Wellbore leakoff agent evaluation method and wellbore seal integrity evaluation device

Abstract

The present application relates to the technical field of oilfield production engineering, and particularly relates to a wellbore plugging agent evaluation method and a wellbore sealing integrity evaluation device. The present application mainly solves the problem that the existing wellbore plugging agent evaluation method cannot evaluate the performance of the plugging agent under the working conditions of high pressure, high CO2 and other acid gas wells. The present application comprises the following steps: selecting a plurality of plugging agents with different formulations according to the working conditions of the experimental area, and respectively performing basic performance testing, injection performance testing, interfacial cementation strength evaluation and corrosion performance evaluation; performing long-term corrosion resistance experiment on the plugging agent; and using the wellbore sealing integrity evaluation device to perform full-size wellbore sealing integrity evaluation experiment on the plugging agent. The wellbore plugging agent evaluation method optimizes different plugging agents through laboratory experiments, and simulates the actual production conditions through full-size experiments, so as to finally screen out the plugging agent that meets the field working conditions, thereby providing guarantee for efficient treatment of gas wells.

Description

Technical Field

[0001] This invention relates to the field of oilfield production technology, specifically to a method for evaluating wellbore plugging agents and a device for evaluating wellbore sealing integrity. Background Technology

[0002] Ensuring the integrity of the gas wellbore is a prerequisite for safe and efficient production. The production casing and cement sheath are critical well barriers. Casing corrosion, perforation, damage, and micro-annular gaps between the casing and cement sheath leading to wellbore leakage will affect the safety of the gas well. When leakage occurs, chemical plugging technology is currently one of the most important methods for wellbore remediation. However, commonly used plugging agents cannot meet the requirements of high-pressure, high-CO2 acid gas conditions in terms of corrosion resistance, plugging strength, gas sealing performance, and shelf life. Therefore, it is necessary to conduct basic performance evaluations of CO2-resistant plugging agents under field operating conditions to provide technical support for the remediation of casing leakage and external flow wells.

[0003] Current evaluation methods for plugging agents include some that measure leakage in fractures and matrix, allowing technicians to better understand the agent's performance, but these methods cannot evaluate the agent's resistance to corrosion by acidic gases such as CO2, nor can they conduct full-scale experiments that simulate field conditions. Other methods can achieve automated quantitative addition of reagents and automatic stirring for simultaneous multi-data measurement, but cannot evaluate the performance of high-performance, high-temperature, and pressure-bearing plugging agents. Some methods can simulate downhole sealing of micro-fractures in the cement sheath, but cannot evaluate the compressive strength of the plugging agent. Still others cannot evaluate the performance of plugging agents with different formulations. In summary, current wellbore plugging agent evaluation methods lack a complete process for indoor experimental selection of plugging agent systems and a method for simulating CO2 corrosion resistance experiments under actual field conditions. This leads to the problem of unsuitable plugging agents being selected in some gas wells with casing and cement sheath leaks, adversely affecting gas well safety management. Summary of the Invention

[0004] To overcome the shortcomings of existing wellbore plugging agent evaluation methods that cannot assess the performance of plugging agents under production conditions of high-pressure, high-CO2, and other acidic gas wells, this invention provides a wellbore plugging agent evaluation method. This method optimizes different plugging agent formulations through laboratory experiments and simulates actual field production conditions through full-scale experiments, ultimately selecting plugging agents that meet the field conditions and providing a guarantee for efficient gas well management.

[0005] The technical solution of this invention is: a method for evaluating wellbore plugging agents, comprising:

[0006] S1. Based on the working conditions of the experimental area, select several different plugging agents and conduct basic performance tests, injection performance tests, interface bonding strength evaluations, and corrosion performance evaluations respectively.

[0007] S2. Conduct a long-term corrosion resistance test on the sealing agent that meets the working conditions of the experimental area as tested in step S1.

[0008] S3. A full-scale wellbore seal integrity evaluation test was conducted on the plugging agent that met the experimental area working conditions as tested in step S2 using a wellbore seal integrity evaluation device.

