Method and well tool for well interventions

Abstract

A method is disclosed for use in a well intervention such as a plug and abandonment operation using a single well tool (1). The well tool (1) comprises a washer module (14). The method comprises: With the well tool (1) positioned so that the washer module (14) is at a perforated section (5b) of a well (7); supplying a fluid under pressure via the washer module (14) into the perforated section (5b) of the well; checking the integrity of the annulus (3) in the region of the perforated section (5b) by means of volume, pressure and / or temperature sensors (24); and performing an additional check of the integrity of the annulus (3) in the region of the perforated section (5b) using an acoustic sensor system (26) for measuring acoustic signals at the well tool (1). The acoustic sensor system (26) includes one or more acoustic sensor(s) located on the well tool (1).

Description

[0001] METHOD AND WELL TOOL

[0002] FOR WELL INTERVENTIONS

[0003] TECHNICAL FIELD

[0004] The present invention relates to the oil and gas industry and in particular to a method for use during a well intervention such as a plug and abandonment operation for a well. The invention also relates to a related well tool for use with the method. The example embodiments may include checking the integrity of the well during preparation for later plugging of the well, advantageously using the same tool.

[0005] BACKGROUND

[0006] Well tools of various designs are required to perform well interventions of various types. A plug and abandonment (P&A) operation is carried out when a wellbore is no longer to be used, for example as it is no longer economically producing oil and / or gas, or for other reasons. The P&A of a well is typically done in line with regulatory requirements, e.g. regulations set by national government. It involves sealing the well by setting a plug in a region of the well so that there is no flow of fluid to the surface and so that there is no migration of formation fluid. This may be done temporarily or permanently.

[0007] As a part of a well intervention such as a P&A operation it is best practice to check the integrity of the well, e.g. before the plug is set. This is done in order to provide confidence that the set plug will work as expected. It may also provide information that will guide the placement of the plug and / or the use of additional operations before the plug is set. There are generally also regulatory requirements for testing the integrity of the plug once it has been set. Often the latter involve a leak test of some form. A common requirement during plug and abandonment operations is to have a plug set inside an inner casing string and a further plug set in the annulus between the inner casing string and the outer casing string. The plug will then extend across the full cross-sectional area of the well and seal both vertically and horizontally in the well. This can provide a so-called rock-to-rock barrier.

[0008] Prior to setting a plug it is known to carry out perforation and washing operations, such as to prepare the well for setting plugs in the annulus. Such operations are also required in various other well interventions. In a perforation operation the casing or liner of the well is perforated such as by use of cutting devices or by dedicated perforation guns. The perforated section can then be washed by application of fluid under pressure. Debris resulting from the perforation and washing operations is then removed from the well before a barrier material (typically cement) is placed by pumping it through the perforations into the annulus and into any open regions outside of the casing.

[0009] Archer Oiltools markets a number of products for use in relation to P&A operations, including the various products in the StrongholdR™ range of systems. These systems allow for “one-trip” perforation, washing, cleaning and / or cementing operations in order to provide safer and more economical P&A. These one-trip methods can replace traditional P&A techniques that required up to three runs. In an example of such a combined operation a tool string with a washing tool (washer module) comprising two (or four) opposite packing assemblies is passed down the well pipe and the two opposite packing assemblies are placed on opposite sides of the cut or in the perforated section of the well pipe. Fluid is pumped down through the tool string and out through the radial port between the two packing assemblies. The packing assemblies then prevent the liquid from flowing up or down along the tool string and the liquid will thus have to flow through the cuts or perforations in the well pipe. The applicant's own patent EP3036395 describes washing the annulus and then using the same tool to cement the annulus and indirectly also the casing, so that a plug of cement is formed in the well. EP3036395 thus discloses a multitasking tool capable of performing perforation, washing and cementing in a single trip.

[0010] In some examples the Archer Oiltools products also include verification of the integrity of the annulus as a means to ensure the long-term integrity for the plug after it is set. For example, the StrongholdR™ FortifyR™ System provides a replacement to traditional integrity testing via pressure and temperature sensors that are used in addition to volume verification during a pressure test of a perforated section of the well. From this product it is hence known to perform perforation, washing, integrity checking, and then cementing in a single trip.

[0011] However, despite the advances in the art provided by such existing products there remains a need to further improve the methods and well tools available to use during well interventions such as P&A operations.

[0012] SUMMARY OF THE INVENTION

[0013] Viewed from a first aspect, the present invention provides a method for use in a well intervention using a single well tool, the well tool having a washer module, the method comprising:

[0014] - with the well tool positioned so that the washer module is at a perforated section of the well, supplying a fluid under pressure via the well tool into the perforated section of the well; checking the integrity of the annulus in the region of the perforated section by means of volume, pressure and / or temperature sensors; and performing an additional check of the integrity of the annulus in the region of the perforated section using an acoustic sensor system for measuring acoustic signals at the well tool, the acoustic sensor system including one or more acoustic sensor(s) located on the well tool.

[0015] With this method it is possible to verify the integrity of the annulus via two independent systems thereby providing a greater confidence in the effectiveness of a subsequent operation, e.g. to set a plug when the well intervention includes one or more steps of a plug and abandonment operation. There may hence be a first verification system comprising the volume, pressure and / or temperature sensors, as well as a second verification system comprising the acoustic sensor system. One or both of the steps of checking the integrity using volume, pressure and / or temperature sensors and / or using an acoustic sensor system may be performed during the supply of fluid under pressure and / or whilst previously supplied fluid is held under pressure at the perforated section of the well. In some cases multiple steps for checking the integrity may be done concurrently and / or started simultaneously. Thus, the first verification system may be used at the same time as the second verification system (and optionally also further verification systems). In this regard the reference to verifying the integrity of the annulus may include gathering information in order to assess the condition of the well structures such as one or more casing(s) and liner(s), as well as potentially checking the integrity of geological formations outside of the well.

[0016] There may also be one or more added functions for the single well tool, which may advantageously be configured to perform those functions in added steps of the method during a single run. The well intervention may hence comprise various functions in order to perform multiple steps of one or more well operations, such as more than one of the steps that are needed for slot recovery operations, including for example a plug and abandonment operation. For example, setting of the plug is advantageously performed with the same single well tool during the same run. The well tool may comprise a bridge plug device for use when setting the plug. The washer module may be configured to provide a washer fluid for washing and / or sealing fluid, e.g. a cement, for the plug and thus the method may include setting a plug using fluid provided via the washer module. This may be done using the same fluid pathways. The fluid supplied under pressure for checking the integrity of the annulus, i.e. with the first verification system, may be a washing fluid. This could be supplied during a washing operation or as a standalone integrity verification operation. In some example embodiments the well tool comprises a perforator module for perforating one or more section(s) of the well to thereby form the perforated section. The perforator module may comprise a perforating tool. Thus, the method may include perforating the well prior to the step of positioning the tool so that the washer module is at the perforated section of the well. Alternatively, the well tool may be used in a pre-perforated well in some situations, e.g. if it is convenient to use a different perforating tool to perforate the well in a previous run.

[0017] Having some or all of the above features in the single well tool allows for further operations from the same multitasking tool in a single run, creating further improvements in time and efficiency for the well intervention, e.g. by permitting multiple steps of a plug and abandonment operation in a single run. The tool may have additional capabilities as well, such as via other optional features as discussed herein.

[0018] The fluid under pressure may be supplied via the washer module into the perforated section of the well. The washer module may include an upper sealing arrangement and a lower sealing arrangement for enclosing a section of the well in order to allow for increased pressure in that section of the well during supply of fluid by the washer module, e.g. during supplying the fluid for the step of checking integrity. The sealing arrangements may be placed above and below one or more fluid outlets for the supply of fluid at the washer module, e.g. one or more radial holes or other fluid pathways. In example embodiments, each sealing arrangement may comprise one or more sealing elements, wherein each sealing element is configured to prevent fluid flow across the sealing element, at least in one direction. In example embodiments the sealing arrangements comprise retractable elements (e.g., as the sealing elements), for example retractable cups, allowing for the region of the well at the washer module to be selectively enclosed by actuation of the retractable elements.

