DK178835B1

DK178835B1 - Circulating sub with activation mechanism and a method thereof

Info

Publication number: DK178835B1
Application number: DKPA201470715A
Authority: DK
Inventors: Sigurd Solem
Original assignee: Advancetech Aps
Priority date: 2014-03-14
Filing date: 2014-11-20
Publication date: 2017-03-06
Also published as: US20180328141A1; EP3221548A4; RU2017121271A3; WO2016078671A1; RU2017121271A; CA2968427A1; RU2711522C2; EP3221548A1; DK201470715A1

Abstract

The present invention relates to an activation method, an activation mechanism and a downhole tool comprising the activation mechanism. The activation mechanism comprises a pressure switch for turning power to the electrical components, a control unit connected to a pressure sensor for sensing the internal pressure of the drilling fluid located in a first fluid conduit. The control unit controls an actuator unit connected to a moveable valve element. The actuator unit moves the valve element from a closed position when activated. A seat for the valve element is arranged relative to a second fluid conduit so that the valve element closes the second conduit when it is placed in its seat. This provides a very fast and accurate activation method that involves the use of balls or RFID tags. Furthermore, the downhole tool can be activated even if no actual flow is passing through the tool.

Description

Circulating sub with activation mechanism and a method thereof Field of the Invention

The present invention relates to an activation mechanism for activating a circulating sub of a drill string and comprising: at least one sensor configured to sense at least a pressure of a drilling fluid located in a first fluid conduit in the circulating sub when installed, the first fluid conduit being connected to a first opening and a second opening in the circulating sub; a control unit connected to the sensor and configured to monitor the sensed signal of the sensor, wherein the control unit is configured to electronically activate the movement of at least one moveable valve element based on the sensed signal, and where the moveable valve element is configured to be arranged relative to at least a second fluid conduit in the circulating sub when installed, wherein the valve element is configured to move between an open position and a closed position, wherein the second fluid conduit is in fluid communication with the first fluid conduit, and the valve element comprises at least one valve end configured to close the second fluid conduit in the closed position and to open the second fluid conduit in the open position.

The present invention also relates to a circulating sub for positioning in a borehole and comprising: an outer housing facing an inner wall of the borehole where the outer housing is configured to be placed inside the borehole, a first fluid conduit connected to a first opening in one end of the circulating sub and a second opening in the other end of the circulating sub for leading a drilling fluid through the circulating sub, and at least a second fluid conduit in fluid communication with the first fluid conduit via at least one inner opening and connected to at least one outer opening located in an outer surface of the housing.

The present invention finally relates to a method for activating a circulating sub using an activation mechanism as mentioned above, where the method comprises the steps of positioning the circulating sub at a predetermined depth of a borehole, increasing a pressure of a drilling fluid located in the first fluid conduit of the circulating sub, monitoring the pressure of the drilling fluid inside the first fluid conduit using at least one pressure sensor, and activating the circulating sub when a certain event is detected using a control unit.

Background of the Invention

Today, various activation systems are used to selectively activate downhole tools, such as circulating subs, under-reamers and other types of downhole tools. It is known to drop balls of various sizes into the drilling fluid to activate or deactivate a circulating sub having a corresponding number of ball retainers for receiving these balls. Such an activation system only has a limited number of activations/deactivations, typically between five to seven times, and determined by the size of the ball retainers. Once full, the circulating sub must be retrieved and the ball retainers emptied before it can be lowered into the drilling hole again. Furthermore, the ball may be stopped in the fluid passageway by accumulated solid particles, thereby blocking the circulation of drilling fluid and causing an increase in pressure above the blockage which could damage the downhole tool or even the operation equipment located at ground level.

Another activation system solving this problem uses a radio frequency (RF) receiver or transceiver arranged in the circulating sub to wirelessly communicate with one or more radio frequency identification (RFID) tags being dropped into the drilling fluid. Once within communication range of the receiver/transceiver, the RFID device is able to communicate with the circulating sub for activating or deactivating a selected circulating sub. An exemplary solution thereof is disclosed in US 2013/0319767 A1 wherein active or passive RFID tags are used to activate a desired function of the circulating sub based on the command received from the RFID tag. A pressure sensor in the circulating sub can be used instead to detect mud pulses or flow rate signals for activating the circulating sub.

Both types of activation systems provide a slow and time consuming process since each ball or RFID tag first has to be pumped via the drilling fluid from the ground level to the selected downhole tool before the downhole tool can be activated or deactivated. It often takes more than one hour for the RFID tag or ball to reach a downhole tool located at a depth of about 3000 metres as the speed by which the RFID tag or ball travels depends on the pumping speed and the internal diameter of the drilling string.

