Method and system for remotely operating a plug assembly in a well

Abstract

The invention relates to a method for remotely operating a plug assembly (2, 130) in a well, the well comprising a bore (1, 100), the plug assembly (2, 130) being arranged within the bore (1, 100), the method comprising steps of: – performing a sequence of operations on a valve (125) on a wellhead assembly (120) to obtain a sequence of variations of bottom hole pressure within the bore (1, 100); – detecting the variations of bottom hole pressure by at least one sensor (4) on the plug assembly (2, 130); and – responsive to said detecting, operating the plug assembly (2, 130).

Description

[0001] METHOD AND SYSTEM FOR REMOTELY OPERATING A PLUG ASSEMBLY IN A WELL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method and system for remotely operating a plug assembly in a well. The present disclosure also relates to a computer program comprising instructions to cause a plug assembly in a well to execute steps in said method, and a plug assembly comprising a computer readable medium having stored thereon said computer program.

[0004] TECHNICAL BACKGROUND

[0005] Bridge plugs are important tools in drilling and well operations to create seals or isolations between different sections or zones in the well. However, their installation and retrieval are costly and time-consuming, and require intervention accompanied by operational and health, safety, and environmental (HSE) risks.

[0006] In some solutions, a high-pressure pump rigged up on the surface at a wellsite is used to create a sequenced pressure pattern (similar to Morse Code) that is programmed into a bridge plug. When a correct condition is met, a barrier valve in the plug will open / close to allow / block fluid flow through a tubing in the well. Such solution requires mobilization of the pump or other equipment on the surface and personnel to the wellsite to create the pressure pulses / signals.

[0007] US7967071 describes a completion assembly comprising a downhole electronic actuating mechanism, a downhole hydraulic pump and a hydraulically operated valve member. The electronic actuation mechanism monitors hydrostatic pressure using a sensor on the assembly, monitors time using a timer, and operates the pump to move the valve between the open and closed positions when the pressure and / or the time meet the predetermined conditions.

[0008] US9376889 describes a downhole valve assembly operable to control production fluid flow around an obstruction in a production tubing string. The downhole valve assembly comprises a tubular body that includes an axial passage extending through the body and one or more ports extending substantially radially through the body. The downhole valve assembly also includes one or more actuating members operable to move relative to the body. Movement of the actuating members selectively opens the ports such that a fluid flow path through the ports is defined between an annulus region outside of the valve assembly and the axial passage such that the blockage can be bypassed.

[0009] Therefore, there is a need for providing an improved method and system for remotely operating a plug assembly in a well.

[0010] SUMMARY OF THE INVENTION

[0011] The invention relates to a method for remotely operating a plug assembly in a well in a subterranean formation, the well comprising a bore, the plug assembly being arranged within the bore, the method comprising steps of:

[0012] - performing a sequence of operations on a valve on a wellhead assembly to obtain a sequence of variations of bottom hole pressure within the bore;

[0013] - detecting the variations of bottom hole pressure by at least one sensor on the plug assembly; and

[0014] - responsive to said detecting, operating the plug assembly.

[0015] The variations of bottom hole pressure may comprise one or more increases of bottom hole pressure. These increases may be due to the natural pressure within the subterranean formation.

[0016] In some variations, the sequence of operations on the valve is a sequence of openings and closures of the valve, at predetermined time intervals.

[0017] In some variations, the predetermined time intervals between successive openings and closures of the valve is between 0.5 hour and 72 hours, preferably between 1 hour and 60 hours, more preferably between 1 .5 hour and 50 hours.

[0018] In some variations, detecting the variations of bottom hole pressure comprises one or more of the following:

[0019] - detecting a succession of increases and decreases in the bottom hole pressure within a predetermined period of time;

[0020] - detecting that the bottom hole pressure passes one or more predetermined thresholds of pressure a predetermined number of times within a predetermined period of time;

[0021] - detecting that the bottom hole pressure stays in a predetermined pressure value window for a predetermined period of time;

[0022] - detecting that the bottom hole pressure increases and / or decreases at a predetermined rate within a predetermined period of time; and - detecting that the bottom hole pressure has a predetermined number of peaks above predetermined pressure value within a predetermined period of time;

[0023] - detecting that the bottom hole pressure successively increases above one or more predetermined pressure values and decreases below one or more predetermined pressure values, for a predetermined number of times and within a predetermined period of time.

