The present invention relates to a method of plugging a well extending into a hydrocarbon bearing formation. The invention also relates to a method of pressure testing the plugged well. The invention also provides an apparatus for plugging and pressure testing a well.
Oil and gas wells have in general three different purposes, as producers of hydrocarbons, injectors of water or gas for reservoir pressure support or for depositing purposes, or as exploration wells. At some point it is likely to be necessary to satisfactorily plug and seal these wells, e.g. after the wells have reached their end-of life and it is not economically feasible to keep the wells in service (so-called “plug and abandon”), or for some temporary purpose (e.g. “slot recovery”). Plugging of wells is performed in connection with permanent abandonment of wells due to decommissioning of fields or in connection with permanent abandonment of a section of well to construct a new wellbore (known as side tracking or slot recovery) with a new geological well target.
A well is constructed by drilling a hole into the reservoir using a drilling rig and then inserting sections of steel pipe, casing or liner into the hole to impart structural integrity to the wellbore. Cement is injected between the outside of the casing or liner and the formation and then tubing is inserted into the casing to connect the wellbore to the surface. For ease of reference, all of these entities inserted into the well are referred to here as “tubulars”. When the reservoir is to be abandoned, either temporarily or permanently, a plug must be established across the full cross-section of the well. This is generally achieved by removal of the tubulars from the well bore by pulling the tubulars to the surface or by section milling. Plugs are then established across the full cross-section of the well, in order to isolate the reservoir(s) and prevent flow of formation fluids between reservoirs or to the surface. It is generally necessary to remove the tubulars from the wellbore because in general it is not possible to be certain that the quality of the sealant (e.g. cement) behind the tubular(s), i.e. between the tubular(s) and the formation, is adequate to form part of the plug—thereby necessitating the installation and verification of a completely new cross-sectional plug.
To save having to remove an entire length of tubular from a well, a tool may be inserted into the well to cut the tubulars at a point beneath that at which the plug is to be formed, with only the upper detached parts of the tubulars being removed from the well. It is also possible to use a milling tool to mill away a part of the tubulars at the location where the plug is to be formed or to use explosive charges or perforation guns to remove parts of the tubular at said location.
An improperly plugged well is a serious liability so it is important to ensure that the well is adequately plugged and sealed. However, it can be difficult to accurately determine the quality of a well plug, and regulations will therefore typically over specify plug requirements by some significant margin. Regulations may require for example that an abandoned well be plugged so as to seal the well over at least 50 metres. In the event that the quality of a plug can be adequately determined in situ, it may be possible to relax the requirements, e.g. reduce the length of the plug, without compromising safety. A reduced plug length may significantly reduce operational costs.
WO 2014/117848 relates to a method of pressure testing a plugged well for the purpose of determining plug quality. According to this document, two or more plugs are formed in a well at longitudinally spaced-apart locations. A fluid communication path is provided between the surface of the well and an intermediate space between adjacent plugs. Pressure testing of the plugs is performed by introducing a fluid under pressure into the intermediate space. The fluid is introduced through the fluid communication path. Pressure sensors in the intermediate region then enable the integrity of at least one of the plugs to be determined.
WO 2015/044151 relates to a method of sealing a well in which a wireline is employed to locate a stinger in a location within a wellbore where one or more openings have been created in a tubing installed in the wellbore to expose the formation. A sealant, e.g. cement, is injected through the stinger to form a plug at said location.
WO 2014/117846 relates to a method of plugging a well in which one or more explosive charges are detonated within a tubular or tubulars extending through the well in order to remove, fragment and or cut one or more sections of the tubulars around the entire circumference of the well to expose the surrounding formation or cement. The well is subsequently filled in the exposed region with a sealing material so as to form one or more plugs within the well.
U.S. Pat. No. 2,918,124 A, US 2009/260817 A1, US 2003/150614 A1, U.S. Pat. Nos. 5,667,010 A, 3,053,182 A, WO 2012/096580 A1 and US 2005/028980 A1 describe methods relating to well plug and abandonment.
Currently, placement of plugs is typically performed by pumping the cement from the well topside through a drill pipe or coil tubing. Due to uncertainty of placement and contamination with other fluids, a rather long length is required per plug, e.g. 50 m, to achieve the required plug integrity. After the cement is placed and has cured, the cement plug is typically subjected to a large downwards force, for example 10 tonnes, and pressure tested to ensure that the cement is set properly. This constitutes integrity testing of the cement plug, to ensure it meets specified standards for permanent or temporary abandonment of a well, for example.