Yet another solution is to use an indexing type activation system in which the mode of the downhole tool is changed every time the pumps circulating the drilling fluid are turned off and on. The disadvantage of this solution is that the sequence of modes is determined by the indexing mechanism, thus the operator must follow the indexing sequence to select a desired mode. Furthermore, it is well known that such indexing mechanisms have a complex configuration that is prone to mechanical failures. WO 2013/103907 A1 discloses an under-reamer having a pressure activated flow switch mechanism for activating and deactivating the under-reamer. The flow switch mechanism comprises a piston configured to move between an open position and a closed position based on the different pressures. A spring element pushes the piston towards an upper seat of the housing to form a seal in the closed position. Once the differential pressure of the passing drilling fluid exceeds the spring force, the piston is axially moved to the open position where it contacts a lower seat of the housing. Thereby, allowing drilling fluid to enter an upper chamber while drilling fluid is ventilated from a lower chamber out through an outer opening. The drilling fluid in the upper chamber further acts on another piston which radially moves the cutting block out of the housing. The spring element forces the piston back to the closed position when the spring force exceeds the combined forces of the differential pressure and the friction of an annular seal located between the piston and the surrounding housing. This activation mechanism has a complex configuration and requires an actual flow through the under-reamer tool for activating the cutting block. US 2013/0284424 A1 discloses a circulating sub comprising a housing having a central fluid path in fluid communication with a bypass path in the sidewall of the housing. The bypass path has an inlet opening facing the central fluid path and an outlet opening facing the annulus surrounding the sub. A moveable piston is arranged inside an interior chamber relative to this bypass path and comprises a plug facing a plug seat located in the bypass path. A pressure sensor is used by a controller in the interior chamber to detect an activation signal via mud pulses or downlink signals transferred through the passing mud in the central fluid path. Upon activation, the controller ignites a combustible agent wherein the combustion gases push the piston into the bypass path until the plug comes into contact with the plug seat. This closes off the bypass path. This configuration provides a single-use activation after which the circulating sub must be retrieved from the borehole and reset. This activation mechanism can only be accessed and reset by taking the sub apart which adds to the complexity and costs of the sub.

There is a need for providing an improved method that allows for a fast and accurate activation of a downhole tool, such as a circulating sub, without the use of a ball or RFID tag or a complicated downhole link.

Object of the Invention

An object of this invention is to provide an activation mechanism that overcomes the drawbacks of the prior art.

An object of this invention is to provide an activation mechanism that allows for a fast and accurate activation of a downhole tool.

An object of this invention is to provide an activation mechanism capable of activating the downhole tool without an actual flow of drilling fluid.

An object of the invention is to provide a downhole tool with an integrated activation mechanism that reduces the risk of a seal failing during operation.

Description of the Invention

An object of the invention is achieved by an activation mechanism, characterised in that the control unit is electrically connected to at least one actuator unit arranged relative to the valve element, wherein the actuator unit is configured to move the valve element from one position to the other position when activated.

The term “close” means that the valve element is moved into the conduit and substantially blocks off (shut) the fluid passageway so that no drilling fluid can flow through the conduit. The term “open” means that the valve element is moved out of the conduit so that the drilling fluid can flow through the conduit again.

This provides a simple and accurate activation mechanism that does not require a ball or RFID tag to be dropped into the drilling fluid for activating the downhole tool. This allows for a very fast activation/deactivation process compared to activation systems using a ball or RFID tag. In example, this configuration allows a downhole tool locat- ed at a depth of about 3000 metres to be activated within a few minutes, e.g. about three minutes. Furthermore, no indexing systems are needed to select an operation mode of the downhole tool, as the operation mode can be selected during the start-up process of the pumping system, thus no cycling between start and stop of the pumping system is needed to select the operation mode.

This configuration allows the activation mechanism to be integrated into the downhole tool or arranged as a standalone unit configured to be connected to the downhole tool. This configuration is well-suited for any type of downhole tools in which a bypass of the main fluid flow is desired. The drilling fluid may be any type of air, mist, foam, inert gas, or even any mixture or combination of different gravity fluids or gases.

In one embodiment, the control unit is configured to apply at least one predetermined time window to the sensed signal and to determine whether the sensed signal remains stable relative to a predetermined threshold value within the time window or not, where the valve element is activated if a stable pressure level is detected.

The terms “stable”, “stable level” and “stable pressure level” are defined by a predetermined threshold level or band having an upper and a lower limit value centred relative to the threshold value where the sensed parameter, e.g. the pressure, remains within the upper and lower limit values for at least the during of the time window.

The control unit may be any type of analogue, digital or logical electronic circuit suitable of processing and monitoring the electrical signals received from the sensors, e.g. the pressure sensor. Alternatively, another type of sensor may be used to detect a signal representative of the pressure of the drilling fluid. In a preferred configuration, the control unit comprises a controller, e.g. a microprocessor, configured to at least monitor the sensed pressure within a predetermined/first time window. The control unit/controller is further configured to compare the sensed pressure with at least one/first threshold level defining at least one/first operation mode. This operation mode may simply be to activate or deactivate the downhole tool. The control unit/controller is configured to determine whether the pressure of the drilling fluid remains stable within the first time window, i.e. within the upper and lower limit values of the threshold value. If a stable level is detected, then the control unit/controller sends a predetermined control signal or command to the downhole tool for activa-tion/deactivation of the tool or an operation mode thereof. The detection of a stable level of the sensed parameter allows a simpler and less complex activation process compared to downhole link systems using mud pulses or even flow pulses.

