Evaluation method for water-bearing trap reconstruction gas storage in faulted basin

Abstract

The application provides a method for evaluating reconstruction of a water-bearing trap in a faulted basin, comprising the following steps: step 1, establishing a static sealing evaluation system of the water-bearing trap in the faulted basin; step 2, testing triaxial peak compressive strength of the cap rock to determine upper and lower limit points of the alternating stress; step 3, carrying out a dynamic breakthrough pressure test of the target trap cap rock to establish a curve relationship between the dynamic breakthrough pressure of the cap rock and the alternating number; step 4, carrying out a fatigue failure test of the target trap cap rock to establish a curve relationship between the fatigue failure of the cap rock and the alternating number; step 5, evaluating the dynamic sealing property of the cap rock; and step 6, establishing a finite element analysis model to obtain the upper limit injection pressure of the water-bearing trap in the faulted basin. The method for evaluating reconstruction of the water-bearing trap in the faulted basin can predict the upper limit injection pressure of the water-bearing trap, has strong applicability, and provides a set of scientific and reasonable technical methods for reconstruction of the water-bearing trap in the faulted basin.

Description

Technical Field

[0001] This invention relates to the technical field of natural gas resource exploration and development, and in particular to an evaluation method for converting water-bearing traps in rift basins into gas storage facilities. Background Technology

[0002] Natural gas, as a highly efficient and clean energy source, has been widely used in both residential and numerous industrial sectors due to its economic and environmental benefits. The consumption of natural gas in cities and other industrial sectors often exhibits significant peaks due to seasonal variations. Because of its irreplaceable role in peak shaving and ensuring gas supply security, the construction of underground gas storage facilities has gradually gained increasing attention from more and more countries.

[0003] my country's oil and gas reservoirs are mainly concentrated in continental strata, and their scale is relatively small. This limits the potential for constructing underground gas storage facilities from depleted oil and gas reservoirs. However, constructing natural gas storage facilities by finding aquifer traps in rift basins holds promise for establishing large-scale underground natural gas storage facilities. Especially in the centers of large industrial cities and near major cities, not all depleted oil and gas fields are suitable for underground gas storage construction, but aquifer structures can always be found. In such cases, converting existing aquifer traps in rift basins into underground gas storage facilities becomes the preferred solution.

[0004] Current research indicates that converting aquifer traps in rift basins into underground gas storage facilities is more challenging and risky than constructing facilities from depleted gas reservoirs, both in terms of technical difficulty, risk, construction period, and investment. Constructing aquifer gas storage facilities is a comprehensive and complex systems engineering project. Not only is site selection constrained by many factors, but a scientific, rational, and effective suitability evaluation of the target trap for aquifer gas storage conversion, as well as the prediction of dynamic sealing performance and upper limit injection pressure, are essential. However, existing technologies lack a practical and effective method for screening and evaluating aquifer trap gas storage facilities in rift basins.

[0005] Chinese patent application CN201710981250.1 discloses a method for evaluating the sealing performance of a lithologic gas reservoir. The method includes the following steps: evaluating the sealing performance of the cover plate and bottom plate by first evaluating the macroscopic sealing performance of the cover plate and bottom plate, and then evaluating the microscopic sealing performance of the cover plate and bottom plate; evaluating the sealing performance of the lateral boundaries by first evaluating the microscopic sealing performance of the lateral boundaries, then evaluating the spatial morphology of the lateral boundaries, and finally evaluating the dynamic performance of the lateral boundaries; and verifying the overall sealing capability of the gas reservoir.

[0006] Chinese patent application CN201910641325.0 discloses a logging evaluation method for fault sealing. This method includes: selecting typical reference wells in the hanging wall and footwall of the fault to be evaluated; using the DC index to characterize the pressure properties of the two sides of the fault; using gas logging interpretation results to characterize the fluid properties of the two sides of the fault; establishing an evaluation index formula; and evaluating the fault sealing.

[0007] Chinese patent application number CN201610390275.X discloses a dynamic evaluation method for gas injection well control in a gas storage facility. This method includes: a derivation step: deriving a dimensionless gas injection rate decline model; a modeling step: establishing a theoretical model of gas injection rate based on the dimensionless gas injection rate decline model; a graphing step: introducing a normalized pseudo-pressure function and a material balance pseudo-time function, and establishing a theoretical graph of dimensionless gas injection rate versus material balance pseudo-time based on the gas injection rate theoretical model; a curve fitting step: obtaining a curve showing the relationship between dimensionless gas injection rate and material balance pseudo-time, and matching the fitted curve with the dimensionless gas injection rate relationship curve and the theoretical graph of dimensionless gas injection rate versus material balance pseudo-time; and a calculation step: calculating the storage and permeability parameters during the gas injection process of the gas well.

[0008] The existing technologies described above are significantly different from the present invention and have failed to solve the technical problem we want to address. Therefore, we have invented a new evaluation method for the reconstruction of water-bearing traps and gas storage facilities in rift basins. Summary of the Invention

[0009] The purpose of this invention is to provide a scientific and reasonable evaluation method for converting water-bearing traps into gas storage facilities in rift basins, which predicts the upper limit injection pressure of water-bearing traps, has strong applicability, and provides a complete set of scientific and reasonable technologies for the conversion of water-bearing traps into gas storage facilities in rift basins.

[0010] The objective of this invention can be achieved through the following technical measures: an evaluation method for converting water-bearing traps in rift basins into gas storage facilities, comprising:

[0011] Step 1: Establish a static sealing performance evaluation system for water-bearing traps in rift basins;

[0012] Step 2: Determine the triaxial peak compressive strength of the caprock to identify the upper and lower limits of the alternating stress.

[0013] Step 3: Conduct dynamic breakthrough pressure tests on the caprock of the target trap and establish the curve relationship between the dynamic breakthrough pressure of the caprock and the number of cycles.

[0014] Step 4: Conduct fatigue failure tests on the target trap caprock and establish the curve relationship between fatigue failure of the caprock and the number of cycles.

[0015] Step 5: Evaluate the dynamic sealing performance of the cap layer;

[0016] Step 6: Establish a finite element analysis model to obtain the upper limit injection pressure of the water-bearing trap in the rift basin.

[0017] The objective of this invention can also be achieved through the following technical measures:

[0018] In step 1, based on existing experience in gas storage construction and relevant expert advice, combined with geological data, field exploration results, and seismic logging interpretations, the suitability of various technical indicators for favorable traps in rift basins is obtained. The weights of the indicators are determined by the analytic hierarchy process (AHP), and a static sealing performance evaluation system for water-bearing traps in rift basins is established.

[0019] In step 1, the technical indicators include: number of caprock layers, caprock breakthrough pressure, caprock strength, caprock lithology, closure height, trap type, trap burial depth, trap geostress, trap stability, hydrodynamic conditions, reservoir suitability, gas storage capacity, caprock permeability, aquifer permeability, and aquifer porosity.

