Validation of a well annulus washing operation

Abstract

A method of validating a well annulus (101) washing operation is disclosed An annulus washing tool (100) is arranged at a perforated section of a well pipe (103), providing a washing fluid flow (110) into the annulus (101) of the well pipe. An acoustic sensor (115, 117) is arranged inside an inner bore (102) of the well pipe, detecting acoustic signals generated by the washing fluid flow (110). An annulus washing assembly comprising an annulus washing tool (100) is configured to provide a washing fluid flow (110). The annulus washing assembly comprises an acoustic sensor (115, 117).

Description

VALIDATION OF A WELL ANNULUS WASHING OPERATIONTechnical Field

[0001] The present invention relates to validation of a well annulus washing operation. There is disclosed a method and a tool for validating completeness of an annulus washing operation.Background Art

[0002] In some situations, during the lifetime of a hydrocarbon well, it may be necessary to wash the well annulus. A typical scenario is when a plug shall be installed in the well by setting a cement plug in the annulus and main bore.

[0003] Before cement is introduced in the annulus, the operator washes the annulus such that the quality of the installed plug is not jeopardized. If the cement is introduced in an unwashed annulus, impurities (e.g. barite from settled drilling mud) may result in a poor plug quality.

[0004] Moreover, although having performed a washing operation, the operator may wish to know if the washing operation has been successful or not. An object of the present invention may be to provide a method and a tool for verifying a successful annulus washing operation.

[0005] Publication WO2017034558 A1 discloses a method for characterizing material in a well annulus by measuring the acoustic noise. For instance, if a drilling fluid flows through the annulus, acoustic sensors will record the sound produced and a program can compare the sound to pre-defined acoustic profiles. Hence, when the flowing fluid changes from one type of fluid to another type of fluid, for instance from a drilling fluid to a spacer fluid, this can be detected by measuring the produced sound. This publication also discloses recording of a mixed flow, in which case the recorded sound will not match any of the acoustic profiles. The acoustic sensors recording the sound are attached to the outer surface of the well casing, at different locations along its extension.

[0006] Publication US2020340332 discloses a tool for washing an annulus outside a well casing. The tool comprises a pressure sensor for sensing pressures inside thecasing. The pressure measurement is used to ensure correct placement of the washing tool with respect to the perforations in the casing.Summary of invention

[0007] There is disclosed a method of validating a well annulus washing operation. The method comprises: a) with an annulus washing tool arranged at a perforated section of a well pipe, providing a washing fluid flow into the annulus of the well pipe. The method further comprises: b) with an acoustic sensor arranged inside the inner bore of the wellpipe, detecting acoustic signals generated by the washing fluid flow.

[0008] The acoustic sensor can be part of the annulus washing tool.

[0009] Furthermore, the acoustic sensor can be, during step a), located at the location of the perforations.

[0010] In some embodiments of the method, the acoustic sensor can comprise an upper acoustic sensor which is part of the annulus washing tool above the wash fluid ports, such as nozzles, of the annulus washing tool. Alternatively, the acoustic sensor can comprise an upper acoustic sensor being supported on a string that supports the annulus washing tool, at a position above the annulus washing tool. The upper acoustic sensor can, during step a), be arranged inside the inner bore, above the location of the perforations.

[0011] In some embodiments, the method can comprise the following step: c) based on detected acoustic signals, calculating an amount of material that has been washed out of the annulus with the washing fluid flow.

[0012] In such embodiments, the method may further comprise the following steps: d) calculating an amount of material present in the portion of the annulus before the washing operation in step a); and e) calculating an annulus wash index by dividing the amount of material, as calculated in step c), by the amount of material as calculated in step d).

[0013] There is also disclosed an annulus washing assembly, comprising an annulus washing tool with wash fluid ports, e.g. nozzles, configured to provide a washing fluid flow. The annulus washing assembly further comprises an acoustic sensor.

[0014] In some embodiments, the annulus washing tool comprises the said acoustic sensor.

[0015] The annulus washing assembly may comprise an upper acoustic sensor arranged above the wash fluid ports. The upper acoustic sensor can be in addition to or instead of the abovementioned acoustic sensor that is part of the annulus washing tool.

[0016] Advantageously, the upper acoustic sensor can be arranged several meters, for instance at least twenty meters, forty meters or even eighty meters above the wash fluid ports.

[0017] In some embodiments of the annulus washing assembly, the annulus washing tool further comprises an upper casing bore sealing arrangement and a lower casing bore sealing arrangement. Moreover, the wash fluid ports, for instance nozzles, can be arranged between the upper and lower casing bore sealing arrangements, and the acoustic sensor can be arranged above the wash fluid ports.

[0018] The casing bore sealing arrangements may be in the form of wash cups. Alternatively, the casing bore sealing arrangements can be in the form of flexible expandable elements, such as expandable rubber elements.

[0019] Advantageously, the annulus washing assembly can comprise or can be connected to a computer-readable memory unit or a computing unit programmed to calculate an annulus wash index.