[0019] It is particularly beneficial to use retractable elements in combination with the proposed two modes of integrity checking. The retractable elements allow for checking of integrity via sensor operations with the perforated section under pressure, e.g. a pressure integrity test using volume and / or pressure sensors and / or a “listening” test using the acoustic sensor(s). In addition, the retractable elements can be retracted during optional added sensing steps, e.g. there may be use of the acoustic sensor(s) during washing and / or debris removal operation(s) whilst the retractable elements are not deployed and thus do not restrict fluid flow in the well. The presence of retractable elements for the sealing arrangements may thus enhance flexibility and / or effectiveness of the multiple types of sensors used for checking integrity. The retractable elements of example embodiments are actuatable elements that may for example move between a deployed configuration and a stowed configuration. The deployed configuration may allow for the sealing arrangement to form a pressure containing barrier around the well tool, e.g. by contact between the retractable element and an inner wall of a casing of the well. The stowed configuration may be a configuration in which the retractable element has a reduced radial extent, e.g. with a radially outermost part of the retractable element moved inward toward a centre of the well tool. The retractable elements may be retractable cups as mentioned above. The method may include using a control device for selecting the required configuration of the retractable elements sealing arrangements and / or for operating the retractable elements. There may be a control device in the washer module; a control device in a separate control module, which may be as discussed below; and / or a remote control device, e.g. in a topside location. The control device may be arranged to operate the retractable elements in accordance with the method steps set out herein.

[0020] The configuration of the sealing arrangements / retractable elements may be changed by fluid pressure, e.g. by fluid pressure provided from a surface location. In other words, the retractable elements may be operated by fluid pressure. For example, an increase in fluid pressure may move the actuatable elements to the deployed configuration and a decrease in fluid pressure may move the actuatable elements to the stowed configuration.

[0021] As they are actuatable elements then the retractable elements should be differentiated over purely passive parts, e.g. elastically deformable or otherwise collapsible elements that move only due to external forces such as a restriction in the diameter of the passage through the well. The retractable elements as described herein are advantageously active elements capable of controlled movement, e.g. under control of a control device as mentioned above. They do not rely on forces external to the well tool to move them. The well tool may for example comprise an actuation mechanism (e.g. at the washer module) for actuation of the retractable elements. There may be an upper actuation mechanism for actuation of the retractable element(s) of the upper sealing arrangement and a lower actuation mechanism for actuation of the retractable element(s) of the lower sealing arrangement. Alternatively, there may be a single actuation mechanism for simultaneous deployment of both the upper and lower sealing arrangements. The actuation mechanism(s) may comprise one or more of a piston, a spring, a thread, a lever, a sliding sleeve, a solenoid, a motor, a pump, and / or other suitable parts.

[0022] An advantage of having actuatable sealing arrangements, e.g. in the form of the retractable elements, is that the sealing arrangements can be configured in the stowed configuration while running the single well tool into and out of the wellbore, and configured in the deployed configuration when the single well tool is at a position in the wellbore where e.g. integrity testing, washing and / or cementing is to be performed. A control device, e.g. as mentioned above, may be arranged to control the actuatable sealing arrangements to place them in a desired configuration according to the status of the tool. Consequently, the single well tool may pass (particularly narrow) restrictions in the wellbore that would otherwise not have been possible to pass (with e.g. collapsible sealing arrangements or “always active” sealing arrangements). A further advantage of being able to configure the sealing arrangements in the stowed configuration while running into the hole is that excessive wear or damage, which may be caused by the sealing arrangements being dragged against a casing of the well and / or against different restrictions in the wellbore, will be reduced or even avoided. This may be particularly beneficial in combination with the second proposed mode of integrity checking, i.e. during the “listening” test by use of the acoustic sensor(s). Even if the sealing arrangements prove to be intact during a pressure test, small damages or tears on the elements could create micro leaks that may only be picked up by the acoustic sensor(s). Furthermore, such micro leaks may be confused with micro leaks in the annulus during an annulus integrity test, and as such, a failed test may be concluded even though the integrity of the annulus is intact. In other words, the activatable elements may provide a higher accuracy in the interpretation of measurements from the acoustic sensor by minimizing “road noise” and other similar unwanted background noise.

[0023] A further potential advantage of using actuatable sealing arrangements is that in some example implementations the force exerted by the sealing arrangements against a casing of the well may be increased for operations when the tool is stationary in the well to improve integrity, e.g. during annulus integrity testing, and then decreased for operations when the tool may move within the wellbore, e.g. during washing and / or cementing.

[0024] The acoustic sensor system comprises one or more acoustic sensor(s) that are capable of detecting acoustic signals at the well tool. The acoustic signals may comprise infrasonic, audible and / or ultrasonic sound waves. This may be done by measuring acoustic signals in fluid(s) around the well tool. The acoustic sensor(s) may be configured to measure and record an acoustic signature including acoustic energy generated by fluids in the annulus. The acoustic sensor(s) are located on the well tool and advantageously are located near to the washer module. They may be placed within the washer module or they may be located in a separate sensor module or control module. The acoustic sensor system of example embodiments is a passive acoustic detector that includes acoustic sensor(s) for receiving acoustic signals but does not require any acoustic transmitter. Thus, the acoustic sensor system may comprise only receiving sensors without any acoustic transmitter. In this way the acoustic sensor system can be differentiated from an active acoustic system, including ultrasonic systems as used for cement bond logs, where the system is active in that must include both transmitting and receiving functions. During an annulus integrity test, the characteristics and location of the noise signal may differ from one leak to another, and from one test to another, and the receiver or sensor may have to rely on a signal that is in principle totally unknown. Thus, signal / noise improvement techniques utilizing a transmitter cannot always be effectively used for such a noise detection system.

[0025] The one or more acoustic sensor(s) may include sensors such as hydrophones, piezoelectric sensors, piezoresistive sensors, electromagnetic sensors, ultrasonic sensors, accelerometers, or the like. The acoustic sensor system advantageously provides full-spectrum acoustic sensing that accurately measure a broad frequency bandwidth and amplitude of acoustic energy.

[0026] Multiple sensors may be used for redundancy, or where the acoustic sensor(s) have different characteristics, such as sensitivity, bandwidth etc. to be able to improve the overall characteristics of the acoustic sensor system. Each sensor may be optimized for different frequency ranges to optimize response over an entire measurement range.

[0027] The one or more acoustic sensor(s) may comprise a protective housing. When there is more than one acoustic sensor, each acoustic sensor may comprise a protective housing.

[0028] In some embodiments, the one or more acoustic sensor(s) may be ultrasonic acoustic sensor(s). An example of an applicable acoustic sensor assembly is described in e.g. European patent EP3420186B1, which belongs to the applicant.

[0029] The one or more acoustic sensor(s) may be arranged to sense sound and ultrasound waves up to 100kHz, 200kHz, 300kHz, 500kHz, 800kHz or 1MHZ. The combination of sound and ultrasound expands sensitivity to a wider range of frequencies and thereby increases the capability and probability for detecting and localizing a leak, and with higher localization accuracy. Tools based on traditional hydrophones typically only operate in the audible range, or optionally extended to include a low frequency range of ultrasound.

[0030] The acoustic sensor(s) may be arranged to sense waves only in the ultrasonic frequency range. For example, the acoustic sensor(s) may only sense waves with a frequency equal to or above 100kHz. Higher frequencies may contain useful information regarding a leak, and it is possible to determine characteristics of a leak or flow by relying on high frequency information. However, in many applications higher frequency noise components propagating along the tool string may be present, which leads to a reduced resolution. Hence, by having the sensors being able to sense only higher frequency waves, the signal-to-noise ratio and resolution is improved.

[0031] In some embodiments, the acoustic sensor(s) may be ultrasonic contact transducers. Such sensors have good sensitivity over a wide bandwidth, with particularly high sensitivity in the ultrasonic range.

[0032] The ultrasonic contact transducer may be a single-element, piezoelectric transducer.

[0033] The acoustic sensor(s) may be suspended in an insulating means arranged in a compartment of a tool element. The compartment may be a through-bore of the tool element. Arranging the sensor in a through-bore may ensure that forces arising from the wellbore pressure are balanced out. As such, the tool may operate in areas with high pressure.

[0034] The acoustic sensor(s) may be arranged to interface a wellbore fluid.

[0035] Optionally, the insulating means may have an acoustic impedance different from an acoustic impedance of the tool element for ultrasonic signals. When the acoustic insulation means has an acoustic impedance different from an acoustic impedance of the tool element the background noise signals carried along the tool body will be partially reflected and scattered at the interface between the two different materials with different acoustic impedance. A larger difference in impedance will increase reflection.

[0036] The characteristic impedance of the acoustic insulation means may be 20%, 30%, 40% or 50% lower than the characteristic impedance of the tool element.

[0037] In some embodiments, the tool element is made of metal, while the acoustic insulation means is manufactured in polymers or rubber.

[0038] The tool element may form part of the well tool.

[0039] The tool element may form part of the washer module, and / or form part of a separate sensor module or control module. Optionally, the tool element may be positioned between the sealing arrangements of the washer module.

