NO20180620A1 - Method and apparatus for suspending a well - Google Patents

Abstract

There is described a method of suspending flow in a well, the method comprising the step of placing a first plug in a production tubular in an upper wellhead section, above a downhole safety valve, where the first plug is: adapted to fit into the production tubular to form a fluid seal in the production tubular to form a barrier for containing well fluid: equipped with instrumentation for obtaining information by measuring physical conditions below the plug: and equipped with means for transmitting said obtained information to an operator. There is also described an apparatus for suspending flow in the well.

Description

The invention relates to a method for suspending an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well or other types of wells by setting one or more shallow mechanical bridge plugs containing instrumentation for measuring fluid characteristic's below the lowermost plug, and optionally above the plug or in between the plugs, in the upper wellhead region above a downhole safety valve, forming primary and secondary barriers containing the borehole fluids from the surrounding environment. Suspension of a well may be required for a number of causes, such as temporary abandonment, Christmas tree servicing or replacement, and others.

The method applies primarily to surface application but may equally be adapted to subsea applications.

One of the inventions significant features is that it may allow for carrying out a well suspension operation without need to enter the well through an inflow tested downhole safety valve which therefore may remain in position from initial preparations for well suspension until the well again is brought into production.

Another significant feature is that the invention provides a method for suspending a well which does not involve deep entry into the well and thereby may allow use of equipment for setting plugs with limited range compared to traditional types e.g. a mechanical lubricator tool. A further significant feature is that the invention may provide monitoring of all volumes enclosed by the production tubular.

Current practice utilised in the oil and gas industry makes use of a deep set mechanical bridge plug set close by the producing formation complimented by an inflow tested downhole safety valve, which in combination with a drop protection device is considered acceptable providing the downhole safety valve exhibits zero leakage. It is however common that a downhole safety valve exhibits some leakage and in such case a shallow set mechanical bridge plug or tubing hanger plug is required in addition to the deep set mechanical bridge plug in order to achieve acceptable barrier protection. Current practice is thoroughly documented in NORSOK D-010 "Well integrity in drilling and well operations” which is in line with international standards and requirements such as described in relevant API and ISO publications (American Petroleum Institute, International Organization for Standardization) and is only discussed briefly herein.

Further references to a plug, unless specifically stated otherwise may mean any type of mechanical plug, a bridge plug, a tubing hanger plug, a BPV plug set in a wellhead profile etc.

The procedure for setting and retrieving a deep set plug requires the use of intervention equipment such as a wireline or a coiled tubing equipment assembly or drill pipe with associated handling equipment.

Such equipment represents considerable cost, weight, volume, safety and handling issues. In some instances such equipment may have to be mobilised from an offshore location representing significant safety and handling challenges both onshore and during lifting onto an offshore installation as well as during operation. Further the equipment may not be immediately available causing loss of production and revenue.

Setting and retrieving a deep set plug is relatively time consuming and not without risk. Potential pressure differentials across a plug caused by changes in well pressure during a suspension period, needs to be equalised, or near equalised prior to initiating a controlled release and retrieval of a plug. Without means of detecting fluid properties below a plug, such as pressure, temperature or fluid composition, the pressure differential across a plug must be equalised by trial prior to release and retrieval. Commonly the pressure above a plug is set at an anticipated value before jarring or otherwise manipulating the plug until released, and if unsuccessful reducing/increasing the pressure and trying again, repeatedly if necessary until the plug is released. Significant mechanical force is applied in the process and the procedure may cause damage to the inner wall of the tubular and to the plug. In a worst instance it may not be possible to release the plug leading to it having to be removed by milling. In some instances a pressure differential may be caused by changes to the static conditions of the well such as thermal expansion etc. and the excess pressure may be bled off with little volume flow across the released plug. However if a considerable portion of gas is trapped below the plug this may when released form an expanding gas volume migrating upwards in the production tubular and represents a different type of hazard requiring proper containment and disposal of, prior to returning the well to its normal operating state. By knowing the physical properties of a fluid contained by a plug it is possible to exactly predict the result of each action taken during a plug retrieval process.