[0024] In some variations, operating the plug assembly consists in opening or closing off the passage of fluid in the bore.

[0025] In some variations, the plug assembly comprises one or more flow ports configured to open and close; when the flow ports are open, fluid can pass the plug assembly within the bore; and when the flow ports are closed, fluid cannot pass the plug assembly within the bore.

[0026] In some variations, the at least one sensor on the plug assembly comprises a pressure sensor positioned above the one or more flow ports of the plug assembly.

[0027] In some variations, the well is selected from a geothermal well, a hydrocarbon production well, a water production well, a water injection well and a gas injection well, for example a CO2 storage injection well, and is preferably a hydrocarbon production well.

[0028] In some variations, the method further comprises:

[0029] - injecting fluid into the bore at one or more injection points.

[0030] In some variations, the fluid is a gas selected from nitrogen, carbon dioxide and hydrocarbons, or a liquid selected from water, hydraulic oil and aqueous solutions.

[0031] In some variations, the fluid is gas and is injected via a gas lift line.

[0032] In some variations, the one or more injection points are located between the plug assembly and the surface.

[0033] In some variations, the steps of injecting gas and performing the sequence of operations on the valve are performed at an off-site facility remote from an installation site of the well.

[0034] The invention further relates to a computer program comprising instructions to cause a plug assembly in a well to execute the abovementioned steps of detecting and operating in any and all the variations of the method described above.

[0035] The invention further relates to a plug assembly comprising a computer- readable medium having stored thereon this computer program. The present disclosure provides an efficient and convenient way to remotely control the plug assembly operation in the well, which is based on valve operations on the wellhead assembly and bottom hole pressure detection. In contrast to some solutions, the present disclosure does not use an additional pump (on the surface or subsurface) to create pressure pulses / signals to control the plug assembly operation. Instead, a sequenced pressure pattern to control the plug assembly operation is generated by timed / sequenced opening and closing of valve(s) on the wellhead assembly. The bottom hole pressure buildup is preferentially natural (owing to pressure within the subterranean formation) or in a variant is obtained (partly or entirely) by fluid injection, such as gas lift or similar. While operation of the plug assembly is programmed, a sequenced pressure pattern to trigger such programmed operation is enabled by controlling the valve operation. In contrast to the method and system in US7967071 , operation of the plug assembly can be more conveniently and flexibly controlled. An off-site operator for example at a central control room can remotely control the valve operations to operate the plug assembly as needed. No mobilization of further equipment or personnel on site is required, thus operational costs and HSE risks can be reduced.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Non-limiting examples will now be described in reference to the accompanying drawings, where:

[0038] FIG. 1 schematically shows an installation suitable for implementing the method of the invention.

[0039] FIG. 2 schematically shows an example of a plug assembly deployed in a well.

[0040] FIG. 3 is a graphical view of an example of variations of bottom hole pressure.

[0041] DETAILED DESCRIPTION

[0042] The present disclosure will now be described in more detail without limitation in the following description.

[0043] Making generally reference to FIG. 1 , it is provided a method for remotely operating a plug assembly 130 in a well. The well comprises a bore 100, and the plug assembly 130 is arranged within the bore 100. The method comprises steps of: - performing a sequence of operations on a valve 125 on a wellhead assembly 120 to obtain a sequence of variations of bottom hole pressure within the bore 100;

[0044] - detecting the variations of bottom hole pressure by at least one sensor on the plug assembly 130; and

[0045] - responsive to said detecting, operating the plug assembly 130.

[0046] The well can be a production well and / or an injection well, for example a hydrocarbon production well, a water production well, a water injection well and a gas injection well. The injection well can be used to inject a fluid for storage (such as a CO2 storage injection well), or for another purpose, such as enhanced oil recovery. The well can also be a geothermal well (be it a production well or an injection well).

