A method for evaluating stability of a small well spacing double well salt cavern gas storage

Abstract

The application provides a kind of small well spacing double well salt cavern gas storage stability evaluation method, and relates to underground engineering technical field.The method technical scheme: first, the geological structure characteristics of the rock layer where the gas storage is located are determined by using three-dimensional seismic exploration technology, then the three-dimensional shape measurement of the first well and the second well salt cavity of the gas storage is carried out by using the sonar instrument, and the three-dimensional image and volume of the salt cavity are synthesized.After that, data wells are drilled in the gas storage construction block, the data well cores are extracted for testing, the physical and mechanical parameters of salt rock, mudstone and interlayer in the core are obtained, and the geomechanical numerical model of the salt cavity of the gas storage is established and simulated.Finally, according to the shear dilatancy safety factor, the maximum deformation of the cavity top, the volume shrinkage rate and the critical safety value of the plastic zone, the stability of the gas storage is evaluated, and the well spacing is optimized according to the result.The application has strong operability and can be used to optimize the double well spacing to improve the stability of the small well spacing double well salt cavern gas storage.

Description

Technical Field

[0001] This invention relates to the field of underground engineering technology, and in particular to a stability evaluation method for a small-well-spaced twin-well salt cavern gas storage facility. Background Technology

[0002] Salt cavern reservoirs are typically constructed using the single-well oil pad method, while the small-well-interval dual-well water-soluble cavity-building technology is a novel cavity-building method proposed in the last 20 years. This method, by alternating water injection and brine discharge from the first and second wells, can increase the water injection and discharge rate, improve the cavity-building speed, and shorten the reservoir construction cycle. Therefore, it has advantages such as fast cavity-building speed, high injection-production efficiency, and simple cavity-building process.

[0003] The basic process for creating a cavity in a dual-well system with a small well spacing is generally as follows: Drill two vertical wells 15-30 m apart at their centerlines into the target salt layer to connect the underground salt layer to the surface. Connect the bottom ends of the two vertical wells using a single-well convection method. Arrange the tubing according to the cavity creation requirements. Insert the production casing and cavity creation casing into the two vertical wells respectively, inject protective fluid, and then inject fresh water or unsaturated brine from one well, while high-concentration brine flows out from the other well. Adjust the positions of the inlet and outlet water alternately as needed, raise the height of the cavity creation casing and oil cushion layer step by step, and replenish the amount of protective fluid to finally obtain a cavity shape that meets the requirements of an oil and gas storage facility.

[0004] The principle of water-soluble cavity construction in small-well-spacing dual-well systems is similar to that of single-well systems. The difference lies in the fact that small-well-spacing dual-well water-soluble cavity construction utilizes only two wellbores—an injection pipe and a brine discharge pipe—instead of the central and intermediate pipes found in single-well systems. During injection and production operations, small-well-spacing dual-well systems employ a dual-well structure, allowing for different injection and production methods such as one injection and one production, or simultaneous injection and production. This significantly increases the gas injection and production rate. Small-spacing dual-well systems can form more stable and larger-volume cavities within a given thickness of salt layer, increasing the storage capacity of the gas reservoir and improving the utilization efficiency of salt strata. However, the safety and stability of the surrounding rock compared to single-well systems requires further practical improvement. Therefore, it is necessary to study stability evaluation methods for small-well-spacing dual-well gas reservoirs to ensure the stability of the surrounding rock during gas injection and production from dual-well single cavities and large-capacity salt cavities. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility, addressing the shortcomings of the prior art.

[0006] The technical solution adopted in this invention is:

[0007] The stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility includes the following steps:

[0008] Step 1: Use 3D seismic exploration technology to determine the geological structure characteristics of the rock strata where the salt cavern gas storage is located;

[0009] The geological structural features include: the sedimentary environment of the salt-bearing layer where the cavity is located, the distribution of fault structures, the distribution characteristics of salt rocks, the characteristics of the top and bottom plates of the salt layer, and the distribution characteristics of interlayers;

[0010] The distribution characteristics of salt rocks include: salt layer thickness, grade, and physicochemical properties;

[0011] Step 2: Perform three-dimensional morphological measurements on the salt cavities of the first and second wells of the salt cavern gas storage facility, and synthesize three-dimensional images and volumes of the salt cavities;

[0012] The three-dimensional morphological measurement was performed using a sonar instrument.

