Method and system for evaluating the seal integrity of an aquifer reservoir caprock using a cap assembly

Abstract

This invention discloses a method and system for evaluating the sealing performance of caprocks in aquifer reservoirs using a caprock-reservoir assembly. Foamed cement is used to adjust the mix proportions to obtain a transition layer similar in density and porosity to the caprock, serving as a bond between the caprock and reservoir. This system can be applied to caprocks of any lithology, fully considering the initial structural characteristics of the caprock, i.e., using pre-fabricated fractures to fully simulate the complex fractures or faults present in the original caprock. Gas leakage detection of the caprock body is conducted by simulating the cyclic injection and production of gas into the reservoir under simulated formation conditions. Real-time analysis of gas leakage along the caprock body allows for effective evaluation of caprock sealing failures and leakage caused by different types of caprocks and caprocks with different fracture characteristics during the injection and production process of the underlying reservoir. This provides a reference for establishing the upper limit operating pressure of aquifer gas storage facilities with different types of caprocks.

Description

Technical Field

[0001] This invention relates to the field of safe operation technology of aquifer gas storage facilities, and in particular to a method and system for evaluating the sealing performance of the aquifer gas storage cover using a storage cover assembly. Background Technology

[0002] Currently, my country's gas storage facilities are mainly depleted gas reservoirs, supplemented by salt cavern gas storage, but lack aquifer gas storage. However, underground aquifers are widely distributed, offering a larger site selection area compared to depleted gas reservoirs and salt cavern gas storage, and possess enormous development potential. The United States, France, Germany, and Russia have already achieved commercial operation of underground aquifer gas storage facilities, but China lacks the relevant technologies for constructing such facilities. Furthermore, the caprock sealing of aquifer gas storage is a key factor restricting safe construction, achieving full capacity and production, and optimizing injection and production design. Therefore, a method is needed to evaluate the caprock sealing of large-scale aquifer gas storage facilities. Summary of the Invention

[0003] This invention provides a method and system for evaluating the sealing performance of the cap layer of an aquifer reservoir using a cap-storage assembly, which enables the evaluation of the cap layer sealing performance of large-scale aquifer gas storage facilities.

[0004] This invention provides a method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-sump assembly, comprising:

[0005] Foamed cement is used to bond caprock samples and reservoir rock samples together to form a reservoir-caprock sample assembly;

[0006] The reservoir-caprock sample assembly was wrapped with heat shrink tubing and placed in a triaxial loading chamber. The inlet of the gas leak detection device was connected to the caprock sample.

[0007] A confining pressure is applied to the enclosed reservoir-caprock sample assembly, and test gas is introduced into the reservoir-caprock sample. The sealing performance of the caprock is then detected by the gas leakage detection device.

[0008] Specifically, after the formation of the reservoir-caprock sample assemblage, the process further includes:

[0009] The reservoir-caprock sample assembly was placed in a vacuum pressurization saturation device and vacuumed for 18–24 hours. Then, it was saturated in deionized water for 24 hours under a pressure of 10–20 MPa.

[0010] Specifically, after placing the reservoir-caprock sample assembly into a vacuum pressurization saturation device, evacuating for 18–24 hours, and then saturating it in deionized water at 10–20 MPa for 24 hours, the process further includes:

[0011] The water-saturated reservoir-caprock sample assembly was sealed with sealant.

[0012] Specifically, connecting the air inlet of the gas leak detection device to the caprock sample includes:

[0013] The gas inlet of the gas leak detection device is connected to the gas channel in the upper pad block with gas channel on the upper surface of the caprock sample.

[0014] Specifically, it also includes:

[0015] The chain of the lateral displacement measuring sensor is wound around the heat shrink tubing, and the lateral deformation of the reservoir caprock sample assembly is monitored through the lateral displacement measuring sensor;

[0016] The measuring end of the longitudinal displacement measuring sensor is connected to the upper pressure head in the triaxial loading chamber, and the longitudinal deformation of the reservoir caprock sample assembly is monitored through the longitudinal displacement measuring sensor.

