Prediction method for rock permeability in elastic-viscoelastic-viscoplastic deformation stage

Abstract

The invention provides a method for predicting rock permeability in an elastic-viscoelastic-viscoplastic deformation stage, and belongs to the technical field of rock permeability prediction. In order to effectively predict permeability evolution trends of rocks in different deformation stages and overcome the defects in the prior art, the invention provides a method for predicting permeability of rocks in an elastic-viscoelastic-viscoplastic deformation stage. Obtaining triaxial compressive strength data of the rock under different confining pressure level conditions; setting a creep stress level, and performing a rock sample creep-seepage experiment to obtain axial deformation data of the rock sample and gas pressure data of a gas inlet end and a gas outlet end of the sample; the axial load of the rock sample is unloaded to a hydrostatic pressure state, the confining pressure is kept unchanged, and a seepage experiment in a pressure relief deformation recovery stage is carried out; the method is applied to calculation and prediction of the rock permeability.

Description

Technical Field

[0001] The invention provides a method for predicting rock permeability in an elastic-viscoelastic-viscoplastic deformation stage, belonging to the technical field of rock permeability prediction. Background Art

[0002] With the development of geotechnical engineering and mining engineering in recent years, the challenges faced by engineering have gradually increased, especially the increase in construction depth, which has made the environment around the engineering structure more complicated, that is, the deep environment. Existing studies have shown that in deep environments, rock and other loaded media will be affected by high ground stress and high osmotic pressure, changing their mechanical properties and seepage characteristics; taking deep rock tunnels as an example, the mechanical properties and permeability of rocks around the tunnels are crucial to maintaining the stability of the tunnels. Due to the existence of the deep environment, the number of tunnel water seepage accidents caused by rock deformation caused by high ground stress and high osmotic pressure has gradually increased, seriously affecting the stability of the tunnel; in addition, the deformation behavior of rocks will affect the permeability, and during long-term service, rocks will produce elastic deformation, viscoelastic deformation and viscoplastic deformation under the influence of high ground stress, causing the rock permeability to change, which will also affect the stability of the tunnel structure. Therefore, predicting the permeability of rocks at different deformation stages is of great significance for the safe operation of the tunnel.

[0003] At present, there are corresponding testing methods for rock and coal deformation and permeability in geotechnical engineering and mining engineering. A lot of work has been done in the measurement of instantaneous elastic deformation, creep deformation and permeability. Although permeability testing under the influence of creep deformation has been carried out, the permeability evolution trend in the elastic, viscoelastic deformation and viscoplastic deformation stages has not been analyzed in detail. At this stage, there is a lack of effective prediction methods.

[0004] The prediction of rock permeability in the elastic, viscoelastic and viscoplastic deformation stages can well reflect the deformation and permeability evolution of the tunnel surrounding rock during the service process, and provide important technical support for exploring the actual mechanical response and permeability of the tunnel surrounding rock in deep geotechnical engineering. Research on the prediction method of rock permeability in the elastic, viscoelastic and viscoplastic deformation stages plays a significant role in guiding the safe operation and production of deep engineering. Summary of the invention

[0005] The present invention provides a method for predicting the permeability of rocks in the elastic-viscoelastic-viscoplastic deformation stage in order to effectively predict the permeability evolution trend of rocks in different deformation stages and overcome the deficiencies of the prior art.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage, comprising the following permeability prediction steps:

[0007] Step S1, performing a triaxial compression test on rock to obtain triaxial compressive strength data of rock under different confining pressure levels;

[0008] Step S2, using the triaxial compressive strength data as a reference, setting the creep stress level, and conducting a rock sample creep-seepage experiment to obtain the axial deformation data of the rock sample and the gas pressure data at the gas inlet and gas outlet ends of the sample;

[0009] Step S3, after the creep-seepage experiment duration of the rock sample reaches a preset period, the axial load of the rock sample is unloaded to the hydrostatic pressure state, the confining pressure remains unchanged, and the seepage experiment in the pressure relief deformation recovery stage is carried out, and the axial and lateral creep deformation data of the rock sample in the pressure relief deformation recovery stage and the gas pressure data at the air inlet and air outlet of the rock sample are monitored;

[0010] Step S4, drawing a creep-time curve and a deformation recovery curve according to the deformation data of the rock sample in the creep-seepage experiment stage and the pressure relief deformation recovery stage;