[0020] In step 1, the gas storage capacity is calculated using the following formula:

[0021] ;

[0022] In the formula, Q is the storage capacity of the gas storage facility, V is the aquifer trap volume, T0 is the temperature of natural gas under standard conditions, T is the aquifer temperature, P0 is the surface standard pressure, Z is the natural gas deviation coefficient, and Pmop is the upper limit pressure of the gas storage facility converted from an aquifer trap in a rift basin.

[0023] In step 1, the trap type is an anticline structure; the structural closure degree of the trap is greater than or equal to 100 meters; the burial depth of the trap is within the range of 250 meters to 3500 meters; the geostress coefficient of the trap should be between 0.55 and 1.3; and the stability of the trap should be such that no major geological disasters occur or may occur.

[0024] In step 1, the caprock is argillaceous rock or evaporite; the caprock breakthrough pressure is greater than or equal to 1 MPa; the caprock permeability should be less than 0.1 millidarcy; the aquifer net thickness is greater than or equal to 10 meters; the aquifer porosity is greater than or equal to 5%; and the aquifer permeability is greater than or equal to 10 millidarcy.

[0025] In step 1, the hydrodynamic conditions are selected for traps with unclosed boundaries and large water volume; the well density should be no more than 20 abandoned old wells.

[0026] In step 1, when using the analytic hierarchy process (AHP) to determine the weights of the indicators, the conversion of water-bearing traps in rift basins into gas storage facilities is taken as the target layer, the trap sealing performance, structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale and technical feasibility are taken as the criteria layer, and the technical indicators are taken as the evaluation layer. The AHP is then used to determine the weight values ​​of each technical indicator.

[0027] In step 1, the overall suitability for converting a water-bearing trap in a rift basin into a gas storage facility is calculated using the following formula:

[0028] ;

[0029] In the formula, M represents the overall suitability for constructing a gas storage site in an aquifer. For the first The weight values ​​corresponding to the technical indicators For the first The suitability of the technical indicators.

[0030] In step 2, based on the evaluation results of step 1, the triaxial peak compressive strength of the caprock is determined by taking geological core samples on site and using a rock triaxial mechanical testing machine while keeping the confining pressure constant, thereby determining the upper and lower limits of the alternating stress.

[0031] In step 3, based on the gas storage injection and production years, the number of alternations is determined, and a gas breakthrough pressure tester is used to conduct a dynamic breakthrough pressure test on the target trap caprock, establishing a curve relationship between the dynamic breakthrough pressure of the caprock rock and the number of alternations.

[0032] In step 3, the dynamic breakthrough pressure test of the caprock includes the following steps:

[0033] S31. Based on the core sampling depth at the site, prepare rock samples with a size of 25×50mm;

[0034] S32. With a pressure gradient of 0.0226 MPa / m, calculate the confining pressure under the fault burial depth condition, i.e.:

[0035] ;

[0036] In the formula, d is the depth of the stratum where the core is located, in meters;

[0037] S33. Apply confining pressure at a constant rate to a predetermined value and test the initial breakthrough pressure value of the specimen;

[0038] S34. Using a triaxial rock testing machine with a loading rate of 0.001 mm / s, determine the peak compressive strength of the caprock. MPa;

[0039] S35. Take 0.1 times the peak compressive strength of the rock. As the lower limit point, respectively with 0.6 With 0.8 The upper limit point;

[0040] S36. Keep the confining pressure constant, starting from the minimum load (i.e., the origin), repeatedly apply cyclic loads at a loading rate of 1 kN / s, and conduct breakthrough pressure tests at 0, 15, 30, 45, and 60 cycles respectively to obtain the dynamic breakthrough pressure changes of the target trap caprock.

[0041] In step 4, a triaxial rock testing machine is used to determine the number of alternation cycles based on the gas storage injection and production years, and fatigue failure tests are conducted on the caprock of the target trap to establish the curve relationship between the fatigue failure of the caprock and the number of alternation cycles.

[0042] In step 4, the fatigue failure test includes the following steps:

[0043] S41. Based on the core samples taken from the overlying rocks at the site, prepare core samples with a size of 50×100mm;

[0044] S42. Select rock core samples and use a rock mechanics testing machine to perform uniaxial compressive strength loading at a loading rate of 0.001 mm / s to determine the uniaxial compressive strength P of the caprock.

[0045] S43. Rock alternating mechanics tests were conducted with upper limit loads of 0.5P, 0.6P, and 0.7P and a lower limit load of 0.1P, respectively, and the number of cyclic loading cycles were selected as 20, 40, and 60 cycles, respectively.

[0046] S44. After the cyclic loading is completed, the displacement control loading is carried out at a rate of 0.001 mm / s until failure.

[0047] In step 5, the dynamic sealing performance of the caprock is evaluated by combining the test results from steps 3 and 4 and using the rock fatigue failure criterion and the dynamic breakthrough pressure variation relationship of the caprock.

[0048] In step 6, a finite element analysis model is established based on the on-site seismic exploration data. According to the Mohr-Coulomb shear failure criterion, tensile failure criterion, rock fatigue failure criterion and capillary sealing mechanism, the upper limit injection pressure of the water-bearing trap in the rift basin is obtained.

[0049] In step 6, when shear failure occurs at the weak cemented surface of the gas storage surrounding rock, the Mohr-Coulomb shear failure criterion is applied; when tensile stress occurs in the gas storage surrounding rock, the tensile failure criterion is applied; when judging the dynamic sealing capacity of the caprock, the capillary sealing mechanism is applied; and when judging the change in the dynamic sealing capacity of the caprock, the fatigue failure criterion is applied.

[0050] In step 6, the upper limit injection pressure of the converted gas storage facility from a water-bearing trap in the rift basin is calculated using the following formula:

[0051] S61. The capillary closure mechanism is used as a prerequisite for predicting the upper limit injection pressure.

[0052] S62. The maximum operating pressure during the gas storage injection and production process is obtained by adopting the Mohr-Coulomb shear failure criterion.

[0053] S63. Using the tensile failure criterion, the minimum horizontal principal stress of the gas storage tank during the injection and production process is obtained;

[0054] S64. Calculate using the upper limit pressure formula, that is:

[0055] ;

[0056] In the formula, Inject pressure to the upper limit of the gas storage facility for the conversion of water-bearing traps in rift basins. This refers to the pore pressure of the formation above the caprock. To enable the caprock to dynamically overcome pressure, For the minimum horizontal principal stress of the cap layer, It is obtained through capillary pressure and injection pore pressure. It is obtained based on the minimum horizontal principal stress, and finally based on Get the upper limit of injection pressure.

