Method and device for describing shale permeability change

Abstract

The embodiment of the invention provides a method and a device for describing the change of shale permeability, and solves the problem of how to simulate the influence of a lifting process on the shale permeability. Comprising the following steps: acquiring the maximum buried depth; loading the shale sample to an overlying strata stress condition corresponding to the maximum buried depth, and then carrying out pre-compaction to obtain a first permeability corresponding to the depth before lifting; carrying out a still water unloading test to obtain a second group of permeability corresponding to different overlying strata stress conditions, and simulating the evolution law of the permeability of the shale in the still water unloading lifting process; acquiring peak value horizontal extrusion stress, and carrying out an unloading test on the basis of the peak value horizontal extrusion stress to obtain equivalent extrusion breaking strength; a third group of permeability is obtained in the unloading test process, and the permeability evolution law in the lifting process after the shale stratum is subjected to horizontal extrusion stress is simulated; and simulating the permeability change in the shale formation lifting process by utilizing the first permeability, the second group of permeability and the third group of permeability in combination with the equivalent extrusion failure strength.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration technology, and specifically to a method and apparatus for describing changes in shale permeability. Background Technology

[0002] The Sichuan Basin in my country possesses enormous shale gas resource potential, but its formation was severely damaged by multiple complex tectonic movements during its formation period. The varying degrees of shale gas loss have resulted in significant differences in gas content across different tectonic zones within the basin. Therefore, clarifying the shale gas loss mechanism, process, and controlling factors is crucial for explaining the differences in shale gas content and, consequently, for guiding shale gas exploration and development. Accurately calculating shale gas loss requires understanding the permeability changes during shale uplift. This necessitates first clarifying the shale gas loss mechanism and influencing factors through experiments, thereby simulating the loss process and calculating the loss amount. Existing experimental methods mostly study permeability changes in shale during static water loading and unloading. However, actual formations are subjected to differential stress during burial and uplift, especially during uplift. Different horizontal compressive stresses or unloading rates lead to different permeability changes, and the impact of different horizontal compressive stress intensities, uplift rates, and uplift amplitudes on shale alteration remains unclear. Currently, there is no systematic laboratory simulation method or mathematical model for ultra-low permeability shale that can be used to study the impact of geostress changes during uplift on shale permeability. Summary of the Invention

[0003] In view of this, embodiments of the present invention provide a method and apparatus for simulating changes in shale permeability, solving the problem of how to simulate the impact of changes in geostress during uplift on shale permeability.

[0004] In a first aspect, an embodiment of the present invention provides a method and apparatus for simulating changes in shale permeability, comprising:

[0005] Obtain the maximum burial depth of the shale sample;

[0006] After loading the shale sample to the stress conditions of the overlying strata corresponding to the maximum burial depth, pre-compact it to obtain the first permeability corresponding to the depth before uplift.

[0007] A second set of permeabilities was obtained under different stress conditions of the overlying strata through hydrostatic unloading tests to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0008] The peak horizontal compressive stress is obtained, and an unloading test is carried out based on the peak horizontal compressive stress until the stress of the overlying strata is reduced to the minimum or the shale sample is destroyed, so as to obtain the equivalent compressive failure strength; wherein, the equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress of the overlying strata is reduced to the minimum or the shale sample is destroyed.

[0009] A third set of permeability was obtained during the unloading test to simulate the permeability evolution during the uplift of shale formations under horizontal compressive stress.

[0010] The permeability changes during the uplift of shale formations are simulated by using the first permeability, the second set of permeability, and the third set of permeability, combined with the equivalent compression failure intensity.

[0011] In one embodiment, prior to conducting the hydrostatic unloading test, the method further includes:

[0012] Uniaxial compression tests were conducted to obtain the elastic modulus and Poisson's ratio of the shale samples; and / or

[0013] Triaxial compression failure tests were conducted under different overlying strata stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying strata stresses. Based on the compressive strength, cohesion, and internal friction angle corresponding to different overlying strata stresses, the relationship between the overlying strata stress and the horizontal compressive stress corresponding to shale fracture was obtained according to the Mohr-Coulomb fracture criterion.

[0014] In one embodiment, obtaining the peak horizontal compressive stress includes:

[0015] Under the stress conditions of the overlying strata corresponding to the maximum burial depth, the horizontal compressive stress is increased in a stress loading mode until the peak horizontal compressive stress is reached; wherein, when carrying out triaxial compression failure tests under different overlying strata stresses, the first compressive strength is obtained under the highest overlying strata stress used, and the peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying strata stress.

[0016] In one embodiment, the unloading test conducted based on the peak horizontal compressive stress until the stress in the overlying strata is reduced to the minimum or the shale sample is destroyed includes: conducting unloading tests with different stress path unloading modes; the stress path unloading modes include: the horizontal compressive stress unloading rate is twice the overlying strata stress unloading rate, the overlying strata stress and the horizontal compressive stress are unloaded at the same rate, and the overlying strata stress unloading rate is twice the axial compression unloading rate.

[0017] In one embodiment, obtaining a third set of permeability during the unloading test includes: conducting the unloading test in an axial displacement control mode, and testing the permeability once each time the stress change of the overlying strata reaches a preset change value, in order to obtain a third set of permeability.

[0018] In one embodiment, simulating permeability changes during shale formation uplift by utilizing the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compressive failure intensity, includes: establishing the following mathematical model.

[0019]

[0020] Among them, K a,0 K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 Δσ represents the permeability during the uplift of the shale formation; Δσ represents the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

[0021] In one embodiment, the equivalent compressive failure strength is obtained by the following formula:

[0022]

[0023] Where Δσ is the difference between the horizontal stress and the equivalent vertical stress after fracture; σ1 is the compressive stress at the critical point of shale fracture; and σ3 is the vertical stress at the critical point of shale fracture. This is the internal friction angle at the critical point of shale fracturing.

[0024] Secondly, an embodiment of the present invention provides an apparatus for simulating changes in shale permeability, comprising:

[0025] The maximum burial depth acquisition module is used to obtain the maximum burial depth of shale samples;

[0026] The first permeability acquisition module is used to pre-compact the shale sample after loading it to the stress conditions of the overlying strata corresponding to the maximum burial depth, so as to obtain the first permeability corresponding to the depth before uplift.

[0027] The second permeability acquisition module is used to conduct hydrostatic unloading tests to obtain the second set of permeability under different overlying strata stress conditions, so as to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0028] Peak horizontal compressive stress acquisition module, used to acquire peak horizontal compressive stress;

[0029] The equivalent compressive failure strength acquisition module is used to conduct unloading tests based on the peak horizontal compressive stress until the stress of the overlying strata drops to the minimum or the shale sample fails, so as to obtain the equivalent compressive failure strength; wherein, the equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress of the overlying strata drops to the minimum or the shale sample fails.