Another aspect complicating setting of a plug is scale and/ or wax deposits formed on the interior of a production tubular walls. Such scale may impair or make it impossible to set a plug in place and obtain a pressure tight seal at a desired location and may require removal prior to setting a plug. Such scale/ wax removal operation at depth is far more complex and time consuming for a deep set plug than for a shallow set plug.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provides a useful alternative to prior art. The object is achieved through features, which are specified in the description below and in the claims that follow. The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

The well suspension method disclosed employs at least one plug set in an upper wellhead region above a downhole safety valve. Through use of enhanced monitoring of the wellbore volumes the suspension method avoids use of any deep set plug and subsequent any need for special, heavy equipment such as wireline, coiled tubing or drill pipe for setting and retrieval.

The suspension method disclosed may make use of a commonly available lubricator tool such as described in US 4,460,039 instead of the aforementioned specialized equipment meaning that an operation carried out according to the disclosed method may be performed in shorter time requiring considerably less equipment with a higher degree of predictability and safety. Necessary wireline equipment typically consists of 5-10 lifts and weighs in excess of 50 tons while a lubricator tool typically consists of a single lift weighing less than 2 tons, making logistics, handling and operation simpler and safer. Due to lesser weight and size such lubricator tools may be stored offshore, ready for immediate use when needed while mobilisation of a wireline unit or equivalent equipment from an onshore location may require days, weeks or even months, representing vastly more cost and complexity.

Reduced equipment handling lowers the risk of accidents happening during shipping, handling and operation. In addition performing well suspension by employing the method provides enhanced operational awareness and situation predictability consequently leading to improved safety.

The invention is more specifically a method for suspending a well by blocking the wellbore passage at a location in the upper wellhead instead of a location close to the producing formation and compensating for the increased risk associated with the increased fluid volume subject to contact with the producing formation by monitoring such volume or volumes and making such information available to an operator consequentially increasing overall operational predictability and safety and reducing the amount of equipment and time required for a suspension operation.

According to a first aspect the invention, there is provided a method of suspending flow in a well, the method comprising the step of placing a first plug in a production tubular in an upper wellhead section, above a downhole safety valve, wherein the first plug is: adapted to fit into the production tubular to form a fluid seal in the production tubular to form a barrier for containing well fluid; equipped with instrumentation for obtaining information by measuring physical conditions below the plug; and equipped with means for transmitting said obtained information to an operator. A control unit may be used to communicate with the instrumentation of the first plug and to make the information transmitted from the plug available to an operator. The control unit may be located inside or outside of the tubular. The well may typically be a completed well, a producing well, and the method may typically be a way of suspending production flow in the well. The well may be an oil well, a gas well, a water injection well, a water disposal well, a gas injection well, a condensate well or another type of well.

An advantage of the method according to the first aspect of the invention compared to prior art is that a deep-set plug may be avoided by applying the method.

The method may comprise the step of setting a second plug in the well to form a secondary barrier. The second plug may comprise instrumentation for obtaining information by measuring physical conditions below the second plug. Furthermore, the second plug may comprise means for transmitting said information to an operator. Setting a second plug may be advantageous to establish two barriers in the well. The downhole safety valve may in some situations be an acceptable primary barrier, but in other situations it may not be. When the downhole safety valve is not accepted as a primary barrier, the second plug may be necessary to fulfil regulations regarding well integrity.

One of, or both of the first plug and the second plug may comprise instrumentation for obtaining information by measuring physical conditions above the plug. Measuring physical conditions in several chambers in the well may be advantageous to provide information regarding e.g. leaks and pressure conditions, which may be vital information to avoid serious incidents.

The method may comprise the step of transferring information from the first and/or the second plug to an operator, and/or the step of transferring information from an operator to the first and/or the second plug. The step of transferring information may be performed e.g. by means of acoustic signalling and/or by means of electromagnetic signalling. Other means may also be used for transferring information. Furthermore, the step of transferring information may comprise the step of lowering the control unit down through the tubular towards the first and/or the second plug. The transfer of information may be performed applying by employing methods known from prior art, such as transferring information acoustically via a tubular.

The physical conditions may include fluid pressure, fluid temperature, fluid density, viscosity, pH and/or refractive index. The data obtained from measuring the physical conditions may be used to determine a type of fluid. Enabling detection of fluid type may provide vital information. E.g. it may be possible to detect whether the fluid below a barrier is gas or liquid, and/or whether it is water or hydrocarbons.