[0013] The specific steps for sonar detection are as follows:

[0014] S1: Place the sonar probe on a horizontal plane at a certain depth inside the salt cavity and emit sound pulses toward the wall of the salt mine cavity. Detect the echo signal and transmit the signal back to the ground computer system to obtain the horizontal measurement distance of the cavity at a certain depth.

[0015] S2: Change the measurement depth to obtain the horizontal measurement distance of salt mine cavity at different depths;

[0016] S3: The top, bottom and abnormal parts of the salt cavern gas storage are tilted to obtain the measurement distance at different tilt angles; the abnormal part is the irregular contour of the cavity wall caused by the cavity top or tilted interlayer between the first well and the second well, which is a local cantilevered, finger-like protrusion.

[0017] S4: Using sonar ranging and imaging analysis software, synthesize a three-dimensional image and volume of the entire salt cavity;

[0018] Step 3: Drill data wells in the near field within the salt cavern gas storage area, extract core samples from the data wells for testing, and obtain the physical and mechanical parameters of the salt rock, mudstone, and interlayers in the core samples;

[0019] The core samples from the data wells were tested for the following: density, uniaxial compressive strength, tensile strength, internal friction angle, cohesion, steady-state creep rate, breakthrough pressure, permeability, and porosity. Salt rock underwent all of these tests; mudstone and interlayers underwent all tests except for the breakthrough pressure test.

[0020] Step 4: Establish a geomechanical numerical model of the salt cavity in the gas storage facility;

[0021] Step 4.1: Determine the three-dimensional shape and dimensions of the salt cavity based on the three-dimensional image and volume determined in Step 2;

[0022] Step 4.2: Establish a three-dimensional geomechanical numerical model of the salt cavern gas storage cavity: The model is a cuboid, and the length of each side of the cuboid should not be less than 5 times the maximum diameter of each side of the salt cavern gas storage cavity. The salt rock interlayer is located in the middle of the model. The center lines of the first well and the second well are 15~30 m apart, and the salt cavity is watertight.

[0023] Step 4.3: Uniform internal pressure is applied to the surface of the cavity wall of the salt cavity; initial geostress is applied to the three-dimensional geomechanical model, and the average gravity of the overlying rock strata is applied to the top surface of the model; horizontal constraints are applied to the four vertical planes of the three-dimensional geomechanical model to limit horizontal deformation of the model; fixed constraints are applied to the bottom of the three-dimensional geomechanical model to limit horizontal and vertical deformation.

[0024] Step 5: Evaluate the dynamic stability of the gas storage facility with different well spacing and storage capacity parameters;

[0025] Step 5.1: Use the established three-dimensional geomechanical model to simulate and calculate the stress, deformation, failure zone, and seepage pressure of the surrounding rock of the gas storage tank;

[0026] Step 5.2: Determine the well spacing, i.e., the distance between the center points of the first and second wells. Since the well spacing is closely related to the roof span, a smaller wellhead spacing results in a more stable cavity, but a larger plastic superposition area between the tubing strings, leading to stress concentration near the tubing strings, causing damage and collapse, thus affecting the stability of the gas storage facility. Conversely, a larger wellhead spacing results in a larger roof span, making the roof more prone to deformation and damage, which can also cause deformation and bending of the tubing strings. Determine the storage capacity parameters, including cavity working pressure, circulation cycle, and maximum gas production rate. Perform static numerical simulation analysis of the cavity for multiple sets of well spacing and storage capacity parameters, and compare numerical simulations of periodic injection-production internal pressure operation and ground subsidence.

[0027] Among them, the working pressure of the cavity refers to the force exerted by the natural gas on the cavity wall during the stable operation of the salt cavern gas storage; the cycle period refers to the time required for the salt cavern gas storage to complete a full operating cycle of gas injection and gas extraction; and the maximum extraction rate is the maximum rate at which the natural gas pressure in the cavity decreases during emergency gas extraction in the salt cavern gas storage.

[0028] Step 5.3: Based on the calculation formulas for shear dilatation safety factor, equivalent strain, maximum deformation at the top of the cavity, volume shrinkage rate, plastic zone, and natural gas seepage range, plot the calculated surrounding rock stress, deformation, and seepage pressure into a cloud map.

[0029] Step 5.4: Evaluate the stability of the gas storage facility based on the shear dilatation safety factor, equivalent strain, maximum deformation at the cavity top, volumetric shrinkage rate, plastic zone, and critical safety value of natural gas seepage range. All of these indicators should be below the critical safety value, which can be determined with reference to the "Design Specification for Salt Cavern Gas Storage Cavities". Afterwards, adjust and optimize the well spacing and storage capacity parameters of the gas storage facility based on the above evaluation results.