[0020] In some embodiments, the detected acoustic signals can be used to calculate the removed or washed-out mass in real time. In such embodiments one may have a data link to surface, for instance with a through-wired drill pipe or through-wired coiled tubing. This enables the operator to monitor the progress of the washing process during operation.

[0021] Alternatively, the washing assembly may comprise a data storage unit for storing the detected acoustic signals. The operator may then perform calculations when the assembly has been retrieved to surface.Detailed description of the invention

[0022] While various features of the invention have been presented in general terms above, a non-limiting and more detailed example of embodiment will be presented in the following with reference to the drawings, in which:Fig. 1 is a schematic view of an annulus washing tool arranged inside a well pipe;Fig. 2 is a particle count time based showing a reduced number of particles over time indicating progressing washing / clean-up effect.;Fig. 3 is an energy histogram time based with dark line showing flow noise / noise base line.Fig. 4 is a signature log time based showing particle impacts versus particle size.

[0023] Fig. 1 depicts an annulus washing tool 100 configured for washing an annulus 101 outside a well pipe, here in the form of a casing 103 installed in a subsea well 105. The well pipe (i.e. casing) 103 has an inner bore 102, which for the present embodiment is termed a casing bore 102.

[0024] The annulus washing tool 100 is part of an annulus washing assembly 10, which is installed in the subsea well 105. The annulus washing assembly 10 can typically comprise a drill string or coiled tubing (not shown) or another string for suspending the annulus washing tool 100.

[0025] It shall be appreciated that although the shown tool is termed an annulus washing tool, it may be part of a plug setting tool string, configured to perform several additional steps needed to set a wellbore plug (typically perforation, washing and cementing - PWC).

[0026] In the situation shown in Fig. 1 , the casing 103 has already been perforated with a perforation tool (not shown). The resulting perforations 103a constitute fluid communication between the casing bore 102 and the annulus 101 outside of it. The annulus washing tool 100 is arranged at a perforated section of a well pipe 103, providing a washing fluid flow 110 through perforations 103a in the well pipe, into the annulus 101 , and back through perforations into the inner bore 102 of the well pipe.

[0027] The annulus washing tool 100 comprises a casing bore sealing arrangements, which in the shown embodiment are in the form of an upper wash cup 107 and a lower wash cup 109 (sometimes also called swab cups). These are arranged at a mutual distance along the tool. In the shown embodiment, there are also arranged an upper back-up wash cup 107a and a lower back-up wash cup 109a. The wash cups are configured to seal against the casing bore 102. The skilled reader will appreciate that other types of washing tools can be without wash cups.

[0028] Instead of having the casing bore sealing arrangements in the form of the shown cups 107, 109, they could be in the form of expandable elements, such as expandable rubber elements. In this manner, the operator is enabled to actuate them, i.e. the sealing function against the casing bore 102, when in the desired position inside the casing 103. After the washing procedure, the operator can deactivate them.

[0029] Between the upper and lower wash cups 107, 109 there is a plurality of wash fluid ports, which in this embodiment is in the form of nozzles 111 . As indicated with arrows in Fig. 1 , a washing fluid flow 110 exits the wash fluid nozzles 111 and flows through perforations 103a at the location between the upper and lower wash cups 107, 109. The washing fluid flow 110 flows further upwards and re-enters the casing bore 102 through perforations 103a above the upper back-up wash cup 107a. The washing fluid flow 110 further flows upwards (i.e. towards the surface) through the casing bore 102.

[0030] This washing process cleans out material that shall be removed from the annulus 101. The material can be particles 113 (for instance settled barite). During the cleaning process, the annulus washing tool 100 is moved downwards through the casing 103, cleaning the annulus 101 along a predetermined length.

[0031] Also schematically shown in Fig. 1 , the annulus washing tool 100 comprises an acoustic sensor 115. The acoustic sensor 115 detects acoustic signals originating from the washing fluid flow 110. The presence of particles 113 during the washing procedure will affect the characteristics of the acoustic signals or sound. Thus, the sound produced by washing fluid containing particles will be different from the sound produced by washing fluid without particles. Consequently, the operator is enabled todetect when the particles in the annulus 101 has been successfully washed away with the washing fluid.

[0032] The annulus washing tool 100 can further or alternatively comprise an upper acoustic sensor 117. The upper acoustic sensor 117 is arranged above the acoustic sensor 115 and can detect acoustic signals originating from the upwardly directed washing fluid flow 110 in the casing bore 102. Advantageously, the upper acoustic sensor 117 is arranged above the perforated section of the casing 103 during the washing procedure. All the washed-out particles 113 will then flow through the casing bore 102 and past the upper acoustic sensor 117.

[0033] While the upper acoustic sensor 117 in the shown embodiment is a part of the annulus washing tool 100, in other embodiments the upper acoustic sensor 117 could be located further above the annulus washing tool 100. For instance, the upper acoustic sensor 117 can be supported above the annulus washing tool 100, by the string (not shown) supporting the annulus washing tool 100.