A lubricator tool may be used to set the first and/or the second plug. Other intervention equipment may otherwise be used, such as a pipe, a wireline, or coiled tubing. Using the intervention equipment may advantageously provide a barrier in the form of the intervention equipment while installing the first and/or second plug.

The first and the second plug may be mechanically connected, which may allow for setting and/or retrieving the plugs to be performed in a single well entry operation. The first and second plug may be parts of an apparatus, that may be referred to as a tandem plug, further comprising a middle section with a smaller diameter, such that a chamber comprising fluid may be formed in the production tubular between the plugs when the plugs are set as barriers in the tubular. The tandem plug may comprise instrumentation for obtaining information by measuring physical conditions below the lowermost plug, above the uppermost plug, and/or in the chamber between the two plugs when the tandem plug is in operational use. The tandem plug may further comprise means for transmitting said information to an operator.

The method may further comprise the step of installing one or more sensors for monitoring one or more annular volumes. For each annular volume, a sensor may be installed at an outlet leading to an annulus valve. When using a deep-set plug, the portion of the well where leak paths may occur between the production tubular and the annular volumes may be sealed off. As a deep-set plug is avoided by using the method according to the first aspect of the invention, said portion of the well may not be sealed off, and leak paths may occur. It may therefore be advantageous to install one or more sensors to detect/monitor a leak.

The method according to the first aspect of the invention may comprise one or more of the following steps:

Shutting the well in by closing the downhole safety valve and all Christmas tree valves leading from the production tubular towards the process. A shutting of the downhole safety valve may be followed by a leak-off test ensuring the integrity of the downhole safety valve;

Mounting a lubricator tool to the Christmas tree. The first plug may be assembled in the lubricator tool. Pressure testing may be performed if needed;

Opening Christmas tree valves to allow the lubricator to access the production tubular. A pressure test may be performed if needed;

Stroking the lubricator piston in to the production tubular and setting the first plug at a shallow location above the downhole safety valve;

Establishing a primary barrier by use of the first plug;

Assembling the second plug in the lubricator tool;

Setting the second plug in the wall of the production tubular or in a tubing hanger profile;

Establishing a secondary barrier by use of the second plug;

Removing the intervention equipment when two barriers have been established;

- Monitoring one or more volumes having direct or indirect interface with at least one of the first and the second plug by use of instrumentation for measuring physical conditions of a well fluid;

Mounting a lubricator tool to the Christmas tree to retrieve one or more plugs following an intervention procedure. Pressure testing if needed.

- Retrieving the second plug;

Retrieving the first plug while maintaining double barriers at all times;

Removing the lubricator tool;

Bringing the well back into production;

Setting a tandem plug comprising a first and a second plug to establish two barriers in one operation; and

Retrieving the tandem plug comprising the first and the second plug.

According to a second aspect of the invention, there is provided an apparatus for suspending flow in a well, the apparatus comprising a first plug, the first plug comprising instrumentation for obtaining information by measuring physical condition in a well and means for transmitting said information to an operator. The apparatus may further comprise a second plug. The second plug may comprise instrumentation for obtaining information by measuring physical conditions in a well and/or for transmitting said information to an operator. The means for transmitting information may be means for transmitting information acoustically, and/or means for transmitting magnetically.

The instrumentation for obtaining information by measuring physical conditions of the first and/or the second plug may comprise instrumentation for obtaining information by measuring physical conditions below the plug in operational use.

The first and the second plug of the apparatus may be mechanically connected. The apparatus may comprise a middle section, between the first and the second plug, comprising the mechanical connection between the first and the second plug. The middle section may be of a smaller diameter than the plugs and may be adapted to form a chamber in a tubular in operational use. The apparatus' means for obtaining information may be arranged to measure physical conditions below the lowermost plug, above the uppermost plug, and/or between the two plugs, when installed in a production tubular, in operational use.