[0030] The deformation, plastic zone volume, and natural gas seepage range can be obtained from numerical results, while the shear dilatation safety factor is... In the formula, a and b are the fitting coefficients, which need to be obtained through experimental fitting. , These are the first invariant of element stress and the second invariant of stress deviator, respectively; the equivalent effect becomes In the formula For partial strain, , These are the first and second invariants of the strain tensor, respectively; and the volumetric shrinkage rate. In the formula , These represent the total volume of the gas storage chamber after melting and under the current operating conditions, respectively.

[0031] The beneficial effects of adopting the above technical solution are as follows: The stability evaluation method for small-well-spacing dual-well salt cavern gas storage provided by the present invention has simple evaluation steps, clear evaluation indicators, and strong operability. It can realize the quantitative evaluation of the stability of small-well-spacing dual-well salt cavern gas storage, optimize the spacing between the two wells to improve the stability of small-well-spacing dual-well salt cavern gas storage, and at the same time, it can also give reasonable measures based on the stability evaluation results to prevent the gas storage from possible operational instability and damage, which is more in line with the actual engineering geological conditions. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating a method for evaluating the stability of a small-well-spacing dual-well salt cavern gas storage facility according to the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the small-well-spacing dual-well salt cavern gas storage facility of the present invention.

[0034] Figure 3 This is a cross-sectional view of the small-well-spacing dual-well salt cavern gas storage model of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0036] In this embodiment, a stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility is described, such as... Figure 1 As shown, the specific steps include:

[0037] Step 1: Use 3D seismic exploration technology to determine the geological structure characteristics of the rock strata where the salt cavern gas storage cavity is located;

[0038] The geological structural features include: the sedimentary environment of the salt-bearing layer where the cavity is located, the distribution of fault structures, the distribution characteristics of salt rocks, the characteristics of the top and bottom plates of the salt layer, and the distribution characteristics of interlayers;

[0039] The distribution characteristics of salt rocks include: salt layer thickness, grade, and physicochemical properties;

[0040] This embodiment:

[0041] Acquire 3D seismic data, including stratigraphic parameters such as geological features of salt-bearing strata;

[0042] The geological structural features of the rock strata region where the cavity is located were determined using three-dimensional seismic exploration technology, including: the sedimentary environment of the salt-bearing layer where the salt cavity is located, the distribution of fault structures, the distribution characteristics of salt rocks, the characteristics of the top and bottom plates of the salt layer, the distribution characteristics of interlayers, and other geological features.

[0043] Step 2: Perform three-dimensional morphological measurements on the first and second wells of the salt cavern gas storage chamber, and synthesize a three-dimensional image and volume of the salt cavern;

[0044] The three-dimensional morphological measurement was performed using a sonar instrument.

[0045] The specific steps for sonar detection are as follows:

[0046] S1: Place the sonar probe on a horizontal plane at a certain depth inside the salt cavity and emit sound pulses toward the wall of the salt mine cavity. Detect the echo signal and transmit the signal back to the ground computer system to obtain the horizontal measurement distance of the cavity at a certain depth.

[0047] S2: Change the measurement depth to obtain the horizontal measurement distance of salt mine cavity at different depths;

[0048] S3: The top, bottom and abnormal parts of the cavity of the salt cavern gas storage are tilted to obtain the measurement distance at different tilt angles; the abnormal part is the irregular contour of the cavity wall caused by the cavity top or tilted interlayer between the first well and the second well, which is a local cantilevered, finger-like protrusion.

[0049] S4: Using sonar ranging and imaging analysis software, synthesize a three-dimensional image and volume of the entire salt cavity;

[0050] This embodiment: Three-dimensional morphological measurement of the salt cavity in the first and second wells.

[0051] Sonar cavity measurement of the cavities in the first and second wells of the salt cavity can be carried out by placing the sonar probe on a horizontal plane at a certain depth inside the salt cavity and emitting sound pulses towards the wall of the salt cavity. The echo signal is detected and transmitted back to the ground computer system to obtain the horizontal measurement distance of the salt cavity at a certain depth. By changing the measurement depth, the horizontal measurement distance of the salt cavity at different depths can be obtained. Then, tilt measurements are performed on the top, bottom and abnormal parts of the salt cavity to obtain the measurement distance at different tilt angles. Finally, a three-dimensional image and volume of the entire salt cavity can be synthesized.