[0009] Furthermore, the experimental conditions include temperature, pressure, casing perforation width, CO2 content, and formation water properties.

[0010] Furthermore, the long-term corrosion resistance test in step S2 includes CO2 corrosion model test, triaxial stress strength test, elastic modulus test, and permeability test.

[0011] Furthermore, the full-size wellbore seal integrity evaluation experiment in step S3 includes:

[0012] S31. Process several simulated seams on the casing, install the casing liner inside the casing, and assemble the wellbore sealing integrity evaluation device.

[0013] S32. Add cement slurry between the casing and the outer shell, and cure it at the operating temperature.

[0014] S33. Remove the inner liner of the sleeve, add the sealing agent into the sleeve, and make sure the height of the sealing agent is at least 5cm higher than the upper end of the simulated seam. Apply pressure until the sealing agent cures.

[0015] S34. After the sealant has cured, remove any excess sealant from the casing.

[0016] S35. Tighten the flange on the sleeve and fill the sleeve with CO2 gas to the site operating pressure. After the pressure reaches the evaluation pressure, turn off the gas source. If there is no pressure drop within the specified time, it indicates that the plugging agent is qualified. If a pressure drop occurs, re-select a plugging agent suitable for the site operating conditions and repeat steps 1 to 3 until there is no pressure drop.

[0017] Furthermore, the simulated seam is fabricated using a core drilling seam fabrication device.

[0018] Furthermore, in step 32, after the cementing slurry is added to the sealing evaluation device, it is stirred with a glass rod to remove any entrained air.

[0019] Furthermore, in step 32, after the cementing slurry is added to the sealing evaluation device, the cement ring is sealed with plastic wrap and placed in the operating temperature for 3-5 days for curing.

[0020] A wellbore sealing integrity evaluation device according to the wellbore plugging agent evaluation method includes a housing and a casing. The housing is located outside the casing, and a cement ring is filled between the housing and the casing. The casing has several simulated seams, and an upper casing flange and a lower casing flange are respectively provided at the upper and lower ends of the casing. The upper casing flange and the lower casing flange are connected by a tie rod. The upper casing flange has a through hole, and a pressure sensor is connected to the through hole. A gas source interface is connected to the pressure sensor.

[0021] Furthermore, the height of the outer shell and the cement ring is not greater than the height of the sleeve.

[0022] Furthermore, a pressure valve is provided between the pressure sensor and the flange on the sleeve.

[0023] Furthermore, it also includes a casing liner, which is located inside the casing and is removed after the cement sheath has solidified.

[0024] The outer surface of the sleeve liner is provided with a raised ridge corresponding to the simulated seam, and the raised ridge matches the simulated seam.

[0025] This invention has the following beneficial effects: By adopting the above-mentioned scheme, the plugging agent evaluation process simulates actual on-site production conditions, conducts experimental tests on different plugging agent formulations in sequence, clarifies the basic performance and injection performance of plugging agents of different formulation systems, and preliminarily selects plugging agent systems suitable for different environments; CO2 corrosion model tests are carried out based on the selected plugging agent systems to clarify the triaxial stress, elastic modulus, and permeability of the plugging agent; and sealing integrity evaluation experiments are conducted on the selected plugging agents. The full-size, full-process plugging agent evaluation simulates the actual downhole porosity and voids, and the accurate indoor experimental parameters obtained provide accurate plugging agent types for on-site applications, providing technical support for the treatment of gas well casing leakage and external well run-through, achieving the goal of safe, economical, and efficient plugging, and ensuring safe and green production of gas wells. Attached Figure Description

[0026] Figure 1 This is a flowchart of the present invention;

[0027] Figure 2 This is a schematic diagram of the wellbore sealing performance evaluation device in this invention;

[0028] Figure 3 This is the stress-strain curve of the special resin sealing agent before corrosion in the embodiment;

[0029] Figure 4 The stress-strain curve of the special resin sealing agent in the example under 100°C and 40MPa vapor phase corrosion for 15 days is shown.