[0030] The third permeability acquisition module is used to acquire the third permeability during the unloading test to simulate the permeability evolution law during the uplift of shale formations under horizontal compressive stress.

[0031] The permeability change simulation module is used to simulate the permeability change during the uplift of shale formations by using the first permeability, the second set of permeability and the third set of permeability, combined with the equivalent compression failure intensity.

[0032] Thirdly, an embodiment of the present invention provides an electronic device including a memory and a processor, wherein the memory is used to store one or more computer instructions, wherein the one or more computer instructions, when executed by the processor, implement the method for simulating shale permeability changes as described above.

[0033] Fourthly, an embodiment of the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, is used to implement the method for simulating shale permeability changes as described above.

[0034] This invention provides a method and apparatus for describing changes in shale permeability. By establishing a mathematical model, the changes in shale permeability during uplift are accurately simulated. The parameters in the mathematical model are clarified through experiments. The model can be applied to the assessment and calculation of shale gas loss, thereby explaining the reasons for the differences in gas content of shale at different uplift amplitudes and providing important basis for exploration. Attached Figure Description

[0035] Figure 1 The diagram shown is a flowchart illustrating a method for describing changes in shale permeability according to an embodiment of the present invention.

[0036] Figure 2 The diagram shown is a schematic representation of the relationship between the experimental stage, overlying stratum stress, and horizontal compressive stress corresponding to a simulated differential burial and uplift process according to an embodiment of the present invention.

[0037] Figure 3 The diagram shown is a schematic representation of the experimental results of simulating the change in shale permeability during a static water unloading and uplift process, according to an embodiment of the present invention.

[0038] Figure 4The diagram shown is a schematic representation of the experimental results of simulating the relationship between shale permeability and differential stress before compression and uplift, according to an embodiment of the present invention.

[0039] Figure 5 The diagram shown is a schematic representation of the experimental results of the relationship between shale permeability and effective overlying strata stress during a simulated uplift process, according to an embodiment of the present invention.

[0040] Figure 6 The diagram shown is a structural schematic of a device for describing changes in shale permeability according to an embodiment of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1:

[0043] This embodiment provides a method for simulating changes in shale permeability, such as... Figure 1 As shown, the method for simulating changes in shale permeability includes:

[0044] Step 01: Obtain the maximum burial depth of the shale sample.

[0045] Optionally, a set of cylindrical shale samples can be prepared first using a wire cutting device, and then the samples can be dried at high temperature and vacuumed in a drying oven to obtain the final shale samples used for the experiment.

[0046] Furthermore, the maximum burial depth of the shale sample obtained includes obtaining the maximum burial depth based on the burial uplift history of the core well.

[0047] Step 02: After loading the shale sample to the stress conditions of the overlying strata corresponding to the maximum burial depth, pre-compact it to obtain the first permeability corresponding to the depth before uplift.

[0048] The formula for calculating the stress in the overlying strata corresponding to the maximum burial depth is as follows:

[0049] σ3=ρgD1

[0050] Where σ3 is the stress of the overlying strata corresponding to the maximum burial depth; D1 is the maximum burial depth before uplift.

[0051] Step 03: Conduct hydrostatic unloading tests to obtain the second set of permeability under different overlying strata stress conditions, in order to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0052] Specifically, a hydrostatic unloading test was conducted based on the overlying strata stress (confining pressure) conditions corresponding to the maximum burial depth determined in step 01. The second set of permeability K was tested under several uniformly distributed overlying strata stress conditions. a,1 To simulate the evolution of permeability in shale during hydrostatic unloading and uplift, and to obtain the compressibility coefficient C during hydrostatic unloading. f .

[0053] Optionally, in stress-controlled mode, the permeability of low-permeability shale samples is tested using the pulse decay method. Since the test time is long, the stress loading rate can be manually adjusted to 0 when testing permeability.

[0054] Permeability testing can be performed using gas permeability measurement. Inert gases such as helium are generally chosen for this test. For shale gas samples, methane can be used directly for more accurate results, but the adsorption effect must be considered, and the sample should be saturated with methane before testing. Regarding fluid pressure, it should be as high as possible within the laboratory's achievable range, while still meeting effective stress requirements, to minimize the impact of gas slippage.

[0055] Step 04: Obtain the peak horizontal compressive stress. Based on the peak horizontal compressive stress, conduct unloading tests until the stress in the overlying strata drops to its minimum or the shale sample fails, to obtain the equivalent compressive failure strength. The equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress in the overlying strata drops to its minimum or the shale sample fails.

[0056] The equivalent compressive failure strength is obtained by the following formula:

[0057]

[0058] Where Δσ is the equivalent compressive failure strength; σ1 is the compressive stress at the critical point of shale fracture; and σ3 is the vertical stress at the critical point of shale fracture. This is the internal friction angle at the critical point of shale fracturing.

[0059] Optionally, before conducting the hydrostatic unloading test, the method further includes: conducting a uniaxial compression test to obtain the elastic modulus and Poisson's ratio of the shale sample; conducting triaxial compression failure tests under different overlying stratum stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying stratum stresses; and, based on the compressive strength, cohesion, and internal friction angle corresponding to the different overlying stratum stresses, obtaining the relationship between the overlying stratum stress and the horizontal compressive stress corresponding to rock fracture according to the Mohr-Coulomb fracture criterion. Specifically, triaxial compression failure tests are conducted under three different overlying stratum stresses (confining pressures): first overlying stratum stress, second overlying stratum stress, and third overlying stratum stress, to obtain the corresponding compressive strength, cohesion c, and internal friction angle. The stress in the first overlying stratum is less than that in the second overlying stratum, which is less than that in the third overlying stratum. Optionally, the stress in the third overlying stratum can be equal to the stress in the overlying stratum corresponding to the maximum burial depth obtained in step 01. Obtaining the relationship between the stress in the overlying stratum corresponding to rock fracture and the horizontal compressive stress can predict the fracture strength of the rock under different overlying stratum stresses. It can also provide a reference for determining the fracture criticality when conducting unloading tests, thereby increasing the density of test points.