[0040] A well tool according to the above may have the advantage that it is significantly less affected by wellbore background noise propagating along the tool string. Thus, the signal to noise ratio may be improved both for stationary and dynamic logging operations. This allows for an improved resolution in depth profiling of the actual noise image, giving better discrimination of two or more closely separated leaks and better resolution of noise characteristics along distributed flow paths.

[0041] Thus, the acoustic sensor system of some embodiments is advantageously highly sensitive over a broad bandwidth and able to detect very small leaks / low energy leaks propagating in micro cracks in the annulus, which would have been impossible to detect by e.g. a prior art pressure test. This make the acoustic sensor system particularly well suited as a second integrity verification system for well interventions such as P&A operations, as an operator may want certainty that well integrity is maintained for the foreseeable future.

[0042] The volume, pressure and / or temperature sensors, which may be a part of a first verification system as noted above, may be located at the well tool and thus may take measurements at a downhole location when in use. The well tool may comprise at least one volume sensor and at least one pressure sensor, and optionally also at least one temperature sensor. The sensors may be placed between the upper and lower sealing arrangements of the washer module, thus enabling measurements in an area between the sealing arrangements. Alternatively, these sensors may be at a topside location such as at a pump for supply of the fluid to the washer module. There may be sensors at both of the well tool and at a topside location. When sensors are located at the well tool, e.g. between the upper and lower sealing arrangements of the washer module, an isolation arrangement may be present at the well tool, allowing an internal volume of the well tool above the isolation arrangement to be isolated from an internal volume of the well tool below the isolation arrangement. As such, the sensors may be isolated from an internal volume of the well tool above the isolation arrangement. Consequently, the volume monitored by the sensors becomes smaller, which improves accuracy of the measurements (e.g. by that a smaller possible leak leads to a larger relative change in volume). The isolation arrangement may be a valve at the well tool.

[0043] The method may include additional integrity checks at different stages of the process and / or using different sensor systems. The well tool may comprise a cement bond log (CBL) device, e.g. located in a sensor module or control module along with the acoustic sensor system. The method may comprise using the cement bond log for assessment of the integrity of the annulus as a yet further integrity check alongside the other two integrity checks.

[0044] The method may comprise checking integrity of the annulus prior to a perforation step in order to determine if perforation is required. A pre-perforation integrity check may be done using any one, or more than one, of the available sensor systems. In one example a cement bond log is used for the pre-perforation integrity check. Advantageously, where the well tool also includes a perforator module, then the method may include using the single well tool in a single run that includes: a pre-perforation integrity check; then, if required, perforation of a casing of the well using the perforator module; and then the above integrity checking steps can be performed at the resulting perforated section(s) of the well. The method may comprise checking integrity during or after a plug is set, e.g. during or after provision of sealing fluid such as cement via the washer module. This may be done using any one, or more than one, of the available sensor systems.

[0045] The single well tool may comprise a Casing Collar Locator (CCL) tool for depth correlation and for determining the position of casing collars. As such, the operator can avoid forming perforations at the casing collars, as this may be ineffective and / or potentially harmful to the perforating tool depending on the type of perforating tool used. The CCL may alternatively or additionally be used for determining the position of perforations in a casing. The single well tool may also comprise Measurement While Drilling (MWD) systems and / or other measurement tools and logging tools that may be used to evaluate physical properties of the wellbore and surrounding rock formations.

[0046] The single well tool may comprise a sensor module or a control module that holds the acoustic sensor system and optionally also a cement bond log, if present. The sensor (or control) module may also hold the CCL tool, the MWD system and / or the other measurement and logging tools, if present. The sensor (or control) module may be located adjacent to the washer module, e.g. immediately above or below the washer module. As noted above the single well tool may comprise a perforator module. This may be located adjacent to the washer module, e.g. immediately above or below the washer module. In one example embodiment the single well tool has a sensor module or control module above the washer module and a perforator module below the washer module. The method may comprise using such a tool in a so-called “pump and pull” operation where a sequence of perforated sections is formed during lowering of the tool and where these perforated sections are first washed and then sealed in a sequential way during raising of the tool. This method may advantageously include multiple integrity checks during the processing of each of the plurality of perforated sections.

[0047] Embodiments of the method may include setting a plug in the same run as the other steps discussed herein. The single well tool may be configured to provide a bridge plug during the well intervention, which may comprise a plug and abandonment operation. The single well tool may comprise a bridge plug module in addition to the other modules. The bridge plug module may be at a lowermost part of the well tool, i.e. the bottom part when the well tool is in use within a wellbore. An internal plugging element may be provided as a part of the bridge plug module, wherein the internal plugging element can be activated in order to block or restrict flow of fluid in the well, such as to contain a sealing fluid supplied via the washer module. The method may include activating the internal plugging element during or before the flow of sealing fluid into the perforated section(s) of the well. The activation of the internal plugging element is advantageously done remotely, such as via control from a topside location along with remote control and / or monitoring of other steps during the well intervention.

[0048] The washer module is arranged to supply a fluid (e.g. a washing fluid) under pressure, such as by means of one or more fluid outlets dispersed over an area of the tool at the washer module. The fluid outlets may be radial holes. The radial holes may be arranged in a spaced-apart relationship around a circumference of the washer module. Advantageously the washer module is also able to supply a sealing fluid under pressure using the same fluid outlets. The fluid(s) may be supplied to a perforated section of the well that has been enclosed using the upper and lower sealing arrangements.

[0049] The perforator module is for perforating the casing as a part of the well intervention. This perforation may be done in reaction to analysis of integrity of the well done in the same run by the single well tool or based on data obtained by some earlier process. The perforator module may comprise a mechanical perforating tool including cutting elements such as knives, rotary tools, or other mechanical means known in the art for forming perforations in the casing. The perforator module may alternatively comprise perforator guns for forming perforations in the casing. In example embodiments knives are used, e.g. knives deployed by hydraulic pressure or by a mechanical system. It may be an advantage to use perforator knives rather than perforator guns since they can be used multiple times during the same run, e.g. to perforate at several locations. In example embodiments, the perforator module may be a slotting tool comprising a cutter wheel assembly for forming perforations in the casing. An example of a tool that works according to this principle is the Holte Casing Perforator provided by Holte Drilling Manufacturing of Oregon, USA. An advantage of using a slotting tool may be increased efficiency, as more perforations may be formed in a shorter amount of time compared to other mechanical perforators. Another advantage is that the slotting tool may form smaller perforations, which may enhance washing efficiency by that the washing fluid will exit the casing at a higher velocity.

[0050] With the use of a perforator module as well as a washer module that can supply sealing fluid then the single well tool can carry out a perforation, washing and cementing operation in a single run, with the added benefits of improved verification of annulus integrity from the proposed multi-stage integrity checks.

[0051] As noted above, the sealing fluid may comprise cement for forming a cement plug. The sealing fluid may also comprise other fluids such as Sandaband®, Thermaset® (Wellcem), Liquid Stone® or similar.

[0052] In embodiments of the method all of the steps discussed herein may be performed by the single well tool in a single trip into the well. By way of example, the method may comprise the following steps performed in a single run:

[0053] • optionally using the single well tool for testing integrity of the annulus to determine if perforation is required;

[0054] • perforating the casing using the perforator module to form one or more perforated section(s);

[0055] • locating the well tool at a first perforated section of the well;

[0056] • sealing off a lower portion of the well below the first perforated section using the lower sealing arrangement;

[0057] • sealing off an upper portion of the well above the first perforated section using the upper sealing arrangement, with this optionally being done at the same time, or alternatively before / after, the step of sealing off the lower portion;

[0058] • supplying fluid to the first perforated section through the washer module;

[0059] • checking the integrity of the annulus in the region of the first perforated section using at least two separate integrity checks as set out above, with this optionally being carried out during the supply of fluid through the washer module and / or after the supply of fluid with fluid being held under pressure at the perforated section of the well;

[0060] The method may comprise forming an upper perforated section in an area about a top of a plugging interval and a lower perforated section in an area about a bottom of the plugging interval. The method may comprise locating the well tool at the lower perforated section and supplying fluid to the lower perforated section through the washer module. As such, the lower perforated section may be the first perforated section of the well. The upper perforated section may provide a fluid path in the area about the top of the plugging interval. As such, checking the integrity of the annulus in the region of the first perforated section using the at least two separate integrity checks may comprise checking the integrity of the plugging interval.

[0061] This method may additionally comprise repeated steps when there are multiple perforated sections, for example multiple perforated sections of a single plugging interval, or multiple perforated sections of several different plugging intervals.

[0062] The method may comprise raising and or lowering the tool during a washing process in order to wash a perforated section and optionally also further perforated sections, thereby washing a plurality of perforated sections that together form a perforated region of the well. These perforated sections may each have been formed by the perforator module at an earlier time during the same run.