[0052] Step 3: Drill data wells in the near field within the salt cavern gas storage area, extract core samples from the data wells for testing, and obtain the physical and mechanical parameters of the salt rock, mudstone, and interlayers in the core samples;

[0053] The core samples from the data wells were tested for the following: density, uniaxial compressive strength, tensile strength, internal friction angle, cohesion, steady-state creep rate, breakthrough pressure, permeability, and porosity. Salt rock underwent all of these tests, while mudstone and interlayers underwent tests other than the breakthrough pressure test.

[0054] In this embodiment, core samples from the data well were extracted for laboratory testing to obtain the physical and mechanical parameters of the salt rock, mudstone, and interlayers.

[0055] Core sampling was conducted using data wells to obtain core samples from the reservoir construction area. The core sampling range extended from the surface to 100m below the bottom of the salt rock layer, obtaining core samples of salt rock, mudstone, and interlayers. According to the requirements of the "Standard for Engineering Rock Mass Testing Methods (GBT50266-2013)," the core samples were processed into standard specimens for different testing types. These specimens underwent density testing, uniaxial compressive strength testing, tensile strength testing, internal friction angle testing, cohesion testing, steady-state creep rate testing, breakthrough pressure testing, permeability testing, and porosity testing. Interlayer specimens were soaked in saturated brine before undergoing the aforementioned rock mechanics testing to obtain the basic physical and mechanical parameters of the sediment. To ensure the reliability of the experimental results, 3-5 specimens were tested under the same conditions for rock mechanics testing.

[0056] Step 4: Establish a geomechanical numerical model of the salt cavity;

[0057] Step 4.1: Perform three-dimensional morphological measurement of the salt cavity based on Step 2;

[0058] Step 4.2: Assume the top burial depth of the small-spacing twin-well cavity is 1743m, the bottom burial depth is 1975m, the maximum diameter is 90m, and the well spacing is taken as 10m, 20m, and 30m respectively. If the cavity bottom is taken as the origin of the vertical direction of the model, the burial depth of 1640m can be taken as the upper surface of the model, and the burial depth of 2075m can be taken as the lower surface of the model. Establish a three-dimensional geomechanical numerical model: the model size can be a cube of 500m×500m×435m. Assume the gas storage is placed in the middle of the model, and the model contains seven horizontal interlayers, each with a thickness of 2m. A schematic diagram of the small-spacing twin-well salt cavern gas storage structure is shown below. Figure 2 As shown.

[0059] The upper surface of the model (1640m) is under stress boundary conditions, and the average density of the overlying rock strata is 2.5 × 10⁻⁶. 3 kg / m 3 Therefore, the vertical load component at the upper boundary of the model is 41 MPa; the lower surface of the model (2075 m) is constrained in the X, Y, and Z directions, and the longitudinal surfaces around the model are simply supported in the corresponding normal directions, as shown below. Figure 3 As shown in Table 1, the mechanical parameters of the salt rock and its interlayers are shown in Table 1.

[0060] Table 1 Mechanical parameters

[0061]

[0062] Step 4.3: Uniform internal pressure acts on the surface of the cavity wall of the salt cavity; initial geostress is applied to the three-dimensional geomechanical model, and the average gravity of the overlying rock strata is applied to the top surface of the model; horizontal constraints are applied to the four vertical planes of the three-dimensional geomechanical model to limit horizontal deformation of the model; fixed constraints are applied to the bottom of the three-dimensional geomechanical model to limit horizontal and vertical deformation; simplified planar diagram of the mechanical boundary constraint model of the gas storage tank;

[0063] This embodiment establishes a geomechanical numerical model of a small-well-spaced twin-well salt mine cavity;

[0064] Sonar was used to detect the salt cavity morphology of the first and second wells, and a three-dimensional geomechanical model was established. The model size can be a cube of 500m × 500m × 435m. It is assumed that the gas storage tank is located in the center of the model, which contains seven horizontal interlayers, each 2m thick. The upper surface of the model (1640m) is under stress boundary conditions, and the average density of the overlying strata is 2.5 × 10⁻⁶. 3 kg / m 3 Therefore, the vertical load component at the upper boundary of the model is 41 MPa; the lower surface of the model (2075 m) is constrained in the X, Y, and Z directions, and the longitudinal surfaces around the model are simply supported in the corresponding normal directions, as shown below. Figure 3As shown. This three-dimensional geomechanical model still needs to be meshed, and the mesh size independence, convergence of the calculation results, and mesh quality of the three-dimensional geomechanical model need to be checked to ensure the reliability of the calculation results;