[0060] Specifically, obtaining the peak horizontal compressive stress includes: under the overlying stratum stress condition corresponding to the maximum burial depth, increasing the horizontal compressive stress in a stress loading mode until the peak horizontal compressive stress is reached; wherein, when conducting triaxial compression failure tests under different overlying stratum stresses, a first compressive strength is obtained under the highest overlying stratum stress used, and the peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying stratum stress. Optionally, the preset percentage is 60%, that is, under the overlying stratum stress (confining pressure) condition corresponding to the maximum burial depth, the horizontal compressive stress (axial compression) is slowly increased in a stress loading mode, corresponding to 60% of the compressive strength obtained under the third overlying stratum stress condition, to ensure that no microcracks are formed in the sample, and the 60% of the compressive strength obtained under the third overlying stratum stress condition plus the overlying stratum stress is used as the peak horizontal compressive stress of the second stage loading test.

[0061] Furthermore, after obtaining the peak horizontal compressive stress, the method further includes: increasing the horizontal compressive stress under the stress condition of the overlying strata corresponding to the maximum burial depth using a stress loading mode, and obtaining a fourth set of permeability under a preset number of uniformly distributed differential stress conditions; wherein the differential stress is the difference between the horizontal compressive stress and the stress of the overlying strata; based on the fourth set of permeability, the permeability evolution law of shale before it is subjected to horizontal compressive stress but has not yet been uplifted can be simulated.

[0062] Furthermore, the unloading test conducted based on the peak horizontal compressive stress until the overlying stratum stress is reduced to its minimum or the shale sample is destroyed includes: conducting unloading tests using different stress path unloading modes; the stress path unloading modes include: the horizontal compressive stress unloading rate is twice the overlying stratum stress unloading rate, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate, and the overlying stratum stress unloading rate is twice the axial compression unloading rate. It can be understood that by conducting the third stage of the unloading test using three different stress path unloading modes until the overlying stratum stress is reduced to its minimum or the sample is destroyed, the equivalent compressive failure strength Δσ is obtained. In the first stress path, the horizontal compressive stress (axial compression) unloading rate is twice the overlying stratum stress (confining pressure) unloading rate; in the second stress path, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate; and in the third stress path, the overlying stratum stress unloading rate is twice the axial compression unloading rate.

[0063] Step 05: Obtain the third set of permeability during the unloading test to simulate the permeability evolution during the uplift of shale formations under horizontal compressive stress.

[0064] Because the shale unloading process is prone to sudden collapse, making it impossible to describe the post-peak stress-strain curve and measure permeability changes in a timely manner, unloading must be carried out using a slow axial displacement control mode, and permeability K must be tested every time the stress of the overlying strata changes by a certain value. a，2 This allows us to obtain a third set of permeability values ​​to simulate the permeability evolution during the uplift process of shale formations subjected to horizontal compressive stress.

[0065] Step 06: Using the first permeability, the second set of permeability, and the third set of permeability, combined with the equivalent compression failure intensity, to simulate the permeability change during the uplift process of shale formations.

[0066] The method of simulating permeability changes during shale formation uplift by utilizing the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compressive failure intensity, includes: establishing the following mathematical model.

[0067]

[0068] Among them, K a,0 K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 Δσ represents the permeability during the uplift of the shale formation; Δσ represents the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

[0069] This embodiment simulates the permeability evolution at various stages of formation uplift based on the formation's burial and uplift history. Since the main factors influencing rock permeability include overlying strata stress, horizontal compressive stress, and stress path, this experimental method is divided into three stages: a stage where both overlying strata stress and horizontal compressive stress increase simultaneously; a stage where overlying strata stress remains constant while horizontal compressive stress increases; and a stage where both overlying strata stress and horizontal compressive stress are unloaded. This embodiment implements different stress paths to achieve weak, medium, and strong alteration, establishing a mathematical model of permeability changes under different equivalent compressive intensities. It simulates the permeability evolution during formation uplift under different degrees of alteration, allowing for the simultaneous study of the relationship between shale permeability, stress, and damage. This can then be applied to changes in capillary sealing capacity and the evaluation of shale gas loss.

[0070] Example 2:

[0071] This embodiment provides a mathematical model to describe the change in shale permeability during the uplift process, including:

[0072] First, obtain the permeability changes during the hydrostatic unloading and uplift process of the shale layer:

[0073]

[0074] Among them, K a,0 C represents the permeability at a depth of D1 before elevation; f K is the compression factor; a,1 The permeability at depth D2 is the baseline permeability at the current depth, unaffected by compression.

[0075] Secondly, to obtain the permeability change during the compression and uplift process, it is necessary to first obtain the permeability change of shale before compression but before uplift. This requires obtaining the permeability change after fracturing, specifically the cohesion (c) and the internal friction angle. The relationship between the compressive stress σ1 and the vertical stress σ3 at the critical time of shale fracture is described as follows:

[0076]

[0077] When the shale layer is uplifted to a certain depth and fractures, the cohesion becomes zero.

[0078]

[0079] Here, we define a parameter, equivalent compressive failure strength, which is the difference Δσ between the horizontal stress and the equivalent vertical stress after fracture. This is used to describe the effect of the change in compressive strength on the permeability change after fracture. The equivalent compressive failure strength experienced by shale after fracture and loss of cohesion is:

[0080]

[0081] This value can also be understood as an equivalent description of the degree of fault dislocation after uplift to a certain depth and subsequent fracturing. It is assumed that under continuous stress differential, fault dislocation increases, and permeability continuously changes. Therefore, the mathematical model for permeability changes during shale formation uplift is:

[0082]

[0083] Wherein, β is the equivalent coefficient of the degree of fault dislocation.

[0084] Example 3:

[0085] The following are specific embodiments of the present invention, and the technical solution of the present invention will be further described in conjunction with the accompanying drawings.

[0086] This embodiment uses the method for describing shale permeability changes described in Embodiment 1, taking the Longmaxi Formation shale in Well D1 in the Fuling area as an example, to specifically illustrate an experimental method for describing shale permeability changes during uplift, including the following steps:

[0087] (1) Cylindrical shale samples with a diameter of 25 mm and a length of 50 mm were prepared using a wire cutting device. The samples were then dried at a high temperature of 60 degrees Celsius in a drying oven while being vacuumed. The samples were weighed every 6 hours using a ten-thousandth balance until the weight remained almost constant.

[0088] (2) Based on the burial and uplift history of well D1, the maximum burial depth of the Longmaxi Formation shale is 8000m. The average density of the overlying strata is taken as 2.5g / cm3. According to formula 6, the stress of the overlying strata is σ3 = 200MPa. The formation fluid pressure is set as hydrostatic pressure Pp = 80MPa, then the effective stress of the overlying strata is 120MPa.

[0089] (3) Uniaxial compression tests were conducted on the Longmaxi Formation shale, and its elastic modulus E = 20 GPa and Poisson's ratio υ = 0.25 were obtained.