[0047] In the present description, the term “well” means a drillhole boring in a subterranean formation. For example, a hydrocarbon production well is designed to bring hydrocarbons to the surface, created by drilling down into a hydrocarbon reserve or reservoir. Preferably, the hydrocarbon production well is an oil well or gas well.

[0048] The well may be onshore or offshore (subsea).

[0049] In some embodiments, the plug assembly 130 is directly placed in a drilled bore which does not comprise a tubing, or in a section of a drilled bore which does not comprise a tubing. In other embodiments, the plug assembly 130 is placed within a tubing arranged in the bore of the well. For example, in case the well is a hydrocarbon production well, this tubing may be the production tubing. Herein, whenever reference is made to a bore, this reference should be understood as relating more precisely to the tubing in the bore, if the plug assembly is indeed positioned in such tubing.

[0050] In the following, a detailed description is provided by making reference to a hydrocarbon production well, but it applies similarly to other types of wells.

[0051] By “bottom hole pressure" is meant the pressure within the well which is detected by at least one sensor on the plug assembly.

[0052] In some embodiments, the sequence of operations on the valve is a sequence of openings and closures of the valve, at predetermined time intervals.

[0053] In some embodiments, the predetermined time interval between successive openings and closures of the valve is between 0.5 hour and 72 hours, preferably between 1 hour and 60 hours, more preferably between 1.5 hour and 50 hours.

[0054] Preferably, the wellhead assembly is a so-called “Christmas tree” or “tree” known in the field of hydrocarbon production. The wellhead assembly may be located onshore or offshore (e.g., at the bottom of the sea). If it is located onshore, the valve(s) which is I are operated may be designated as surface valve(s).

[0055] The wellhead assembly may comprise at least one valve to control a flow of hydrocarbon fluid out of the well. The at least one valve to control a flow of hydrocarbon fluid out of the well may comprise a wing valve and / or a choke valve. The wing valve is used to shut off flow from the well. The choke valve serves to control the flow rate of fluids being produced and to regulate the downstream pressure by restricting the flow area. The wellhead assembly may further comprise a control valve to control the injection of fluid which will be described below, e.g. the injection of gas via a gas lift line.

[0056] Preferably, the plug assembly is programmed to operate responsive to detecting the variations of bottom hole pressure. Preferably, the plug assembly is pre-programmed prior to insertion into the well. For example, the plug assembly may be programmed to operate responsive to detecting that the variations of bottom hole pressure follow a predetermined pattern or satisfy a predetermined condition.

[0057] In some embodiments, detecting the variations of bottom hole pressure comprises one or more of the following:

[0058] - detecting a succession of increases and decreases in the bottom hole pressure within a predetermined period of time;

[0059] - detecting that the bottom hole pressure passes one or more predetermined thresholds of pressure a predetermined number of times within a predetermined period of time;

[0060] - detecting that the bottom hole pressure stays in a predetermined pressure value window for a predetermined period of time;

[0061] - detecting that the bottom hole pressure increases and / or decreases at a predetermined rate within a predetermined period of time; and

[0062] - detecting that the bottom hole pressure has a predetermined number of peaks above predetermined pressure value within a predetermined period of time;

[0063] - detecting that the bottom hole pressure successively increases above one or more predetermined pressure values and decreases below one or more predetermined pressure values, for a predetermined number of times and within a predetermined period of time.

[0064] In some embodiments, operating the plug assembly consists in opening or closing off the passage of fluid in the bore. Closing off the passage of fluid may entail complete closure or partial closure (so as to block for instance at least 90 %, or at least 95% of the flow rate in comparison with the open state).

[0065] Preferably, the plug assembly comprises a valve that is shiftable, rotatable, or movable from a first position, in which the passage of fluid in the bore is opened, to a second position, in which the passage of fluid in the bore is closed. Examples of valves may include, but not limited to, ball valves, sleeves, circulation valves, tester valves, and other types of valves.

[0066] In some embodiments, the plug assembly comprises one or more flow ports configured to open and close. When the flow ports are open, fluid can pass the plug assembly within the bore, and when the flow ports are closed, fluid cannot pass the plug assembly within the bore.