Having the first plug and the second plug be mechanically connected may be advantageous as it may make an installation and/or retrieval operation less time-consuming and more efficient. Having a middle section of smaller diameter that may form a chamber in the well when the apparatus is in operational use may be further advantageous as it may separate the two plugs and make them count as two separate barriers. Furthermore, the chamber may contain one or more fluids that may be monitored by the apparatus' means for obtaining information by measuring physical conditions, which may be used to gather information regarding the barrier integrity of one or more of the plugs.

A deep set plug is currently employed for well suspensions since it is desirable to place a first plug as close to the producing formation as possible thereby limiting the volume susceptible to pressure change and/or to gas influx and subsequently the total volume of gas influx and gas contained below a plug. If exact information as to what is contained behind a plug is made available to an operator prior to bringing a well out of suspension, any required actions may be predicted, planned for and implemented when retracting a plug and bringing the well safely out from suspension into its normal operating condition.

If such were the case the volume contained behind a plug has little or no significance and the location of the plug is of lesser or no importance, thus placing the plug, or plugs further away from the formation, i.e. higher up in the well is feasible both from a technical, operational and safety viewpoint.

In the following is described a preferred embodiment illustrated by the accompanying drawings, wherein:

Figure 1 Illustrates a production well (1) in producing mode where there is fluidic connection between the hydrocarbon producing formation (F) and the outlet from the production master valve (23) represented by the volume (Vp) allowing free flow of formation fluids from the formation (F), through the production tubular perforations (P), production tubular (31), down hole safety valve (4o), manual master valve (25), hydraulic master valve (24) and production master valve (23) to production.

In producing mode the wellhead (3o) will be equipped with a Christmas tree (2o) allowing for closing production through the production master valve (2a), hydraulic master valve (24) and manual master valve (25), or diverting the flow from the well through the kill valve (22). The swab valve (21) allows introduction of intervention equipment for well suspension or reworking.

The production well extends from the wellhead (3o) or if mounted a Christmas tree (2o) down to the producing formation (F) through a production tubular (31) which at the hydrocarbon bearing formation (F) is perforated (P) to allow inflow of well fluids. The production tubular is contained within several casings (32) forming annular volurnes (VA, VB and Vc) running from the wellhead (31) to casing shoes (36) sealed towards the surrounding formation or casing packers (37) sealed towards the production tubular (31) and cemented (C) towards the surrounding formation. Each annular volume (VA, VB and Vc) is contained by annulus valves (33, 34, and 35).

A downhole safety valve (4o) is arranged in the production tubular as well as an annular safety valve (5o) arranged to close the annulus formed between the production tubular (3i) and the innermost casing (32).

The production well (1) elements form two barriers isolating the formation (F) fluids from the surrounding environment (E). A primary barrier (PB) is formed by the formation (F), cement (C), production tubular (3i), packers (3z) and downhole safety valve (4a). A secondary barrier (SB) is formed by the primary barrier (PB), casing (32), cemented casing shoe (3B), annular safety valve (5o), wellhead (3o) and Christmas tree (2o) valves (21, 22, 2a, 24, and 25).

Figure 2 Illustrates a production well (1) having been suspended by setting a first plug (6o)

(deep set) below the downhole safety valve (4o), closing the downhole safety valve (4o) and setting a second plug (7o) (shallow set) in the upper wellhead section above the downhole safety valve (4o). Setting a deep plug requires intervention equipment capable of deep entry into the well, such as a wireline unit, a coiled tubing unit or drill pipe. The monitored volume (M) is limited to the volume (VWH-P2) above the second plug (7o) and may be complimented by a downhole pressure gauge or tubing to annulus communication providing pressure reading of the volume (VDHSV-PI).

Figure 3 Illustrates a production well (1) having been suspended according to the invention by closing the downhole safety valve (4o), setting a shallow first plug (6o) above the downhole safety valve (4o). The first plug (6o) is instrumented and the monitored volume (M) includes the volume (VWH-PI) above the first plug (6o), the volume (VPI-DHSV) between the first plug (6o) and the downhole safety valve (4o) and the volume (VOHSV-F) between the downhole safety valve (4o) and the formation (F) monitored directly by a downhole pressure gauge or tubing to annulus communication providing pressure reading of the volume or through metering below the first plug (6o) through normal static condition leakage through the closed downhole safety valve (4o).