[0011] Step S5, combining the gas pressure decay data at the gas inlet and outlet of the rock sample, and using the permeability transient solution method to calculate the permeability of the rock sample in the creep deformation stage and the deformation recovery stage respectively;

[0012] Step S6, obtaining an empirical formula for the permeability evolution of the rock sample under the influence of creep deformation based on the creep deformation and permeability experimental data of the rock sample;

[0013] Step S7: Based on the strain superposition principle of the Xiyuan creep model, the creep deformation increment Δε in the permeability evolution empirical formula is converted into creep Decomposed into elastic deformation increment Δε E , viscoelastic deformation increment Δε VE , viscoplastic deformation increment Δε VP The values ​​of each deformation increment are obtained from the curve drawn in step S4, and the permeability prediction formula of the rock sample at different deformation stages is further obtained;

[0014] Step S8, according to the permeability evolution law in the pressure relief deformation recovery stage, respectively calculate the dynamic change data of the permeability of the rock sample in the elastic deformation of instantaneous recovery, the viscoelastic deformation of delayed recovery, and the viscoplastic deformation stage of failure to recover in the pressure relief deformation recovery stage, and respectively determine the weight coefficient a1 before the elastic deformation term, the weight coefficient a2 before the viscoelastic deformation term, and the weight coefficient a3 before the viscoplastic deformation term in the permeability evolution empirical formula;

[0015] Step S9: Based on the weight coefficient values ​​of each deformation item determined in step S8, a rock permeability calculation formula is constructed to distinguish the elastic, viscoelastic, and viscoplastic deformation stages. According to the constructed rock permeability calculation formula, the permeability of the monitored rock in the elastic, viscoelastic, and viscoplastic deformation stages is predicted respectively.

[0016] The specific method of performing the rock triaxial compression test in step S1 is:

[0017] Step S11, selecting and preparing rock samples:

[0018] Select rock blocks from the geotechnical engineering site, use coring equipment to coring the rock blocks, and process them into cylindrical rock samples with specifications of 50mm diameter × 100mm height;

[0019] Step S12: installing rock samples:

[0020] Apply vaseline evenly on both ends of the rock sample and wrap it with a thermoplastic tube to isolate the sample from the liquid outside the thermoplastic tube.

[0021] Place the rock sample wrapped with thermoplastic tube at the center of the boss of the triaxial loading chamber base and fix it. Install the axial LVDT and circumferential deformation sensors so that the sensors are parallel to the surface of the rock sample. Connect the wires of each sensor, assemble the triaxial loading chamber, and check the air tightness of the loading chamber.

[0022] Step S13, measuring the triaxial strength parameters of the rock sample:

[0023] The MTS rock mechanics test system was used to conduct triaxial compression tests on rock samples under different confining pressure conditions. The confining pressure was loaded in pressure control mode and kept constant after reaching the set confining pressure value. The axial direction was loaded in displacement control mode until the rock sample was destroyed and the test was terminated.

[0024] The basic mechanical parameters of rock samples are obtained through experiments, including elastic modulus, Poisson's ratio, internal friction angle, cohesion, and triaxial compression strength.

[0025] The specific method for performing the rock sample creep-seepage experiment in step S2 is:

[0026] Step S21, using the MTS rock mechanics testing system to conduct creep-seepage experiments on rock samples at different creep stress levels, with the axial pressure and confining pressure being loaded in a pressure control mode and kept constant after reaching a set deviatoric stress state;

[0027] The gas pressure at the gas inlet and outlet of the rock sample is set to 2MPa respectively and maintained for 12 hours to make the gas inside the rock sample saturated. After saturation, the gas pressure at the gas outlet of the rock sample is set to 1MPa, so that the rock sample can seep under a gas permeability pressure difference of 1MPa.

[0028] Step S22: Use the axial LVDT and the circumferential deformation sensor to monitor the axial and circumferential creep deformation data of the rock sample, and simultaneously record the attenuation of the gas pressure difference at both ends of the rock sample.