The time window may be selected based on the operating flow rate, the operating pressure or the dimensions of the borehole. The upper and lower limits may be determined based on the threshold value and/or the tolerance of the pumping system. The operating pressure may be selected between 10 and 100 bar. The time windows may be selected between 1 minute and 10 minutes, e.g. between 3 and 5 minutes. The upper and lower limit values may be selected between ±1 to 10% of the selected activa-tion/threshold level or the operating level.

In one embodiment, the control unit is further configured to apply at least a second time window to the sensed signal, and the control unit is further configured to determine whether the sensed signal remains stable relative to at least a second threshold value within the second time window or not.

In this configuration, the control unit/controller is configured to compare the sensed pressure to two or more threshold levels each defining an operation mode of the same downhole tool or an activation level for individual downhole tools. The individual downhole tools may be connected to the same activation mechanism or, alternatively, to individual activation mechanisms each designed for a selected threshold level. The individual downhole tools may further have the same configuration or different configurations depending on the desired application and/or position in the borehole. This allows multiple operation modes and/or downhole tools to be activated or controlled via the activation mechanism.

The second time window may be the same as the first window or have a different length and/or shape. The second threshold value may be the same as the first threshold value or have a value that is higher or lower than the first threshold value. The limit values for the first and second threshold values may be the same or they may differ for each threshold value, e.g. define different threshold ranges. This allows the activation or threshold levels to be optimised for each downhole tool and/or each operation mode for enabling a better control of multiple operation modes and downhole tools.

The control unit/controller may further be configured to detect a temporary drop or reduction in the sensed signal, e.g. the sensed pressure. The drop or reduction may be defined by a predetermined amplitude and/or time length. This allows the control unit to verify that the selected downhole tool or operation mode has been activated or deactivated. The second time window may be applied after this temporary drop or reduction has been detected, or after the pumping pressure has been increased or lowered to the second threshold value.

The control unit is configured to control the actuator unit which in turn moves the valve element in at least one predetermined direction, e.g. in an axial direction. The direction of movement may be parallel or orthogonal to the axial/longitudinal direction of the downhole tool. Any type of actuator unit may be used to move the valve element, e.g. a linear actuator, a piston or another suitable actuator unit. The actuator unit may be powered by an electrical, mechanical or hydraulic power unit integrated into or connected to the control unit. This allows the control unit to control the movement and/or speed of the valve element.

In an exemplary embodiment, the actuator unit comprises a solenoid element for inductively moving a magnetic or magnetic conductive rod or tube, e.g. a push rod, which in turn is mechanically connected to the valve element. The solenoid element is arranged relative to the rod/tube so that a magnetic field is directed into the material, e.g. steel or a ferromagnetic material, of the rod or tube. The rod or tube may form part of the valve element. An external or internal power unit, e.g. a battery, may be used to supply the solenoid. This allows for a simple and quick movement of the valve element using a minimum of components. A spring element may be arranged relative to the rod or tube for biasing the movement towards the closed position. This provides a failure safe function to the activation mechanism in which the valve element is held in the closed position. The valve element is also pushed back towards the closed position when the activation mechanism is deactivated.

In one embodiment, the valve element is a poppet valve arranged inside a chamber of the activation mechanism, wherein the poppet valve is configured to move relative to the chamber when activated.

The valve element is positioned inside a chamber, e.g. a first chamber, formed in the activation mechanism or in the downhole tool where the valve element is able to move relative to the chamber when activated or deactivated. The chamber may be formed in an outer housing of the downhole tool. The valve element may be formed as a poppet valve where one end is connected to the rod or tube, or the rod or tube may form part of that end. The valve element may be a solid or hollow element, e.g. with no internal fluid conduits. The rod tube may alternatively be connected to a housing or retainer configured to hold the one end of the valve element. The other end of the valve ele-ment/poppet valve is shaped to be brought into contact with a seat, e.g. a valve seat, located relative to the second fluid conduit, e.g. a branch thereof. This valve end is configured to substantially close the second fluid conduit when placed in the seat, e.g. the closed position.

At least a second valve element may be arranged in the first chamber or in at least a second chamber. The second valve element may be arranged relative to the second fluid conduit, e.g. another branch thereof, or at least another/third fluid conduit in fluid communication with the first fluid conduit. Optionally, a second actuator unit may be connected to the second valve element for moving that valve element where this actuator unit is controlled by the control unit. The at least two valve elements and/or actuator units may have the same or different configurations, optionally the valve elements may be activated/moved at the same pressure level or at different pressure levels. This allows the activation mechanism to control the fluid bypass of two or more fluid conduits, thus allowing for an improved control of the bypass of the drilling fluid.

Alternatively, the first valve element as described above may be arranged relative to two or more branches of the second fluid conduit and/or two or more fluid conduits in fluid communication with the first fluid conduit. This allows for an increased bypass of the drilling fluid.