[0017] This invention also provides a system for evaluating the sealing performance of aquifer caprock using a caprock assembly, comprising: a caprock sample assembly as described above, a heat shrink tubing, a triaxial loading chamber, a gas leak detection device, a gas storage tank, an extraction component, a first valve, and a second valve; the heat shrink tubing is wrapped around the surface of the caprock sample assembly; the caprock sample assembly is placed in the triaxial loading chamber; the inlet of the extraction component is connected to the outlet of the gas storage tank, and the outlet of the extraction component is connected to a reservoir rock sample within the caprock sample assembly; the first valve is located on a pipeline between the extraction component and the caprock sample assembly; the inlet of the gas leak detection device is connected to a caprock sample within the caprock sample assembly; and the second valve is located on a pipeline between the gas leak detection device and the caprock sample assembly.

[0018] Specifically, it also includes: an upper pad with a gas channel and a lower pad with a gas channel; the upper pad with a gas channel is disposed at the top of the caprock sample in the reservoir-caprock sample assembly; the lower pad with a gas channel is disposed at the bottom of the reservoir sample in the reservoir-caprock sample assembly; the outlet end of the gas extraction component is connected to the gas channel in the lower pad with a gas channel; the inlet end of the gas leakage detection device is connected to the gas channel in the upper pad with a gas channel.

[0019] Specifically, it also includes: lateral displacement measurement sensors and longitudinal displacement measurement sensors;

[0020] The chain of the lateral displacement measuring sensor is in contact with the heat shrink tubing, and the measuring end of the longitudinal displacement measuring sensor is connected to the upper pressure head in the triaxial loading chamber.

[0021] Specifically, it also includes: a pressure gauge; the pressure gauge is placed on the pipeline between the first valve and the reservoir caprock sample assembly.

[0022] Specifically, it also includes: a third valve; the third valve is placed on the bypass between the first valve and the reservoir-caprock sample assembly.

[0023] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0024] Foamed cement is used to adjust the mix ratio to create a transition layer with density and porosity similar to the caprock, serving as a bond between the caprock and reservoir. This method is applicable to caprocks of any lithology, such as mudstone, dolomite, gypsum rock, and limestone, and fully considers the initial structural characteristics of the caprock. Pre-fabricated fractures are used to simulate the complex fractures or faults (such as angle, length, density, and filling characteristics) present in the original caprock. Gas leakage detection of the caprock body is conducted by simulating the cyclic injection and production of gas into the reservoir under simulated formation conditions. Real-time analysis of gas leakage along the caprock body allows for effective evaluation of caprock sealing failures and leakage during injection and production into the underlying reservoir for different types of caprocks and caprocks with varying fracture characteristics. This provides a reference for establishing the upper limit operating pressure of aquifer gas storage facilities with different caprock types.

[0025] Furthermore, the embodiments of the present invention also have the following advantages:

[0026] 1. After the reservoir-caprock sample assembly is formed, it is placed in a vacuum pressurization saturation device and vacuumed for 18 to 24 hours. Then, it is placed in deionized water for 24 hours under 10 to 20 MPa conditions to avoid interference from residual air in the reservoir-caprock sample assembly, thereby ensuring the reliability of the caprock sealing evaluation.

[0027] 2. The reservoir-caprock sample assembly was sealed with sealant to avoid the adverse effects of vertical migration after the reservoir rock sample migrated laterally to the outer end face on the caprock sealing performance evaluation, thus improving the accuracy of the caprock sealing performance evaluation.