[0090] (4) Triaxial compression tests were conducted under three effective overlying strata pressures (confining pressures) of 40 MPa, 80 MPa, and 120 MPa. The compressive strength under an effective overlying strata pressure (confining pressure) of 120 MPa was 250 MPa. In addition, the cohesion of the shale was found to be 21.9 MPa and the internal friction angle was 39.85°.

[0091] (5) This embodiment is based on Figure 2 The OAB-C2 path is implemented.

[0092] (6) In the first stage, the overlying strata were pre-compacted under an effective overburden pressure (confining pressure) of 120 MPa, and the permeability K was measured. a,0=16.6×10⁻³ mD. Nitrogen gas was introduced until the sample was saturated, then the sample was unloaded back to the initial stress conditions. Permeability K was tested under five overlying rock stress conditions. a,1 The evolution of permeability of shale during the static water unloading and uplift process was simulated, such as... Figure 3 The compression coefficient C is obtained. f =0.0287MPa-1.

[0093] K a,1 =0.0166e -0.086pgΔh

[0094] (7) In the second stage, under the effective overlying stratum pressure of 120 MPa, the horizontal compressive stress (axial pressure) is slowly increased in a stress loading mode. The difference between the horizontal compressive stress and the overlying stratum stress is called the differential stress. This continues until the differential stress reaches 60% of the compressive strength, i.e., 150 MPa. Permeability is tested four times under four different stress conditions to simulate the permeability evolution of shale before it is subjected to horizontal compressive stress but before it is uplifted. Figure 4 .

[0095] (8) In the third stage, the unloading process is carried out under a differential stress of 150 MPa. The stress of the overlying strata and the horizontal compressive stress are unloaded at the same rate, and the unloading is controlled by a slow axial displacement. The equivalent compressive failure strength is obtained according to Formula 4:

[0096] Δσ=σ1-4.57σ3

[0097] The permeability K is tested every time the stress change in the overlying strata reaches a preset value. a,2 A total of 19 times, such as Figure 5 Based on the fitting experimental results obtained from the planning solution, the equivalent coefficient β = 0.2 for the degree of fault faulting was obtained. The permeability evolution law of the shale formation under horizontal compressive stress was simulated.

[0098]

[0099] Example 4:

[0100] This embodiment provides a device 100 for describing changes in shale permeability, such as... Figure 6 The device 100 for describing shale permeability changes includes: a maximum burial depth acquisition module 10, a first permeability acquisition module 20, a second set of permeability acquisition modules 30, a peak horizontal compressive stress acquisition module 40, an equivalent compressive failure strength acquisition module 50, a third set of permeability acquisition modules 60, and a permeability change simulation module 70.

[0101] The maximum burial depth acquisition module 10 is used to acquire the maximum burial depth of shale samples;

[0102] The first permeability acquisition module 20 is used to pre-compact the shale sample after loading it to the stress conditions of the overlying strata corresponding to the maximum burial depth, so as to obtain the first permeability corresponding to the depth before uplift.

[0103] The second set of permeability acquisition modules 30 is used to carry out hydrostatic unloading tests to obtain the second set of permeability under different stress conditions of the overlying strata, so as to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0104] The peak horizontal compressive stress acquisition module 40 is used to acquire the peak horizontal compressive stress.

[0105] The equivalent compressive failure strength acquisition module 50 is used to conduct an unloading test based on the peak horizontal compressive stress until the stress of the overlying strata drops to the minimum or the shale sample is destroyed, so as to obtain the equivalent compressive failure strength; wherein, the equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress of the overlying strata drops to the minimum or the shale sample is destroyed.

[0106] The third permeability acquisition module 60 is used to acquire a third set of permeability during the unloading test to simulate the permeability evolution law during the uplift process of shale formations subjected to horizontal compressive stress.

[0107] The permeability change simulation module is used to simulate the permeability change during the uplift of shale formations by using the first permeability, the second set of permeability and the third set of permeability, combined with the equivalent compression failure intensity.

[0108] Furthermore, the maximum burial depth acquisition module 10 is used to obtain the maximum burial depth based on the burial uplift history of the core well. The formula for converting the stress of the overlying strata corresponding to the maximum burial depth is as follows:

[0109] σ3=ρgD1

[0110] Where σ3 is the stress of the overlying strata corresponding to the maximum burial depth; D1 is the maximum burial depth before uplift.

[0111] Furthermore, the second set of permeability acquisition modules 30 is used to conduct hydrostatic unloading tests based on the overlying strata stress (confining pressure) conditions corresponding to the maximum burial depth determined in step 01, and to obtain the second set of permeability K under several uniformly distributed overlying strata stress conditions. a,1 To simulate the evolution of permeability in shale during hydrostatic unloading and uplift, and to obtain the compressibility coefficient C during hydrostatic unloading. f .

[0112] Optionally, in stress-controlled mode, the permeability of low-permeability shale samples is tested using the pulse decay method. Since the test time is long, the stress loading rate must be manually adjusted to 0 when testing permeability.

[0113] Permeability testing can be performed using gas permeability measurement. Inert gases such as helium are generally chosen for this test. For shale gas samples, methane can be used directly for more accurate results, but the adsorption effect must be considered, and the sample should be saturated with methane before testing. Regarding fluid pressure, it should be as high as possible within the laboratory's achievable range, while still meeting effective stress requirements, to minimize the impact of gas slippage.

[0114] The device 100 for describing shale permeability changes also includes a parameter acquisition module. This module is used to conduct uniaxial compression tests to obtain the elastic modulus and Poisson's ratio of the shale sample; and to conduct triaxial compression failure tests under different overlying strata stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying strata stresses; based on the compressive strength, cohesion, and internal friction angle corresponding to the different overlying strata stresses... The relationship between the stress in the overlying strata and the horizontal compressive stress corresponding to rock fracture was obtained based on the Mohr-Coulomb fracture criterion. Specifically, triaxial compression failure tests were conducted under three different overlying strata stresses (confining pressures): the first, second, and third overlying strata stresses, to obtain the corresponding compressive strength, cohesion c, and internal friction angle. The stress in the first overlying stratum is less than that in the second overlying stratum, which is less than that in the third overlying stratum. Optionally, the stress in the third overlying stratum can be equal to the stress in the overlying stratum corresponding to the maximum burial depth obtained in step 01. Obtaining the relationship between the stress in the overlying stratum corresponding to rock fracture and the horizontal compressive stress can predict the fracture strength of the rock under different overlying stratum stresses. It can also provide a reference for determining the fracture criticality when conducting unloading tests, thereby increasing the density of test points.