In one embodiment, one or more sealing elements are arranged in an inner surface of the chamber, wherein the sealing elements remain in contact with an outer surface of the valve element during movement of the valve element.

The chamber comprises at least one inner surface facing a corresponding outer surface of the valve element. Optionally, the inner chamber has a first end facing the actuator unit and a second end facing the second fluid conduit where each of the first and second ends faces a corresponding end of the valve element. The sealing elements, e.g. one, two or more, may be arranged on the at least one inner surface or a dedicated inner surface of the chamber. The sealing element may be O-rings, GT-rings or any other suitable sealing element. This allows the sealing elements to remain in contact with the valve element at all times during the movement, thus forming a continuous seal. This reduces the risk of the sealing element failing compared to conventional downhole units, since no openings are formed in the valve element and thus no openings are moved past the sealing elements.

In conventional downhole tools, the outer opening of the outer housing matches an opening provided in the body of the centrally placed valve or sleeve. Drilling fluid is guided through the sleeve or valve and out through the openings and further out of the bottom end of the tool. Sealing elements located adjacent to the opening of either the outer housing or the valve or sleeve seal off the area between these two units. During movement, the outer housing is moved relative to the valve or sleeve so that the opening of the housing is moved past one of the sealing elements on the valve or sleeve, or vice versa. This increases the risk of the sealing element failing as it is being forced out of its seat or cavity. The present invention solves this problem by placing the valve element in the outer housing so no openings in the valve element are needed.

In one embodiment, the control unit is further connected to an activation circuit, e.g. a pressure switch, which is configured to activate the control unit at a predetermined pressure level.

The control unit is electrically connected to an activation circuit for reducing the power consumption of the electrical components. The activation circuit is configured to wake up the control unit, e.g. turn power on, when the pressure inside the first fluid conduit exceeds a predetermined/third threshold level. Any suitable activation circuit may be used to wake up the control unit, such as a simple pressure switch. The control unit then monitors the internal pressure of the drilling fluid in the first fluid conduit and activates or deactivate a desired operation mode or downhole tool as described above if a stable pressure level is detected. Once the activation circuit determines, e.g. simply by detection, that the pressure drops below the third threshold level, the control unit enters a sleep mode, e.g. power is turned off. This allows the control unit to only be activated when the internal pressure of the drilling fluid reaches a predetermined pressure level, thus reducing the power consumption and increasing the operation time.

The control unit may also be configured to enter sleep mode after completing one or more task, such as activation of the selected operation mode or downhole tool and optionally verifying the activation as described above. The control unit may be further configured to activate the downhole tool when a certain event is detected, such as excessive vibrations, cocking of a jarring tool.

In one embodiment, the activation mechanism is configured to be implemented in a cavity located in an outer housing of the circulating sub.

The activation mechanism according to the invention has a small enough configuration for implementation or installation in an outer cavity located in the housing of the downhole tool, while most conventional activation mechanisms are designed for im-plementation/installation in a central cavity of the downhole tool. This allows for a more optimal fluid passageway in the central through hole, e.g. the first fluid conduit, of the downhole tool, since there are no flow restrictions or at least a reduced number of flow restrictions in the downhole tool.

An object of the invention is also achieved by a circulating sub characterised in that at least one activation mechanism as described above is arranged in at least one cavity provided in the outer surface of the outer housing.

This provides a downhole tool with a simple and accurate activation mechanism that does not require a ball retainer for receiving one or more dropped balls, or a RF transceiver or receiver for communication with a dropped RFID tag. This reduces the complexity and number of components needed to activate the downhole tool. The activation mechanism described above allows for an activation or deactivation of the downhole tool by means of the internal pressure of the drilling fluid only; no fluid flow is required. The downhole tool is activated/deactivated by means of the pressure of the drilling fluid, this allows for a much faster activation compared to conventional indexing systems and ball or RFID tag systems.

The downhole tool comprises a central through hole, e.g. the first fluid conduit, extending from a first end, e.g. the top end, to a second end, e.g. the bottom end, for leading the drilling fluid being pumped into the drilling string through the downhole tool. The housing has a smaller diameter than the inner diameter of the borehole so that an annular is formed along the outer surface for leading the drilling fluid and cuttings back to the ground level. At least one bypass conduit, e.g. the second fluid conduit, is provided in the housing and connected to an outer opening and an inner opening for bypassing at least some of the drilling fluid. A cavity is formed in the outer surface in which the activation mechanism is placed. The valve element is arranged relative to the second fluid conduit and a seat located in the cavity. The seat and second fluid conduit are arranged so that the valve element, when placed in the seat, closes the conduit so substantially no drilling fluid is led through the second conduit. By placing the activation mechanism within the housing of the downhole tool, e.g. between the inner and outer wall surfaces, the number of flow restricting elements in the fluid passageway can be reduced or even eliminated so that substantially a full-bore can be achieved, i.e. operating at maximum power or operation speed.

In one embodiment, a removable cover is arranged at the opening of the cavity for closing off the cavity and an optional seal is provided between the cover and the outer housing.

