NO345981B1

NO345981B1 - Method and apparatus for suspending a well

Info

Publication number: NO345981B1
Application number: NO20180620A
Authority: NO
Inventors: Kåre Olav Krogenes; Jan Erik Skjold
Original assignee: Icon Instr As
Priority date: 2017-05-11
Filing date: 2018-04-30
Publication date: 2021-12-06
Also published as: NO20180620A1

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.

Document US 2015/0204155 A1 discloses a well completion system that two barriers and a sensor to gauge a pressure between the two barriers and a communication device to communicate the gauged pressure.

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 plug in a production tubular in an upper wellhead section, above a downhole safety valve, wherein the 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 plug may be referred to as “the first plug”.

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 plug, wherein the 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 in a well; and equipped with means for transmitting said information to an operator.

The plug may be referred to as “the first plug”. 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 40, manual master valve 25, hydraulic master valve 24 and production master valve 23 to production.

In producing mode the wellhead 30 will be equipped with a christmas tree 20 allowing for closing production through the production master valve 23, 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 30 or if mounted a christmas tree 20 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 volumes VA, VB, 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, VC is contained by annulus valves 33, 34, 35.

A downhole safety valve 40 is arranged in the production tubular as well as an annular safety valve 50 arranged to close the annulus formed between the production tubular 31 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 31, packers 37 and downhole safety valve 40. A secondary barrier SB is formed by the primary barrier PB, casing 32, cemented casing shoe 36, annular safety valve 50, wellhead 30 and christmas tree 20 valves 21, 22, 23, 24, 25.

Figure 2 Illustrates a production well 1 having been suspended by setting a first plug 60 (deep set) below the downhole safety valve 40, closing the downhole safety valve 40 and setting a second plug 70 (shallow set) in the upper wellhead section above the downhole safety valve 40. 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 70 and may be complimented by a downhole pressure gauge or tubing to annulus communication providing pressure reading of the volume VDHSV-P1.

Figure 3 Illustrates a production well 1 having been suspended according to the invention by closing the downhole safety valve 40, setting a shallow first plug 60 above the downhole safety valve 40. The first plug 60 is instrumented and the monitored volume M includes the volume VWH-P1 above the first plug 60, the volume VP1-DHSV between the first plug 60 and the downhole safety valve 40 and the volume VDHSV-F between the downhole safety valve 40 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 60 through normal static condition leakage through the closed downhole safety valve 40.

Figure 4 Illustrates a production well 1 having been suspended according to the invention by closing the downhole safety valve 40, setting a shallow first plug 60 above the downhole safety valve 40, and setting a shallow second plug 70 above the first plug 60. Setting a shallow plug may be done by use of a lubricator tool. The first plug 60 is instrumented and the monitored volume M includes the volume VWH-P2 above the second plug 70, the volume VP2-P1 between the second plug and the first plug 60, the volume VP1-DHSV between the first plug 60 and the downhole safety valve 40 and the volume VDHSV-F between the downhole safety valve 40 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 60 through normal static condition leakage through the closed downhole safety valve 40.

Figure 5 Illustrates a production well 1 prepared for wireline 80 intervention. Other item numbering is the same as in figure 1. The primary barrier PB is maintained while the downhole safety valve 40 remains in a closed position and the secondary barrier SB is maintained while the swab valve 21 remains in a closed position or while the swab valve 21 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 90 intervention. Other item numbering is the same as in figure 1. The primary barrier PB is maintained while the downhole safety valve 40 remains in a closed position and the secondary barrier SB is maintained while the swab valve 21 remains in a closed position or while the swab valve 21 remains in an open position and the lubricator tool 90 forms part of the secondary barrier SB envelope following pressure testing.

Figure 7a Illustrates a mechanical plug 100 with seals 101, which when actuated, seals and separates the volume of the production tubular 31 above the plug from that which is below the plug 100. The plug 100 may be mechanically locked in its position by means of a locking device 102 which may intrude into the production tubular 31 or equivalent devices designed to fit into a groove in the production tubular 31.

The mechanical plug 100 is also equipped with an instrument section 104 which in this example has been adapted to fit between the mechanical plugs 100 main body and its bull nose 103 mounted at its lower end. The instrument section 104 may have fluid connection with the borehole volumes above and below the plug and may form the pressure retaining element of the plug 100, separating the two volumes. The instrument section may contain instrumentation 104 for measuring physical conditions above and/or below the plug 100 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 P1, temperature below the plug T1 and physical properties such as density ρ1 or other property allowing determination of fluid type (gas, crude oil, brine, water etc.) and if plural (ρ1, ρ2 or more) allowing determination of rate of change Q1 (cm<3>/min) and thus flow/inflow. The following plugs are of this type, Figure 3 - plug 60 and Figure 4 - plug 60.

Figure 7b Illustrates a mechanical plug 11 with seals 111, which when actuated, seals and separates the volume of the production tubular 31 above the plug from that which is below the plug 110. The plug 110 may be mechanically locked in its position by means of a locking device 112 which may intrude into the production tubular 31 or equivalent devices designed to fit into a groove in the production tubular 31. The following plugs are of this type, Figure 2 - plug 60 and plug 70, Figure 4 - plug 70.