[0067] Preferably, the one or more flow ports of the plug assembly may be configured as a sliding sleeve door, which can be shifted between an open position and a closed position. Preferably, operating the plug assembly consists in opening or closing off the passage of fluid in the bore by shifting the sliding sleeve door to the open position or the closed position.

[0068] In some embodiment, the sensor on the plug assembly is positioned above the one or more flow ports of the plug assembly.

[0069] Preferably, the plug assembly may comprise two or more sensors, at least one positioned above the one or more flow ports of the plug assembly. Optionally, one pressure sensor may be provided above the one or more flow ports and one pressure sensor may be provided below the one or more flow ports. A temperature sensor may also be provided.

[0070] Here, the terms “above” and “below” mean that a part referred to as “above” is relatively closer to the top of a well than a part referred to as “below”, irrespective of the well being a horizontal well, a vertical well or an inclining well. “Above" thus means downstream, relative to the hydrocarbon flow from the reservoir to the surface, while “below” means upstream, in the example of a hydrocarbon production well.

[0071] Preferably, operating the plug assembly is also based on one or more further parameter(s) in addition to the variations of bottom hole pressure. For example, a clock time and / or an elapsed time, a measured temperature and / or temperature change, and combinations thereof may also be monitored and combined with the detected variations of bottom hole pressure, and the plug assembly may be operated responsive to such combined condition. In other words, operations on the valve on the wellhead assembly may be controlled in light of the monitoring of the one or more further parameter, so as to obtain the intended variations of bottom hole pressure to trigger operations of the plug assembly. For this purpose, the plug assembly may further comprise a timer, a temperature sensor, and / or any sensor or detector for such one or more further parameter.

[0072] In preferred variations of the method, fluid is injected into the bore, via an injection line 110, at one or more injection points 115. The injection of fluid may be continuous, concomitantly to performing the sequence of operations on the valve. Alternatively, it may be discontinuous, for example it may take place only when the valve is closed.

[0073] In the present invention, the variations of bottom hole pressure are not solely caused by variations in the injection of fluid. The variations of bottom hole pressure following a predetermined pattern or satisfying a predetermined condition are enabled by controlling operations on the valve. Fluid injection, if present, assists in achieving or accelerating pressure buildup within the bore.

[0074] The fluid which may be injected may be a gas or a liquid. The gas may be nitrogen, carbon dioxide or a hydrocarbon gas. The liquid may be water (such as brine), hydraulic oil or any aqueous solution.

[0075] In preferred variations, the fluid is gas and the injection line 110 is a gas lift line. Such gas may be a hydrocarbon gas, for example primarily comprising methane and ethane. In other variations, the fluid may be injected through a chemical injection line.

[0076] The one or more injection points may be located between the plug assembly and the surface, or between the plug assembly and the bottom of the well, or both between the plug assembly and the surface, and between the plug assembly and the bottom of the well.

[0077] In the method of the invention, if the passage of fluid in the bore is partially or fully open in the plug assembly, the bottom hole pressure increases after closing the valve on the wellhead assembly. In some cases, the bottom hole pressure increases in the absence of fluid injection, due to the natural pressure in the subterranean formation (e.g., hydrocarbon reservoir) wherein the well is positioned. However, the injection of fluid may accelerate the rate of increase in the bottom hole pressure. Merely by way of example, in the absence of fluid injection, after closing the valve, it may take from 12 hours to 10 days for the bottom hole pressure to sufficiently increase (so that for example one or more predetermined thresholds of pressure are passed) before the valve can be opened to trigger a decrease in bottom hole pressure. Still merely by way of example, in the presence of fluid injection, after closing the valve, it may take from 0.5 to 12 hours for the bottom hole pressure to sufficiently increase (so that for example one or more predetermined thresholds of pressure are passed) before the valve can be opened to trigger a decrease in bottom hole pressure.