The open chamber defined by the cavity is closed off by means of a cover or hatch for preventing drilling fluid or cuttings from entering the activation mechanism and potentially causing a failure. The cover/hatch may be fastened to the outer surface by suitable fastening means, such bolts, screws, a snap-fit coupling or another arrangement. A seal or sealing element, e.g. a rubber element, an O-ring or another suitable seal, may be arranged between the cover/hatch and the outer housing for sealing off the chamber. This allows for easy access to the activation mechanism in the event of servicing or replacement of the activation mechanism.

One or more balancing arrangements, e.g. balance pistons, may be located at the top end or bottom end of the downhole tool. The balancing arrangement may be configured to regulate or balance the pressure inside the downhole relative to the pressure of the drilling fluid located above or below the downhole tool.

In one embodiment, at least one of the openings of the second fluid conduit comprises a nozzle configured to regulate the speed of the drilling fluid entering or exiting the second conduit.

Two or more outer openings may be arranged in the outer surface for distributing the bypassed fluid and/or optimizing the bypass of drilling fluid. The outer openings may form branches of the same fluid conduit or different fluid conduits as described above. Alternatively, two or more cavities may be arranged in the outer surface for receiving and holding two or more activation mechanisms which each is arranged relative to at least a second or third fluid conduit. A nozzle is provided at the inner and/or outer opening of the second fluid conduit for regulating the speed of the drilling fluid. An inner/first nozzle may be configured to increase the speed of the drilling fluid entering the conduit. An outer/second nozzle may be configured to further increase the speed of the drilling fluid exiting the conduit. The nozzles may be placed at a predetermined angle relative to the longitudinal direction of the downhole tool, e.g. in an angle of 90 degrees or in an acute angle where the nozzle at least partly faces the first/top end of the downhole tool. The nozzles may be mounted at the openings or integrated into the openings. The nozzles may be made of a wear resistant material, such as tungsten carbide or another suitable ma terial. This allows the pressure of the drilling fluid inside the drilling string to be reduced as well as an increase in the flow of the circulating drilling fluid, if needed. The increase in the flow in the annular space may be used to dissolve or break up any packed off areas or remove accumulated cuttings from areas likely to get packed off or blocked by the cuttings, such as the transition area between two different liners.

The downhole tool may be any type of downhole in which a bypass function is desired, such as a circulating sub, a packoff assembly (packoff buster). The downhole tool may advantageously be placed in positions along the borehole where packoffs are likely to form, such as in areas where changes in the diameter of the borehole occur, e.g. at the transition area between different liners. Alternatively, the activation mechanism described above may be connected to or integrated into a jarring tool for releasing a stuck or lodged downhole tool, such as the jarring tool described in US 2012/0227970 Al.

An object of the invention is finally achieved by a method for activating a circulating sub using an activation mechanism as described above, characterised in that the step of activating the circulating sub comprises moving a valve element arranged in a chamber of the activation mechanism between a closed position and an open position so that at least a second fluid conduit is either open for leading at least a part of the drilling fluid through the second fluid conduit or closed off.

This provides a fast and accurate method for activating or deactivating a downhole tool without the use of balls or RFID tags being dropped into the drilling fluid. This method allows for a very fast action process compared to activation systems using balls or RFID tags. As example, the process for activating a downhole tool at a depth of about 3000 metres takes several hours, e.g. more than one hour, while the present invention enables the activation process to be completed within minutes, e.g. three minutes. Furthermore, the complexity as well as the number of components needed to activate the downhole tool can be reduced compared to conventional activation systems, thus reducing costs.

This configuration enables the downhole tool to be activated without requiring an actual flow through the downhole tool, thus allowing it to be operated in packed off boreholes or situations where no circulating flow can be established.

In one embodiment, the sensed pressure is monitored within at least one predetermined time window, and the circulating sub is activated by the control unit if it is determined that the pressure has remained stable relative to at least one predetermined threshold value within the time window.

This enables the downhole tool to be activated or deactivated once the pressure has reached a predetermined activation level for that downhole tool or an operation mode thereof. When the control unit has determined that a stable pressure level has been detected, a control signal is sent to an actuator unit for initiating the movement of the valve element. The actuator unit then moves the valve element from the closed position where the second fluid conduit is closed to the open position where the second conduit is open, or vice versa if that mode or tool is deactivated. This allows at least some of the drilling fluid to be bypassed from the first fluid conduit to a pressure chamber located inside the downhole tool or to the annular spacing located at the outer surface of the housing of the downhole tool. This also allows for an endless number of activations or deactivations without having to retrieve the downhole tool to empty a ball retainer.

The control unit may continue to monitor the sensed pressure for detecting a change, e.g. a drop, in the pressure which indicates that the downhole tool or the selected operation mode has been activated. The pressure of the pumped drilling fluid may then be increased to the operation level or another activation level for another mode or downhole tool.

According to an embodiment, the sensed pressure is monitored within at least a second time window, and a second downhole tool or another operation mode of the first downhole tool is activated by the control unit if it is determined that the pressure has remained stable relative to at least a second threshold value within the second time window.