[0065] Step 5: Evaluate the dynamic stability of the gas storage facility with different well spacing and storage capacity parameters;

[0066] Step 5.1: Determine the well spacing and storage capacity parameters, including operating pressure, circulation period, and maximum gas production rate. Assume the gas storage tank is filled with saturated brine after cavity formation. Assume the brine inside the tank exerts a uniform internal pressure of 22 MPa on the tank wall surface and perform cavity stability calculations. Based on the principle that the upper limit pressure of the gas storage tank should not exceed 80% of the overlying formation pressure and fracture pressure, or the pressure gradient of the Jintan gas storage tank is 1.7 MPa / 100m, the upper limit pressure can be taken as 29 MPa. The lower limit pressure gradient of the Jintan gas storage tank is 0.7 MPa / 100m, i.e., the lower limit pressure is 13 MPa.

[0067] Numerical simulations of different well spacing schemes were carried out on the established three-dimensional geomechanical model. Based on multiple sets of working pressure, cycle period, and gas production rate conditions, the shear dilatation safety factor, equivalent strain, deformation, volume shrinkage rate, and plastic zone volume of the surrounding rock were obtained to comprehensively evaluate the long-term operational stability of the gas storage facility and determine a reasonable well spacing scheme.

[0068] Step 5.2: Based on the calculation formulas for shear dilatation safety factor, equivalent strain, maximum deformation at the top of the cavity, volume shrinkage rate, plastic zone, and natural gas seepage range, plot the calculated stress, deformation, and seepage pressure into a cloud map.

[0069] Step 5.3: Based on the shear dilatation safety factor, equivalent strain, maximum deformation at the top of the cavity, volume shrinkage rate, plastic zone, and critical safety value of natural gas seepage range, conduct an evaluation and adjust and optimize the well spacing and storage capacity parameters of the gas storage facility;

[0070] Wherein, the deformation is the vertical displacement of each node in the cavity top unit, the plastic zone volume is the total volume of the surrounding rock unit undergoing tensile and shear failure, and the natural gas seepage range is the maximum range of pore pressure change in the surrounding rock caused by gas injection and production. All of these parameters can be obtained from numerical results. The shear dilatation safety factor is... In the formula, a and b are the fitting coefficients, which need to be obtained through experimental fitting. , These are the first invariant of element stress and the second invariant of stress deviator, respectively; the equivalent effect becomes In the formula For partial strain, , These are the first and second invariants of the strain tensor; and the volumetric shrinkage rate. In the formula , These represent the total volume of the gas storage chamber after melting and under the current operating conditions, respectively.

[0071] This example assesses the dynamic stability of gas storage facilities with different well spacing and storage capacity parameters.

[0072] Based on the aforementioned three-dimensional geomechanical model, boundary conditions, and load conditions, the well spacing and storage capacity parameters were determined. Static numerical simulation analysis of the karst cavity and numerical simulation analysis of periodic injection-production internal pressure operation and ground subsidence were performed to simulate and calculate the stress, deformation, failure zone, and seepage pressure of the surrounding rock of the gas storage facility. Based on the calculation formulas for the shear dilatation safety factor, equivalent strain, maximum deformation at the cavity top, volume shrinkage rate, plastic zone, and natural gas seepage range, the calculated stress, deformation, and seepage pressure were plotted as contour maps. Based on the critical safety values ​​of the shear dilatation safety factor, equivalent strain, maximum deformation at the cavity top, volume shrinkage rate, plastic zone, and natural gas seepage range, an evaluation was conducted, and the well spacing and storage capacity parameters of the gas storage facility were adjusted and optimized.

[0073] This embodiment: The stability of the gas storage facility is determined by combining on-site monitoring and stability evaluation indicators;