[0078] With or without fluid injection, opening the valve on the wellhead assembly leads to a decrease in bottom hole pressure. Then closing the valve again shuts off the fluid flow in the well and the bottom hole pressure in the well increases again. By controlling operations on the valve on the wellhead assembly, in combination with bottom hole pressure build-up over time, a desired pattern of variations of the bottom hole pressure can be obtained. Such control can be performed fully remotely, without on-site intervention. The pressure pattern thus obtained can be used to remotely operate the plug assembly.

[0079] If, on the other hand, the passage of fluid in the bore is fully closed in the plug assembly, then the injection of fluid is necessary in order to obtain an increase in bottom hole pressure (above the plug assembly) when the valve is closed. Then, opening the valve leads to a decrease in bottom hole pressure (above the plug assembly). Again, when the valve is open, it may be advantageous to discontinue the injection of fluid.

[0080] In some embodiments, the steps of injecting fluid (if present) and performing the sequence of operations on the valve are performed at an off-site facility 140 remote from an installation site of the well. Such off-site facility may comprise a central control room.

[0081] The operations on the valve and optionally the injection of fluid may be controlled manually, for example by an operator at the central control room while monitoring the bottom hole pressure, or automatically, for example based on a computer program which is programmed to cause a predetermined operation depending on the monitored bottom hole pressure.

[0082] The invention also provides a computer program comprising instructions to cause a plug assembly in a well to execute the steps of detecting and operating in the above-described method.

[0083] The invention also provides a plug assembly comprising a computer- readable medium having stored thereon said computer program.

[0084] Preferably, the plug assembly is battery-powered. For example, the plug assembly may be powered by a lithium-based battery, since it has a high current capacity at a high temperature rating. Preferably, the plug assembly is entirely independent of any control lines or electronic signaling from the surface of the well bore.

[0085] More generally, all statements given for the method for remotely operating a plug assembly in a well according to the disclosure are also applicable to the computer program for performing steps in said method, as well as the plug assembly comprising a computer-readable medium having stored thereon said computer program.

[0086] FIG. 2 schematically shows an example of a plug assembly deployed in a hydrocarbon production well. FIG. 2 shows that a plug assembly 2 is connected to a bridge plug 3 which is above the plug assembly 2 in a production tubing 1. The bridge plug 3 is installed within the production tubing 1 , for example owing to a profile 8 which engages I grips the wall of the production tubing 1 . The bridge plug 3 comprises a sealing member 9 such as an elastomeric ring which provides sealing between the outer surface of the bridge plug 3 and the wall of the production tubing 1 .

[0087] In the example of FIG. 2, the plug assembly 2 comprises a sensor 4 configured to detect variations of bottom hole pressure and positioned above flow ports 5. Only three flow ports 5 are shown in FIG. 2, but the number of flow ports is not limited thereto. In the example of FIG. 2, the plug assembly 2 also comprises a further pressure sensor 6 positioned below the flow ports, and a temperature sensor 7 positioned below the sensor 6. FIG. 2 shows the plug assembly 2 in an open state, in which the flow ports 5 are open and fluid passes the plug assembly as illustrated with arrows.

[0088] More specifically, fluid successively flows around a downstream portion of the plug assembly 2, into the flow parts 5, within a central lumen of an upstream portion of the plug assembly 2, within a central lumen of the bridge plug 3, and then out of the bridge plug 3 back to the open lumen of the production tubing 1 , above the sealing member 9. Fluid may not directly flow around the plug assembly 2 and around the plug bridge 3 due to the sealing member 9.

[0089] When the flow ports 5 are closed, the passage of fluid is blocked.

[0090] FIG. 3 illustrates a graphical view of an example of variations of bottom hole pressure to operate the plug assembly. Upper lines on the graph show a bottom hole pressure in a unit of pound per square inch (psi) plotted on a time scale (unit: 3 hours). Lower lines on the graph show a status of the plug assembly and a status of the valve on the wellhead assembly (in this example, a choke valve on the wellhead assembly), respectively.

[0091] During the course in FIG. 3, gas is continuously injected into the production tubing via the gas lift line.