[0034] Based on detected acoustic signals or sound from the upper acoustic sensor 117, and / or recorded acoustic signals from the acoustic sensor 115, one may calculate the amount or mass of particles 113 that has been washed out from the annulus with the washing fluid flow 110.

[0035] Knowing the amount of material or particles 113 that has been removed from the annulus 101 may assist in validating that the annulus 101 has been sufficiently washed. By knowing the volume of the washed section of the annulus and comparing it to the amount of washed-out material, one can indicate how much of the material has been removed (washed out).

[0036] One can calculate an annulus wash index by dividing the amount of washed- out material by the initial amount of material present in the annulus. For instance, the amount of washed-out material divided by the initial amount of material can equal 0.95, giving an annulus wash index of 0.95 or, alternatively 95 %.

[0037] Estimation of the initial amount of material in the portion of the annulus that shall be washed can be based on one or more of well logs, fluid type, and well age.

[0038] With the acoustic sensor 115 and / or the upper acoustic sensor 117, one can provide a particle energy histogram, of which an example is shown in Fig. 2. Theparticle energy histogram shows the distribution of the particle sizes of the material that has been removed from the annulus 101 and that is lifted with the washing fluid flow 110. This enables the operator (i.e. with a computer) to calculate the amount of material that has been removed and lifted up from the annulus 101 .

[0039] Fig. 3 and Fig. 4 are showing energy histogram and signature log respectively which can be used to compute distribution of the particle sizes of the material that has been removed from the annulus. To distinguish the detected acoustic signals that originates from particles from the noise of the fluid flow, one may use multi-frequency filtering / thresholding. Furthermore, one can advantageously use simultaneous (parallel) processing in both time domain and frequency domain.

[0040] The thick horizontal line in Fig.3 is the flow noise (noise baseline). The acoustic sensor 115 and / or the upper acoustic sensor 117 can preferably be optimized for particle detection. The sensors that are optimized to be used in this application are typically fast response, high frequency sensors.

[0041] As the skilled person will appreciate, when using terms like above and below, or upper and lower, it is referred to the positions along the extension of the well, which may be non-vertical and even horizontal. Hence, the terms above and upper mean closer to the wellhead than the terms below and lower.

[0042] While Fig. 1 depicts a situation where one well pipe (casing) is perforated, there could also be two perforated well pipes such that the washing fluid flows into a first and a second annulus.

[0043] Having described example embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.

Claims

Claims1 . A method of validating a well annulus (101 ) washing operation, comprising the following steps: a) with an annulus washing tool (100) arranged at a perforated section of a well pipe (103), providing a washing fluid flow (110) into the annulus (101 ) of the well pipe; b) with an acoustic sensor (115, 117) arranged inside an inner bore (102) of the well pipe, detecting acoustic signals generated by the washing fluid flow (110).

2. A method according to claim 1 , wherein the acoustic sensor (115) is part of the annulus washing tool (100) and is, during step a), located at the location of the perforations (103a).

3. A method according to claim 1 or claim 2, wherein the acoustic sensor comprises- an upper acoustic sensor (117) being part of the annulus washing tool(100) above wash fluid ports (111 ) of the annulus washing tool; or- an upper acoustic sensor (117) being supported on a string that supports the annulus washing tool (100), at a position above the annulus washing tool; wherein the upper acoustic sensor (117) during step a) is arranged inside the inner bore (102), above the location of the perforations (103a).

4. A method according to one of the preceding claims, comprising c) based on detected acoustic signals, calculating an amount of material(113) that has been washed out of the annulus (101 ) with the washing fluid flow (110).

5. A method according to claim 4, further comprising the following steps: d) calculating an amount of material present in the portion of the annulus(101 ) before the washing operation in step a); e) calculating an annulus wash index by dividing the amount of material(113), as calculated in step c), by the amount of material as calculated in step d).

6. An annulus washing assembly, comprising an annulus washing tool (100) comprising wash fluid ports (111 ) configured to provide a washing fluid flow(110), wherein the annulus washing assembly further comprises an acoustic sensor (115, 117).

7. An annulus washing assembly according to claim 6, wherein the annulus washing tool (100) comprises the acoustic sensor (115).

8. An annulus washing assembly according to claim 6 or claim 7, further comprising an upper acoustic sensor (117) arranged above the wash fluid ports(111 ).

9. An annulus washing assembly according any one of claims 6 to 8, wherein the annulus washing tool (100) further comprising an upper casing bore sealing arrangement (107) and a lower casing bore sealing arrangement (109), wherein the wash fluid ports (111 ) are arranged between the upper and lower casing bore sealing arrangements (107, 109), and wherein the acoustic sensor (115,117) is arranged above the wash fluid ports (111 ).

10. An annulus washing assembly according to any one of claims 6 to 9, wherein the annulus washing assembly comprises or is connected to a computer-readable memory unit or a computing unit programmed to calculate an annulus wash index.

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