[0115] Further, the peak horizontal compressive stress acquisition module 40 is used to increase the horizontal compressive stress in a stress loading mode under the overlying stratum stress condition corresponding to the maximum burial depth. Specifically, when conducting triaxial compression failure tests under different overlying stratum stresses, a first compressive strength is obtained under the highest overlying stratum stress used. The peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying stratum stress. Optionally, the preset percentage is 60%, that is, under the overlying stratum stress (confining pressure) condition corresponding to the maximum burial depth, the horizontal compressive stress (axial compression) is slowly increased in a stress loading mode, corresponding to 60% of the compressive strength obtained under the third overlying stratum stress condition, to ensure that no microcracks form in the sample. The 60% of the compressive strength obtained under the third overlying stratum stress condition plus the overlying stratum stress is used as the peak horizontal compressive stress for the second stage of the loading test.

[0116] The device 100 for describing the change in shale permeability further includes a fourth permeability acquisition module. The fourth permeability acquisition module is used to increase the horizontal compressive stress under the stress condition of the overlying stratum corresponding to the maximum burial depth in a stress loading mode, and obtain a preset number of uniformly distributed differential stress conditions for the fourth permeability. The differential stress is the difference between the horizontal compressive stress and the stress of the overlying stratum. Based on the fourth permeability, the permeability evolution law of shale before it is subjected to horizontal compressive stress but before it is uplifted is simulated.

[0117] Furthermore, the equivalent compressive failure strength acquisition module 50 is used to conduct unloading tests under different stress path unloading modes; the stress path unloading modes include at least two of the following: the horizontal compressive stress unloading rate is twice the overlying stratum stress unloading rate, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate, and the overlying stratum stress unloading rate is twice the axial compression unloading rate. It can be understood that the third stage of the unloading test is conducted using three different stress path unloading modes until the overlying stratum stress is reduced to its minimum or the sample fails, obtaining the equivalent compressive failure strength Δσ. In the first stress path, the horizontal compressive stress (axial compression) unloading rate is twice the overlying stratum stress (confining pressure) unloading rate; in the second stress path, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate; and in the third stress path, the overlying stratum stress unloading rate is twice the axial compression unloading rate.

[0118] Furthermore, the permeability change simulation module 70 utilizes the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compression failure intensity, to simulate the permeability change during the uplift of shale formations, including: establishing the following mathematical model.

[0119]

[0120] Among them, K a,0K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 ρ represents the permeability during the uplift of the shale formation; β is the equivalent coefficient for the degree of fault faulting; Δσ is the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

[0121] Because the shale unloading process is prone to sudden collapse, making it impossible to describe the post-peak stress-strain curve and measure permeability changes in a timely manner, unloading must be carried out using a slow axial displacement control mode, and permeability K must be tested every time the stress of the overlying strata changes by a certain value. a，2 To simulate the permeability evolution of shale formations during uplift under horizontal compressive stress.

[0122] Example 5:

[0123] This embodiment provides an electronic device, which may be a mobile phone, computer, or tablet computer, etc., including a memory and a processor. The memory stores a computer program, which, when executed by the processor, implements the method for describing changes in shale permeability as described in Embodiment 1. It is understood that the electronic device may further include an input / output (I / O) interface and communication components.

[0124] The processor is used to execute all or part of the steps in the method describing changes in shale permeability, as described in Embodiment 1. The memory is used to store various types of data, which may include, for example, instructions for any application or method in the electronic device, as well as application-related data.

[0125] The processor may be implemented as an Application Specific Integrated Circuit (ASIC), Digital Signal Processor (DSP), Programmable Logic Device (PLD), Field Programmable Gate Array (FPGA), controller, microcontroller, microprocessor, or other electronic components, and is used to execute the method for describing shale permeability changes in Embodiment 1 above.

[0126] The memory can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Read-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0127] The method for describing changes in shale permeability provided in this embodiment, based on the above modules, includes:

[0128] Step 01: Obtain the maximum burial depth of the shale sample.

[0129] Optionally, a set of cylindrical shale samples can be prepared first using a wire cutting device, and then the samples can be dried at high temperature and vacuumed in a drying oven to obtain the final shale samples used for the experiment.

[0130] Furthermore, the maximum burial depth of the shale sample obtained includes obtaining the maximum burial depth based on the burial uplift history of the core well.

[0131] Step 02: After loading the shale sample to the stress conditions of the overlying strata corresponding to the maximum burial depth, pre-compact it to obtain the first permeability corresponding to the depth before uplift.

[0132] The formula for calculating the stress in the overlying strata corresponding to the maximum burial depth is as follows:

[0133] σ3=ρgD1

[0134] Where σ3 is the stress of the overlying strata corresponding to the maximum burial depth; D1 is the maximum burial depth before uplift.

[0135] Step 03: Conduct hydrostatic unloading tests to obtain the second set of permeability under different overlying strata stress conditions, in order to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0136] Specifically, a hydrostatic unloading test was conducted based on the overlying strata stress (confining pressure) conditions corresponding to the maximum burial depth determined in step 01. The second set of permeability K was tested under several uniformly distributed overlying strata stress conditions. a,1To simulate the evolution of permeability in shale during hydrostatic unloading and uplift, and to obtain the compressibility coefficient C during hydrostatic unloading. f .

[0137] Optionally, in stress-controlled mode, the permeability of low-permeability shale samples is tested using the pulse decay method. Since the test time is long, the stress loading rate can be manually adjusted to 0 when testing permeability.

[0138] Permeability testing can be performed using gas permeability measurement. Inert gases such as helium are generally chosen for this test. For shale gas samples, methane can be used directly for more accurate results, but the adsorption effect must be considered, and the sample should be saturated with methane before testing. Regarding fluid pressure, it should be as high as possible within the laboratory's achievable range, while still meeting effective stress requirements, to minimize the impact of gas slippage.

[0139] Step 04: Obtain the peak horizontal compressive stress. Based on the peak horizontal compressive stress, conduct unloading tests until the stress in the overlying strata drops to its minimum or the shale sample fails, to obtain the equivalent compressive failure strength. The equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress in the overlying strata drops to its minimum or the shale sample fails.

[0140] The equivalent compressive failure strength is obtained by the following formula:

[0141]

[0142] Where Δσ is the equivalent compressive failure strength; σ1 is the compressive stress at the critical point of shale fracture; and σ3 is the vertical stress at the critical point of shale fracture. This is the internal friction angle at the critical point of shale fracturing.