This provides a simple and accurate method for activating or deactivating multiple operation modes of a downhole tool and/or multiple downhole tools by using the same activation mechanism or individual activation mechanisms. This configuration allows the multiple operation modes and/or multiple downhole tools to be activat-ed/deactivated by simply regulating the pressure of the drilling fluid, no indexing system is needed. Furthermore, the operation modes and/or downhole tools can be activated or deactivated using different threshold levels as described above. The activation or threshold levels may be selected so that they do not interfere with the operation of other downhole tools of the drilling string.

In one configuration, the downhole tool further comprises at least one vibration sensor connected to the control unit which monitors the vibrations of the downhole tool and in part the drilling string. The control unit compares the sensed vibrations to one or more threshold parameters, e.g. a reference frequency, pattern, amplitude or any other relevant parameters. If the sensed vibrations exceed the threshold parameters, then the control signal is sent to the actuator unit for moving the valve element so that the second fluid conduit is open. This allows the pressure of the pumped drilling fluid to be reduced while increasing the flow. This warns the operator at ground level that the drilling vibrations are out of range without using measure-while-drilling (MWD) signals.

In another configuration, the downhole tool is configured as a jarring tool or is connected to a jarring tool. The control unit compares the sensed pressure to one or more reset levels for determining if the jarring tool is recocked or not. The control unit may generate another control signal once the pressure reaches a selected reset level or if the sensed pressure remains stable at the reset level within another time window. The control unit may be configured to detect a drop having a predetermined amplitude and/or time length which indicates that the jarring tool has been cocked.

In one embodiment, an action circuit activates the control unit when the pressure of the drilling fluid exceeds a predetermined pressure level.

The electrical components are powered by an external or internal power source, such as a battery. Power to the electrical components is controlled by an optional activation circuit, e.g. a pressure switch, which turns on power when the pressure of the drilling fluid exceeds an activation level/the third threshold level. The control unit then switches from a sleep mode to a normal mode in which it monitors the pressure of the drilling fluid located in the first fluid conduit. The control unit activates or deactivates a selected operation mode or downhole tool if a stable pressure level has been detected as described above. The control unit enters sleep mode again and the power is turned off if once the activation or deactivation process is completed or if the sensed pressure drops below the activation level/the third threshold level. This saves power as the downhole tool is only activated at a predetermined pressure level, thereby reducing the power consumption and increasing the operation time.

Description of the Drawing

The invention is described by example only and with reference to the drawings, wherein:

Fig. 1 shows an activation mechanism according to the present invention integrated into a downhole tool seen from a top end;

Fig. 2 shows a downhole tool with three activation mechanisms seen from a top end;

Fig. 3 shows a longitudinal cross-section of the activation mechanism of fig. 1 in a closed position;

Fig. 4 shows a longitudinal cross-section of the activation mechanism of fig. 1 in an open position;

Fig. 5 shows an exemplary application of the downhole tool placed in a borehole in a deactivated state; and

Fig. 6 shows the downhole tool of fig. 5 in an activated state.

In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

List of reference numbers 1 Activation mechanism 2 Downhole tool 3 Outer housing 4 Outer surface 5 Cavity 6 First fluid conduit, first hole 7 Second fluid conduit 8 Inner opening 9 Inner surface 10 Inner wall of borehole 11 Pressure sensor 12 Control unit 13 Pressure switch 14 Actuator unit 15 Valve element 16 Rod 17 Chamber 18 Housing for valve element 19 Seat for valve element 20 Sealing elements 21 Annular spacing 22 Top end 23 Bottom end 24 Drill string 25 Borehole

Detailed Description of Embodiments of the Invention

Fig. 1 shows an exemplary embodiment of an activation mechanism 1 according to the present invention. The activation mechanism 1 is integrated into a downhole tool 2 in the form of a circulating sub. The downhole tool 2 and the activation mechanism 1 are seen from a top end (shown in figs. 3-4) where the top end, a bottom end (shown in figs. 3-4) and other components of the downhole tool 2 are omitted for illustrative purposes.

The downhole tool 2 comprises an outer housing 3 configured to be placed in a bore hole where an outer surface 4 of the housing 3 faces an inner wall (shown in figs. 3-4) of the borehole. A cavity 5 is formed in the outer surface 4 for receiving and holding the activation mechanism 1. The cavity 5 is closed off by a cover or hatch (not shown) so the drilling fluid in the borehole does not come into contact with the electrical components. A first hole 6 is formed inside the housing 3, e.g. at the centre, extending in the longitudinal direction of the downhole tool 2. The first hole 6 forms a first fluid conduit for leading drilling from the top end, through the downhole tool 2 and out of the bottom end. A second hole 7 is formed in the wall of the housing 3 and forms a second fluid conduit for bypassing at least some of the drilling fluid. The second fluid conduit 7 is fluid communication with the first fluid conduit 6 via an inner opening 8 and with an annular spacing (shown in figs. 3-4) via an outer opening (shown in figs. 3-4). The activation mechanism 1 is arranged relative to the second fluid conduit 7 so that a valve element (shown in figs. 3-4) is able to control the fluid flow through the second fluid conduit 7.