[0030] Figure 5The stress-strain curve of the special resin sealing agent in the example at 100℃, 40MPa, and liquid phase corrosion for 15 days is shown.

[0031] Figure 6 These are the results of the wellbore sealing performance test.

[0032] In the diagram, 1-Gas source interface, 2-Pressure sensor, 3-Pressure valve, 4-Upper flange of the casing, 5-Outer shell, 6-Cement ring, 7-Casing, 8-Simulated seam, 9-Sealing agent, 10-Inner pipe, 11-Lower flange of the casing, 12-Tie rod. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it is necessary to understand that the orientations or positional relationships indicated by terms such as "upper," "lower," "left," "right," "inner," "outer," "top," and "bottom" are based on the orientations or positional relationships shown in the accompanying drawings. They are intended only to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] Depend on Figure 1 As shown, a method for evaluating wellbore plugging agents includes the following steps:

[0036] S1. Select several different plugging agents based on the working conditions of the experimental area. The working conditions of the experimental area include temperature, pressure, casing hole width, CO2 content, formation water properties, etc. The plugging agents include resin plugging agents and resin cement plugging agents. The selected plugging agents should meet the on-site construction requirements of the experimental area.

[0037] Based on the on-site working conditions, several selected sealing agents were evaluated through experiments. Each sealing agent underwent basic performance testing, injection performance testing, interfacial bonding strength evaluation, and corrosion performance evaluation. To streamline the evaluation process, if the result of one test for a sealing agent did not meet the requirements of the working conditions, the next test was not required. The above test methods are well-known to those skilled in the art and will not be elaborated upon here.

[0038] S2. After basic performance testing, injection performance testing, interfacial bonding strength evaluation, and corrosion performance evaluation, the sealing agents that meet all test requirements are selected for long-term corrosion resistance testing. The long-term corrosion test includes CO2 corrosion model testing, triaxial stress strength testing, elastic modulus testing, and permeability testing. Similarly, if one test result of a sealing agent does not meet the operating conditions, the next test is not required. Likewise, the above test methods are well known to those skilled in the art and will not be described in detail here.

[0039] S3. Using a wellbore sealing integrity evaluation device, conduct a wellbore sealing integrity evaluation experiment on the plugging agent that meets the experimental area working conditions requirements in steps S1 and S2. Holes or cracks are machined on the casing to simulate the downhole casing damage condition. The tested plugging agent is injected into the casing and allowed to enter the simulated holes or cracks. After the plugging agent has solidified, the wellbore sealing integrity evaluation is carried out.

[0040] The full-size wellbore seal integrity evaluation experiment in step S3 includes:

[0041] S31. Prepare the sealant that has been tested in steps S1 and 2;

[0042] Several simulated slots are processed on the casing. The simulated slots can be processed using a core drilling device and can be either slots or holes to simulate the damage condition of the downhole casing.

[0043] A casing liner is installed inside the casing to prevent cement from entering the casing during cement pouring. The outer surface of the casing liner has protruding ridges corresponding to each simulated seam, and the length, width, and height of the protruding ridges match the simulated seams. In this way, when the casing liner is installed on the casing, the protruding ridges enter the simulated seams, temporarily occupying the simulated seams and preventing cement from entering them.

[0044] Assemble the wellbore sealing performance evaluation device by placing the casing and outer shell on the lower flange of the casing; at this time, it is not necessary to connect the upper flange of the casing.

[0045] S32. After mixing the prepared cement slurry evenly, add it to the annular space between the casing and the outer shell. Stir it multiple times with a glass rod to remove any entrained air. Wrap the upper port of the sealing evaluation device with plastic wrap to seal the upper end of the cement ring. Place it in the operating temperature for 3-5 days for curing.

[0046] S33. After the cement curing is completed, remove the inner lining of the casing and add the sealing agent into the casing. The height of the sealing agent should be at least 5cm higher than the upper end of the simulated joint. Apply pressure until the sealing agent cures.