[0143] Optionally, before conducting the hydrostatic unloading test, the method further includes: conducting a uniaxial compression test to obtain the elastic modulus and Poisson's ratio of the shale sample; conducting triaxial compression failure tests under different overlying stratum stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying stratum stresses; and, based on the compressive strength, cohesion, and internal friction angle corresponding to the different overlying stratum stresses, obtaining the relationship between the overlying stratum stress and the horizontal compressive stress corresponding to rock fracture according to the Mohr-Coulomb fracture criterion. Specifically, triaxial compression failure tests are conducted under three different overlying stratum stresses (confining pressures): first overlying stratum stress, second overlying stratum stress, and third overlying stratum stress, to obtain the corresponding compressive strength, cohesion c, and internal friction angle. The stress in the first overlying stratum is less than that in the second overlying stratum, which is less than that in the third overlying stratum. Optionally, the stress in the third overlying stratum can be equal to the stress in the overlying stratum corresponding to the maximum burial depth obtained in step 01. Obtaining the relationship between the stress in the overlying stratum corresponding to rock fracture and the horizontal compressive stress can predict the fracture strength of the rock under different overlying stratum stresses. It can also provide a reference for determining the fracture criticality when conducting unloading tests, thereby increasing the density of test points.

[0144] Specifically, obtaining the peak horizontal compressive stress includes: under the overlying stratum stress condition corresponding to the maximum burial depth, increasing the horizontal compressive stress in a stress loading mode until the peak horizontal compressive stress is reached; wherein, when conducting triaxial compression failure tests under different overlying stratum stresses, a first compressive strength is obtained under the highest overlying stratum stress used, and the peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying stratum stress. Optionally, the preset percentage is 60%, that is, under the overlying stratum stress (confining pressure) condition corresponding to the maximum burial depth, the horizontal compressive stress (axial compression) is slowly increased in a stress loading mode, corresponding to 60% of the compressive strength obtained under the third overlying stratum stress condition, to ensure that no microcracks are formed in the sample, and the 60% of the compressive strength obtained under the third overlying stratum stress condition plus the overlying stratum stress is used as the peak horizontal compressive stress of the second stage loading test.

[0145] Furthermore, after obtaining the peak horizontal compressive stress, the method further includes: increasing the horizontal compressive stress under the stress condition of the overlying strata corresponding to the maximum burial depth using a stress loading mode, and obtaining a fourth set of permeability under a preset number of uniformly distributed differential stress conditions; wherein the differential stress is the difference between the horizontal compressive stress and the stress of the overlying strata; based on the fourth set of permeability, the permeability evolution law of shale before it is subjected to horizontal compressive stress but has not yet been uplifted can be simulated.

[0146] Furthermore, the unloading test conducted based on the peak horizontal compressive stress until the overlying stratum stress is reduced to its minimum or the shale sample is destroyed includes: conducting unloading tests using different stress path unloading modes; the stress path unloading modes include: the horizontal compressive stress unloading rate is twice the overlying stratum stress unloading rate, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate, and the overlying stratum stress unloading rate is twice the axial compression unloading rate. It can be understood that by conducting the third stage of the unloading test using three different stress path unloading modes until the overlying stratum stress is reduced to its minimum or the sample is destroyed, the equivalent compressive failure strength Δσ is obtained. In the first stress path, the horizontal compressive stress (axial compression) unloading rate is twice the overlying stratum stress (confining pressure) unloading rate; in the second stress path, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate; and in the third stress path, the overlying stratum stress unloading rate is twice the axial compression unloading rate.

[0147] Step 05: Obtain the third set of permeability during the unloading test to simulate the permeability evolution during the uplift of shale formations under horizontal compressive stress.

[0148] Because the shale unloading process is prone to sudden collapse, making it impossible to describe the post-peak stress-strain curve and measure permeability changes in a timely manner, unloading must be carried out using a slow axial displacement control mode, and permeability K must be tested every time the stress of the overlying strata changes by a certain value. a，2 This allows us to obtain a third set of permeability values ​​to simulate the permeability evolution during the uplift process of shale formations subjected to horizontal compressive stress.

[0149] Step 06: Using the first permeability, the second set of permeability, and the third set of permeability, combined with the equivalent compression failure intensity, to simulate the permeability change during the uplift process of shale formations.

[0150] The method of simulating permeability changes during shale formation uplift by utilizing the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compressive failure intensity, includes: establishing the following mathematical model.

[0151]

[0152] Among them, K a,0 K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 ρ represents the permeability during the uplift of the shale formation; β is the equivalent coefficient for the degree of fault faulting; Δσ is the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

[0153] This embodiment simulates the permeability evolution at various stages of formation uplift based on the formation's burial and uplift history. Since the main factors influencing rock permeability include overlying strata stress, horizontal compressive stress, and stress path, this experimental method is divided into three stages: a stage where both overlying strata stress and horizontal compressive stress increase simultaneously; a stage where overlying strata stress remains constant while horizontal compressive stress increases; and a stage where both overlying strata stress and horizontal compressive stress are unloaded. This embodiment implements different stress paths to achieve weak, medium, and strong alteration, establishing a mathematical model of permeability changes under different equivalent compressive intensities. It simulates the permeability evolution during formation uplift under different degrees of alteration, allowing for the simultaneous study of the relationship between shale permeability, stress, and damage. This can then be applied to changes in capillary sealing capacity and the evaluation of shale gas loss.

[0154] Example 6:

[0155] This embodiment also provides a computer-readable storage medium. The functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. If the functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium.

[0156] Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0157] The aforementioned storage media include: flash memory, hard disks, multimedia cards, card-type memory (e.g., SD or DX memory), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, disks, optical discs, servers, APP application stores, and various other media capable of storing program verification codes, on which computer programs are stored. When the computer program is executed by a processor, it can implement the following method steps:

[0158] Step 01: Obtain the maximum burial depth of the shale sample.

[0159] Optionally, a set of cylindrical shale samples can be prepared first using a wire cutting device, and then the samples can be dried at high temperature and vacuumed in a drying oven to obtain the final shale samples used for the experiment.

[0160] Furthermore, the maximum burial depth of the shale sample obtained includes obtaining the maximum burial depth based on the burial uplift history of the core well.

[0161] Step 02: After loading the shale sample to the stress conditions of the overlying strata corresponding to the maximum burial depth, pre-compact it to obtain the first permeability corresponding to the depth before uplift.

[0162] The formula for calculating the stress in the overlying strata corresponding to the maximum burial depth is as follows:

[0163] σ3=ρgD1

[0164] Where σ3 is the stress of the overlying strata corresponding to the maximum burial depth; D1 is the maximum burial depth before uplift.