[0092] As seen in FIG. 3, initially at time To, the valve on the wellhead assembly is open and the bottom hole pressure is at a reference value of about 1 ,300 psi for about 24 hours. In this state, the plug assembly is in a closed state in which the passage of fluid in the production tubing is closed. At time Ti , the valve is closed for about 9 hours. The bottom hole pressure (as sensed by the sensor of the plug assembly) starts to increase. The increasing bottom hole pressure passes two thresholds Th1 and Th2, about 1 ,900 psi (Th1 ) and about 2,200 psi (Th2) in this example. The bottom hole pressure then reaches a peak value, about

[0093] 2.500 psi in this example, and the valve is opened again at time T2. The bottom hole pressure starts to decrease, while passing again the two thresholds Th1 and Th2. When the bottom hole pressure reaches a bottom value, about 1 ,500 psi in this example, the valve is closed again at time T3.

[0094] In the example of FIG. 3, a sequence of operations on the valve, consisting of opening, closing for about 9 hours and opening, provides a pattern of the bottom hole pressure, consisting of an increase from the reference value of about 1 ,300 psi to the peak value of about 2,500 psi over the time interval of about 7.5 hours and a subsequent decrease from the peak value to the bottom value of about

[0095] 1.500 psi over the time interval of about 1.5 hours, while passing the two thresholds of about 1 ,900 psi and about 2,200 psi. As seen in FIG. 3, this sequence of operations on the valve is repeated three times over the time interval from time T1 to time Te to obtain substantially the same pattern of the bottom hole pressure three times, that provides a first profile of the bottom hole pressure.

[0096] In the example of FIG. 3, when this complete first profile of the bottom hole pressure has been detected at time Te, the plug assembly is shifted to the open state. The bottom hole pressure then starts to decrease to reach the reference value of about 1 ,300 psi.

[0097] In FIG. 3, the valve is left opened over a transition period of about 28 hours in this example from time Te to time T7, during which the bottom hole pressure is at the reference value of about 1 ,300 psi. After the transition period, the valve is closed again at time T7. Then the same sequence of operations on the valve as the sequence which provided the first profile of the bottom hole pressure during time T1 to time Te is repeated three times, so that a second profile of the bottom hole pressure similar to the first profile is obtained over the time interval from time T7 to time Ts.

[0098] In the example of FIG. 3, when the complete second profile of the bottom hole pressure has been detected at time Ts, the plug assembly is shifted to the closed state. The bottom hole pressure then starts to decrease again to reach the reference value of about 1 ,300 psi.

[0099] In the example of FIG. 3, the first profile of the bottom hole pressure with three peaks serves as a signal to trigger the open state of the plug assembly, and the second profile of the bottom hole pressure with three peaks serves as a signal to trigger the closed state of the plug assembly. However, the variations of bottom hole pressure to trigger operations of the plug assembly may not be limited to the specific pattern in FIG. 3. The first profile to trigger the open state of the plug assembly may be the same as or different from the second profile to trigger the closed state of the plug assembly. The first and / or the second profile may comprise one, two, three, four or more peak and / or bottom values, and the peak and / or bottom values may be all the same or differ from each other. Although there are two thresholds in the example of FIG. 3, the number and the value of the threshold(s) may vary.

[0100] The shift from the closed state to the open state (or the opposite) may be, in the example of FIG. 3, triggered as a result of the sensed bottom hole pressure successively increasing above Th1 and above Th2, and then decreasing below Th2 and below Th1 , three times, within a predetermined period of time. Of course, the number and values of the thresholds, the number of sequences of threshold passings and the period of time over which all or part of the thresholds have to be passed can be adjusted to optimize the reliability and rapidity of the detection.

[0101] In the example of FIG. 3, the reference value of the bottom hole pressure (plateaued bottom hole pressure reached when the valve has been open for a sufficiently long period of time) is the same when the plug assembly is in the open state and when the plug assembly is in the closed state. But this is not necessarily the case, as pressure from the reservoir may affect the reference value of the bottom hole pressure when the plug assembly is in the closed state.

[0102] The variations of bottom hole pressure may not be limited to a linear increase and / or decrease, but may comprise an increase and / or decrease in a stepped manner. Time intervals for operations, pressure increase / decrease and transitions may not be limited to a scale and a range in the example of FIG. 3, but may appropriately be set, for example to be several seconds, minutes, hours, days, weeks or months.