[0028] 3. By using lateral displacement measurement sensors and longitudinal displacement measurement sensors, the deformation characteristics of rock samples during gas migration within the reservoir-caprock sample assemblage can be monitored, thereby enabling a better understanding of the causes of changes in caprock sealing. Attached Figure Description

[0029] Figure 1 A flowchart of a method for evaluating the sealing performance of an aquifer reservoir cap using a reservoir cap assembly, provided in an embodiment of the present invention;

[0030] Figure 2This is a schematic diagram of the system for evaluating the sealing performance of an aquifer reservoir cap layer using a reservoir cap assembly, as provided in an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of the structure of the reservoir-caprock sample assembly in an embodiment of the present invention;

[0032] Among them, 1-caprock sample, 2-reservoir rock sample, 3-foamed cement, 4-sealant, 5-heat shrink tubing, 6-triaxial loading chamber, 7-gas leak detection device, 8-lateral displacement measuring sensor, 9-longitudinal displacement measuring sensor, 10-gas storage tank, 11-extraction component, 12-first valve, 13-second valve, 14-upper pad with gas channel, 15-lower pad with gas channel, 16-pressure gauge, 17-third valve, 18-base, 19-upper pressure head, h1-thickness of caprock sample, h2-thickness of reservoir rock sample. Detailed Implementation

[0033] This invention provides a method and system for evaluating the sealing performance of the cap layer of an aquifer reservoir using a cap-storage assembly, which can evaluate the sealing performance of the cap layer of a large-scale aquifer gas storage facility.

[0034] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0035] See Figure 1 The method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly provided in this embodiment of the invention includes:

[0036] Step S110: Use foamed cement 3 to bond caprock sample 1 and reservoir rock sample 2 to form a reservoir-caprock sample assembly;

[0037] To avoid interference from residual air in the reservoir-caprock sample assemblages and thus ensure the reliability of caprock sealing evaluation, the following steps are taken after the reservoir-caprock sample assemblages are formed:

[0038] After determining the length and diameter of the rock samples, the reservoir-caprock rock sample assembly was placed in a vacuum pressurization saturation device and vacuumed for 18–24 hours. Then, it was saturated in deionized water for 24 hours under conditions of 10–20 MPa.

[0039] To avoid the adverse effects of vertical migration of reservoir rock sample 2 after its lateral migration to the outer end face on the caprock sealing evaluation, and to improve the accuracy of the caprock sealing evaluation, after placing the reservoir-caprock sample assembly in a vacuum pressurization saturation device, evacuating for 18–24 hours, and then saturating it in deionized water at 10–20 MPa for 24 hours, the following steps are also included:

[0040] Use sealant 4 to seal the water-saturated reservoir caprock sample assembly.

[0041] Step S120: Wrap the reservoir-caprock sample assembly with heat shrink tubing 5, place it in the triaxial loading chamber 6, and connect the gas inlet of the gas leak detection device 7 to the caprock sample 1.

[0042] Specifically, the gas leak detection device 7 is connected to the gas inlet of the caprock sample 1, including:

[0043] The gas leak detection device 7 is connected to the gas channel in the upper pad 14 with gas channel on the upper surface of the caprock sample 1.

[0044] Step S130: Apply confining pressure to the encased reservoir-caprock sample assembly, introduce test gas into reservoir rock sample 2, and test the sealing performance of the caprock using gas leakage detection device 7.

[0045] To monitor the deformation characteristics of rock samples during gas migration within the reservoir-caprock assemblage, thereby better identifying the causes of changes in caprock sealing, the following measures are also included:

[0046] The chain of the lateral displacement measuring sensor 8 is wrapped around the heat shrink tubing 5, and the lateral deformation of the reservoir caprock sample assembly is monitored through the lateral displacement measuring sensor 8.

[0047] The measuring end of the longitudinal displacement measuring sensor 9 is connected to the upper pressure head 19 in the triaxial loading chamber 6, and the longitudinal deformation of the reservoir caprock sample assembly is monitored through the longitudinal displacement measuring sensor 9.

[0048] In this embodiment, the lateral displacement measuring sensor 8 is a CR108 circumferential gauge from Beijing Zhongchuang, and the longitudinal displacement measuring sensor 9 is a UMD750S sensor from Uniway.