[0057] The evaluation method for converting water-bearing traps into gas storage facilities in rift basins according to this invention includes: establishing a static evaluation system for the geological sealing performance of water-bearing traps in rift basins; obtaining the suitability of various technical indicators corresponding to favorable traps in rift basins based on trap sealing performance, trap structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale, and technical feasibility; determining the weight values ​​of each technical indicator using the analytic hierarchy process (AHP); obtaining the comprehensive storage suitability of favorable traps based on the suitability of each technical indicator and the weight values ​​of each indicator; obtaining the evaluation results based on a pre-set suitability level table for converting water-bearing traps into gas storage facilities in rift basins; conducting alternating permeability breakthrough pressure tests and fatigue failure tests on the caprock of favorable traps to evaluate the dynamic sealing performance of the caprock; and using finite element software for numerical simulation, combined with the Mohr-Coulomb failure criterion and tensile failure criterion to predict the upper limit injection pressure of the water-bearing trap. This invention establishes a geological static sealing evaluation system for converting water-bearing traps into gas storage facilities in rift basins, clarifies the dynamic sealing test method and principle of favorable trap caprock, and predicts the upper limit injection pressure of water-bearing traps. It has strong applicability and provides a complete set of scientific and reasonable technical methods for converting water-bearing traps into gas storage facilities in rift basins.

[0058] The evaluation method for converting water-bearing traps into gas storage facilities in rift basins, as described in this invention, compared to existing technologies, employs a measurable geological static sealing evaluation system, incorporates dynamic sealing tests during experimental operations, and utilizes numerical simulation prediction technology. This makes the evaluation of converted gas storage facilities more scientific and effective, providing a scientific and reasonable technical method for the exploration and construction of converted water-bearing trap gas storage facilities in rift basins. Attached Figure Description

[0059] Figure 1 A flowchart of a specific embodiment of the evaluation method for converting water-bearing traps in rift basins into gas storage facilities according to the present invention;

[0060] Figure 2 This is a hierarchical structure diagram of evaluation indicators for the reconstruction of a water-bearing trap gas storage facility in a rift basin, as described in a specific embodiment of the present invention.

[0061] Figure 3 This is a schematic diagram of the dynamic breakthrough pressure test loading method for caprock in a specific embodiment of the present invention;

[0062] Figure 4 This is a graph showing the relationship between the dynamic breakthrough pressure value of the cap layer and the number of alternation cycles in a specific embodiment of the present invention;

[0063] Figure 5 This is a schematic diagram of a loading method for fatigue failure testing of caprock in a specific embodiment of the present invention;

[0064] Figure 6 This is a graph showing the relationship between fatigue life and number of alternation cycles in a specific embodiment of the present invention.

[0065] Figure 7 This is a finite element geomechanical analysis model diagram in a specific embodiment of the present invention;

[0066] Figure 8 This is a structural diagram of the concentrated section of the Guantao Formation reservoir in the Xia 552 well area, according to a specific embodiment of the present invention.

[0067] Figure 9 This is a static breakthrough pressure test curve of the cap layer in a specific embodiment of the present invention;

[0068] Figure 10 This is a location map of Dongying City on the world geostress map, according to a specific embodiment of the present invention.

[0069] Figure 11 This is a partial enlarged view of Dongying City and a schematic diagram illustrating the meaning of the icons in a specific embodiment of the present invention;

[0070] Figure 12 This is a schematic diagram of a dynamic breakthrough pressure test of the cover layer with an alternating amplitude of 70% in a specific embodiment of the present invention;

[0071] Figure 13 This is a schematic diagram of peak intensity-alternation number in a specific embodiment of the present invention;

[0072] Figure 14 This is a schematic diagram of fatigue life in a specific embodiment of the present invention;

[0073] Figure 15 This is a structural diagram of well T1 in Xia 552 well area according to a specific embodiment of the present invention;

[0074] Figure 16 This is a schematic diagram of the basic geometric dimensions of Xia 552 in a specific embodiment of the present invention;

[0075] Figure 17 This is a schematic diagram of the Xia 552 finite element calculation model in a specific embodiment of the present invention;

[0076] Figure 18 This is a diagram showing the variation of the stress moiré circle in a specific embodiment of the present invention;

[0077] Figure 19 This is a minimum principal stress cloud diagram of the cap layer in a specific embodiment of the present invention;

[0078] Figure 20 This is a schematic diagram of the minimum principal compressive stress at the reservoir-capsule interface in a specific embodiment of the present invention;

[0079] Figure 21 This is a schematic diagram of the minimum principal compressive stress in a specific embodiment of the present invention. Detailed Implementation

[0080] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0081] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0082] like Figure 1 As shown, Figure 1 This is a flowchart of the evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin, according to the present invention. The evaluation method includes the following steps:

[0083] S1. Based on existing experience in gas storage construction and relevant expert advice, combined with geological data, field exploration results, and seismic logging interpretation, the suitability of various technical indicators corresponding to favorable traps in rift basins is obtained. The analytic hierarchy process is used to determine the weights of the indicators, and a static geological sealing evaluation system for water-bearing traps in rift basins is established. Figure 2 (as shown)

[0084] Technical indicators include: number of caprock layers, caprock breakthrough pressure, caprock strength, caprock lithology, closure height, burial depth, hydrodynamic conditions, reservoir suitability, gas storage capacity, caprock permeability, aquifer permeability, and aquifer porosity.

[0085] The storage capacity of the gas storage facility is calculated using the following formula:

[0086] ;

[0087] In the formula, Q is the storage capacity of the gas storage facility, V is the closed volume of the aquifer, T0 is the temperature of natural gas under standard conditions, T is the temperature of the aquifer, P0 is the standard surface pressure, and Z is the natural gas deviation coefficient.

[0088] The trap type is an anticline structure;

[0089] The structural closure degree of the trap is greater than or equal to 100 meters;

[0090] The burial depth of the trap is in the range of 250 meters to 3500 meters.

[0091] The caprock is composed of argillaceous rock or evaporite;

[0092] The breakthrough pressure of the cap layer is greater than or equal to 1 MPa;

[0093] The permeability of the caprock should be less than 0.1 millidarcy.

[0094] The net thickness of the aquifer is greater than or equal to 10 meters;

[0095] The porosity of the aquifer is greater than or equal to 5%;

[0096] The aquifer permeability is greater than or equal to 10 millidarcy.

[0097] The hydrodynamic conditions should be selected as close as possible to traps with open boundaries and large water volumes.

[0098] The stress coefficient of the trap should be between 0.55 and 1.3;

[0099] The stability of the trap should be such that no major geological disasters occur or may occur;

[0100] The well density should be such that no more than 20 abandoned old wells are present.