[0074] The high-pressure gas storage facility is measured every 5 years using cavity measuring equipment to obtain the volume shrinkage rate and cavity wall deformation. The surface subsidence of the gas storage facility is measured annually using GPS and a level to obtain the surface subsidence. The critical safety values ​​of the shear dilatation safety factor, equivalent strain, maximum cavity top deformation, volume shrinkage rate, plastic zone, and natural gas seepage range are adjusted in real time using the above field monitoring data to ensure the scientific validity and reliability of the determined gas storage facility stability evaluation indicators.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for evaluating the stability of a small well spacing double well salt cavern gas storage, characterized in that: Includes the following steps: Step 1: Use 3D seismic exploration technology to determine the geological structure characteristics of the rock strata where the salt cavern gas storage is located; Step 2: Perform three-dimensional morphological measurements on the salt cavities of the first and second wells of the salt cavern gas storage facility, and synthesize three-dimensional images and volumes of the salt cavities; Step 3: Drill data wells in the near field within the salt cavern gas storage area, extract core samples from the data wells for testing, and obtain the physical and mechanical parameters of the salt rock, mudstone, and interlayers in the core samples; Step 4: Establish a geomechanical numerical model of the salt cavity in the gas storage facility; Step 5: Evaluate the dynamic stability of the gas storage facility with different well spacing and storage capacity parameters; The specific method for step 4 is as follows: Step 4.1: Determine the three-dimensional shape and dimensions of the salt cavity based on the three-dimensional image and volume determined in Step 2; Step 4.2: Establish a three-dimensional geomechanical numerical model of the salt cavern gas storage cavity: The model is a cuboid, and the length of each side of the cuboid should not be less than 5 times the maximum diameter of each side of the salt cavern gas storage cavity. The salt rock interlayer is located in the middle of the model. The center lines of the first well and the second well are 15~30 m apart, and the salt cavity is watertight. Step 4.3: Uniform internal pressure is applied to the surface of the cavity wall of the salt cavity; initial geostress is applied to the three-dimensional geomechanical model, and the average gravity of the overlying rock strata is applied to the top surface of the model; horizontal constraints are applied to the four vertical surfaces of the three-dimensional geomechanical model to limit horizontal deformation of the model; fixed constraints are applied to the bottom of the three-dimensional geomechanical model to limit horizontal and vertical deformation. The specific method for step 5 is as follows: Step 5.1: Determine the well spacing and reservoir capacity parameters, including working pressure, circulation period and maximum gas production rate; perform static numerical simulation analysis of the cavity and numerical simulation analysis of the periodic injection and production internal pressure operation and ground subsidence on the established three-dimensional geomechanical model; Step 5.2: Based on the calculation formulas for shear dilatation safety factor, equivalent strain, maximum deformation at the top of the cavity, volume shrinkage rate, plastic zone, and natural gas seepage range, plot the calculated stress, deformation, and seepage pressure into a cloud map; Step 5.3: Based on the shear dilatation safety factor, equivalent strain, maximum deformation at the top of the cavity, volume shrinkage rate, plastic zone, and critical safety value of natural gas seepage range, conduct an evaluation and adjust and optimize the well spacing and storage capacity parameters of the gas storage facility.

2. The stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility according to claim 1, characterized in that: The geological structural features include: the sedimentary environment of the salt-bearing layer where the cavity is located, the distribution of fault structures, the distribution characteristics of salt rocks, the characteristics of the top and bottom plates of the salt layer, and the distribution characteristics of interlayers; among which, the distribution characteristics of salt rocks include: the thickness, grade, and physicochemical properties of the salt layer.

3. The method for evaluating the stability of a small well spacing double well salt cavern gas storage according to claim 1, characterized in that: Step 2 involves using a sonar instrument to perform three-dimensional morphological measurements of the salt cavities in the first and second wells of the salt cavern gas storage facility.

4. The stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility according to claim 3, characterized in that: The specific method for step 2 is as follows: Step 2.1: Place the sonar probe at a certain depth in the salt cavity and emit an acoustic pulse toward the wall of the salt mine cavity. Detect the echo signal and transmit the signal back to the ground computer system to obtain the horizontal measurement distance of the cavity at a certain depth. Step 2.2: Change the measurement depth to obtain the horizontal measurement distance of the salt mine cavity at different depths; Step 2.3: Perform tilt measurements on the top, bottom, and abnormal parts of the salt cavern gas storage to obtain the measurement distance at different tilt angles; the abnormal part is the irregular contour of the cavity wall caused by the cavity top or tilted interlayer between the first well and the second well, which is a local cantilevered, finger-like protrusion. Step 2.4: Use sonar ranging and imaging analysis software to synthesize a three-dimensional image and volume of the entire salt cavity.

5. The stability evaluation method for a small-well-spacing dual-well salt cavern gas storage facility according to claim 4, characterized in that: The tests conducted on the core samples from the data well in step 3 include: density testing, uniaxial compressive strength testing, tensile strength testing, internal friction angle testing, cohesion testing, steady-state creep rate testing, breakthrough pressure testing, permeability testing, and porosity testing. Salt rock will undergo all of the above tests; mudstone and interlayers will undergo all tests except for the breakthrough pressure test.

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