[0049] See Figure 2 The system for evaluating caprock sealing performance using a reservoir-caprock composite core, provided in this embodiment of the invention, includes: a reservoir-caprock sample assembly as described above, a heat-shrink tubing 5, a triaxial loading chamber 6, a gas leak detection device 7, a gas storage tank 10, an extraction component 11, a first valve 12, and a second valve 13; the heat-shrink tubing 5 is wrapped around the surface of the reservoir-caprock sample assembly; the reservoir-caprock sample assembly is placed in the triaxial loading chamber 6; the inlet end of the extraction component 11 is connected to the outlet end of the gas storage tank 10, and the outlet end of the extraction component 11 is connected to the reservoir sample 2 in the reservoir-caprock sample assembly; the first valve 12 is installed on the pipeline between the extraction component 11 and the reservoir-caprock sample assembly; the inlet end of the gas leak detection device 7 is connected to the caprock sample 1 in the reservoir-caprock sample assembly; and the second valve 13 is installed on the pipeline between the gas leak detection device 7 and the reservoir-caprock sample assembly.

[0050] Specifically, the reservoir-caprock sample assembly is placed on base 18 in triaxial loading chamber 6.

[0051] The structure of the system for evaluating caprock sealing performance using reservoir-caprock composite core samples provided in this embodiment of the invention is described in detail. It further includes: an upper pad 14 with gas channels and a lower pad 15 with gas channels; the upper pad 14 with gas channels is disposed at the top of caprock sample 1 in the reservoir-caprock composite; the end face of the upper pad 14 with gas channels contacts the top of caprock sample 1; the lower pad 15 with gas channels is disposed at the bottom of reservoir sample 2 in the reservoir-caprock composite; the outlet end of the extraction component 11 is connected to the gas channel in the lower pad 15 with gas channels; and the inlet end of the gas leakage detection device 7 is connected to the gas channel in the upper pad 14 with gas channels.

[0052] In order to monitor the deformation characteristics of rock samples during the migration of gas within the reservoir-caprock sample assemblages, and thus better identify the causes of changes in caprock sealing, the system also includes: a lateral displacement measurement sensor 8 and a longitudinal displacement measurement sensor 9.

[0053] The chain of the lateral displacement measuring sensor 8 is in contact with the heat shrink tubing 5, and the measuring end of the longitudinal displacement measuring sensor 9 is connected to the upper pressure head 19 in the triaxial loading chamber 6.

[0054] In this embodiment, the lateral displacement measuring sensor 8 is a CR108 circumferential gauge from Beijing Zhongchuang, and the longitudinal displacement measuring sensor 9 is a UMD750S sensor from Uniway.

[0055] In order to monitor the gas pressure changes at the reservoir injection end in real time and adjust the injection and production rate of the aquifer gas storage tank, a pressure gauge 16 is also included; the pressure gauge 16 is placed on the pipeline between the first valve 12 and the reservoir caprock sample assembly.

[0056] The structure of the system for evaluating caprock sealing performance using reservoir-caprock composite cores provided in this embodiment of the invention is further described, including: a third valve 17; the third valve 17 is placed on the bypass between the first valve 12 and the reservoir-caprock composite.

[0057] In this embodiment, the gas storage tank 10 is a nitrogen cylinder, and the gas extraction component 11 is an ISCO constant speed and constant pressure pump.

[0058] The steps for evaluating the caprock sealing performance during repeated injection and production in an aquifer gas storage facility according to embodiments of the present invention are as follows:

[0059] Step 1: For a specific aquifer gas storage facility, obtain basic parameters such as the density, porosity, compressive strength, and tensile strength of the caprock of the gas storage geological body, and based on these parameters, prepare foamed cement 3 with similar density and porosity characteristics to the caprock of the gas storage facility.