Figure 4 Illustrates a production well (1) having been suspended according to the invention by closing the downhole safety valve (4o), setting a shallow first plug (6o) above the downhole safety valve (4o), and setting a shallow second plug (7o) above the first plug (6o). Setting a shallow plug may be done by use of a lubricator tool. The first plug (6o) is instrumented and the monitored volume (M) includes the volume (VWH-P2) above the second plug (7o), the volume (VP2-PI) between the second plug and the first plug (6o), the volume (VPI-DHSV) between the first plug (6o) and the downhole safety valve (4o) and the volume (VDHSV-F) between the downhole safety valve (4c) and the formation (F) monitored directly by a downhole pressure gauge or tubing to annulus communication providing pressure reading of the volume or through metering below the first plug (6o) through normal static condition leakage through the closed downhole safety valve (4o).

Figure 5 Illustrates a production well (1) prepared for wireline (8o) intervention. Other item numbering is the same as in figure 1. The primary barrier (PB) is maintained while the downhole safety valve (4o) remains in a closed position and the secondary barrier (SB) is maintained while the swab valve (2i) remains in a closed position or while the swab valve (2i) remains in an open position and the wireline unit (80) forms part of the secondary barrier (SB) envelope following pressure testing.

Figure 6 Illustrates a production well (1 ) prepared for lubricator tool (9o) intervention. Other item numbering is the same as in figure 1. The primary barrier (PB) is maintained while the downhole safety valve (4o) remains in a closed position and the secondary barrier (SB) is maintained while the swab valve (2i) remains in a closed position or while the swab valve (2i) remains in an open position and the lubricator tool (9o) forms part of the secondary barrier (SB) envelope following pressure testing.

Figure 7a Illustrates a mechanical plug (10o) with seals (10i), which when actuated, seals and separates the volume of the production tubular (3i) above the plug from that which is below the plug (10o). The plug (10o) may be mechanically locked in its position by means of a locking device (102) which may intrude into the production tubular (3i) or equivalent devices designed to fit into a groove in the production tubular (3i).

The mechanical plug (10o) is also equipped with an instrument section (104) which in this example has been adapted to fit between the mechanical plugs (10o) main body and its bull nose (103) mounted at its lower end. The instrument section (I O4) may have fluid connection with the borehole volumes above and below the plug and may form the pressure retaining element of the plug (10o), separating the two volumes. The instrument section may contain instrumentation (104) for measuring physical conditions above and/or below the plug (10o) such as pressure, temperature, density etc. and means of transmitting such information by commonly known methods such as through tubular acoustic, electromagnetic etc. from within the borehole to a location within or outside of the borehole and made available to an operator. Data may typically include pressure above the plug (P2), temperature above the plug (T2), pressure below the plug (Pi), temperature below the plug (Ti) and physical properties such as density (pi) or other property allowing determination of fluid type (gas, crude oil, brine, water etc.) and if plural (pi, p2 or more) allowing determination of rate of change (Qi) (cm<3>/min) and thus flow/inflow. The following plugs are of this type, Figure 3 - plug (60) and Figure 4 - plug (6a).

Figure 7b Illustrates a mechanical plug (11 ) with seals (11 i), which when actuated, seals and separates the volume of the production tubular (3i) above the plug from that which is below the plug (11o). The plug (1 1□) may be mechanically locked in its position by means of a locking device (H2) which may intrude into the production tubular (3i) or equivalent devices designed to fit into a groove in the production tubular (3i). The following plugs are of this type, Figure 2 - plug (60) and plug (7o), Figure 4 - plug (7o).

Definitions:

Christmas tree (an assembly of valves, spools, and fittings) adapted to fit on top of a wellhead.

Lubricator tool - a long, high-pressure pipe fitted to the top of a wellhead or Christmas tree so that tools may be put into a high-pressure well (see also US 4,460,039).

Wireline unit - the term wireline usually refers to a cabling technology used by operators of oil and gas wells to lower equipment or measurement devices into the well for the purposes of well intervention, reservoir evaluation, pipe recovery and setting and retrieving plugs. A wireline unit includes an intervention blow out preventer with closing and shear rams as well as a lubricator section similar to that of a lubricator tool.