[0047] S34. After the sealant has cured, remove the excess sealant from the casing. When removing the sealant, use micro-grinding to avoid damaging the casing.

[0048] S35. Tighten the flange on the bushing. Slowly or intermittently pressurize the bushing with CO2 gas through the gas source interface to the on-site operating pressure and observe the pressure change. If there is no pressure drop during pressurization, shut off the gas source after pressurizing to the evaluation pressure and observe for any pressure drop for 24 hours. If there is no pressure drop within the specified time, the sealant is qualified; if a pressure drop occurs, reselect a sealant suitable for the on-site operating conditions and repeat steps 1 to 3 until there is no pressure drop.

[0049] This method effectively combines indoor experiments with field conditions, conducting multiple experiments on the plugging agent according to the field conditions. The accurate indoor experimental parameters obtained from the full-size, full-process plugging agent evaluation provide accurate plugging agent types for field applications, providing technical support for the treatment of gas well casing leakage and external well run-through.

[0050] Depend on Figure 2 As shown, the present invention also provides a wellbore sealing integrity evaluation device for a wellbore plugging agent evaluation method, comprising a housing 5 and a casing 7. The casing 7 has several simulated slots 8, which can be slots or holes, and are processed by a core drilling device before device assembly. Both the housing 5 and the casing 7 are fixed to the lower casing flange 11. The housing 5 is located outside the casing 7, and there is an annular cavity between them. During operation, the annular cavity between the housing 5 and the casing 7 is filled with cementing sheath 6. The upper end of the casing 7 is provided with an upper casing flange 4, which is connected to the lower casing flange 11 by a tie rod 12. The tie rod 12 passes through the upper and lower casing flanges and is tightened with a nut to fix the casing 7. To ensure the internal sealing of the casing 7, the height of the housing 5 and the cement sheath 6 should not exceed the height of the casing 7. The flange 4 on the sleeve has a through hole, and a pressure sensor 2 is connected to the through hole. The pressure sensor 2 is connected to the air source interface 1, and a pressure valve 3 is provided between the pressure sensor 2 and the flange 4 on the sleeve.

[0051] The device allows CO2 gas to be injected into the casing 7 via gas source interface 1, and pressure sensor 2 measures the pressure inside the casing, thus simulating operating pressure. This wellbore seal integrity evaluation device also includes a casing liner. During cementing, the casing liner is placed inside the casing 7 to prevent cement from entering gaps during injection. The casing liner is removed after the cement ring 6 has solidified. This wellbore seal integrity evaluation device can simulate downhole casing damage conditions, enabling full-scale, full-process indoor evaluation experiments of plugging agents.

[0052] This plugging agent evaluation process simulates actual on-site production conditions and conducts experimental tests on different plugging agent formulations sequentially. This clarifies the basic performance and injection performance of different formulation systems, and preliminarily selects plugging agent systems suitable for different environments. Based on the selected plugging agent systems, CO2 corrosion model tests are conducted to determine the triaxial stress, elastic modulus, and permeability of the plugging agent. Finally, sealing integrity evaluation experiments are performed on the selected plugging agents. The accurate indoor experimental parameters obtained from the full-scale, full-process plugging agent evaluation provide accurate plugging agent types for on-site applications, offering technical support for the treatment of gas well casing leakage and external well run-through, achieving the goal of safe, economical, and efficient plugging, and ensuring safe and green production of gas wells.

[0053] Example:

[0054] The target well is located in a test area with a bottom hole pressure of 40 MPa, a wellbore temperature of 60-100℃, a CO2 molar content of 5% in the produced gas, and a five-stage completion process. The wellbore diameter is 165.1 mm, the outer diameter of the casing is 139.7 mm, the inner diameter is 121.36 mm, the wellbore-casing clearance is 12.7 mm, and the steel grade is J55.

[0055] Step 1: Based on the site conditions, select several sealant formulations and conduct sealant evaluation and selection experiments. Basic performance tests, injection performance tests, interfacial bonding strength evaluation, and corrosion performance evaluation are conducted for both special resin sealants and resin cement sealants.