[0101] The method of determining the weights of each technical indicator using the analytic hierarchy process includes:

[0102] The conversion of water-bearing traps in rift basins into gas storage facilities is taken as the target layer, while the trap sealing performance, structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale, and technical feasibility are taken as the criteria layer, and technical indicators are taken as the evaluation layer. The weight values ​​of each technical indicator are determined by the analytic hierarchy process.

[0103] The overall suitability for converting a water-bearing trap in a rift basin into a gas storage facility is calculated using the following formula:

[0104] ;

[0105] In the formula, M represents the overall suitability for constructing a gas storage site in an aquifer. For the first The weight values ​​corresponding to the technical indicators For the first The suitability of the technical indicators.

[0106] S2. Based on the above assessment results, the triaxial peak compressive strength of the caprock was determined by taking geological core samples on site and using a rock triaxial mechanical testing machine while maintaining constant confining pressure, so as to determine the upper and lower limits of alternating stress.

[0107] S3. Based on the gas storage injection and production years, determine the number of alternation cycles, and use a gas breakthrough pressure tester to conduct dynamic breakthrough pressure tests on the target trap caprock, establishing a curve relationship between the dynamic breakthrough pressure of the caprock rock and the number of alternation cycles. Figure 3 (as shown)

[0108] like Figure 4 As shown, the dynamic breakthrough pressure test steps for the caprock include:

[0109] S31. Based on the core sampling depth at the site, prepare rock samples with a size of 25×50mm;

[0110] S32. According to standard SY / T5815-2016, with a pressure gradient of 0.0226 MPa / m, calculate the confining pressure under the fault burial depth condition, i.e.:

[0111] ;

[0112] In the formula, d is the depth of the stratum where the core is located, in meters;

[0113] S33. Apply confining pressure at a constant rate to a predetermined value and test the initial breakthrough pressure value of the specimen;

[0114] S34. Using a triaxial rock testing machine with a loading rate of 0.001 mm / s, determine the peak compressive strength of the caprock. MPa;

[0115] S35. Take 0.1 times the peak compressive strength of the rock. As the lower limit point, respectively with 0.6 With 0.8 The upper limit point;

[0116] S36. Keep the confining pressure constant, starting from the minimum load (i.e., the origin), repeatedly apply cyclic loads at a loading rate of 1 kN / s, and conduct breakthrough pressure tests (upper limit point tests) at 0, 15, 30, 45, and 60 cycles respectively to obtain the dynamic breakthrough pressure changes of the target trap caprock.

[0117] S4. Using a triaxial rock testing machine, based on the gas storage injection and production years, determine the number of alternation cycles, conduct fatigue failure tests on the caprock of the target trap, and establish the curve relationship between the fatigue failure of the caprock and the number of alternation cycles. Figure 5 (as shown)

[0118] like Figure 6 As shown, the fatigue failure test steps include:

[0119] S41. Based on the core samples taken from the overlying rocks at the site, prepare core samples with a size of 50×100mm;

[0120] S42. Select rock core samples and use a rock mechanics testing machine to perform uniaxial compressive strength loading at a loading rate of 0.001 mm / s to determine the uniaxial compressive strength P of the caprock.

[0121] S43. Rock alternating mechanics tests were conducted with upper limit loads of 0.5P, 0.6P, and 0.7P and a lower limit load of 0.1P, respectively, and the number of cyclic loading cycles were selected as 20, 40, and 60 cycles, respectively.

[0122] S44. After the cyclic loading is completed, the displacement control loading is carried out at a rate of 0.001 mm / s until failure.

[0123] S5. Combining the test results of S3 and S4, the dynamic sealing performance of the caprock is evaluated by using the rock fatigue failure criterion and the dynamic breakthrough pressure change relationship of the caprock.

[0124] S6. Based on the on-site seismic exploration data, a finite element analysis model was established. According to the Mohr-Coulomb shear failure criterion, tensile failure criterion and capillary sealing mechanism, the upper limit injection pressure of the water-bearing trap in the rift basin was obtained.

[0125] The judgment criteria include the Mohr-Coulomb shear failure criterion, tensile failure criterion, rock fatigue failure criterion, and capillary sealing mechanism;

[0126] When shear failure occurs at the weak cemented surface of the surrounding rock of a gas storage facility, the Mohr-Coulomb shear failure criterion shall be applied.

[0127] When tensile stress occurs in the surrounding rock of a gas storage facility, the tensile failure criterion should be applied.

[0128] When assessing the dynamic sealing capability of the capillary layer, the capillary sealing mechanism should be applied.

[0129] When assessing changes in the dynamic sealing capacity of caprock, the fatigue failure criterion should be applied.

[0130] The upper limit injection pressure of the gas storage facility is calculated using the following formula:

[0131] S61. The capillary closure mechanism is used as a prerequisite for predicting the upper limit injection pressure.

[0132] S62. The maximum operating pressure during the gas storage injection and production process is obtained by adopting the Mohr-Coulomb shear failure criterion.

[0133] S63. Using the tensile failure criterion, the minimum horizontal principal stress of the gas storage tank during the injection and production process is obtained;

[0134] S64. Calculate using the aforementioned upper limit pressure formula, i.e.:

[0135] ;

[0136] In the formula, Inject pressure to the upper limit of the gas storage facility for the conversion of water-bearing traps in rift basins. This refers to the pore pressure of the formation above the caprock. To enable the caprock to dynamically overcome pressure, For the minimum horizontal principal stress of the cap layer, It is obtained through capillary pressure and injection pore pressure. It is obtained based on the minimum horizontal principal stress, and finally based on Get the upper limit of injection pressure.

[0137] In a specific embodiment 1 of the present invention, the evaluation method for converting a water-bearing trap in a rift basin into a gas storage facility includes:

[0138] S1. Identify the primary or secondary structural units of the water-bearing traps in the rift basin as the research object. First, conduct a static evaluation of the geological sealing performance of the target traps. Based on the pre-established evaluation level table, determine the overall suitability for reservoir construction, as follows:

[0139] S101. Based on the trap sealing performance, trap structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale, and technical feasibility, obtain the suitability of various technical indicators corresponding to the favorable traps in the rift basin, as shown in Table 1.

[0140] Table 1. Evaluation Standards for Technical Indicators of Gas Storage Facilities Converted from Graben Basins

[0141]

[0142]

[0143] Specifically, the technical indicators include: trap type, caprock breakthrough pressure, structural closure, burial depth, hydrodynamic conditions, reservoir suitability, gas storage capacity, caprock permeability, aquifer permeability, and aquifer porosity, as detailed below:

[0144] The storage capacity of the gas storage facility is calculated using the following formula:

[0145] ;

[0146] In the formula, Q is the storage capacity of the gas storage facility, V is the closed volume of the aquifer, T0 is the temperature of natural gas under standard conditions, T is the temperature of the aquifer, P0 is the standard surface pressure, and Z is the natural gas deviation coefficient.