[0029] The specific method of calculating the permeability using the permeability transient solution method in step S5 is:

[0030] It is assumed that at the beginning of the experiment, the pressure difference between the upper and lower ends of the rock sample is P0, and the fluid flows from top to bottom. During this process, the pressure at the upper end of the rock sample gradually decreases, and the pressure at the lower end gradually increases. When the flow time is t, the pressure difference between the upper and lower ends decreases to P(t). At this time, the change of the pressure difference between the upper and lower ends of the rock sample with time is described by a negative exponential function, and the expression is:

[0031] P(t)=P0·e -at ;

[0032] in:

[0033]

[0034] Combining the above expressions, the calculation formula for the transient permeability experimental data k is:

[0035]

[0036] Where: β is the gas compression coefficient; V is the volume of the gas chamber; P0 and P(t) are the osmotic pressure differences at the beginning and end of the permeability measurement, respectively, satisfying P(t) = P u -P d ; t is the duration of permeability measurement; A and L are the cross-sectional area and height of the rock sample, respectively.

[0037] The empirical formula for permeability evolution under the influence of creep deformation obtained in step S6 is specifically:

[0038] k creep =k0(1-aΔε creep ) b ;

[0039] Where: k creep is the permeability under the influence of creep deformation; k0 is the initial permeability of the rock sample; Δε creep is the creep deformation increment of the rock sample; a and b are unknown coefficients.

[0040] The permeability prediction formula of the rock sample at different deformation stages obtained in step S7 is specifically:

[0041]

[0042] Where a1, a2 and a3 are the weight coefficients of each deformation term, reflecting the influence of different deformation stages on the permeability evolution.

[0043] The beneficial effects of the present invention compared with the prior art are as follows: the present invention provides a method for predicting rock permeability in elastic, viscoelastic and viscoplastic deformation stages, takes into account the degree of influence of different deformation stages on rock permeability, can well describe the permeability evolution characteristics of rocks in different deformation states, and is applicable to permeability prediction in different deformation stages; the present invention uses creep-seepage experiments, unloading deformation recovery stage seepage experiments, and combines the deformation and permeability monitoring results of the two experimental results to perform parameter identification on the rock permeability calculation formula in elastic, viscoelastic and viscoplastic deformation stages. The results show that the permeability prediction method can well describe the permeability evolution trend in different deformation stages, verifying the effectiveness of the prediction method. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will be further described below in conjunction with the accompanying drawings:

[0045] Figure 1 A flow chart of the steps for predicting rock permeability according to the present invention;

[0046] Figure 2 It is a curve diagram of creep and pressure relief deformation recovery in an embodiment of the present invention;

[0047] Figure 3 This is a data effect diagram of the evolution of permeability in the creep and pressure relief deformation recovery stages in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] like Figure 1As shown, the present invention provides a permeability prediction scheme for rocks in various deformation stages of elasticity, viscoelasticity and viscoplasticity, and the main prediction steps include: conducting conventional triaxial compression tests on rocks to obtain triaxial compressive strength of rocks under different confining pressure levels; using conventional triaxial compressive strength data as a reference, setting creep stress levels, and conducting creep-seepage experiments on rock samples and seepage experiments in the pressure relief deformation recovery stage; drawing creep-time curves based on sample deformation data and gas pressure data at both ends of the sample, and calculating the permeability of the sample in the creep stage and the deformation recovery stage using a permeability transient solution method; combining creep deformation and permeability experimental data to obtain an empirical formula for permeability evolution under the influence of creep deformation; according to the strain superposition principle of the Western model, decomposing the creep deformation of the empirical formula for permeability evolution into the superposition of elastic deformation, viscoelastic deformation and viscoplastic deformation to form permeability prediction formulas for different deformation stages, and the weight coefficients before each deformation term need to be determined in combination with the permeability evolution data of different deformation recovery stages, thereby establishing a method for predicting the permeability evolution law of rocks in different deformation stages.