[0103] Instead of completely opening and completely closing the valve, it is also possible to transition the valve between a fully closed state and a partially open state, or between a partially open state and a fully open state, or between two partially open states, or between more than two states (including for example a fully closed state, a fully open state and a partially open state).

Claims

CLAIMS1. A method for remotely operating a plug assembly (2, 130) in a well in a subterranean formation, the well comprising a bore (1 , 100), the plug assembly being arranged within the bore, the method comprising steps of: performing a sequence of operations on a valve (125) on a wellhead assembly (120) to obtain a sequence of variations of bottom hole pressure within the bore (1 , 100); detecting the variations of bottom hole pressure by at least one sensor (4) on the plug assembly (2, 130); and responsive to said detecting, operating the plug assembly (2, 130).

2. The method according to claim 1 , wherein the variations of bottom hole pressure comprise one or more increases of bottom hole pressure which are due to the natural pressure within the subterranean formation.

3. The method according to claim 1 or 2, wherein the sequence of operations on the valve (125) is a sequence of openings and closures of the valve (125), at predetermined time intervals.

4. The method according to claim 3, wherein the predetermined time intervals between successive openings and closures of the valve (125) is between 0.5 hour and 72 hours, preferably between 1 hour and 60 hours, more preferably between 1 .5 hour and 50 hours.

5. The method according to any one of claims 1 to 4, wherein detecting the variations of bottom hole pressure comprises one or more of the following: detecting a succession of increases and decreases in the bottom hole pressure within a predetermined period of time;detecting that the bottom hole pressure passes one or more predetermined thresholds of pressure a predetermined number of times within a predetermined period of time; detecting that the bottom hole pressure stays in a predetermined pressure value window for a predetermined period of time; detecting that the bottom hole pressure increases and / or decreases at a predetermined rate within a predetermined period of time; and detecting that the bottom hole pressure has a predetermined number of peaks above predetermined pressure value within a predetermined period of time; detecting that the bottom hole pressure successively increases above one or more predetermined pressure values and decreases below one or more predetermined pressure values, for a predetermined number of times and within a predetermined period of time.

6. The method according to any one of claims 1 to 5, wherein operating the plug assembly (2, 130) consists in opening or closing off the passage of fluid in the bore (1 , 100).

7. The method according to claim 6, wherein the plug assembly (2, 130) comprises one or more flow ports (5) configured to open and close, when the flow ports (5) are open, fluid can pass the plug assembly (2, 130) within the bore (1 , 100), and when the flow ports (5) are closed, fluid cannot pass the plug assembly (2, 130) within the bore (1 , 100).

8. The method according to claim 7, wherein the at least one sensor (4) on the plug assembly (2, 130) comprises a pressure sensor positioned above the one or more flow ports (5) of the plug assembly (2, 130).

9. The method according to any one of claims 1 to 8, wherein the well is selected from a geothermal well, a hydrocarbon production well, a water production well, a water injection well and a gas injection15 well, for example a CO2 storage injection well, and is preferably a hydrocarbon production well.

10. The method according to any one of claims 1 to 9, further comprising: injecting fluid into the bore (1 , 100) at one or more injection points, wherein the fluid is preferably a gas selected from nitrogen, carbon dioxide and hydrocarbons, or a liquid selected from water, hydraulic oil and aqueous solutions.

11. The method according to claim 10, wherein the fluid is gas and is injected via a gas lift line.

12. The method according to any one of claims 10 to 11 , wherein the one or more injection points are located between the plug assembly (2, 130) and the surface.

13. The method according to any one of claims 1 to 12, wherein the steps of injecting gas and performing the sequence of operations on the valve are performed at an off-site facility remote from an installation site of the well.

14. A computer program comprising instructions to cause a plug assembly (2, 130) in a well to execute the steps of detecting and operating in the method according to any one of claims 1 to 13.

15. A plug assembly (2, 130) comprising a computer-readable medium having stored thereon the computer program of claim 14.

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