[0060] Step 2: Based on the site-scale caprock thickness (a), reservoir thickness (b), and physical properties obtained from drilling core samples, cylindrical caprock sample 1 and reservoir sample 2 are cut from the core samples. Similar reservoir-caprock composite cores are fabricated in the laboratory according to proportional relationships. The caprock sample thickness h1 is designed to be 100a / (a+b), and the reservoir sample thickness h2 is 100b / (a+b). The reservoir and caprock samples are processed into cylinders with a diameter of 50mm. 5mm thick foamed cement 3 is used to bond caprock sample 1 and reservoir sample 2, equivalent to an actual caprock thickness of 100a / (a+b)-5, simulating the original formation's reservoir-caprock composite relationship. The resulting reservoir-caprock composite is shown below. Figure 3 As shown, Type I indicates that there are no obvious fissures in the caprock sample 1. The caprock sample 1 can be salt rock, gypsum salt, carbonate rock, mudstone, etc. Type II indicates that the caprock sample 1 contains obvious fissures or microfissures.

[0061] Step 3: Place the reservoir caprock sample assembly bonded by the above-mentioned foamed cement 3 into a vacuum pressurization saturation device, vacuum for 18-24 hours, and saturate in deionized water at a pressure of 10-20 MPa for 24 hours.

[0062] Step 4: After the water-saturated reservoir-caprock sample assembly is sealed with sealant 4, it is further wrapped with heat shrink tubing 5 and placed in the triaxial loading chamber 6. A lateral displacement measuring sensor 8 and a longitudinal displacement measuring sensor 9 are connected to the end of the caprock sample 1 and the end of the reservoir rock sample 2, respectively.

[0063] Step 5: Apply a specific confining pressure to the reservoir-caprock sample assembly based on the actual formation stress conditions of the gas storage facility. After the confining pressure stabilizes, use an ISCO constant-speed, constant-pressure pump to inject nitrogen from the nitrogen cylinder into the lower reservoir rock sample 2 through the injection port. Continue injecting nitrogen until the pressure indicated by the ISCO constant-speed, constant-pressure pump reaches 50% of the tensile strength of reservoir rock sample 2. Stabilize the pressure for 2 hours, then stop injecting nitrogen and close the first valve 12.

[0064] Step 6: Turn on the gas leak detection device 7 and measure the concentration of injected gas in the sealed space inside the upper pad 14 with gas channel on the upper part of the caprock sample 1 in real time within 24 hours. This will give you the leakage situation caused by the injected gas in the reservoir sample 2 moving along the caprock sample 1.

[0065] Step 7: In step 5, increase the injection pressure of the ISCO constant speed and pressure pump to 60% of the tensile strength of reservoir rock sample 2, continue the experiment, and use the gas leakage detection device 7 to measure the gas concentration in the sealed space of the central hole of the upper pad block 14 with gas channel, and measure the gas leakage in real time over 24 hours.

[0066] Step 8: In step 5, continue to increase the injection pressure of the ISCO constant speed and constant pressure pump to reach 80% of the tensile strength of reservoir rock sample 2. Continue the above experiment and use the gas leakage detection device 7 to determine the gas leakage that occurs along the caprock sample 1.

[0067] Step 9: If no gas leakage occurs along the caprock sample 1 within 24 hours as described in Step 8, open the third valve 17 to vent the reservoir sample 2. Then, after 10 cycles of gas injection and production, repeat Steps 5 to 8 to test the gas tightness of the caprock.

[0068] Step 10: Repeat step 9, continuously increasing the number of injection and extraction cycles to 20, 30, 40, 50, etc., until the gas leakage detection device 7 detects gas leakage in the caprock sample 1 and the leakage rate is high.

[0069] The embodiments of the present invention can effectively evaluate the evolution of the sealing performance of caprocks with different configurations during repeated gas injection and production in aquifer gas storage facilities.