[0165] Step 03: Conduct hydrostatic unloading tests to obtain the second set of permeability under different overlying strata stress conditions, in order to simulate the evolution of permeability of shale during hydrostatic unloading and uplift.

[0166] Specifically, a hydrostatic unloading test was conducted based on the overlying strata stress (confining pressure) conditions corresponding to the maximum burial depth determined in step 01. The second set of permeability K was tested under several uniformly distributed overlying strata stress conditions. a,1 To simulate the evolution of permeability in shale during hydrostatic unloading and uplift, and to obtain the compressibility coefficient C during hydrostatic unloading. f .

[0167] Optionally, in stress-controlled mode, the permeability of low-permeability shale samples is tested using the pulse decay method. Since the test time is long, the stress loading rate can be manually adjusted to 0 when testing permeability.

[0168] Permeability testing can be performed using gas permeability measurement. Inert gases such as helium are generally chosen for this test. For shale gas samples, methane can be used directly for more accurate results, but the adsorption effect must be considered, and the sample should be saturated with methane before testing. Regarding fluid pressure, it should be as high as possible within the laboratory's achievable range, while still meeting effective stress requirements, to minimize the impact of gas slippage.

[0169] Step 04: Obtain the peak horizontal compressive stress. Based on the peak horizontal compressive stress, conduct unloading tests until the stress in the overlying strata drops to its minimum or the shale sample fails, to obtain the equivalent compressive failure strength. The equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress in the overlying strata drops to its minimum or the shale sample fails.

[0170] The equivalent compressive failure strength is obtained by the following formula:

[0171]

[0172] Where Δσ is the equivalent compressive failure strength; σ1 is the compressive stress at the critical point of shale fracture; and σ3 is the vertical stress at the critical point of shale fracture. This is the internal friction angle at the critical point of shale fracturing.

[0173] Optionally, before conducting the hydrostatic unloading test, the method further includes: conducting a uniaxial compression test to obtain the elastic modulus and Poisson's ratio of the shale sample; conducting triaxial compression failure tests under different overlying stratum stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying stratum stresses; and, based on the compressive strength, cohesion, and internal friction angle corresponding to the different overlying stratum stresses, obtaining the relationship between the overlying stratum stress and the horizontal compressive stress corresponding to rock fracture according to the Mohr-Coulomb fracture criterion. Specifically, triaxial compression failure tests are conducted under three different overlying stratum stresses (confining pressures): first overlying stratum stress, second overlying stratum stress, and third overlying stratum stress, to obtain the corresponding compressive strength, cohesion c, and internal friction angle. The stress in the first overlying stratum is less than that in the second overlying stratum, which is less than that in the third overlying stratum. Optionally, the stress in the third overlying stratum can be equal to the stress in the overlying stratum corresponding to the maximum burial depth obtained in step 01. Obtaining the relationship between the stress in the overlying stratum corresponding to rock fracture and the horizontal compressive stress can predict the fracture strength of the rock under different overlying stratum stresses. It can also provide a reference for determining the fracture criticality when conducting unloading tests, thereby increasing the density of test points.

[0174] Specifically, obtaining the peak horizontal compressive stress includes: under the overlying stratum stress condition corresponding to the maximum burial depth, increasing the horizontal compressive stress in a stress loading mode until the peak horizontal compressive stress is reached; wherein, when conducting triaxial compression failure tests under different overlying stratum stresses, a first compressive strength is obtained under the highest overlying stratum stress used, and the peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying stratum stress. Optionally, the preset percentage is 60%, that is, under the overlying stratum stress (confining pressure) condition corresponding to the maximum burial depth, the horizontal compressive stress (axial compression) is slowly increased in a stress loading mode, corresponding to 60% of the compressive strength obtained under the third overlying stratum stress condition, to ensure that no microcracks are formed in the sample, and the 60% of the compressive strength obtained under the third overlying stratum stress condition plus the overlying stratum stress is used as the peak horizontal compressive stress of the second stage loading test.

[0175] Furthermore, after obtaining the peak horizontal compressive stress, the method further includes: increasing the horizontal compressive stress under the stress condition of the overlying strata corresponding to the maximum burial depth using a stress loading mode, and obtaining a fourth set of permeability under a preset number of uniformly distributed differential stress conditions; wherein the differential stress is the difference between the horizontal compressive stress and the stress of the overlying strata; based on the fourth set of permeability, the permeability evolution law of shale before it is subjected to horizontal compressive stress but has not yet been uplifted can be simulated.

[0176] Furthermore, the unloading test conducted based on the peak horizontal compressive stress until the overlying stratum stress is reduced to its minimum or the shale sample is destroyed includes: conducting unloading tests using different stress path unloading modes; the stress path unloading modes include: the horizontal compressive stress unloading rate is twice the overlying stratum stress unloading rate, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate, and the overlying stratum stress unloading rate is twice the axial compression unloading rate. It can be understood that by conducting the third stage of the unloading test using three different stress path unloading modes until the overlying stratum stress is reduced to its minimum or the sample is destroyed, the equivalent compressive failure strength Δσ is obtained. In the first stress path, the horizontal compressive stress (axial compression) unloading rate is twice the overlying stratum stress (confining pressure) unloading rate; in the second stress path, the overlying stratum stress and the horizontal compressive stress are unloaded at the same rate; and in the third stress path, the overlying stratum stress unloading rate is twice the axial compression unloading rate.

[0177] Step 05: Obtain the third set of permeability during the unloading test to simulate the permeability evolution during the uplift of shale formations under horizontal compressive stress.

[0178] Because the shale unloading process is prone to sudden collapse, making it impossible to describe the post-peak stress-strain curve and measure permeability changes in a timely manner, unloading must be carried out using a slow axial displacement control mode, and permeability K must be tested every time the stress of the overlying strata changes by a certain value. a，2 This allows us to obtain a third set of permeability values ​​to simulate the permeability evolution during the uplift process of shale formations subjected to horizontal compressive stress.

[0179] Step 06: Using the first permeability, the second set of permeability, and the third set of permeability, combined with the equivalent compression failure intensity, to simulate the permeability change during the uplift process of shale formations.

[0180] The method of simulating permeability changes during shale formation uplift by utilizing the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compressive failure intensity, includes: establishing the following mathematical model.