[0063] Where there is a plurality of perforated sections the method may additionally comprise supplying a sealing fluid to each of the perforated sections. During the step of supplying the sealing fluid, the tool may be lifted through and above the first perforated section in order to pass the tool through the other perforated section(s) while continuing pumping of the sealing fluid.

[0064] A perforated section may in one example comprise the perforations formed by one single actuation of the perforator module. For example, a perforated section may comprise perforations formed by one single deployment of knives by hydraulic activation of the perforator module, or, by the firing of a single perforating gun. A perforated section may in other examples comprise perforations formed by two or more activations of the perforator module, or, by the firing of two or more perforating guns. In some examples, the perforated section may be less than one meter long. Alternatively, the perforated section may be one meter long, two meters long, or longer. In some examples, the perforated section may be at least 30 meters long, at least 50 meters long, or at least 100 meters long, e.g. a longer perforated section formed by multiple activations of the perforator module. Longer perforated sections, such as in the latter examples, may be referred to as a perforated region of the well.

[0065] Example embodiments of the method of the first aspect may include the following processes for a well intervention (such as a plug and abandonment operation) with all the processes being performed using the single well tool:

[0066] • Diagnostics / Logging to establish the annulus barrier situation, for example using a CBL.

[0067] • Perforating the casing and testing the annulus integrity.

[0068] • Set a bridge plug as the cement base.

[0069] • Place a cement barrier inside the main bore.

[0070] • If the annulus barrier is considered insufficient then there are added steps of perforating the casing, washing the annulus and placing cement in the washed annulus.

[0071] A step-by-step procedure for an example method may include the following processes for a well intervention including a plug and abandonment operation using the single well tool:

[0072] 1. Make up the single well tool on the surface. 2. Convey the single well tool into wellbore, e.g. using a coiled tubing string, an umbilical or a drill pipe string.

[0073] 3. Reach the target depth for the plug barrier.

[0074] 4. Optionally logging the casing section (e.g. CBL, Ultrasonic) to determine if the annulus barrier is sufficient.

[0075] 5. At least when data about the annulus barrier indicates it is necessary, perforating using the perforator module and testing the integrity of the annulus barrier using the checking steps discussed above.

[0076] 6. If the integrity of the annulus barrier is acceptable, setting a bridge plug as a base and place a cement (or other sealing fluid) barrier in main bore above.

[0077] 7. If the integrity of the annulus barrier is not acceptable, perforating the casing section and setting a base, then washing and placing a cement (or other sealing fluid) barrier in the annulus and in the main bore.

[0078] 8. There may be repeated steps during lowering and raising of the tool, e.g. to form a longer perforated region with a plurality of perforated sections, and to wash and seal each of the plurality of perforated sections.

[0079] 9. Pulling the tool out of the hole.

[0080] If the annulus barrier is determined to be sufficient in the above step 4, an option is to go straight to step 6. However, step 5 may be performed for contingency. If the annulus barrier is determined to be insufficient in the above step 4, an option is to go straight to step 7. However, step 5 may also here be performed for contingency. Preferably, step 5 is performed in any case, as the two separate integrity checks as discussed above are more reliable than a CBL.

[0081] In variations of the method there may be other steps, optionally using the same single well tool, such as cutting the casing, removing casing sections using a spear or similar, and / or expanding the casing prior to other operations. The method may be used with a wellbore having a casing that is a production tubing including control lines at the outside of the tubing. In that case a step of cutting the casing may also include cutting / ablation of the control lines. A CCL, such as that described above, can be usefully included in the well tool along with casing cutting features since it will be a benefit to know the depth of the collars in order to better ensure that all the planned ablations are made. An example of a prior art tool and method for cutting and removing casing is disclosed in the applicant’s patent NO346193B1. Casing expansion may be performed to provide an annulus fundament for subsequent displacement of sealing fluid in the annulus. Any of the methods set out above may comprise a step of cutting control lines located outside of a casing / tubing, for example in order to avoid any leaks / fluid paths passing through / along the control lines. A step of cutting of control lines may be done with any suitable cutting tool, including that mentioned above, and may for example be done in the same step as cutting the casing.

[0082] In some embodiments, the coiled tubing string, umbilical or drill pipe string is through-wired for improved signal communication.

[0083] The wellbore may contain two or more concentric casing strings or tubing strings. Thus, the wellbore may contain two or more casing (or tubing) annuli in a region where the above-described example methods are to be performed.

[0084] Viewed from a second aspect, the present invention provides a well tool for a well intervention, the well tool comprising: a washer module for supplying a fluid under pressure via the well tool into the perforated section of the well; a first verification system for checking the integrity of the annulus in the region of the perforated section when it is exposed to fluid under pressure, the first verification system comprising one or more volume, pressure and / or temperature sensor(s); and a second verification system for performing an additional check of the integrity of the annulus in the region of the perforated section, the second verification system comprising an acoustic sensor system for measuring acoustic signals at the well tool, the acoustic sensor system including one or more acoustic sensor(s) located on the well tool.

[0085] With this well tool it is possible to verify the integrity of the well in an improved way, such as via use of the well tool in a method as discussed above. The well tool of the second aspect may hence be the single well tool of the first aspect and it may be configured to carry out a method as discussed above. The volume, pressure and / or temperature sensors may be used for measuring properties of a fluid in the region of the perforated section, in particular a fluid supplied under pressure via the washer module. The acoustic sensor system may be used for measuring acoustic signals at the well tool, i.e. also in the region of the perforated section.

[0086] There may also be one or more added functions for the single well tool, which may advantageously be configured to be used in added method steps during a single run. For example, the well tool may comprise a bridge plug device for use when setting the plug. The washer module may be configured to provide a sealing fluid, e.g. a cement, for the plug. This may be done using the same fluid pathways that are used for the washing fluid. In some example embodiments the well tool comprises a perforator module for perforating one or more section(s) of the well to thereby form the perforated section.

[0087] The washer module can be for washing a perforated section of the well by use of the same system that supplies fluid under pressure. It may include an upper sealing arrangement and a lower sealing arrangement for enclosing a section of the well in order to allow for increased pressure in that section of the well during supply of fluid by the washer module, e.g. during supplying the fluid. The sealing arrangements may be placed on the washer module above and below one or more fluid outlets for the supply of fluid at the washer module, e.g. radial holes or other fluid pathways. In example embodiments the sealing arrangements comprise retractable elements, for example retractable cups, allowing for the region of the well at the washer module to be selectively enclosed by actuation of the retractable elements.

[0088] The retractable elements of example embodiments are actuatable elements that may for example be configured to move between a deployed configuration and a stowed configuration. The deployed configuration may allow for the sealing arrangement to form a pressure containing barrier around the well tool, e.g. by contact between the retractable element and an inner wall of the casing. The stowed configuration may be a configuration in which the retractable element has a reduced radial extent, e.g. with a radially outermost part of the retractable element moved inward toward a centre of the well tool. The retractable elements may be retractable cups as mentioned above in relation to the method aspects. The well tool may comprise an actuation mechanism (e.g. at the washer module) for actuation of the retractable elements. There may be an upper actuation mechanism for actuation of the retractable element(s) of the upper sealing arrangement and a lower actuation mechanism for actuation of the retractable element(s) of the lower sealing arrangement. Alternatively, there may be a single actuation mechanism for simultaneous deployment of both the upper and lower sealing arrangements. The actuation mechanism(s) may comprise one or more of a piston, a spring, a thread, a lever, a sliding sleeve, a solenoid, a motor, a pump, and / or other suitable parts.

[0089] The well tool may include a control device as discussed above, such as a control device in the washer module or a control device in a separate control module, which may be as discussed below. Alternatively, or additionally, the well tool may be used together with a remote control device, e.g. in a topside location. The control device may be arranged to operate the retractable elements in accordance with the method steps set out above.

[0090] The acoustic sensor system comprises one or more acoustic sensor(s) that are capable of detecting acoustic signals at the well tool. This may be done by measuring acoustic signals in fluid(s) around the well tool. The acoustic sensor(s) may be configured to measure and record an acoustic signature including acoustic energy generated by fluids in the annulus. The acoustic sensor(s) are located on the well tool and advantageously are located near to the washer module. They may be placed within the washer module or they may be located in a separate sensor or control module. The acoustic sensor system of example embodiments is a passive acoustic detector that includes acoustic sensor(s) for receiving acoustic signals but does not require any acoustic transmitter. Thus, the acoustic sensor system may comprise only receiving sensors without any acoustic transmitter.