[0056] Basic performance tests revealed that the density of the special resin sealant was 1.09 g / cm³. 3 The curing time is 680 minutes, and the viscosity changes to tackiness after 2 hours. It exhibits good injection performance, with an interfacial bonding strength of 21.77 MPa. After a 3-day gas-liquid two-phase corrosion test at 60℃, the sealant sample showed no cracks, pits, or other corrosion marks. The triaxial strength, elastic modulus, and permeability after corrosion met on-site requirements. The density of the resin-cement sealant is 1.81 g / cm³. 3 The thickening time at 60℃ is 260 minutes, and the injection performance is good. The interfacial bonding strength is 5.06MPa. After a gas-liquid two-phase corrosion test at 60℃ for 3 days, the plugging sample is intact with no obvious corrosion marks. The triaxial strength, elastic modulus and permeability after corrosion meet the requirements of the field.

[0057] Step 2: The selected specialty resin sealant and resin cement sealant underwent CO2 corrosion model tests, triaxial stress strength tests, elastic modulus tests, and permeability tests, respectively. The experimental conditions were: temperature 100℃, pressure 40MPa, and time 15 days. Tests showed that the cured body of the specialty resin sealant after corrosion was intact with no obvious corrosion marks. Figure 3 It is the stress-strain curve of the special resin sealant before corrosion. Figure 4This is the stress-strain curve of a special resin sealant after 15 days of vapor phase corrosion, derived from... Figure 4 and Figure 3 The comparison shows that the compressive strength decreases by 5.50% after vapor phase corrosion; Figure 5 It is the stress-strain curve after liquid phase corrosion, from Figure 5 and Figure 3 The comparison shows that the compressive strength decreased by 2.23% after liquid phase corrosion. Tests showed that the elastic modulus increased, and the permeability was almost zero before and after corrosion.

[0058] The resin-cement sealant cured completely without obvious corrosion marks after corrosion. The compressive strength after vapor phase corrosion was 64.6 MPa, and after liquid phase corrosion it was 65.6 MPa, with an increased elastic modulus. The permeability decreased by 27.91% after vapor phase corrosion and increased by 47.98% after liquid phase corrosion. Both sealant formulations met the requirements of the test area.

[0059] Step 3: Conduct high-temperature and high-pressure full-size wellbore seal integrity evaluation experiments on the two types of plugging agents.

[0060] (1) Prepare the test equipment and test materials. According to the on-site working conditions, prepare a sleeve with N80 steel grade, outer diameter 139.7mm, wall thickness 9.17mm, and simulated seam on the sleeve; cement ring thickness 12.7mm.

[0061] (2) The inner lining is installed inside the casing, which is close to the inner wall of the casing and filled with artificial annular seams to prevent cement slurry from flowing into the casing along the leakage channel.

[0062] (3) After the prepared cement slurry is mixed evenly, it is added to the annular space between the outer shell and the casing in the evaluation device. It needs to be stirred multiple times with a glass rod to remove the entrained air.

[0063] (4) Wrap the upper port of the wellbore sealing evaluation device with plastic wrap, seal the cement ring, and place it at 60℃ for 3-5 days for curing.

[0064] (5) Remove the inner lining of the casing, add the prepared sealing agent into the casing, the sealing agent should be about 5cm above the upper end of the annular seam, apply 5MPa pressure and cure at 60℃ for 3-5 days.

[0065] (6) After the sealant has completely solidified, remove the excess sealant material from the casing and perform micro-grinding.

[0066] (7) Tighten the sealing cap at the upper end of the sleeve, and slowly or intermittently purge CO2 gas to 40 MPa, observing the pressure change. No pressure drop was observed during the pressurization process. The pressure was then increased to 40 MPa, the gas source was shut off, and no pressure drop was observed for 24 hours. Figure 6 It can be seen that there is no pressure drop.

[0067] After testing, both types of plugging agents met the requirements of this well.