[0147] The trap type is an anticline structure;

[0148] The closure degree of the trap is greater than or equal to 100 meters;

[0149] The burial depth of the trap is in the range of 250 meters to 3500 meters;

[0150] The caprock is composed of argillaceous rock or evaporite;

[0151] The breakthrough pressure of the cap layer is greater than or equal to 1 MPa;

[0152] The permeability of the caprock should be less than 0.1 millidarcy;

[0153] The net thickness of the aquifer is greater than or equal to 10 meters;

[0154] The porosity of the aquifer is greater than or equal to 5%;

[0155] The aquifer permeability is greater than or equal to 10 millidarcy.

[0156] The stress coefficient of the trap should be between 0.55 and 1.3;

[0157] The stability of the trap should be such that no major geological disasters occur or may occur;

[0158] The well density should be such that no more than 20 abandoned old wells are present.

[0159] S102. Use MATLAB to develop the corresponding calculation program and use the analytic hierarchy process to determine the weight values ​​of each evaluation index, as shown in Table 2.

[0160] Table 2. Weighting of Technical Indicators for Gas Storage Reconstruction in Graben Basins

[0161]

[0162]

[0163] Specifically, the method of determining the weight values ​​of each technical indicator using the analytic hierarchy process includes:

[0164] The conversion of water-bearing traps in rift basins into gas storage facilities is taken as the target layer, while the trap sealing performance, structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale, and technical feasibility are taken as the criteria layer, and technical indicators are taken as the evaluation layer. The weight values ​​of each technical indicator are determined by the analytic hierarchy process.

[0165] S103. Based on the suitability of each technical indicator and the weight value of each technical indicator, the comprehensive suitability of the static evaluation of the geological sealing of the converted gas storage facility in the rift basin is obtained.

[0166] Specifically, the overall suitability for constructing aquifer gas storage sites is calculated using the following formula:

[0167] ;

[0168] In the formula, M represents the overall suitability for constructing a gas storage site in an aquifer. For the first The weight values ​​corresponding to the technical indicators For the first The suitability of the technical indicators.

[0169] S104. According to the preset static evaluation suitability level table of geological sealing performance of the converted gas storage facility in the water-bearing trap of the rift basin, as shown in Table 3, the evaluation results are obtained.

[0170] Table 3 Evaluation Grade Table for Gas Storage Reconstructed from Water-Bearing Traps in Rift Basins

[0171]

[0172] S2. Furthermore, based on geological core sampling and alternating stress conditions, a dynamic sealing performance evaluation of the caprock is conducted, as detailed below:

[0173] S201, The experimental solution for the dynamic breakthrough pressure test of the caprock includes:

[0174] Core sampling was conducted on-site to prepare samples with dimensions of 25×50mm;

[0175] According to standard SY / T5815-2016, with a pressure gradient of 0.0226 MPa / m, the confining pressure under the fault burial depth condition is calculated as follows:

[0176] ;

[0177] In the formula, d is the depth of the stratum where the core is located, in meters;

[0178] Apply confining pressure at a constant rate to a predetermined value, and test the breakthrough pressure value of the specimen in its initial state;

[0179] The triaxial peak compressive strength of the caprock was determined using a triaxial rock testing machine with a loading rate of 0.001 mm / s. MPa;

[0180] Take 0.1 As the lower limit point, respectively with 0.6 With 0.8 The upper limit point;

[0181] A triaxial compression testing machine was used to maintain a constant confining pressure. Starting from the minimum load (i.e., the origin), cyclic loads were repeatedly applied at a loading rate of 1 kN / s. Breakthrough pressure tests (upper limit tests) were conducted at 0, 15, 30, 45, and 60 cycles. A schematic diagram of the loading method is shown below. Figure 3 As shown;

[0182] Specifically, the breakthrough pressure test refers to the standard "SY / T 5748-2013 Method for Determining Gas Breakthrough Pressure in Rocks", and the pressure is applied in stages according to the changes in confining pressure and applied gas pressure level over time, such as... Figure 7 As shown;

[0183] Obtain the dynamic breakthrough pressure changes of the caprock in the target trap, and establish the curve relationship between breakthrough pressure and the number of alternation cycles, such as... Figure 4 As shown;

[0184] S202, The fatigue failure test solution for the caprock includes:

[0185] Core samples were taken from the overlying rock at the site and prepared with a size of 50×100mm.

[0186] The confining pressure is determined based on the depth gradient. The formula for calculating the confining pressure is as follows:

[0187] ;

[0188] In the formula, d is the depth of the stratum where the core is located, in meters;

[0189] Core samples were selected, and the triaxial peak compressive strength of the caprock was determined by loading a rock mechanics testing machine under constant confining pressure at a loading rate of 0.001 mm / s.

[0190] Rock alternating mechanics tests were conducted with upper limit loads of 0.5P, 0.6P, and 0.7P, and a lower limit load of 0.1P, respectively, and 20, 40, and 60 cycles of cyclic loading. The schematic diagram of the loading principle is shown below. Figure 5 As shown;

[0191] Specifically, after the cyclic loading ends, the displacement is controlled at a rate of 0.001 mm / s until failure.

[0192] Establish the curve relationship between fatigue failure of the caprock and the number of cycles, such as... Figure 5 As shown;

[0193] S203. The fatigue shear failure of the caprock is evaluated according to the criteria for judging the fatigue failure of the caprock. The criteria are as follows:

[0194] ;

[0195] In the formula, The number of injection and extraction cycles; Effective normal stress;

[0196] S3. Based on the on-site geological data and on-site exploration conditions, establish a finite element analysis model ( Figure 7 As shown in the figure, the upper limit injection pressure of the gas storage facility is predicted. The specific analysis method includes the following steps.

[0197] S301. Based on geological data and field exploration, obtain relevant mechanical parameters of the caprock, reservoir, overlying layer and underlying layer;

[0198] Specifically, it involves understanding the basic physical and mechanical properties of rock masses at each stratum. In practice, this should start with the most basic geological conditions. While analyzing geological data, field exploration should be the main approach to obtain various mechanical parameters of the caprock, reservoir, overlying strata, and underlying strata, providing reliable prerequisites for subsequent finite element mechanical analysis models.

[0199] S302. Establish a finite element analysis model for the target aquifer, such as... Figure 8 As shown;

[0200] S303. Apply different criteria for judging the upper limit injection pressure of the gas storage facility for different situations, and calculate the upper limit injection pressure value of the aquifer gas storage facility by combining various criteria.

[0201] The various criteria mentioned include the tensile failure criterion, the Mohr-Coulomb shear failure criterion, and the capillary closure criterion.

[0202] When the surrounding rock of a gas storage facility fractures, the tensile failure criterion should be applied.