[0181]

[0182] Among them, K a,0 K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 ρ represents the permeability during the uplift of the shale formation; β is the equivalent coefficient for the degree of fault faulting; Δσ is the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

[0183] This embodiment simulates the permeability evolution at various stages of formation uplift based on the formation's burial and uplift history. Since the main factors influencing rock permeability include overlying strata stress, horizontal compressive stress, and stress path, this experimental method is divided into three stages: a stage where both overlying strata stress and horizontal compressive stress increase simultaneously; a stage where overlying strata stress remains constant while horizontal compressive stress increases; and a stage where both overlying strata stress and horizontal compressive stress are unloaded. This embodiment implements different stress paths to achieve weak, medium, and strong alteration, establishing a mathematical model of permeability changes under different equivalent compressive intensities. It simulates the permeability evolution during formation uplift under different degrees of alteration, allowing for the simultaneous study of the relationship between shale permeability, stress, and damage. This can then be applied to changes in capillary sealing capacity and the evaluation of shale gas loss.

[0184] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention. It will be clearly understood by those skilled in the art that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0185] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the shown or discussed mutual couplings, direct couplings, or communication connections may be through some interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, i.e., they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0186] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0187] The block diagrams of devices, apparatuses, devices, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner.

[0188] It should also be noted that in the apparatus, equipment, and methods of this application, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered as equivalent solutions of this application.

[0189] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0190] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, top, bottom, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of the components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0191] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0192] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for simulating changes in shale permeability, characterized in that, include: Obtain the maximum burial depth of the shale sample; After loading the shale sample to the stress conditions of the overlying strata corresponding to the maximum burial depth, pre-compact it to obtain the first permeability corresponding to the depth before uplift. A second set of permeabilities was obtained under different stress conditions of the overlying strata through hydrostatic unloading tests to simulate the evolution of permeability of shale during hydrostatic unloading and uplift. The peak horizontal compressive stress is obtained, and an unloading test is carried out based on the peak horizontal compressive stress until the stress of the overlying strata is reduced to the minimum or the shale sample is destroyed, so as to obtain the equivalent compressive failure strength; wherein, the equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress of the overlying strata is reduced to the minimum or the shale sample is destroyed. A third set of permeability was obtained during the unloading test to simulate the permeability evolution during the uplift of shale formations under horizontal compressive stress. The permeability changes during the uplift of shale formations are simulated by using the first permeability, the second set of permeability, and the third set of permeability, combined with the equivalent compression failure intensity.

2. The method for simulating shale permeability changes according to claim 1, characterized in that, Prior to conducting the static water unloading test, the following is also included: Uniaxial compression tests were conducted to obtain the elastic modulus and Poisson's ratio of the shale samples; and / or Triaxial compression failure tests were conducted under different overlying strata stresses to obtain the compressive strength, cohesion, and internal friction angle corresponding to different overlying strata stresses. Based on the compressive strength, cohesion, and internal friction angle corresponding to different overlying strata stresses, the relationship between the overlying strata stress and the horizontal compressive stress corresponding to shale fracture was obtained according to the Mohr-Coulomb fracture criterion.

3. The method for simulating shale permeability changes according to claim 2, characterized in that, The acquisition of peak horizontal compressive stress includes: Under the stress conditions of the overlying strata corresponding to the maximum burial depth, the horizontal compressive stress is increased in a stress loading mode until the peak horizontal compressive stress is reached; wherein, when carrying out triaxial compression failure tests under different overlying strata stresses, the first compressive strength is obtained under the highest overlying strata stress used, and the peak horizontal compressive stress is obtained based on a preset percentage of the first compressive strength and the overlying strata stress.

4. The method for simulating shale permeability changes according to claim 1, characterized in that, The unloading test, conducted based on the peak horizontal compressive stress until the stress in the overlying strata is reduced to the minimum or the shale sample is destroyed, includes: conducting unloading tests with different stress path unloading modes; the stress path unloading modes include: the horizontal compressive stress unloading rate is twice the overlying strata stress unloading rate, the overlying strata stress and the horizontal compressive stress are unloaded at the same rate, and the overlying strata stress unloading rate is twice the axial compression unloading rate.

5. The method for simulating shale permeability changes according to claim 1, characterized in that, The third set of permeability is obtained during the unloading test, including: conducting the unloading test in axial displacement control mode, and testing the permeability once each time the stress change of the overlying rock reaches a preset change value, so as to obtain the third set of permeability.

6. The method for simulating shale permeability changes according to claim 1, characterized in that, The method of simulating permeability changes during shale formation uplift by utilizing the first permeability, the second set of permeabilities, and the third set of permeabilities, combined with the equivalent compressive failure intensity, includes: establishing the following mathematical model. Among them, K a,0 K represents the permeability of shale at the depth before uplift. a,1 K represents the permeability of shale during the hydrostatic unloading and uplift process. a,2 ρ represents the permeability during the uplift of the shale formation; β is the equivalent coefficient for the degree of fault faulting; Δσ is the equivalent compressive failure strength; C f The compression coefficient is determined based on the second set of permeability during the static water unloading process.

7. The method for simulating shale permeability changes according to claim 1, characterized in that, The equivalent compressive failure strength is obtained by the following formula: Where Δσ is the equivalent compressive failure strength; σ1 is the compressive stress at the critical point of shale fracture; and σ3 is the vertical stress at the critical point of shale fracture. This is the internal friction angle at the critical point of shale fracturing.

8. A device for simulating changes in shale permeability, characterized in that, include: The maximum burial depth acquisition module is used to obtain the maximum burial depth of shale samples; The first permeability acquisition module is used to pre-compact the shale sample after loading it to the stress conditions of the overlying strata corresponding to the maximum burial depth, so as to obtain the first permeability corresponding to the depth before uplift. The second permeability acquisition module is used to conduct hydrostatic unloading tests to obtain the second set of permeability under different overlying strata stress conditions, so as to simulate the evolution of permeability of shale during hydrostatic unloading and uplift. Peak horizontal compressive stress acquisition module, used to acquire peak horizontal compressive stress; The equivalent compressive failure strength acquisition module is used to conduct unloading tests based on the peak horizontal compressive stress until the stress of the overlying strata drops to the minimum or the shale sample fails, so as to obtain the equivalent compressive failure strength; wherein, the equivalent compressive failure strength is the difference between the horizontal stress and the equivalent vertical stress after the stress of the overlying strata drops to the minimum or the shale sample fails. The third permeability acquisition module is used to acquire the third permeability during the unloading test to simulate the permeability evolution law during the uplift of shale formations under horizontal compressive stress. The permeability change simulation module is used to simulate the permeability change during the uplift of shale formations by using the first permeability, the second set of permeability and the third set of permeability, combined with the equivalent compression failure intensity.

9. An electronic device, characterized in that, The system includes a memory and a processor, the memory being used to store one or more computer instructions, wherein the one or more computer instructions, when executed by the processor, implement the method for simulating shale permeability changes as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method for simulating changes in shale permeability as described in any one of claims 1-7.

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