[0068] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for evaluating wellbore plugging agents, characterized in that... include: S1. Based on the working conditions of the experimental area, select several different plugging agents and conduct basic performance tests, injection performance tests, interface bonding strength evaluations, and corrosion performance evaluations respectively. S2. Conduct a long-term corrosion resistance test on the sealing agent that meets the working conditions of the experimental area as tested in step S1. S3. A full-scale wellbore seal integrity evaluation test was conducted on the plugging agent that met the experimental area working conditions as tested in step S2 using a wellbore seal integrity evaluation device.

2. The wellbore plugging agent evaluation method according to claim 1, characterized in that: The experimental conditions include temperature, pressure, casing slot width, CO2 content, and formation water properties.

3. The method for evaluating wellbore plugging agents according to claim 1, characterized in that: The long-term corrosion resistance test in step S2 includes CO2 corrosion model test, triaxial stress strength test, elastic modulus test, and permeability test.

4. The wellbore plugging agent evaluation method according to claim 1, characterized in that: The full-size wellbore seal integrity evaluation experiment in step S3 includes: S31. Process several simulated seams on the casing, install the casing liner inside the casing, and assemble the wellbore sealing integrity evaluation device. S32. Add cement slurry between the casing and the outer shell, and cure it at the operating temperature. S33. Remove the inner liner of the sleeve, add the sealing agent into the sleeve, and make sure the height of the sealing agent is at least 5cm higher than the upper end of the simulated seam. Apply pressure until the sealing agent cures. S34. After the sealant has cured, remove any excess sealant from the casing. S35. Tighten the flange on the sleeve and fill the sleeve with CO2 gas to the site operating pressure. After the pressure reaches the evaluation pressure, turn off the gas source. If there is no pressure drop within the specified time, it indicates that the plugging agent is qualified. If a pressure drop occurs, re-select a plugging agent suitable for the site operating conditions and repeat steps 1 to 3 until there is no pressure drop.

5. The wellbore plugging agent evaluation method according to claim 4, characterized in that: The simulated seam was fabricated using a core drilling seam fabrication device.

6. The wellbore plugging agent evaluation method according to claim 5, characterized in that: In step 32, after the cementing slurry is added to the sealing evaluation device, it is stirred with a glass rod to remove the entrained air.

7. The wellbore plugging agent evaluation method according to claim 6, characterized in that: In step 32, after the cementing slurry is added to the sealing evaluation device, the cement ring is sealed with plastic wrap and placed in the operating temperature for 3-5 days for curing.

8. A wellbore sealing integrity evaluation device for the wellbore plugging agent evaluation method according to any one of claims 1-7, comprising a housing (5) and a casing (7), characterized in that: The outer shell (5) is located outside the sleeve (7), and a cement ring (6) is filled between the outer shell (5) and the sleeve (7); several simulated slits (8) are opened on the sleeve (7), and the upper and lower ends of the sleeve (7) are respectively provided with an upper flange (4) and a lower flange (11), and the upper flange (4) and the lower flange (11) are connected by a tie rod (12); a through hole is opened on the upper flange (4), and a pressure sensor (2) is connected to the through hole, and an air source interface (1) is connected to the pressure sensor (2).

9. The wellbore sealing integrity evaluation device according to claim 8, characterized in that: The height of the outer shell (5) and the cement ring (6) is not greater than the height of the sleeve (7).

10. The wellbore sealing integrity evaluation device according to claim 8, characterized in that: A pressure valve (3) is provided between the pressure sensor (2) and the flange (4) on the sleeve.

11. The wellbore sealing integrity evaluation device according to claim 8, characterized in that: It also includes the casing liner, which is located inside the casing (7). The casing liner is removed after the cement ring (6) solidifies.

12. The wellbore sealing integrity evaluation device according to claim 11, characterized in that: The outer surface of the inner liner of the sleeve is provided with a protruding ridge corresponding to the simulated seam (8), and the protruding ridge matches the simulated seam (8).

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