[0070] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0071] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly, characterized in that, include: Foamed cement is used to bond caprock samples and reservoir rock samples together to form a reservoir-caprock sample assembly; The reservoir-caprock sample assembly was wrapped with heat shrink tubing and placed in a triaxial loading chamber. The inlet of the gas leak detection device was connected to the caprock sample. A confining pressure is applied to the encapsulated reservoir rock sample assembly, test gas is introduced into the reservoir rock sample, and the sealing performance of the caprock is detected by the gas leakage detection device.

2. The method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 1, characterized in that, Following the formation of the reservoir-caprock sample assemblage, the process further includes: The reservoir-caprock sample assembly was placed in a vacuum pressurization and saturation device and vacuumed for 18-24 hours. Then, it was saturated in deionized water for 24 hours under 10-20 MPa conditions.

3. The method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 2, characterized in that, After placing the reservoir-caprock sample assembly into a vacuum pressurization saturation device, evacuating for 18-24 hours, and then saturating it in deionized water at 10-20 MPa for 24 hours, the process further includes: The water-saturated reservoir-caprock sample assembly was sealed with sealant.

4. The method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 1, characterized in that, Connecting the gas leak detection device's inlet to the caprock sample includes: The gas inlet of the gas leak detection device is connected to the gas channel in the upper pad block with gas channel on the upper surface of the caprock sample.

5. The method for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 1, characterized in that, Also includes: The chain of the lateral displacement measuring sensor is wound around the heat shrink tubing, and the lateral deformation of the reservoir caprock sample assembly is monitored through the lateral displacement measuring sensor; The measuring end of the longitudinal displacement measuring sensor is connected to the upper pressure head in the triaxial loading chamber, and the longitudinal deformation of the reservoir caprock sample assembly is monitored through the longitudinal displacement measuring sensor.

6. A system for evaluating the sealing performance of an aquifer reservoir cap layer using a reservoir-cap assembly, said system being implemented based on the method for evaluating the sealing performance of an aquifer reservoir cap layer using a reservoir-cap assembly as described in any one of claims 1-5, characterized in that, include: The system comprises a heat shrink tubing, a triaxial loading chamber, a gas leak detection device, a gas storage tank, an extraction component, a first valve, a second valve, and a reservoir-caprock sample assembly. The heat shrink tubing is wrapped around the surface of the reservoir-caprock sample assembly. The reservoir-caprock sample assembly is placed in the triaxial loading chamber. The inlet of the extraction component is connected to the outlet of the gas storage tank, and the outlet of the extraction component leads to the reservoir rock sample in the reservoir-caprock sample assembly. The first valve is located on the pipeline between the extraction component and the reservoir-caprock sample assembly. The inlet of the gas leak detection device leads to the caprock sample in the reservoir-caprock sample assembly. The second valve is located on the pipeline between the gas leak detection device and the reservoir-caprock sample assembly.

7. The system for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 6, characterized in that, Also includes: An upper pad with a gas channel and a lower pad with a gas channel; the upper pad with a gas channel is disposed at the top of the caprock sample in the reservoir-caprock sample assembly; the lower pad with a gas channel is disposed at the bottom of the reservoir sample in the reservoir-caprock sample assembly; the outlet end of the gas extraction component is connected to the gas channel in the lower pad with a gas channel; the inlet end of the gas leakage detection device is connected to the gas channel in the upper pad with a gas channel.

8. The system for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 6, characterized in that, Also includes: Lateral displacement measurement sensor and longitudinal displacement measurement sensor; The chain of the lateral displacement measuring sensor is in contact with the heat shrink tubing, and the measuring end of the longitudinal displacement measuring sensor is connected to the upper pressure head in the triaxial loading chamber.

9. The system for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 6, characterized in that, Also includes: Pressure gauge; the pressure gauge is placed on the pipeline between the first valve and the reservoir caprock sample assembly.

10. The system for evaluating the sealing performance of an aquifer reservoir cap layer using a cap-storage assembly as described in claim 6, characterized in that, Also includes: The third valve is placed on the bypass between the first valve and the reservoir-caprock sample assembly.

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