A first aspect of the invention relates to a method of plugging a well extending into a formation to facilitate temporary or permanent abandonment of the well. The method comprises conveying a plug placement and verification tool (PPVT) through a tubular, extending through the well, to a plug formation location, the PPVT comprising a stinger for delivering a plugging material into the well, an expandable packer disposed at one end of the stinger and a pressure sensor disposed below the expandable packer. Then the expandable packer is operated to form a seal in the well above the pressure sensor. Then a plugging material is delivered from the stinger into a region of the well above the expandable packer, thereby forming a plug in the well. Thereafter a pressure change is created above the plug and the integrity of the plug is verified using the pressure sensor.
A “stinger” in the context of the invention may be a tubular, with or without attached instrumentation, through which sealant is deployed.
Prior to the step of conveying the PPVT through the tubular to the plug formation location, a mechanical plug or packer may be installed below the plug formation location. The mechanical plug may be a bridge plug.
The method may further comprise, prior to said step of conveying, forming openings in the tubular to expose the formation at least at a first upper location and a second lower location, wherein: the mechanical plug is installed below the second location; and the expandable packer is sealed against a section of the tubular between the first and second locations.
Verifying the integrity of the plug may comprise detecting changes in an output of the pressure sensor. The PPVT may further comprise one or more temperature sensors and the method may further comprise utilizing the one or more temperature sensors to monitor the plugging material hydration during said step of delivering the plugging material from the stinger.
A signal from the pressure sensor may be transmitted to the wellhead through or via the stinger of the PPVT. Alternatively, signals representative of readings from the pressure sensor and/or the one or more temperature sensors may be transmitted wirelessly through the plug, i.e. through the plugging material during and/or after it has been delivered from the stinger into the plug formation location. The wireless transmission may be by means of either, or a combination of, electromagnetic or acoustic waves. For example, a radio-frequency transmitter may be located proximate the pressure sensor, e.g. within or adjacent to the expandable packer. A corresponding radio-frequency receiver may be located on the stinger at a location which is above the plug once it is formed, whereby the transmitter and receiver are arranged to provide a data communication link from the pressure sensor and/or one or more temperature sensors at a suitable frequency. The receiver may be in communication with the wellhead through or via the stinger of the PPVT or via a cabled/fibre optic connection running along the stinger body, in order to relay the pressure and/or temperature sensor readings to the surface. Alternatively, the receiver may be placed at the wellhead itself, if the radio frequency is chosen such that a reliable wireless communication link may be established directly between the transmitter located below the plug and the receiver located at the wellhead. The PPVT may be conveyed on a wireline, drillpipe, or coiled tubing.
The method may further comprise disconnecting the PPVT from the wireline or drill pipe and retrieving the wireline or drill pipe to the surface, leaving the PPVT in situ, thereby forming part of the plug.
The method may further comprise, prior to said step of delivering, disconnecting the stinger from the expandable packer and pressure sensor and, after placement of the plugging material, retrieving the stinger to the surface on the wireline or drill pipe whilst leaving the pressure sensor in place.
The method may further comprise vibrating the PPVT during said step of delivering.
A second aspect of the invention relates to a plug placement and verification tool (PPVT) comprising a stinger, an expandable packer disposed at one end of the stinger;
and a pressure sensor disposed below the expandable packer.
The PPVT may further comprise one or more temperature sensors distributed along the stinger, above the expandable packer. The stinger may comprise a number of nozzles for delivering the plugging material.
For efficient plugging of wells, the inventors have appreciated that it would be desirable to reduce the length of the plug. However, in order to reduce the length of the plug, verification/integrity testing becomes more important. Furthermore, it would be desirable to be able to verify the plug using the same tool as is used to place the plug.
The inventors have appreciated that it is desirable to perform pressure testing of a plug contemporaneously with the plug formation without requiring additional rig/wireline time/trips and without compromising the assessment of the quality of the plug. Indeed, the assessment of the quality of the plug may actually be improved over conventional methods.
The invention may enable placement of shorter yet improved plugs that can be tested and verified without any extra conveyance time, e.g. the invention may eliminate the need to trip a separate verification tool down the well after placement of the plug. Embodiments of the present invention may utilize a single tool to both place and verify a plug. Furthermore, the tool itself may become part of the permanent plug and need not be retrieved from the well after placement of the plug—thereby saving cost/time and reducing operational complexity. The tool may also be used to enable transmission of signals from pressure and temperature gauges through the tool body without having any effect on the integrity of the plug.