[0049] In an embodiment of the present invention, a method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage is specifically provided, comprising the following prediction steps:

[0050] Step S1, conducting a conventional triaxial compression test on rock to obtain the triaxial compressive strength of rock under different confining pressure levels; wherein the specific test steps of the triaxial compression test on rock are as follows:

[0051] Step S11, rock sample selection and preparation. Rock blocks are selected at the deep geotechnical engineering site, and large-sized rock blocks with good integrity and no obvious cracks are screened out. The rock blocks are cored using coring equipment and processed into standard cylindrical samples with a diameter of 50 mm and a height of 100 mm. The diameter and end surface flatness of the rock samples are controlled within the error range; the wave velocity of the rock samples is measured, and samples with similar wave velocity values, i.e., with small differences, are selected as experimental samples;

[0052] Step S12, installation of rock samples. Apply vaseline evenly on both ends of the rock sample to reduce the friction between the loading end of the experimental device and the end face of the specimen to avoid end effect; wrap the rock sample with a thermoplastic tube to isolate the sample from the liquid outside the thermoplastic tube to avoid oil ingress into the sample during the test and rock debris from contaminating the confining oil; place the rock sample wrapped in the thermoplastic tube at the center of the boss of the triaxial loading chamber base and fix it, then start installing the axial LVDT and annular deformation sensor to keep the sensor parallel to the surface of the rock sample; ensure that the wires of each sensor are correctly connected externally, assemble the other components of the triaxial loading chamber, and check the air tightness after assembly;

[0053] Step S13, determination of basic mechanical parameters such as triaxial strength of rock samples. After the rock samples are installed, conventional triaxial compression tests of rock samples under different confining pressure conditions are carried out using the MTS rock mechanics test system; the confining pressure is loaded in pressure control mode, and is kept constant after reaching the set confining pressure value, and the axial direction is loaded in displacement control mode until the rock sample is destroyed, and the test is terminated; the basic mechanical parameters of the rock samples are obtained: elastic modulus, Poisson's ratio, internal friction angle, cohesion, triaxial compression strength, etc.

[0054] Step S2: using conventional triaxial compressive strength data as a reference, setting the creep stress level, carrying out a rock sample creep-seepage experiment, and obtaining the axial deformation data of the rock sample and the gas pressure data at the gas inlet and gas outlet of the sample; wherein the specific steps of the rock sample creep-seepage experiment are as follows:

[0055] Step S21, rock sample creep-seepage experiment. The rock samples used in the experiment are prepared and installed as described in steps S11 and S12; creep-seepage experiments are carried out under different creep stress levels using the MTS rock mechanics testing system, and the axial pressure and confining pressure are loaded in pressure control mode, and remain constant after reaching the set deviatoric stress state; the gas pressure at the inlet and outlet ends of the sample is set to 2MPa respectively, and maintained for 12 hours, so that the gas inside the rock sample is already in a saturated state; after saturation, the gas pressure at the outlet end of the rock sample is set to 1MPa, so that the sample seeps under a gas permeability pressure difference of 1MPa;

[0056] Step S22, measuring sample deformation and gas pressure data. Use axial LVDT and circumferential deformation sensor to monitor the axial and circumferential creep deformation data of the rock sample, and simultaneously record the attenuation of the gas pressure difference at both ends of the sample.

[0057] Step S3, after the creep-seepage experiment of the rock sample reaches a certain period, the axial load of the rock sample is unloaded to the hydrostatic pressure state, the confining pressure remains unchanged, and the seepage experiment in the pressure relief deformation recovery stage is further carried out to monitor the deformation in the pressure relief deformation recovery stage and the gas pressure data at the air inlet and air outlet of the sample;

[0058] The monitoring of the axial and lateral creep deformation and gas pressure difference attenuation data during the pressure relief deformation recovery stage is as described in step S22.

[0059] Step S4: Draw a creep-time curve and a deformation recovery curve based on the deformation data of the rock sample during the creep-seepage experiment stage and the pressure relief deformation recovery stage, such as Figure 2 As shown;

[0060] Step S5, combining the gas pressure decay data at both ends of the rock sample, and using the permeability transient solution method to calculate the permeability of the rock sample in the creep deformation stage and the deformation recovery stage;

[0061] The solution of the permeability transient method is shown in formulas (1) to (3). The permeability evolution trends in the creep deformation stage and the pressure relief deformation recovery stage are as follows: Figure 3 As shown in the figure, compared with the steady-state method, the transient method is more suitable for the permeability measurement of low-permeability rocks. An obvious pressure difference P0 is generated between the upper and lower ends of the sample. The fluid flows from top to bottom. During this process, the pressure at the upper end gradually decreases, while the pressure at the lower end gradually increases. When the flow time is t, the pressure difference between the upper and lower ends decreases to P(t). The change of the pressure difference between the upper and lower ends with time can be described by a negative exponential function:

[0062] P(t)=P0·e -at (1);

[0063] in:

[0064]

[0065] Combining equations (1) and (2), the calculation formula for transient permeability experimental data k can be obtained as follows:

[0066]

[0067] Where β is the gas compression coefficient; V is the volume of the gas chamber; P0 and P(t) are the osmotic pressure differences at the beginning and end of the permeability measurement, respectively, and P(t) = P u -P d ; t is the duration of permeability measurement; A and L are the cross-sectional area and height of the rock sample, respectively.