[0091] The acoustic sensor(s) may include electronic sensors such as hydrophones, piezoelectric sensors, piezoresistive sensors, electromagnetic sensors, ultrasonic sensors, accelerometers, or the like. The acoustic sensor system advantageously provides full-spectrum acoustic sensing that accurately measure a broad frequency bandwidth and amplitude of acoustic energy. The acoustic sensor(s) may be arranged to sense sound and ultrasound waves up to 100kHz, 200kHz, 300kHz, 500kHz, 800kHz or 1MHZ. The combination of sound and ultrasound expands sensitivity to a wider range of frequencies and thereby increases the capability and probability for detecting and localizing a leak, and with higher localization accuracy.

[0092] In some embodiments, the acoustic sensor(s) are arranged to sense waves only in the ultrasonic frequency range. For example, the acoustic sensor(s) may only sense waves with a frequency equal to or above 100kHz. The acoustic sensor(s) may be ultrasonic acoustic sensor(s), e.g ultrasonic contact transducers. Such sensors have good sensitivity over a wide bandwidth, with particularly high sensitivity in the ultrasonic range.

[0093] The ultrasonic contact transducer may be a single-element, piezoelectric transducer.

[0094] The first verification system comprises one or more of volume, pressure and / or temperature sensor(s) that may be located at the well tool and / or may be located at a topside part of the apparatus, e.g. at a pump for providing fluid under pressure to the washer module.

[0095] The well tool optionally comprises a cement bond log (CBL) device, e.g. located in a sensor module or control module along with the acoustic sensor system. The cement bond log may be for assessment of the integrity of the annulus as a yet further integrity check after perforation alongside the other two integrity checks and / or for checking integrity of the annulus during other stages of the method, as discussed above. The CBL may hence be considered as a third verification system.

[0096] The single well tool may comprise a sensor module or control module that holds the acoustic sensor system and optionally also a cement bond log, where present. The sensor module or control module may be located adjacent to the washer module, e.g. immediately above or below the washer module. As noted above the single well tool may comprise a perforator module. This may be located adjacent to the washer module, e.g. immediately above or below the washer module. In one example embodiment the single well tool has a sensor module or control module above the washer module and a perforator module below the washer module. The well tool may be configured to be operated in a so-called “pump and pull” operation where a sequence of perforated sections is formed during lowering of the tool and where these perforated sections are first washed and / or sealed in a sequential way during raising of the tool.

[0097] Thus, the single well tool may be configured to provide a bridge plug during the well intervention, e.g. a bridge plug for a plug and abandonment operation. There may be a bridge plug module in addition to the other modules of the well tool. An internal plugging element may be provided as a part of the bridge plug module, wherein the internal plugging element is for blocking or restricting flow of fluid in the well, such as to contain a sealing fluid supplied via the washer module. The well tool may be configured for remote activation of the internal plugging element, such as via control from a topside location along with remote control and / or monitoring of other steps during the well intervention.

[0098] The washer module is arranged to supply a washing fluid under pressure, such as by means of fluid outlets dispersed over an area of the tool at the washer module. The fluid outlets may be radial holes. The radial holes may be arranged in a spacedapart relationship around a circumference of the washer module. Advantageously the washer module is also able to supply a sealing fluid under pressure using the same fluid outlets. The fluid(s) may be supplied to a perforated section of the well that has been enclosed using the upper and lower sealing arrangements.

[0099] The perforator module is for perforating the casing as a part of the well intervention, e.g. as a part of a plug and abandonment operation. This perforation may be done in reaction to analysis of integrity of the well done in the same run by the single well tool or based on data obtained by some earlier process. The perforator module may comprise mechanical perforating elements such as knives, or perforator guns. In example embodiments knives are used, as discussed above.

[0100] As noted above, the sealing fluid may comprise cement for forming a cement plug. The sealing fluid may comprise fluids such as Sandaband®, Thermaset® (Wellcem), Liquid Stone® or similar.

[0101] The well tool may be configured to carry out a sequence of method steps as discussed above in context of the first aspect. The well tool may comprise a control system and / or control interface for enabling such steps to be performed, which may be done with remote control by a topside human operator and / or by remote (i.e. topside) or local (e.g. on the tool) computer controllers. In example embodiments, individual parts of the well tool may be controlled electronically from surface, e.g. by a surface operator. Individual parts of the well tool may be controlled by a valve system comprising one or more valves, e.g. ball valves, arranged in the well tool. The valves may be configured between an open and a closed position to allow fluid supplied from surface to activate individual parts of the well tool, e.g. the washer module (including the actuatable sealing arrangements on the washer module), the perforator module, the bridge plug device etc. An example of a valve system suitable for this purpose is disclosed in the applicant’s patent NO346525B1. The number of valves used, and the specific position(s) of the valves within the well tool, may depend on the amount and type of individual parts used, and also the sequential arrangement of the different parts. In example embodiments, the well tool is conveyed by a coiled tubing string, an umbilical or a drill pipe string. Preferably, the coiled tubing string, the umbilical or the drill pipe string is through-wired for improved signal communication. This may be particularly beneficial in combination with the valve system. The valve system provides even more flexibility to the well tool, as it allows for unlimited activation and deactivation of the individual parts. Alternatively, the individual parts may be controlled by the dropping of objects from surface, e.g. balls or darts. Such systems / mechanisms are well known in the art and will therefore not be described further herein. In yet another alternative, the individual parts may be controlled by a combination of a valve system and by dropping of objects.

[0102] The well tool may comprise further devices, optionally in additional modules, such as a cutter for cutting the casing, a spear or other device for removing casing sections using a spear or similar, and / or a casing expander for expanding the casing prior to other operations.

[0103] Certain embodiments of the invention will be described in further detail below, by way of example only, and with reference to the accompanying drawings.

[0104] LIST OF FIGURES

[0105] Figure 1 shows a well tool for use in well intervention such as a plug and abandonment operation.

[0106] Figure 2 shows a first step of an example method by use of the well tool, where a CBL tool is used to evaluate the annulus integrity (i.e. the annulus barrier) throughout a plugging interval.

[0107] Figure 3 shows a further step of the example method, where the well tool, by means of a perforating tool, has been used to make perforations in a casing in preparation for an additional annulus barrier integrity test. Figure 4 shows yet a further step of the example method, where an additional annulus barrier integrity test is performed.

[0108] Figure 5 shows yet a further step of the example method, where a PWC operation has commenced to remove and then replace the annulus barrier with new cement.

[0109] Figure 6 shows another embodiment of the well tool, which additionally comprises a casing expander tool.

[0110] Figure 7 shows yet another embodiment of the well tool, which additionally comprises a casing spear tool and a casing cutter tool.

[0111] DESCRIPTION OF EXAMPLES

[0112] Figure 1 shows an example well tool 1. The well tool 1 is for use in well interventions where one or more of the functions of the tool 1 is required. A plug and abandonment operation is an example of a well intervention where the proposed tool 1 provides benefits. In this implementation the well tool 1 may be connected to coiled tubing 10, such as through-wired coiled tubing. It may alternatively be coupled to an umbilical, or a drill pipe string. The example well tool 1 has four main parts, which are a control module 12, a washer module 14, a perforator module 16 and a bridge plug 18.

[0113] The bridge plug 18 comprises a plugging element that can be deployed under remote control, e.g. via electric signals from the surface or by fluid pressure, in order to provide a base for setting a plug via introduction of a sealing fluid into the well. The bridge plug 18 is located further down hole than the other modules as it will be left in the wellbore to support the sealing fluid that is delivered by the washer module 14 above.

[0114] The perforator module 16 is adjacent to and above the bridge plug 18. It can be of known form, e.g. with hydraulically activatable knives 17 for forming perforations in the casing. Such tools can be an activated an unlimited number of times, unlike explosives. This allows for making several perforations in several different locations in the same run, which is advantageous for the herein described method.

[0115] The washer module 14 is adjacent to and above the perforator module 16. This washer module 14 may have similarities to parts of known well tools for combined washing and cementing, such as those described in the applicant’s earlier patent publications NO20211499 and EP3036395. It is configured for supply of both washing fluid and also sealing fluid (e.g. cement) via outlets 22 that are spaced apart around the circumference of the washer module 14. As an added feature compared to the devices of NO20211499 and EP3036395 the washer module 14 additionally allows for actuatable sealing to enclose a section of the well via retractable elements 21 at upper and lower sealing arrangements 20a, 20b. This may be done during a washing operation and / or during supply of a sealing fluid (e.g. cement) such as for setting the plug in a plug and abandonment opertion. In this example the use of the sealing arrangements also has relevance to the integrity testing processes in view of the ability to allow for pressurization of a section of the well. Thus, fluid may be held under pressure in a perforated section of the well in order to test the integrity of the annulus, such as by means of a pressure integrity test. The well tool hence provides a first verification system that uses monitoring of fluid under pressure to determine information relating to the condition of the annulus barrier. To perform such a verification the washer module 14 is provided with volume, pressure and / or temperature sensors 24 for monitoring the fluid that is enclosed by the sealing arrangements 20a, 20b, and to thereby monitor for fluid movement into or out of the annulus.