A third aspect of the invention relates to a method of plugging a well extending into a formation to facilitate temporary or permanent abandonment of the well. The method comprises conveying a plug placement and verification tool (PPVT) through the well, to a plug formation location, the PPVT comprising a stinger for delivering a plugging material into the well, an expandable packer disposed at one end of the stinger, and one or more sensors, and operating the expandable packer to form a seal in the well. The method further comprises delivering a plugging material from the stinger into a region of the well above the expandable packer, thereby forming a plug in the well, and thereafter leaving the stinger in situ to provide a communication path, through the set plug, for signals output by the sensor(s).
A fourth aspect of the invention relates to method of plugging a well extending into a formation to facilitate temporary or permanent abandonment of the well. The method comprises conveying a plug placement and verification tool (PPVT) through the well, to a plug formation location, the PPVT comprising a stinger for delivering a plugging material into the well, an expandable packer disposed at one end of the stinger, and a cup packer located above injection nozzles of the stinger, operating the expandable packer to form a seal in the well, and delivering a plugging material from the stinger into a region of the well above the expandable packer and beneath the cup packer, thereby forming a plug in the well.
Each of the above aspects of the invention may be adapted such that the stinger for delivering a plugging material into the well, the expandable packer and the pressure sensor disposed below the expandable packer do not form a single device (i.e. a single PPVT) but rather are run into the well as separate elements. For example, a first element may comprise the expandable packer with a pressure sensor (and optionally also temperature sensors) on the underside thereof, whilst a second element may comprise the stinger for delivering a plugging material into the well and also, in the fourth aspect, a cup packer located above the injection nozzles of the stinger. The first element may be run into the well first, i.e. before the stinger, and the expandable packer may be sealed against a section of the tubular between the first and second locations. Then, at a later time, the stinger may be landed onto the expandable packer before placing the plugging material. In such an example, it may be advantageous that the pressure and/or temperature sensors communicate with the stinger/wellhead wirelessly such that a cabled connection need not be established between the stinger and the already-installed expandable packer once the stinger is landed thereon.
With reference to
The casing in a well interval to be plugged is opened by any feasible method. For example, in
With reference to
A plug placement and verification tool (PPVT) 116 is lowered down to the opened area, conveyed using drill pipe, coil tubing or wireline 118. Conveyance by means of a wireline may be most cost effective. This is illustrated in
The PPVT is located in the well such that the expandable packer 122 is situated above the lowest perforation zone 130 (or opened casing section) but below the penultimate perforation zone 132. In general, it is sufficient that there be at least one perforated zone below the expandable packer of the PPVT. The expandable packer is actuated once the PPVT has been lowered to the correct location. The packer forms a substantially pressure-tight seal. Thus a small ‘test volume’ is formed between the expandable packer 122 and the mechanical plug 114 below it. This test volume allows for highly sensitive monitoring of pressure changes within it using the pressure sensor 126, optionally in conjunction with the temperature sensor 128 to monitor other properties of the test volume, thereby gaining additional information about the test volume region. If the volume were much larger, e.g. if there were no mechanical plug 114 below the expandable packer, it may not be possible to make such sensitive pressure measurements. Thus the inventors have appreciated that by forming a small test volume the measurement sensitivity is improved, thereby enabling a more reliable and sensitive certification of the plug performance. However, the invention could still be operated without the mechanical plug 114 being installed below the expandable packer—albeit with a potentially reduced pressure measurement sensitivity. Furthermore, the invention could also be operated without the plurality of discrete openings as illustrated in the drawings, and the expandable packer could instead be expanded against the formation in a large opened region, with exposed formation above and below the expandable packer.
With reference to
Alternatively, the stinger may remain attached to the expandable packer when the nozzles on the PPVT are opened. As such, the stinger becomes part of the final plug and is not retrieved to the surface. Other aspects of the method as described above apply also to this scenario.
Once the plug material has cured, the pressure above the plug 134 can be either decreased or increased in order to perform a pressure test of the plug. The tool head 124 of the PPVT has pressure and temperature sensors 126, 128 which can send pressure and temperature readings through the PPVT body and further up the well. The signals can be transmitted up the well, either by mud pulsing or through the casing by a connector device between the PPVT tool and the casing. For example, in the case where the stinger is released from the expandable packer prior to forming the plug, signals may be transmitted from the pressure/temperature sensors below the expandable packer using mud pulsing—the signals being picked up by a receiver on the stinger or drill pipe/wireline above the plug and transmitted further up the well by electromagnetic means, e.g. using a cable or signal on pipe arrangement. Alternatively, in the case where the stinger remains attached to the expandable packer during placement of the plug, the body of the PPVT tool may act as a conductive bridge between the sensors below the expandable packer and the well casing above. In both scenarios the stinger facilitates transmission of data collected by the sensors to the wellhead for monitoring conditions in the well. Alternatively, the PPVT may have fibre optic cables incorporated into it (e.g. in the wall of the PPVT) to facilitate the transmission of data signals from the pressure and/or temperature sensors on the tool head further up the well towards the wellhead. The fibre optic cables themselves may also act as distributed or localised pressure and temperature sensors.