The feature differing a wireline unit from a lubricator tool is that while a lubricator tool may set and retrieve a shallow plug in the upper wellhead section typically limited to 5-10 metres from top of the Christmas tree where the setting depth depends upon the stroke length of the lubricator tool - a wireline unit may set and retrieve a plug at any depth in the well.

For both a lubricator tool and a wireline unit the top of the lubricator assembly includes high-pressure grease-injection section and sealing elements. The lubricator is installed on top of the tree and tested, the plug is placed in the lubricator and the lubricator is pressurized to wellbore pressure. Then the top valves of the tree are opened to enable the plug to be guided mechanically, to fall or to be pumped into the wellbore under pressure. To remove the tools, the reverse process is used: the plug is pulled up into the lubricator under wellbore pressure, the tree valves are closed, the lubricator pressure is bled off, and the lubricator may be opened to remove the plug.

Figure 7c Illustrates a mechanical plug assembly (120) with one locking device (124), two sealing bodies (121 )(122) each with seals (123), which when actuated, seals and separates the volume of the production tubular (31) above the plug sealing portion (121) from that which is below the plug sealing portion (121) and the volume of the production tubular (31) below the plug sealing portion (122) from that which is above the plug sealing portion (122), and forms an enclosed volume between the plug sealing portion (121) and the plug sealing portion (122). Each of the volumes may be monitored by instrumentation (126) attached to the plug. The plug assembly is made such that it may be set in a single run.

Figure 7d Illustrates a mechanical plug assembly (130) with two locking devices (134)(135) and two sealing bodies (131 )(132) each with seals (133), which when actuated, seals and separates the volume of the production tubular (31) above the upper plug sealing portion (131) from that which is below the upper sealing portion (131), and the volume below the lower sealing portion (132) from the volume above the lower sealing portion (132), and forms an enclosed volume between the upper sealing portion (131) and the lower sealing portion (132). Each of the volumes, above the upper sealing portion (131), below the lower sealing portion (132) and between the sealing bodies (131) and (132) may be monitored by instrumentation (136) attached to the plug assembly. The mechanical plug assembly (130) is arranged with a mechanical connection (138) connecting the upper sealing body (131) and upper locking device (134) with the lower sealing body (132) and lower locking device (135). The plug assembly is made such that it may activate both locking devices (134)(135) and all seals (133) in a single run.

Figure 1 shows a well (1 ) in normal production mode and figure 2 shows the same well (1 ) suspended according to currently used methodology. The plugs (6o) and (7o) are placed by use of a wireline unit (8o) such as illustrated in figure 5 while Christmas tree valves (22)(23) are closed and (2I)(24)(25) and downhole safety valve (4o) are opened as required for lowering/ hoisting the wireline and connected tools/ plugs (6o)(7o).

In a first embodiment the invention relates to a method of suspending a production well (1 ) different from current practice in the petroleum industry by replacing a deep set plug (6o) and a shallow set plug (7o) as illustrated in figure 2 - with a shallow set plug (6o) as illustrated in figure 3 arranged with instrumentation sufficiently monitoring the volume above the plug (VWH-PI) and below the plug (VPI-DHSV) extending to the downhole safety valve. In this embodiment the downhole safety valve (4o) forms part of the primary barrier (PB) and the plug (6o) forms part of the secondary barrier (SB).

In a second embodiment figure 4 shows the well (1) suspended according to the invention by use of two plugs (6o) and (7o) incorporating sufficient instrumentation to measure physical characteristics in volumes (VP2-PI) and (VPI-DHSV). In this embodiment the downhole safety valve (4o) and the first plug (6o) form part of the primary barrier (PB) and the plug (7o) forms part of the secondary barrier (SB).

In both embodiments the statutory barrier requirements are fulfilled, however the first embodiment depends upon the quality and state of the downhole safety valve (4o) and presence of pressure status monitoring of the volume below the downhole safety valve (4o). In the second embodiment the downhole safety valve (4o) supported by the first plug (6o) form the primary barrier (PB) and provides as a minimum pressure monitoring of the volume (VPI-DHSV) below the downhole safety valve (4o).