Fig. 2 shows another exemplary embodiment of the downhole tool 2’ having three activation mechanisms 1, Γ, 1” arranged in individual cavities 5, 5’, 5” in the outer surface 4. Each of the activation mechanisms 1, 1’, 1” is arranged relative to a second fluid conduit 7, 7’, 7” for bypassing at least some of the drilling fluid in the first fluid conduit 6. The activation mechanisms 1, 1’, 1” may each have the same or different configurations, e.g. they can be activated simultaneously or individually.

Fig. 3 shows a longitudinal cross-section of the activation mechanism 1 in a deactivated state. The activation mechanism 1 is positioned within the wall of the housing 3 between the outer surface 4 and an inner surface 9. The inner surface 9 faces the first fluid conduit 6. The outer surface 4 faces the inner wall 10 of the borehole.

The activation mechanism 1 comprises a pressure sensor 11 configured to sense the pressure of the drilling fluid located in the first fluid conduit 6. The pressure sensor 11 is electrically connected to a control unit 12 comprising a controller, e.g. a microprocessor, a memory unit, a communication interface for communicating with other downhole tools 2 or other external devices or tools, and other components for controlling the internal communication between the individual components of the activation mechanism 1. A pressure switch 13 configured to sense the pressure of the drilling fluid located in the first fluid conduit 6 is further connected to the control unit 12, e.g. a power unit thereof. The pressure switch 13 is configured to turn on or off power to the electrical components of the activation mechanism 1.

An actuator unit 14 in the form of a solenoid is electrically connected to the control unit 12. The actuator unit 14 is configured to control the movement of the valve element 15 by generating a magnetic field in its wires which influences a rod 16 mechanically connected to the valve element 15. The rod 16 is made of a magnetic conductive material, e.g. steel or a ferromagnetic material. The valve element 15 is moveably arranged inside a chamber 17, e.g. formed in the activation mechanism or the housing 3. One end of the valve element 15 is positioned inside a housing 18 which forms a retainer for the valve element 15. The housing 18 is connected to the rod 16. The other end of the valve element 15 is configured to rest against a seat 19 arranged relative to the second fluid conduit 7 in a closed position as shown in fig. 3, thus closing the second fluid conduit 7 so that no drilling fluid is bypassed via this conduit. This allows the drilling fluid to pass from the top end 22 of the downhole tool 2 and out of the bottom end 23 of the downhole tool 2 via the first fluid conduit 6.

One or more sealing elements 20, two is shown here, are arranged between an outer surface of the valve element 15 and an inner surface of the chamber as shown in figs. 3-4, thereby forming a seal between the chamber 17 and the second fluid conduit 7. The sealing elements 20, e.g. O-rings, remain in contact with the outer surface of the valve element 15 at all times during the moving of the valve element 15. Thus, no openings are moved past either one of the sealing elements 20, thereby reducing the risk that the sealing elements 20 are forced out of its seat or otherwise gets damaged.

Fig. 4 shows the activation mechanism 1 in an activated state where the actuator unit 14 is activated to move the valve element, e.g. in the longitudinal direction, from the closed position to an open position as shown in fig. 4.

The actuator unit 14 is configured to retract the valve element 15 further into the chamber 17 so that the other end of the valve element 15 is brought out of contact with the seat 19. This opens the second fluid conduit 7, thus allowing at least some of the drilling fluid to bypass the first fluid conduit 6 and enter the annular spacing 21. This allows the drilling fluid to pass from the top end 22 of the downhole tool 2 and to partly bypass the first fluid conduit 6 via the second fluid conduit 7.

Figs. 5-6 show an exemplary application of the downhole tool 2 with the activation mechanism (shown in fig. 3-4) installed in a drill string 24 or borehole assembly (BHA) which is positioned in a borehole 25. In exemplary embodiment, the downhole tool 2 is positioned above an under-reamer and/or a drill bit which are configured to widen the borehole and/or extend the borehole.

Cuttings 26 are led towards the top of the borehole 25 via the annular spacing 21 between the drill string and the inner wall 10 of the borehole (here indicated by dotted lines). The cuttings 26 accumulate in the transition area 27 at which the speed of the returning drilling fluid containing the cuttings 26 is slowed down, e.g. due to a widening of the inner diameter of the borehole 25. This causes the cuttings 26 to form a packoff as shown in fig. 5.

The activation mechanism 1 and thus downhole tool 2 remains inactive until the switch 13 turns on power to the electrical components, including the control unit 12. Drilling fluid is then led through the first fluid conduit 6 and back up via the annular spacing 21 as indicated by the arrows in figs. 3-4.