In some embodiments, signals representative of readings from the pressure sensor and/or the one or more temperature sensors may be transmitted wirelessly through the plug, i.e. through the plugging material during and/or after it has been delivered from the stinger into the plug formation location. The wireless transmission may be by means of either, or a combination of, electromagnetic or acoustic waves. For example, a radio-frequency transmitter may be located proximate the pressure sensor, e.g. within or adjacent to the expandable packer. A corresponding radio-frequency receiver may be located on the stinger at a location which is above the plug once it is formed, whereby the transmitter and receiver are arranged to provide a data communication link from the pressure sensor and/or one or more temperature sensors at a suitable frequency. The receiver may be in communication with the wellhead through or via the stinger of the PPVT or via a cabled/fibre optic connection running along the stinger body, in order to relay the pressure and/or temperature sensor readings to the surface. Alternatively, the receiver may be placed at the wellhead itself, if the radio frequency is chosen such that a reliable wireless communication link may be established directly between the transmitter located below the plug and the receiver located at the wellhead
The integrity of the plug can be tested (a process known as “integrity testing”) by applying a differential pressure across the full length of the plug, and monitoring the pressure below the plug in real time. In
The PPVT may be equipped with additional temperature sensors distributed along the body of the PPVT (which is effectively a long steel tube) above the expandable packer to monitor the cement curing process. The temperature sensors can be distributed along the tool body to monitor cement hydration during and after placement.
After removal of the wireline with attached perforation gun, at step 3 a cement stinger 207 is introduced into the casing, at a location adjacent to the perforations. The cement stinger is provided with nozzles close to its lower end in order to allow cement to be pumped through the stinger into the region adjacent to and above the production liner. Just above the nozzles, a cup packer 208 is provided within a retainer 209. A mechanical packer 210 is attached to the bottom of the stinger, beneath the nozzles. In
Step 4 illustrates the situation following raising of the stinger 207 by a small amount in order to release it from the packer 210. This also releases the cup packer 208 from the retainer 209, causing the cup packer to expand and come into contact with the casing 201. To facilitate this expansion, the cup packer may be made of a resilient elastomeric material which allows the containment of the packer within the retainer prior to its release.
Step 6 illustrates the pumping of a sealant, e.g. cement through the stinger 207 and the exit nozzles, into the space above the mechanical packer 210. Due to the concave shape of the cup packer 208, the force exerted by the injected cement forces the cup packer against the casing wall, further enhancing the sealing effect. This in turn pushes the cup packer and the stinger upwards until a plug 211 of sufficient axial extent has been created. To facilitate upward movement of the cup packer and the stinger, at the well head the stinger may be mounted on a hydraulic piston or suchlike.
Whilst in the above-described embodiments the PPVT comprises at least a stinger, expandable packer and sensors as a single tool, in alternative embodiments the stinger, expandable packer and the pressure sensor disposed below the expandable packer do not form a single device (i.e. a single PPVT) but rather are run into the well as separate elements. In an exemplary embodiment, a first element comprises the expandable packer with a pressure sensor (and optionally also temperature sensors) on the underside thereof, whilst a second element comprises the stinger for delivering a plugging material into the well and optionally also a cup packer located above the injection nozzles of the stinger. The first element may be run into the well first, i.e. before the stinger, and the expandable packer may be sealed against a section of the tubular between the first and second locations. Then, at a later time, the stinger may be landed onto the expandable packer before placing the plugging material. In such an example, it may be advantageous that the pressure and/or temperature sensors communicate with the stinger/wellhead wirelessly, as described above, such that a cabled connection need not be established between the stinger and the already-installed expandable packer once the stinger is landed thereon.
It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. In particular, it will be appreciated that various alternative methods of forming the (cement/sealant) plug may be used instead of those described above.
Number | Date | Country | Kind |
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1618747 | Nov 2016 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/NO2017/050285 | 11/6/2017 | WO | 00 |
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WO2018/084719 | 5/11/2018 | WO | A |
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