The volume ((VWH-PI) in figure 3 and (VWH-P2) in figure 2 and figure 4) above the uppermost plug may otherwise usually be monitored by Christmas tree mounted instrumentation and the volume ((VDHSV-PI) in figure 2 and (VDHSV-F) in figure 3 and figure 4) below the downhole safety valve (40) may be monitored by a downhole gauge if installed, or by static monitoring through leakage across the downhole safety valve (4o).

In both the first and the second embodiments as illustrated in figures 3, 4 and 5 the plugs (6o)(7o) may be set and retrieved by use of a lubricator tool (9o) such as illustrated in figure 6. When pressure tested and connected to the Christmas tree (2o) the lubricator tool (9o) may form part of the secondary barrier (SB). AS neither the first or second embodiment require opening of the downhole safety valve (4o) it is possible to maintain a primary barrier (PB) and a secondary barrier (SB) at all times during well suspension operations leading to further enhanced safety versus conventional suspension.

In both embodiments the first plug (6o) is instrumented such as illustrated in figure 7a (10o) enabling measurement of pressure (P2) and temperature (T2) above the plug (10o) and pressure (Pi), temperature (Ti) and density (p1) below the plug. The plug (10o) is equipped with a locking device (1O2) which mechanically locks the plug (10o) to the tubular (3i). The locking may take form of teeth in the locking device (1O2) intruding into the tubular (3i) wall, or take form of a profile which enters into an equivalent groove in the tubular or wellhead. The plug (10o) is equipped with seals (10i) which seal the void between the plug (10o) and the tubular (3i) when activated.

The second plug (7o) is a non-instrumented plug such as illustrated in figure 7b (1 1 o). However both plugs may be instrumented allowing metering of physical characteristics above, below or above and below the plugs, in any relevant combination.

The instrumented plug (10o) in figure 7a, or (6o) in figure 3 and 4, contains an instrument section which may be removable and adapted to most types of plugs without mechanical reworking, e.g. by removing the bullnose (1O3), attaching the instrument section (104) to the plug (1 Oo) in place of the bullnose (103) and reattaching the bullnose (10a) to the instrument section (104) thereby obtaining a similar but elongated version of a non-instrumented plug (110).

The instrument section (104) may contain energy storage devices, logic processing units, electronic circuitry and arrangements for transmitting and/or receiving data to/from an opposite control unit (A) located inside or outside the production tubular, or outside the well in the surrounding environment (E). Data may be transmitted, in one or both directions and an operator may transmit a command initiating a specific action, conversely the plug (10o) may be equipped with actuation devices such as valves, perforation charges etc. which may be actuated from the control unit (A).

Communication may be acoustic or electromagnetic or by any other means of communication such as disclosed in general literature and in other patents and will not be further discussed herein.

When using plugs such as illustrated in figures 7a and 7b each plug needs to be set in a separate run. I.e. a lower plug must be set in place, thereafter the tool used to set the plug must be retracted and connected to the upper plug before setting this, meaning that two separate tool runs are required.

Equal barrier protection and functionality may be achieved by use of special plugs with one or more barriers or one or more plugs mechanically connected each with one or more barriers, in any relevant combination with each other or with plugs as illustrated in figures 7a and 7b.

The plug (10o) as described may find use in other applications and shall not be limited by the method described herein.

Styringsforskriftens § 5 Barrierer

Del skal ela bie res barrierer sore til enhver tid kan

¥ a) identifisere tilstander som kan føre til feil, fare- og ulykkessituasjoner,

3⁄4/ b) redusere muligheten for at feil, fare- og ulykkessituasjoner oppstår og utvikler seg,

«f c) begrense mulige skader og ulemper.

Der del er nødvendig med flere barrierer, skal det være tilstrekkelig uavhengighet mellom barrierene. Operatøren eller den som står for driften av en innretning eller et landanlegg, skal fastsete de strategi til grunn for utforming, bruk og vedlikehold av barrierer, slik at barrierenes funksjon blir Ivaretat landanleggets levetid.

Det skal være kjent hvilke barrierer som er etablert og hvilken funksjon de skal Ivareta, samt hvilke kra tekniske, operasjonelle eller organisatoriske barriereelernentene som er nødvendige for at den enkelte Det skal være kjent hvilke barrierer og barriereelementer som er ute av funksjon eller er svekket.