[0116] The retractable elements 21 of the sealing arrangements 20a, 20b are active elements that can be moved between a deployed and a stowed configuration by an actuation mechanism, such as a piston system, a sleeve system etc. Deployment of the retractable elements 21 may be controlled from surface by use of electrical signals, via the control module 12, or alternatively, by fluid pressure supplied from surface. In figure 1, two sets of retractable elements 21 are shown on each side of the outlets 22. However, the number of retractable elements 21 may be less, i.e. one on each side of the outlets 22, or more.

[0117] The control module 12 also acts as a sensor module. It provides command and control functions as well as certain sensor functions, in particular via an acoustic sensor system 26 and an ultrasonic based cement bond log (CBL) tool 28. Other communications, sensing and monitoring systems may also be present, such as a casing collar locator (CCL), measurement while drilling (MWD) systems and other logging and measurement tools that may be used to evaluate physical properties of the wellbore and surrounding rock formations, as is known for well tools.

[0118] The acoustic sensor system 26 comprises an ultrasonic acoustic sensor assembly, and it is configured to measure acoustic signals at the well tool in order to provide a further check of the integrity of the annulus. The acoustic sensor system 26 hence provides a second verification system using a different sensing principle to the first verification system.

[0119] The ultrasonic acoustic sensor assembly comprises an ultrasonic contact transducer, e.g. a single-element piezoelectric transducer, and is arranged suspended in an acoustic insulation means inside a compartment of a tool element, e.g. a sensor sub, of the control module 12. The ultrasonic acoustic sensor assembly is additionally arranged to interface the wellbore fluid. The acoustic insulation means have an acoustic impedance different from the acoustic impedance of the sensor sub for ultrasonic signals. Thus, background noise signals carried along the tool body will be partially reflected and scattered at the interface between the two different materials with different acoustic impedance. The sensor sub is typically made of steel and the acoustic insulation means may be one or more rubber o-rings. The characteristic acoustic impedance for steel is typically 46MRayl, while plastics and rubber have a characteristic acoustic impedance typically in the range of 1 to 3 MRayl. A larger difference in impedance will increase reflection.

[0120] Multiple assemblies may be used for redundancy, or where the acoustic sensor assemblies have different characteristics, such as sensitivity, bandwidth etc. to be able to improve the overall characteristics of the tool. For example, two sensors optimized for different frequency ranges may be used to optimize response over the entire measurement range.

[0121] In this example the acoustic sensor system 26 is configured to detect sounds at frequencies in the ultrasound range, in particular frequencies equal to or above 100kHz. This allows for fluid leaks and / or displacement of material to be detected. The acoustic sensing system 26 may be used before, during and / or after a washing step, as well as optionally during setting of the plug. In one example the acoustic sensing system 26 is used in parallel with the sensors at the washer module 14 during pressurization of an enclosed region of the well, i.e. with the retractable elements 21 in their deployed state.

[0122] The CBL tool 28 at the control module 12 may be of a known type and it may be used in a conventional way for CBL functions prior to perforation, as well as optionally being used as an added layer of integrity checking during the annulus verification process. In this respect the CBL tool 28 can therefore provide a third verification system for checking the integrity of the annulus.

[0123] Control of the individual modules of the well tool 1 may be achieved by integrated valves used to fluidly isolate different parts of the well tool 1. The valves are preferably remotely controlled (i.e. opened and closed) by a signal, e.g. an electric signal, sent from a surface operator. Patent publication N020210278 discloses an example of a ball valve tool suitable for this purpose. Using such a remotely controlled valve system provides more flexibility compared to e.g. ball drop solutions, and particularly when several tools / modules are combined.

[0124] Possible methods of use of the well tool are set out above in the summary of invention section. The tool is assembled at the surface and lowered to the required location. During this process the CBL tool 28 may be used to check the integrity of the annulus barrier. With the tool at a required depth, the perforator module 16 can be used to perforate the casing (e.g. if the CBL determines that this is required) to provide a perforated section of the well. This may be done for a region extending along the depth of the well, hence providing a plurality of perforated sections. The washer module 14 can be used to wash the perforated section(s) as well as being able to pressurize a perforated section by actuating the retractable elements 21 to enclose the region around the washer module 14. This can be done for injection of fluid into the annulus, such as for pressure testing, for annulus washing and / or for cementing after washing. The washing steps may be carried out from the top down, i.e. for the uppermost perforated section first, before moving to lower perforated section(s).

[0125] Before eventual washing, the integrity of the annulus barrier can be checked using the various verification systems. In case of a plurality of perforated sections, this could be done for more than one perforated section. A plurality of perforated sections could be formed in the same plugging interval, or, across different plugging intervals.

[0126] After washing the annulus, the washer module 14 may be used to provide a sealing fluid such as cement via the outlets 22. Where there are multiple perforated sections then this can be done from the bottom moving upwards. The sealing fluid can be circulated via the washer module 14 to the perforated annulus. In a variation not shown in the drawings there may be a bypass system allowing for the sealing fluid to rise into the annulus to above the upper sealing arrangement 20a, and run down via the bypass system (not shown) to below the lower sealing arrangement 20b while the tool including the washer module 14 is pulled slowly up. Thus, one can use such a bypass system to carry out a "push and pull" operation in order to cement both the casing annulus and the casing at the same time as described in EP3036395.

[0127] In an example of a “push and pull” operation the retractable elements 21 are used to control the flow of fluid. As noted above the retractable elements 21 have functions relating to the washing steps as well as the pressure testing steps. With this method the well tool may be lowered in the well until the lower sealing arrangement 20b in the form of retractable elements 21 is arranged below the lower part of a first perforated section, with the upper sealing arrangement 20a hence being located above the first perforated section. This allows for circulation of sealing fluid between the lower and the upper sealing arrangement and out through the outlets 22, which in this example comprise a plurality of radial holes arranged between the lower and upper sealing arrangements 20a, 20b. This forces the sealing fluid radially outwardly towards the sidewalls of the casing and outward to the annulus via the perforations in the perforated section. The bridge plug 18 will already have been set in the wellbore in an area below the perforated section during this part of the operation to provide a sealing fluid base inside the casing bore.

[0128] The pumping of the sealing fluid, e.g. cement, is continued until the level of sealing fluid has risen in the well, to a position in which the sealing fluid is at a higher elevation in the well than the elevation of the washer module 14. The well tool 1 is then pulled upwards in a controlled manner while pumping of the sealing fluid continues. The process is controlled so that the level of the sealing fluid above the tool is held substantially constant. The sealing fluid above the washer module 14 can optionally pass through a bypass system (not shown), allowing the sealing fluid to fill the void below the well tool. This helps in ensuring solid sealing fluid across the full cross-sectional area of the perforated sections. An example bypass-system may be similar to that described in EP3036395 and thus may comprise a first set of openings leading from the wellbore towards the inside of the tool, a channel system bypassing the retractable elements 21 and a second set of openings arranged on the other side of the retractable elements 21. The channel system may comprise by-pass lines extending from the openings in the first set of openings to the second set of openings. These may be separate lines leading from one opening to another opening, or alternatively, there may be one or more common lines or a manifold arrangement for the plurality of openings. Sealing fluid can be "sucked" from above the washer module 14 towards the area below the well tool due to a change in pressure over the washer module 14, as the tool is pulled towards the surface, leaving an area without sealing fluid. To solve this, the bypass-system allows for sealing fluid to bypass the barriers formed by the retractable elements 21, thereby providing a whole continuous plug of sealing fluid in the well.

[0129] There is a continued pulling of the well tool 1 until the washer module 14 has been pulled above the end of the perforated region in the well and is hence positioned inside a non-perforated tubular. The pumping of sealing fluid is then stopped and the well tool 1 is pulled above the top of the sealing fluid. A cleaning process can then be performed, e.g. by pumping washing fluid through the tool. The cleaning fluid is preferably another fluid than the sealing fluid, and suitable fluids are known to the person skilled in the art.