[0203] When shear failure occurs at the weak cemented surface of the surrounding rock of a gas storage facility, the Mohr-Coulomb shear failure criterion shall be applied.

[0204] When gas leakage occurs in the capillary of a gas storage facility, the capillary sealing mechanism should be applied, meaning that the pressure of the gas injected into the storage layer should be less than the sum of the water pressure above the capillary and the dynamic breakthrough pressure.

[0205] Specifically, the three criteria are as follows:

[0206] Capillary sealing mechanism:

[0207] Because gas storage facilities undergo periodic injection and extraction activities, the caprock is damaged and deteriorated during multiple rounds of injection and extraction, leading to a gradual decrease in its sealing capacity and affecting the sealing performance of the gas storage trap. The capillary seal is considered a prerequisite for failure under the following two evaluation criteria, and its calculation method is as follows:

[0208] ;

[0209] The water pressure above the caprock, This refers to the dynamic breakthrough pressure of the caprock.

[0210] Tensile failure criterion:

[0211] The surrounding rock of aquifer gas storage facilities has low tensile strength. When the injection pressure inside the storage facility is too high, tensile stress will be generated in the surrounding rock. Special attention should be paid to the tensile failure of the surrounding rock in this situation. Various types of rock exist within the surrounding rock of gas storage facilities, and due to the irregularity of the storage enclosure, elasticity mechanics is not applicable to solving such problems. However, solving these problems using the finite element method is relatively simple. By determining the desired parameters, accurate simulation can be performed based on the actual situation.

[0212] ;

[0213] In the formula, Inject pressure into the gas storage facility. Minimum horizontal principal stress;

[0214] To prevent shear failure of the surrounding rock of the gas storage facility, the minimum horizontal principal stress of the gas storage facility at this time is denoted as... .

[0215] Mohr-Coulomb shear failure criterion:

[0216] Due to the intensive injection and extraction processes at gas storage facilities, deformation of the surrounding rock is inevitable. Because the types of surrounding rock vary and the mechanical properties differ between layers, interlayer slippage and shear failure will occur, thus affecting the local stability of the gas storage facility. The calculation method is as follows:

[0217] ;

[0218] For cohesion and internal friction angle, The normal stress on the physical plane where rock failure occurs. This refers to pore pressure.

[0219] To prevent shear failure of the surrounding rock of the gas storage facility, the minimum operating internal pressure of the gas storage facility at this time is denoted as: .

[0220] S404. Based on the simulation calculated using various judgment criteria, the optimal value is selected as the upper limit injection pressure of the gas storage tank using the upper limit injection pressure formula.

[0221] Specifically, the upper limit injection pressure of the aquifer gas storage tank can be calculated by the following formula:

[0222] ;

[0223] In the formula, This is the upper limit pressure of the aquifer gas storage facility. This refers to the pore pressure of the formation above the caprock. To enable the caprock to dynamically overcome pressure, This represents the minimum horizontal principal stress of the cap layer.

[0224] In a specific embodiment 2 of the present invention:

[0225] 1. Summer 552 target

[0226] The Xia 552 target structure is located in the Linnan Depression, with an aquifer consisting of Guantao Formation sandstone at a depth of 1120m. It is an anticline trap with an area of ​​1.55 km². 2 The enclosure radius is 30m, and the gas storage capacity is 960 million cubic meters. Figure 8 ).

[0227] The Guantao Formation's direct overburden consists of gray and purplish-red mudstone, with a single layer thickness of 3-14.5m and a cumulative thickness of 106.5m.

[0228] As shown in Table 4, one well has been drilled within the trap, and four adjacent wells are also drilled. The reservoir is buried at a depth of 1125-1320m, mainly composed of fine sandstone, with a single layer thickness of 5-28m and a cumulative thickness of 71m. According to the core measurement data of Xiaxie 551 well, the average porosity is 34% and the permeability is 896mD.

[0229] Table 4. Drilling Information Around Xia 552 Trap

[0230]

[0231] 1.1 Interpretation of Field Logging

[0232] Xia 552 is located in Dongying, Shandong Province, tectonically situated in the Linnan Depression of the Guantao Formation. It is a low-amplitude anticline with a closure of approximately 20m, no faults, and a trap area of ​​1.55km². 2 The maximum gas storage capacity is approximately 960 million cubic meters. The direct caprock of the Guantao Formation is gray and purplish-red mudstone, with a single layer thickness of 3-14.5m and a cumulative thickness of 106.5m. The reservoir depth is 1125-1320m, mainly composed of fine sandstone, with a single layer thickness of 5-28m and a cumulative thickness of 71m. There is relatively little structural geological data available, and it can only be determined based on geological data from nearby areas. The average porosity is 34%, the permeability is 896mD, and the geostress coefficient is estimated by referring to existing geostress tests in the Shengli oilfield, combined with relevant empirical formulas and literature data.

[0233] 1.2 Rock mechanical parameter testing

[0234] The product of the stratum depth where the core is located and the pressure gradient is used as the maximum effective overburden pressure. According to the standard SY / T5815-2016, the pressure gradient is selected as 0.0226 MPa / m.

[0235] ;

[0236] According to the loading requirements of standard DZ / T0276.20-2015, confining pressure and axial pressure were applied at a loading rate of approximately 0.05 MPa / s until hydrostatic pressure was reached. After the hydrostatic pressure loading was completed, the test was conducted at an axial loading rate of 0.002 mm / s until the residual strength value could be clearly observed. The specimens mainly underwent shear failure under constant confining pressure loading, and their mechanical parameters are shown in Table 5.

[0237] Table 5 Test Table of Mechanical Parameters of S105 Core

[0238]

[0239] 1.3 Static Breakthrough Pressure of the Cap Layer

[0240] The static breakthrough pressure test curve of the cap layer is as follows: Figure 9 As shown.

[0241] 1.4 Trapped In-situ Stress

[0242] Shengli Oilfield is located in Dongying City, Shandong Province. Since Dongying City's geographical coordinates are 118°E, 38°N, its approximate location can be marked on a world geostress map. A partial enlarged view of Dongying City and the meaning of its icons are shown below. Figure 10 As shown.

[0243] like Figure 11 As shown, the maximum horizontal compressive stress S in Dongying City Hmax The direction is roughly within 20° east of south. The two rock masses are horizontally aligned along the fault plane, indicating a strike-slip fault. The stress field magnitude is S. Hmax >S v >S hmin .