The pressure switch 13 is activated when the internal pressure inside the first fluid conduit 6 exceeds a predetermined pressure level. The control unit 12 then wakes up and monitor the internal pressure inside the first fluid conduit 6 within one or more predetermined time windows. If the control unit 12 determines that the pressure has remained stable within at least one time window, a control signal is generated and is sent to the actuator unit 14. The actuator unit 14 then moves the valve element 15 from the closed position to the open position, thus allows at least some of the drilling fluid to bypass the first fluid conduit 6. This activates the downhole tool 2 and drilling fluid is led through the second fluid conduit 7 (indicated by arrows in fig. 6) and out into the annular spacing 21. This increases the speed of the returning drilling fluid, thereby forcing the packoff to break up so that circulation of the drilling fluid can be resumed.

The present invention is not limited to the illustrated embodiment or the described embodiments herein, and may be modified or adapted without departing from the scope of the present invention as described in the patent claims below.

Claims

An activation mechanism (1) for activating a circulation sub of a drill string (24), comprising: - at least one sensor configured to sense at least one pressure of a drilling fluid which is in a first fluid conduit (6) in said circulation sub after an installation in which the first liquid line (6) is connected to a first opening and a second opening in said circulation sub, - a control unit (12) connected to the sensor and configured to monitor the sensor signal signal, wherein the control unit (12) is configured to electronically control activating the movement of at least one movable valve member (15) based on the sensor signal; - the valve member (15) is configured to be arranged relative to at least one other fluid conduit (7) in said circulation sub, when installed, wherein the valve member (15) is configured to move between an open position and a closed position wherein - the second liquid conduit (7) is in fluid communication with the first liquid conduit (6), and the valve member (15) comprises at least one valve member configured to close the second liquid conduit (7) in the closed position and open the second liquid conduit (7) in the open position, characterized in that the control unit (12) is electrically connected to at least one actuator unit (14) arranged relative to the valve element (15), wherein the actuator unit (14) is configured to move the valve element (15) an infinite number of times from one position to the other position, or vice versa when activated.

Activation mechanism (1) according to claim 1, characterized in that the control unit (12) is configured to apply at least one predetermined time window to the sensor signal and determine whether or not the sensor signal remains stable relative to a predetermined threshold within the time window (1). 15) is activated if a stable pressure level is detected.

Activation mechanism (1) according to claim 1 or 2, characterized in that the valve element (15) is a lifting valve arranged inside a chamber (17) of the activating mechanism (1), wherein the lifting valve is configured to move in relation to the chamber (17). , when activated.

Activation mechanism (1) according to any one of claims 1-3, characterized in that one or more sealing elements (20) are arranged in an inner surface (9) of the chamber (17), wherein the sealing elements (20) remain in contact with a sealing element (20). outer surface (4) of the valve member (15) during movement of the valve member (15).

Activation mechanism (1) according to any one of claims 1-4, characterized in that the control unit (12) is further connected to an activation circuit, e.g. a pressure switch (13) configured to activate the controller (12) at a predetermined pressure level.

Activation mechanism (1) according to any of claims 1-5, characterized in that the activation mechanism (1) is configured to be implemented in a cavity (5) located in an outer housing (3) of the wellbore tool (2).

A circulation sub for placement in a borehole (25), comprising: - an outer housing (3) facing an inner wall (10) of the borehole (25), wherein the outer housing (3) is configured to be placed inside - a first fluid conduit (6) connected to a first aperture at one end of said circulation sub and a second aperture at the other end of said circulation sub to pass a drilling fluid through said circulation sub, - at least one second fluid conduit ( 7) in liquid communication with the first liquid conduit (6) via at least one inner opening (8) and connected to at least one outer opening located in the outer surface (4) of the housing, characterized in that - at least one actuating mechanism (1) according to any one of claims 1 to 6 are arranged in at least one cavity (5) provided in the outer surface (4) of the outer housing (3).

Circulation sub according to claim 7, characterized in that a removable cover is arranged at the opening of the cavity (5) for closing the cavity (5) and that an optional seal is provided between the cover and the outer housing (3).

Circulation sub according to claim 7 or 8, characterized in that at least one of the openings in the second fluid conduit (7) comprises a nozzle configured to control the velocity of drilling fluid entering or exiting the second conduit.

A method of activating a circulating sub using an activating mechanism (1) according to any one of claims 1 to 6, wherein the method comprises the steps of: - placing said circulating sub at a predetermined depth in the borehole (25), - increasing a pressure of a drilling fluid located in the first fluid conduit (6) of said circulation sub, - monitoring the drilling fluid pressure inside the first liquid conduit (6) using at least one pressure sensor (11), - activating said circulating sub when a particular event is recorded during use of a control unit (12), characterized in that - the step of activating said circulating sub comprises moving a valve element (15) arranged in a chamber (17) of the actuating mechanism (1) between a closed position and an open position, such that at least one other fluid conduit (7) is either opened to pass at least one portion of the drilling fluid through the other fluid conduit (7) or closed.

Method for activating a circulation sub according to claim 10, characterized in that the sensed pressure is monitored within at least one predetermined time window and said circulating sub is activated by the control unit (12) if it is determined that the pressure has remained stable relative to at least one predetermined threshold within the time window.

Method for activating a circulation sub according to claim 10 or 11, characterized in that an action circuit activates the control unit (12) when the pressure of the drilling fluid exceeds a predetermined pressure level.