[0130] Figures 2-5 illustrate different steps of a method according to the disclosure. Common for all figures is a wellbore 7 about to be plugged and abandoned. The wellbore 7 comprises a casing 2, an annulus 3 formed between the casing 2 and a surrounding rock formation 6, and a casing bore 4. A plugging interval 30, where a cement plug is about to be formed, is also illustrated. The plugging interval may e.g. be 100 meters long. However, the length of the plugging interval may vary, e.g. due to operator requirements, country specific regulations and so on. The placement of the plugging interval along the wellbore’s length (i.e. the depth / position of the plugging interval) is in the present example pre-decided (i.e. decided before running into the well). However, it may be adjusted, completely changed or completely determined based on downhole surveys as discussed herein (i.e. after the tool is run into the well). Although only one plugging interval 30 is illustrated, the wellbore 7 may include more than one such plugging interval 30, all of which can be plugged in the same trip using the disclosed well tool 1. Also common for figures 2-5 is the well tool 1, which is used to carry out the different method steps for plugging and abandoning the well. The well tool 1 corresponds to the one illustrated in figure 1 and includes from top to bottom the control module 12, the washer module 14, the perforator module 16 and the bridge plug 18. In the present example, the well tool 1 is conveyed into the wellbore by a through-wired coiled tubing string 10. However, the well tool 1 may also be conveyed by use of an umbilical (comprising a fluid conduit) or a drill pipe string, preferably also through-wired. A through-wired string improves signal communication with the different parts of the well tool 1.

[0131] The annulus 3 formed between the casing 2 and the surrounding rock formation 6 can contain various materials, including liquids and solids. For example, the annulus 3 in the plugging area 30 can contain old consolidated cement from a cementing operation performed during the construction phase of the well. Alternatively, or additionally, the annulus 3 in the plugging area can contain different consolidated solids particles, such as from cuttings and / or particles present in drilling fluids. Such particles may settle due to gravity and consolidate over time. Any liquids present may for example be drilling fluids. Hereinafter, we will use the term “annulus barrier” as a collective term for the various materials that may be present in the annulus 3 of the wellbore 7 prior to performing the herein described method steps.

[0132] In theory, if the annulus barrier in the plugging interval 30 is sufficient, only the main casing bore 4 needs to be plugged with a sealing fluid to properly seal that section of the wellbore. However, if the annulus barrier in the plugging interval 30 is insufficient, the annulus barrier must be completely removed and replaced by a new sealing fluid in order to provide a solid rock-to-rock barrier across the plugging interval 30. Known methods such as Perf, Wash and Cement (PWC), section milling, or “cut and pull” can be utilized to gain access to the annulus 3 and thus remove the annulus barrier prior to forming a plug in the area. However, all of these methods are time consuming, so avoiding them can save significant operating time and cost. It is therefore highly desirable to be able to determine, with a high degree of accuracy, if the annulus barrier is sufficient. Furthermore, the degree of accuracy may be especially important in connection with permanent plugging and abandonment, where the operator needs to be sure that well integrity is maintained for the foreseeable future.

[0133] Figure 2 illustrates a first step of the method, wherein the CBL tool 28 is used in an initial step to evaluate the integrity of the annulus 3 (i.e. the annulus barrier) throughout the plugging interval 30. If the CBL indicates that the annulus barrier is sufficient, an option is to set the bridge plug 18 as a cement base and then cement the casing bore 4 to form a cement plug in the plugging interval 30. The cement may be provided through the washer module 14, or through the bottom of the well tool 1. In the case where cement is supplied through the washer module 14, the retractable elements 21 are preferably configured in the stowed configuration.

[0134] If the CBL indicates that the annulus barrier is insufficient, or as an additional contingency, a further step of the method is performed. Figure 3 illustrates a further step of the method where the well tool 1, by means of the perforating tool 16, has been used to make perforations 15 in the casing 2 in preparation for an additional annulus barrier integrity test. The perforating tool 16 has formed an upper perforated section 5a in an area above the plugging interval 30 and a lower perforated section 5b in an area below the plugging interval 30. Figure 3 also illustrates the knives 17 of the perforating tool 16 being extended to form the perforations 15 of the perforated section 5b.

[0135] Figure 4 illustrates a next step of the method where an additional annulus barrier integrity test is performed. The washer module 14 is positioned adjacent the lower perforated section 5b and the retractable elements 21 of the upper and lower sealing arrangements 20a, 20b are in the deployed configuration such as to form a fluid tight seal between the washer module 14 and the casing 2 in an area covering the lower perforated section 5b. A fluid, e.g. a drilling fluid or a washing fluid, is supplied from surface through the coiled tubing string 10. The fluid exits the ports 22 of the washer module 14 and is, due to the seal formed by the retractable elements 21, forced through the perforations 15 into the annulus 3 (illustrated by the arrows). The upper perforated section 5a provides a fluid path in a region about the upper part of the plugging interval 30. As such, a pressure test of the annulus barrier in the plugging interval 30 can be performed. Fluid is supplied until the pressure is equal to or higher than a formation leak-off pressure, e.g. of a former hydrocarbon producing formation located below the plugging interval 30. Then, the supply of fluid may be stopped, and one or more parameters may be monitored for a certain amount of time to see if the annulus barrier is able to hold the pressure. Pressure, volume and / or temperature may be measured by the pressure, volume and / or temperature sensors 24 provided at the well tool 1 before, during and after supply of the fluid. In the present example, the sensor(s) 24 are provided between the upper and lower sealing arrangements 20a, 20b of the washer module 14. Additionally, or alternatively, one or more of these parameters may be monitored by sensors at a surface location, e.g. monitored by pressure sensors at a surface pump. To make sure that the sealing arrangements 20a, 20b are intact, the integrity of the sealing arrangements 20a, 20b is tested against a blank portion of the casing 2 prior to performing the pressure test.

[0136] To improve the sensitivity of the measurements, an isolation arrangement of the well tool 1 (not shown in the drawings) may be closed to separate a volume of an inner bore above the isolation arrangement from a volume of an inner bore below the isolation arrangement. The isolation arrangement may be a valve, e.g. a ball valve, positioned in the well tool above the washer module 14. In the present example, the ball valve is controlled electronically from a surface location. As such, the volume monitored by the sensors 24 can be significantly reduced, which makes any change in the measured parameters of the monitored volume easier to detect. Thus, the sensitivity of the system is increased, and the integrity test becomes more accurate.

[0137] If the pressure test fails, which indicates that the annulus barrier in the plugging interval 30 is insufficient, further steps must be taken before a solid plug can be formed in the plugging interval, as will be described further herein.

[0138] A good pressure test indicates that the annulus barrier in the plugging interval 30 is sufficient. However, in certain cases, a pressure test may not be sensitive enough to detect very small leaks, or micro leaks, propagating in the annulus 3. Even a very small leak can have a significant environmental impact if not detected during well abandonment, as it would allow hydrocarbons and other reservoir fluids to propagate towards the surface and spread in the surrounding environment over time. Thus, the acoustic sensor system 26 functions as a second independent integrity check in addition to the pressure test. As explained in conjunction with figure 1, the acoustic sensor system 26 comprises a single-element piezoelectric transducer, which is able to detect acoustic waves in the ultrasonic range, e.g. frequencies equal to or above 100kHz. Such a sensor system is highly sensitive over a broad bandwidth and can detect micro leaks / low energy leaks that would not have been detectable by the pressure test alone, or by the CBL. For example, flows as low as 0.03 liters per minute can be detected by the acoustic sensor system 26. Thus, by use of the disclosed method, the integrity of the annulus barrier can be determined with greater certainty compared to known methods.

[0139] In the case of a good pressure test, if the “listening test” by means of the acoustic sensor system 26 also indicates that the annulus barrier in the plugging interval 30 is sufficient, then the bridge plug 18 can be set and cement provided in the casing bore 4 to form a cement plug in the plugging interval 30. The cement may be provided through the washer module 14, or through the bottom of the well tool 1. In the case where cement is supplied through the washer module 14, the sealing arrangements 20a, 20b are preferably configured in the stowed configuration.

[0140] In the case of a good pressure test, if the “listening test” indicates that the annulus barrier in the plugging interval 30 is insufficient, then further steps must be taken before a solid plug can be formed in the plugging interval, as will be described further herein.

[0141] Figure 5 illustrates a further step of the method, where a PWC operation has commenced to remove and then replace the annulus barrier with new cement. In figure 5, the bridge plug 18 has been set as a cement base and another perforated section 5c has been formed above the lower perforated section 5b by means of the perforating tool 16. Before the annulus 3 is washed and the plugging interval 30 is ultimately cemented, such perforated sections are formed throughout the whole plugging interval 30 to ensure adequate washing and cement displacement in the annulus 3. Although the bridge plug 18 is shown set before perforating the plugging interval 30, the bridge plug 18 may be set after the perforations are formed, or even after the washing step is performed, as long as it is set before the cementing operation.

