towards the surface; and an electrical energy collection system comprising a collection module electrically connected to the metallic structure at a first location and electrically connected to the metallic structure at a second location spaced from the first location, the first and second locations being chosen so that, in use , there is a potential difference between them due to a cathodic protection electrical current flowing in the structure; and the collection module being arranged to collect electrical energy from the cathodic protection electrical current, the electrical energy collection system being arranged to supply electrical energy to at least one of the sensor module and the communications module, wherein the collection module is arranged to collect electrical energy from dc currents. 29. Downhole well monitoring system according to claim 27 or 28, characterized in that the communication module is arranged to modulate the electrical current flowing in the metallic structure at a signaling location so as to encoding data to allow extraction of the data at a reception location remote from the signaling location by detecting the effect of said modulation on the electrical current at said reception location. 30. Downhole well monitoring system, according to claim 29, characterized by the fact that the communication module is arranged to control the charge generated by the collection module to cause said modulation of the electrical current in the metallic structure at the signage location. 31. Downhole well monitoring system according to any one of claims 27 to 30, characterized in that the sensor module comprises a pressure sensor that is optionally arranged for monitoring the pressure of the well reservoir. 32. Downhole monitoring system according to any one of claims 27 to 31, characterized in that the sensor module comprises a pressure sensor; the pressure sensor is arranged for monitoring the pressure in a well ring; and optionally the pressure sensor is arranged for monitoring the pressure in a closed well ring. 33. Downhole communication repeater system for use in a well installation having a metallic structure conducting electrical current characterized by the fact that it comprises: an electrical energy collection system as defined in any one of claims 1 to 19; and a communications repeater disposed downhole in the wellhead and arranged for communicating with a first device beyond the wellhead using a communication channel that is wireless at least through the wellhead and arranged for communicating with a second device located in the wellhead. well and then below the wellhead so that the communications repeater can act as a repeater between the first and second devices, an electrical energy collection system being arranged to supply electrical energy to the communications repeater. 34. Downhole communication repeater system, for use in a well installation having a metallic structure provided with cathodic protection in order to conduct cathodic protection electrical current, in use, characterized by the fact that the system comprises: a repeater communications device disposed downhole in the wellhead and arranged for communication with a first device beyond the wellhead using a communication channel that is wireless at least through the wellhead and arranged for communication with a second device located in the wellhead and then below the wellhead so that the communications repeater can act as a repeater between the first and second devices; and an electrical energy collection system comprising a collection module electrically connected to the metallic structure at a first location and electrically connected to the metallic structure at a second location spaced from the first location, the first and second locations being chosen so that, in use , there is a potential difference between them due to the cathodic protection electrical current that flows in the structure; and the collection module being arranged to collect electrical energy from the cathodic protection electrical current, the electrical energy collection system being arranged to supply electrical energy to the communications repeater, wherein the collection module is arranged to collect electrical energy from dc currents. 35. Downhole communication repeater system according to claim 33 or 34, characterized in that the communication repeater is arranged to modulate the electrical current flowing in the metallic structure at a signaling location in order to encode data to allow extraction of the data at a reception location remote from the signaling location by detecting the effect of said modulation on the electrical current at said reception location. 36. Downhole communication repeater system according to claim 35, characterized by the fact that the communications repeater is arranged to control the charge generated by the collection module to cause said modulation of the electrical current in the metallic structure in the signaling location. 37. System, according to any of the preceding claims, characterized by the fact that the well is a submarine well. 38. Downhole electrical energy collection system, according to claim 1, characterized by the fact that: the metallic structure comprises at least one course of elongated metallic members conducting electrical current; and the collection module comprises an electrical circuit connected between spaced contacts to collect energy from a potential difference between the spaced contacts, wherein a first of the spaced contacts is made with the at least one course of metallic elongated members at a first location. and a second of the spaced contacts is made with the at least one course of metallic elongated members at a second location and the potential difference is caused by cathodic protection currents flowing in the at least one course of elongated members and, at least in part, the impedance of the at least one course of elongated members.