[0244] 1.5 Static Sealing Performance Evaluation of Xia 552

[0245] Table 6. Results of Static Sealing Performance Evaluation Indicators for Xia 552

[0246]

[0247] To facilitate the quantitative analysis of specific indicators for evaluating caprocks, caprocks are categorized into "good," "relatively good," "medium," and "poor" grades (as shown in Table 6). This is combined with the weighting of each indicator in the overall evaluation system obtained using the analytic hierarchy process (AHP). This allows us to obtain the overall suitability value of the cap layer quality. ,Right now:

[0248] ;

[0249] In the formula, These are the quantitative values ​​for each evaluation indicator; These are the weight values ​​for each evaluation indicator; .

[0250] Based on the calculated M=8.1251, and referring to Table 3, which shows that the static sealing performance of the gas storage facility in the rift basin is good, it is suitable for construction. However, it is still necessary to establish corresponding monitoring points for dynamic observation.

[0251] 2. Dynamic sealing test

[0252] Dynamic breakthrough pressure tests were conducted under cyclic loading conditions of 20, 40, and 60 cycles, with 70% of the peak load amplitude as the threshold value. The results are as follows: Figure 12 As shown;

[0253] 2.3 Fatigue failure test of caprock

[0254] Cyclic loading tests were conducted at 60%, 70%, and 80% of the peak load, respectively, and the results are as follows: Figure 13 As shown.

[0255] Based on the test results of peak load and number of cycles, 0.8P, 0.85P, and 0.9P were set as the upper limit loads, and 0.1P as the lower limit load. The loading rate remained at 1 kN / s. The gas storage tank was subjected to 50 cycles of alternation as its lifespan. The fatigue life of the specimen under high upper limit stress was studied through experiments (Table 7), and the fatigue failure life curve of the target caprock was established. Figure 14 ).

[0256] Table 7 Fatigue Compression Test Scheme

[0257]

[0258] 3. Finite Element Modeling and Analysis

[0259] 3.1 Project Overview

[0260] like Figure 15 As shown, Xia 552 is located in Dongying, Shandong Province, tectonically in the Linnan Depression of the Guantao Formation. It is an anticline structure with a closure of approximately 20m, no faults, and a trap area of ​​1.55km². 2 The maximum gas storage capacity is approximately 960 million cubic meters. The direct caprock of the Guantao Formation is gray and purplish-red mudstone, with a single layer thickness of 3-14.5m and a cumulative thickness of 106.5m. The reservoir depth is 1125-1320m, mainly composed of fine sandstone, with a single layer thickness of 5-28m and a cumulative thickness of 71m. According to the core measurement data of Xiaxie 551 well, the average porosity is 34% and the permeability is 896mD. The drilling data of Xiaxie 552 and adjacent wells are shown in Table 8.

[0261] Table 8. Drilling Status within and Adjacent to Xia 552 Enclosure

[0262]

[0263] 3.2 Computational Model

[0264] Xia 552 is a low-amplitude anticline structure with nearly horizontal strata and an effective trap radius of 702.6m. A schematic diagram of the calculation model is shown below. Figure 16 As shown, the mesh model is input Figure 17 As shown, the model has a horizontal range of 12km and includes four typical strata: overlying layer, caprock, aquifer reservoir, and basement strata.

[0265] Due to the low level of exploration of Xia 552, there is limited core testing data. Only reservoir physical parameters have been tested, while the caprock and other strata were determined by combining data from adjacent areas and relevant literature, as shown in Table 9.

[0266] Table 9. Formation Calculation Parameter Values

[0267]

[0268] 3.3 Upper Limit Injection Pressure Prediction and Stability Analysis

[0269] (1) Critical internal friction angle

[0270] According to the shear failure criterion, when the injection pressure is At MPa, the stress Mohr's circle variation trend of the cap layer is as follows: Figure 18 As shown, the maximum critical internal friction angle at this point is approximately 28.5°. o At this point, local shear failure occurs in the caprock. The corresponding minimum principal compressive stress on the caprock is as follows: Figure 19 As shown, the cap layer was always under compressive stress and did not experience tensile failure.

[0271] (2) Tensile failure

[0272] Based on the tensile failure criterion, the maximum injection pressure at which the caprock fails is simulated, and the corresponding minimum principal stress is calculated; when the maximum injection pressure of the caprock... At MPa, its minimum principal compressive stress approaches 0 ( Figure 20 and Figure 21 Since ABAQUS treats compression as negative and tension as positive in the calculation process, when the compressive stress approaches 0, tensile stress begins to appear, and the cap layer undergoes tensile failure.

[0273] (3) Overcoming pressure

[0274] Due to the lack of measured data on caprock breakthrough pressure, based on the model developed by Soviet scholar Pilipu through experiments regarding the relationship between caprock penetration pressure difference and permeability, namely:

[0275] ;

[0276] In the formula, The pressure difference is measured in MPa. Permeability, in mD.

[0277] According to relevant data from neighboring areas, the breakthrough pressure corresponding to a caprock permeability of 0.001 mD is 10.26 MPa.

[0278] Based on the above empirical formula, the gas pressure injected into the reservoir... It should be less than the water pressure above the cap layer. The sum of the dynamic breakthrough pressure and the critical injection pressure of the caprock can predict a critical injection pressure of approximately 21.56 MPa.

[0279] Table 10 Comprehensive Evaluation Table for Summer 552

[0280]

[0281] As shown in Table 10, during the injection process, under the constraints of three evaluation criteria, the caprock first experienced gas breakthrough, followed by shear failure, and finally tensile failure. Through comparative analysis, 21.56 MPa was selected as the upper limit injection pressure, and the corresponding upper limit pressure coefficient was approximately 1.908.

[0282] In conclusion, Xia 552 is a suitable target for reservoir construction, but it is still necessary to establish corresponding monitoring points for dynamic observation.

[0283] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0284] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. An evaluation method for converting water-bearing traps in rift basins into gas storage facilities, characterized in that... The evaluation methods for converting water-bearing traps in this rift basin into gas storage facilities include: Step 1: Establish a static sealing performance evaluation system for water-bearing traps in rift basins; Step 2: Determine the triaxial peak compressive strength of the caprock to identify the upper and lower limits of the alternating stress. Step 3: Conduct dynamic breakthrough pressure tests on the caprock of the target trap to establish the curve relationship between the dynamic breakthrough pressure of the caprock rock and the number of cycles. The dynamic breakthrough pressure test of the caprock includes the following steps: S31. Based on the core sampling depth at the site, prepare rock samples with a size of 25×50mm; S32. With a pressure gradient of 0.0226 MPa / m, calculate the confining pressure under the fault burial depth condition, i.e.: ； In the formula, d is the depth of the stratum where the core is located, in meters; S33. Apply confining pressure at a constant rate to a predetermined value, and test the initial breakthrough pressure value of the specimen; S34. Using a triaxial rock testing machine with a loading rate of 0.001 mm / s, determine the peak compressive strength of the caprock. MPa; S35. Take 0.1 of the peak compressive strength of the rock. As the lower limit point, respectively with 0.6 With 0.8 The upper limit point; S36. Keep the confining pressure constant, starting from the minimum load, i.e. the origin, and repeatedly apply cyclic loads at a loading rate of 1KN / S. Conduct breakthrough pressure tests at 0, 15, 30, 45, and 60 cycles respectively to obtain the dynamic breakthrough pressure changes of the target trap caprock. Step 4: Conduct fatigue failure tests on the target trap caprock and establish the curve relationship between fatigue failure of the caprock and the number of cycles. Step 5: Evaluate the dynamic sealing performance of the cap layer; Step 6: Establish a finite element analysis model to obtain the upper limit injection pressure of the water-bearing trap in the rift basin.

2. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 1, based on existing experience in gas storage construction and relevant expert advice, combined with geological data, field exploration results, and seismic logging interpretations, the suitability of various technical indicators for favorable traps in rift basins is obtained. The weights of the indicators are determined by the analytic hierarchy process (AHP), and a static sealing performance evaluation system for water-bearing traps in rift basins is established.

3. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 2, characterized in that, In step 1, the technical indicators include: number of caprock layers, caprock breakthrough pressure, caprock strength, caprock lithology, trap type, closure height, trap burial depth, trap stability, trap geostress, hydrodynamic conditions, reservoir suitability, gas storage capacity, caprock permeability, aquifer permeability, and aquifer porosity.

4. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, the gas storage capacity is calculated using the following formula: ； In the formula, Q is the storage capacity of the gas storage facility, V is the aquifer trap volume, T0 is the temperature of natural gas under standard conditions, T is the aquifer temperature, P0 is the surface standard pressure, Z is the natural gas deviation coefficient, and Pmop is the upper limit pressure of the gas storage facility converted from an aquifer trap in a rift basin.

5. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, the trap type is an anticline structure; the structural closure degree of the trap is greater than or equal to 100 meters; the burial depth of the trap is within the range of 250 meters to 3500 meters; the geostress coefficient of the trap should be between 0.55 and 1.3; and the stability of the trap should be free from geological disasters.

6. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, the caprock is argillaceous rock or evaporite; the caprock breakthrough pressure is greater than or equal to 1 MPa; the caprock permeability should be less than 0.1 millidarcy; the aquifer net thickness is greater than or equal to 10 meters; the aquifer porosity is greater than or equal to 5%; and the aquifer permeability is greater than or equal to 10 millidarcy.

7. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, the hydrodynamic conditions are selected for traps with unclosed boundaries and large water volume; the well density should be no more than 20 abandoned old wells.

8. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, when using the analytic hierarchy process (AHP) to determine the weights of the indicators, the conversion of water-bearing traps in rift basins into gas storage facilities is taken as the target layer, the trap sealing performance, structural characteristics, hydrodynamic conditions, reservoir suitability, gas storage scale and technical feasibility are taken as the criteria layer, and the technical indicators are taken as the evaluation layer. The AHP is then used to determine the weight values ​​of each technical indicator.

9. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 3, characterized in that, In step 1, the overall suitability for converting a water-bearing trap in a rift basin into a gas storage facility is calculated using the following formula: ； In the formula, M represents the overall suitability for constructing a gas storage site in an aquifer. For the first The weight values ​​corresponding to the technical indicators For the first The suitability of the technical indicators.

10. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 2, based on the evaluation results of step 1, the triaxial peak compressive strength of the caprock is determined by taking geological core samples on site and using a rock triaxial mechanical testing machine while keeping the confining pressure constant, thereby determining the upper and lower limits of the alternating stress.

11. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 3, based on the gas storage injection and production years, the number of alternations is determined, and a gas breakthrough pressure tester is used to conduct a dynamic breakthrough pressure test on the target trap caprock, establishing a curve relationship between the dynamic breakthrough pressure of the caprock rock and the number of alternations.

12. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 4, a triaxial rock testing machine is used to determine the number of alternation cycles based on the gas storage injection and production years, and fatigue failure tests are conducted on the caprock of the target trap to establish the curve relationship between the fatigue failure of the caprock and the number of alternation cycles.

13. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 12, characterized in that, In step 4, the fatigue failure test includes the following steps: S41. Based on the core samples taken from the overlying rocks at the site, prepare core samples with a size of 50×100mm; S42. Select rock core samples and use a rock mechanics testing machine to perform uniaxial compressive strength loading at a loading rate of 0.001 mm / s to determine the uniaxial compressive strength P of the caprock. S43. Rock alternating mechanics tests were conducted with upper limit loads of 0.5P, 0.6P, and 0.7P and a lower limit load of 0.1P, respectively, and the number of cyclic loading cycles were selected as 20, 40, and 60 cycles, respectively. S44. After the cyclic loading is completed, the displacement control loading is carried out at a rate of 0.001 mm / s until failure.

14. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 5, the dynamic sealing performance of the caprock is evaluated by combining the test results from steps 3 and 4 and using the rock fatigue failure criterion and the dynamic breakthrough pressure variation relationship of the caprock.

15. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 1, characterized in that, In step 6, a finite element analysis model is established based on the on-site seismic exploration data. According to the Mohr-Coulomb shear failure criterion, tensile failure criterion, rock fatigue failure criterion and capillary sealing mechanism, the upper limit injection pressure of the water-bearing trap in the rift basin is obtained.

16. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 15, characterized in that, In step 6, when shear failure occurs at the weak cemented surface of the gas storage surrounding rock, the Mohr-Coulomb shear failure criterion is applied; when tensile stress occurs in the gas storage surrounding rock, the tensile failure criterion is applied; when judging the dynamic sealing capacity of the caprock, the capillary sealing mechanism is applied; and when judging the change in the dynamic sealing capacity of the caprock, the fatigue failure criterion is applied.

17. The evaluation method for converting a water-bearing trap into a gas storage facility in a rift basin according to claim 16, characterized in that, In step 6, the upper limit injection pressure of the converted gas storage facility from a water-bearing trap in the rift basin is calculated using the following formula: S61. The capillary closure mechanism is used as a prerequisite for predicting the upper limit injection pressure. S62. The maximum operating pressure during the gas storage injection and production process is obtained by adopting the Mohr-Coulomb shear failure criterion. S63. Using the tensile failure criterion, the minimum horizontal principal stress of the gas storage tank during the injection and production process is obtained; S64. Calculate using the upper limit pressure formula, i.e.: ； In the formula, The upper limit pressure for converting water-bearing traps in rift basins into gas storage facilities. This refers to the pore pressure of the formation above the caprock. To enable the caprock to dynamically overcome pressure, This represents the minimum horizontal principal stress of the cap layer; It is obtained through capillary pressure and injection pore pressure. It is obtained based on the minimum horizontal principal stress, and finally based on Get the upper limit of injection pressure.

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