[0142] Figure 6 illustrates another embodiment of the well tool 1. The well tool 1 corresponds to the one illustrated in figure 1 but includes in addition a casing expander tool 19 positioned between the perforating tool 16 and the bridge plug 18. In certain cases, it is necessary to provide an annulus fundament for the cement to prevent the cement from dissipating downwards in the annulus due to gravity. Thus, the casing expander tool 19 is used to expand the casing 2 radially outwards to create a physical fundament for the cement in the annulus. The casing 2 may be expanded in an area between the lowermost perforations and the bridge plug 18 to create the annulus fundament. Alternatively, the casing 2 can be expanded in an area below where the bridge plug 18 is to be set. Preferably, the casing 2 is expanded after the annulus section has been washed. The casing may be expanded either before or after the bridge plug 18 is set.

[0143] As can be seen in figure 6, the casing expander tool comprises a number of expansion segments 19a about its outer circumference. The expansion segments 19a are configured so that they can be extended radially and thus form a dent in the surrounding casing. A plurality of such dents may be formed at different depths / elevations in order to provide a sufficient annulus barrier, i.e. to ensure that the cement stays within the plugging interval 30. The expansion segments 19a may be activated by fluid pressure, e.g. by use of fluid pressure supplied from surface through the coiled tubing string 10. Casing expander tools suitable for the abovedescribed purpose are known in the art and will therefore not be described further herein. Although the casing expander tool 19 in the current example is positioned between the perforating tool 16 and the bridge plug 18, it may be placed at different positions within the well tool 1, such as above the washer module 14.

[0144] Figure 7 illustrates yet another embodiment of the well tool 1. The well tool 1 corresponds to the one illustrated in figure 1 but includes in addition a casing spear tool 40 and a casing cutter tool 42 positioned between the perforating tool 16 and the bridge plug 18. The casing cutter tool 42 comprises radially extendable cutter arms 43 configured for cutting and severing the casing 2. The casing cutter tool 42 is configured to be rotated while the cutter arms 43 are forced against the inner surface of the casing 2 to thereby cut and severe the casing 2. When the well tool 1 is conveyed by through-wired coiled tubing (or umbilical), as in the present example, a downhole motor is additionally required in order to rotate the casing cutter tool 42. The casing spear tool 40 comprises slips 41 configured for engaging and holding the inner surface of the casing 2. As such, the casing 2 may be cut and then removed / retrieved by the single well tool 1. The slips 41 may also be used to hold the casing cutter tool 42 at a constant elevation / depth during the cutting process. Casing cutter and spear tools for severing and removing casings are known in the art and will therefore not be described further herein. The casing spear tool 40 and the casing cutter tool 42 may for example be used in a situation where an adequate cement plug cannot be achieved by PWC, e.g. due to that adequate washing of the annulus is not possible.

[0145] The cutter tool 42 and spear tool 40 may be used to create a short or long window. Thus, the method may include cutting the tubing / casing, pulling it upwards a certain distance (long or short), and then cementing the tubing / casing free section. After this the lifted tubing / casing may be lowered on top of the cement once it has adequately solidified / cured.

[0146] Although the casing spear tool 40 and the casing cutter tool 42 are shown positioned between the perforating tool 16 and the bridge plug 18, the tools may be positioned at other locations in the well tool 1, e.g. above the washer module 14. It can be advantageous to have a smaller number of tools between the cement ports and the bridge plug 18, as cement displacement may be negatively affected by a long tool string being pulled through the cement, and because it may be advantageous to displace the cement as close to the bridge plug as possible.

[0147] Figures 6 and 7 illustrate the well tool 1 comprising a casing expander tool 19 and a casing cutter and spear assembly 40 / 42 respectively. However, the well tool 1 could also comprise all these tools at the same time. Thus, the well tool 1 is a modular system where different modules can be added or removed based on what is needed in a particular operation. Having several different tools / modules in the well tool 1 increases the flexibility of the well tool 1 and provides additional contingency options. Thus, the well tool 1 can execute a larger number of tasks in a single trip if necessary.

Claims

CLAIMS:

1. A method for use in a well intervention using a single well tool (1), the well tool (1) having a washer module (14), the method comprising: with the well tool (1) positioned so that the washer module (14) is at a perforated section (5b) of a well (7), supplying a fluid under pressure via the well tool (1) into the perforated section (5b) of the well; checking the integrity of the annulus (3) in the region of the perforated section (5b) by means of volume, pressure and / or temperature sensors (24); and performing an additional check of the integrity of the annulus (3) in the region of the perforated section (5b) using an acoustic sensor system (26) for measuring acoustic signals at the well tool (1), the acoustic sensor system (26) including one or more acoustic sensor(s) located on the well tool (1).

2. The method according to claim 1, wherein the washer module (14) comprises an upper sealing arrangement (20a), a lower sealing arrangement (20b) and one or more fluid outlets (22) for supplying the fluid under pressure, wherein the upper and lower sealing arrangements (20a, 20b) are arranged above and below the one or more fluid outlets (22), respectively, and wherein the method comprises sealing off an upper portion of the well (7) above the perforated section (5b) using the upper sealing arrangement (20a) and sealing off a lower portion of the well (7) below the perforated section (5b) using the lower sealing arrangement (20b).

3. The method according to claim 2, wherein the upper sealing arrangement (20a) and the lower sealing arrangement (20b) each comprises one or more retractable elements (21) configured to move between a stowed configuration and a deployed configuration, and wherein the method comprises moving the one or more retractable elements (21) from the stowed configuration to the deployed configuration prior to supplying the fluid under pressure via the well tool (1) into the perforated section (5b).

4. The method according to claim 2 or 3, wherein the pressure, volume and / or temperature sensors (24) are positioned between the upper and lower sealing arrangements (20a, 20b), and wherein the method comprises measuring pressure, volume and / or temperature in an area between the upper and lower sealing arrangements (20a, 20b).

5. The method according to any preceding claim, wherein the acoustic sensor system (26) is a passive acoustic detector system comprising acoustic sensor(s) for receiving acoustic signals.

6. The method according to any preceding claim, wherein the one or more acoustic sensor(s) are ultrasonic acoustic sensor(s).

7. The method according to any preceding claim, wherein the one or more acoustic sensor(s) are arranged to sense waves with a frequency equal to or above 100kHz.

8. The method according to any preceding claim, wherein the one or more acoustic sensor(s) are arranged to interface a wellbore fluid.

9. The method according to any preceding claim, wherein the well tool (1) comprises a perforator module (16), and wherein the method comprises forming an upper perforated section (5a) in an area about a top of a plugging interval (30) and a lower perforated section (5b) in an area about a bottom of the plugging interval (30).

10. The method according to claim 9, wherein the perforator module (16) comprises one or more activatable cutting elements (17) for forming perforations in the casing (2).

11. The method according to claim 9 or 10, wherein the well tool (1) is positioned so that the washer module (14) is at the lower perforated section (5b), and wherein the method comprises supplying the fluid under pressure via the washer module (14) into the lower perforated section (5b) to check the integrity of the annulus (3) in the plugging interval (30).

12. The method according to any preceding claim, wherein the well tool (1) comprises a CBL tool (28), and wherein the method comprises performing an initial integrity check of the annulus (3) by means of the CBL tool (28).

13. The method according to any preceding claim wherein the well intervention comprises a plug and abandonment operation during which the well tool is used to perform all of the method steps in a single run.

14. An apparatus for a well intervention such as a plug and abandonment operation, the apparatus comprising:a well tool (1) having a washer module (14) for supplying a fluid under pressure via the well tool (1) into a perforated section (5b) of the well (7); a first verification system for checking the integrity of the annulus (3) in the region of the perforated section (5b) when it is exposed to fluid under pressure, the first verification system comprising one or more volume, pressure and / or temperature sensor(s) (24); and a second verification system for performing an additional check of the integrity of the annulus (3) in the region of the perforated section (5b), the second verification system comprising an acoustic sensor system (26) for measuring acoustic signals at the well tool (1), the acoustic sensor system (26) including one or more acoustic sensor(s) located on the well tool (1).

15. An apparatus as claimed in claim 14, wherein the apparatus is arranged to perform the method of any of claims 1 to 13.

16. The apparatus according to claim 14 or 15, wherein the well tool (1) comprises a bridge plug module (18).

17. The apparatus according to claim 14, 15 or 16, wherein the well tool (1) comprises a CCL tool.

18. The apparatus according to any of claims 14 to 17, wherein the well tool (1) comprises a control module (12).

19. The apparatus according to claim 18, wherein the control module (12) comprises the acoustic sensor system (26) and / or the CCL tool.

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