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 60, 70 are placed by use of a wireline unit 80 such as illustrated in figure 5 while christmas tree valves 22, 23 are closed and 21, 24, 25 and downhole safety valve 40 are opened as required for lowering/ hoisting the wireline and connected tools/ plugs 60, 70.

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 60 and a shallow set plug 70 as illustrated in figure 2 - with a shallow set plug 60 as illustrated in figure 3 arranged with instrumentation sufficiently monitoring the volume above the plug VWH-P1 and below the plug VP1-DHSV extending to the downhole safety valve. In this embodiment the downhole safety valve 40 forms part of the primary barrier PB and the plug 60 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 60 and 70 incorporating sufficient instrumentation to measure physical characteristics in volumes VP2-P1 and VP1-DHSV. In this embodiment the downhole safety valve 40 and the first plug 60 form part of the primary barrier PB and the plug 70 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 40 and presence of pressure status monitoring of the volume below the downhole safety valve 40. In the second embodiment the downhole safety valve 40 supported by the first plug 60 form the primary barrier PB and provides as a minimum pressure monitoring of the volume VP1-DHSV below the downhole safety valve 40.

The volume (VWH-P1 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-P1 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 40.

In both the first and the second embodiments as illustrated in figures 3, 4 and 5 the plugs 60, 70 may be set and retrieved by use of a lubricator tool 90 such as illustrated in figure 6. When pressure tested and connected to the christmas tree 20 the lubricator tool 90 may form part of the secondary barrier SB. As neither the first or second embodiment require opening of the downhole safety valve 40 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 60 is instrumented such as illustrated in figure 7a 100 enabling measurement of pressure P2 and temperature T2 above the plug 100 and pressure P1, temperature T1 and density ρ1 below the plug. The plug 100 is equipped with a locking device 102 which mechanically locks the plug 100 to the tubular 31. The locking may take form of teeth in the locking device 102 intruding into the tubular 31 wall, or take form of a profile which enters into an equivalent groove in the tubular or wellhead. The plug 100 is equipped with seals 101 which seal the void between the plug 100 and the tubular 31 when activated.

The second plug 70 is a non-instrumented plug such as illustrated in figure 7b 110. 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 100 in figure 7a, or 60 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 103, attaching the instrument section 104 to the plug 100 in place of the bullnose 103 and reattaching the bullnose 103 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 100 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.

Claims

C l a i m s

1. A method of suspending flow in a completed well (1), the method comprising the step of placing a plug (60, 100, 120, 130) in a production tubular (31) in an upper wellhead section, above a downhole safety valve (40), wherein the plug (60, 100, 120, 130) is: adapted to fit into the production tubular to form a fluid seal in the production tubular (31) to form a barrier for containing well fluid; equipped with instrumentation (104) for obtaining information by measuring physical conditions below the plug (60, 100, 120, 130); and equipped with means for transmitting said obtained information to an operator.

2. The method according to claim 1, wherein the well (1) is a producing well (1).

3. The method according to any one of the preceding claims where a second plug (70) is set in the tubular (31) above the plug (60, 100, 120, 130) and where the plug (60, 100, 110, 120, 130) forms part of a primary barrier (PB) and where a second plug (70) forms part of a secondary barrier (SB) containing the well fluids.

4. Method according to any one of the preceding claims where the method of transferring information from a plug (60, 100, 120, 130) to or from an operator is by means of acoustic signalling.

5. Method according to any one of the preceding claims where the method of transferring information from a plug (60, 100, 120, 130) to or from an operator is by means of electromagnetic signalling.

6. Method according to any one of the preceding claims where communication between a control unit (A) and a plug (60, 100, 120, 130, 70) is achieved by the control unit (A), or part of a control unit being lowered into the well (1) inside the tubular (31).

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

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

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

10. Method according to any one of claims 3 to 9 where the method of setting and retrieving the first plug (60, 100, 120, 130) and the second plug (70) is by use of a lubricator tool (90)

11. Method according to any one of claims 3 to 10 where the first plug (60, 100, 120, 130) and the second plug (70) are mechanically connected allowing setting or retrieval of both plugs (60, 100, 120, 130, 70) in a single well entry operation

12. An apparatus for suspending flow in a well (1), the apparatus comprising a plug (60, 100, 120, 130), wherein the plug (60, 100, 120, 130) is: adapted to fit into the production tubular (31) to form a fluid seal in the production tubular (31) to form a barrier for containing well fluid; equipped with instrumentation (104) for obtaining information by measuring physical conditions below the plug (60, 100, 120, 130) in the well (1); and equipped with means for transmitting said information to an operator.

13. The apparatus according to claim 12, wherein the apparatus further comprises a second plug (70), the second plug (70) comprising instrumentation for obtaining information by measuring physical condition in a well (1) and means for transmitting said information to an operator.

14. The apparatus according to claim 13, wherein the instrumentation for obtaining information by measuring physical conditions of the second plug (70) comprises instrumentation for obtaining information by measuring physical conditions below the plug (60, 100, 120, 130) in operational use.

15. The apparatus according to one of the claims 13 or 14, wherein the plug (60, 100, 120, 130) and the second plug (70) are mechanically connected.

16. The apparatus according to claim 15, wherein the apparatus comprises a middle section of smaller diameter than the plug (60, 100, 120, 130) and the second plug (70), so that the middle section may form a chamber in the well (1) when in operational use.