Det skal settes i verk nødvendige tiltak for å rette opp eller kompensere for manglende eller svekkede b

Styringsforskriftens § 5 Barrierer (veiledning)

Barrierene for å begrense mulige skader og ulemper ved akutt forurensning til havs som nevnt I tredje for å kunne håndtere et bredest mulig spekter av værforhold. Kravene til risikoreduksjon, jf, rammefor 4, og kontinuerlig forbedring, jf. styringsforskriften § 6, medfører at operatørene har ansvar for å bidra t 3⁄4/ å håndtere ulike forhold. Barrierene bør være tilstrekkelig robuste slik at teknisk svikt I enkeltelement svikt i neste barriere.

Claims (20)

C l a i m s

1. A method of suspending flow in a well, the method comprising the step of placing a first plug in a production tubular in an upper wellhead section, above a downhole safety valve, wherein the first plug is: adapted to fit into the production tubular to form a fluid seal in the production tubular to form a barrier for containing well fluid; equipped with instrumentation for obtaining information by measuring physical conditions below the plug; and equipped with means for transmitting said obtained information to an operator.

2. The method according to claim 1 , wherein the well is completed.

3. The method according to claim 1 or 2, wherein the well is a producing well.

4. A method of suspending flow in a well such as a petroleum producing well by placing at least one plug in a production tubular in an upper wellhead section above a downhole safety valve c h a r a c t e r i s e d i n that the method comprises:

- a plug (6o) adapted to fit into a production tubular (3i) forming a fluid seal and which is equipped with instrumentation (64) for measuring physical conditions below the plug (60) and means for transmitting such information to an operator and where the plug (60) forms part of a secondary barrier (SB) containing the well fluids

- a control unit (A) located inside or outside of the tubular adapted to communicate with the plug (60) instrumentation (64) and making the information transmitted from the plug (60) available to an operator

5. The method according to any one of the preceding claims where a second plug (7o) is set in the tubular (3i) above the first plug (60) and where the first plug (60) forms part of a primary barrier (PB) and where the second plug (7o) forms part of a secondary barrier (SB) containing the well fluids

6. Method according to any one of the preceding claims where the method of transferring information from a plug to or from an operator is by means of acoustic signalling

7. Method according to any one of the preceding claims where the method of transferring information from a plug to or from an operator is by means of electromagnetic signalling

8. Method according to any one of the preceding claims where communication between a control unit (A) and a plug (60, 7o) is achieved by the control unit (A), or part of a control unit being lowered into the well inside the tubular

9. Method according to any one of the preceding claims where the physical property includes fluid pressure

10. Method according to any one of the preceding claims where the physical property includes fluid temperature

11. Method according to any one of the preceding claims where the physical property includes fluid type determined by fluid density, viscosity, pH or refractive index

12. Method according to any one of the preceding claims where the method of setting and retrieving the first plug (60) and the secondary plug (7o) is by use of a lubricator tool (9o)

13. Method where the first plug (60) and the second plug (70) are mechanically connected allowing setting or retrieval of both plugs in a single well entry operation

14. An apparatus for suspending flow in a well, the apparatus comprising a first plug, the first plug comprising instrumentation for obtaining information by measuring physical condition in a well and means for transmitting said information to an operator.

15. The apparatus according to claim 14, wherein the apparatus further comprises a second plug, the second plug instrumentation for obtaining information by measuring physical condition in a well and means for transmitting said information to an operator.

16. The apparatus according to any one of claim 14 or 15, wherein the instrumentation for obtaining information by measuring physical conditions of the first and/or the second plug comprises instrumentation for obtaining information by measuring physical conditions below the plug in operational use.

17. The apparatus according to any one of the claims 15 to 16, wherein the first and the second plug are mechanically connected.

18. The apparatus according to claim 17, wherein the apparatus comprises a middle section of smaller diameter than the first and the second plug, such that the middle section may form a chamber in the well when in operational use.

19. Apparatus as described in any of the previous claims consisting of a mechanical tubular plug (10o) equipped with instrumentation (104) for measuring physical conditions above and / or below the plug (60) and means for transmitting such information to an operator

20. Apparatus as described in any of the previous claims consisting of a mechanical tubular plug (10o) equipped with instrumentation (104) for actuating a command and means for receiving such information from an operator