[0068] Step S6: According to the creep deformation and permeability experimental data of the rock sample (see Figure 2 and Figure 3 ), the empirical formula for permeability evolution under the influence of creep deformation is obtained, and the expression is shown in formula (4):

[0069] k creep =k0(1-aΔε creep ) b (4);

[0070] In the formula, k creep is the permeability under the influence of creep deformation; k0 is the initial permeability of the rock sample; Δε creep is the creep deformation increment of the rock sample; a and b are unknown coefficients.

[0071] Step S7: Based on the strain superposition principle of the Xiyuan creep model, the creep deformation increment Δε in the permeability evolution empirical formula is converted into creep Decomposed into elastic deformation increment Δε E , viscoelastic deformation increment Δε VE and the viscoplastic deformation increment ΔεVP The values ​​of each deformation increment are obtained from the data described in S4, and the permeability prediction formula at different deformation stages is formed as shown in formula (5):

[0072]

[0073] Where a1, a2 and a3 are the weight coefficients of each deformation term, reflecting the influence of different deformation stages on the permeability evolution.

[0074] It should be noted that during the creep deformation stage, the pores and cracks inside the rock sample are gradually compressed, which in turn causes the permeability of the sample to gradually decrease, that is, the permeability shows a gradually decreasing trend; during the pressure relief deformation recovery stage, the unloading of the axial load will cause the compression deformation of the rock sample to decrease instantly, and the seepage channels inside the sample will expand synchronously, resulting in an instantaneous increase in the permeability; as the unloading time gradually increases, the viscoelastic deformation caused by the pressure relief is fully recovered, and the compression of the seepage channels caused by it will also gradually recover, and the permeability data will gradually increase; after the pressure relief recovery deformation amount remains constant for a long period of time, it indicates that the deformation recovery is complete, and the deformation that has not yet recovered relative to the initial uncompressed state is called viscoplastic deformation, and the difference in permeability compared to the initial permeability is caused by the viscoplastic deformation.

[0075] Step S8: Combination Figure 3 The permeability evolution law in the unloading deformation recovery stage is calculated, and the dynamic change data of the permeability in the instantaneous elastic deformation, delayed viscoelastic deformation and unrecovered viscoplastic deformation stage of the unloading deformation recovery stage are calculated to determine the weight coefficients a1, a2 and a3 before the elastic deformation, viscoelastic deformation and viscoplastic deformation terms in the empirical formula of permeability evolution;

[0076] Step S9, based on the weight coefficient values ​​of each deformation item determined in step S8, construct a rock permeability calculation formula that can distinguish elastic, viscoelastic and viscoplastic deformation stages, and predict the permeability of the monitored rock in the elastic, viscoelastic and viscoplastic deformation stages according to the constructed rock permeability calculation formula.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage, characterized by: The permeability prediction steps include the following: Step S1, performing a triaxial compression test on rock to obtain triaxial compressive strength data of rock under different confining pressure levels; Step S2, using the triaxial compressive strength data as a reference, setting the creep stress level, and conducting a rock sample creep-seepage experiment to obtain the axial deformation data of the rock sample and the gas pressure data at the gas inlet and gas outlet ends of the sample; Step S3, after the creep-seepage experiment duration of the rock sample reaches a preset period, the axial load of the rock sample is unloaded to the hydrostatic pressure state, the confining pressure remains unchanged, and the seepage experiment in the pressure relief deformation recovery stage is carried out, and the axial and lateral creep deformation data of the rock sample in the pressure relief deformation recovery stage and the gas pressure data at the air inlet and air outlet of the rock sample are monitored; Step S4, drawing a creep-time curve and a deformation recovery curve according to the deformation data of the rock sample in the creep-seepage experiment stage and the pressure relief deformation recovery stage; Step S5, combining the gas pressure decay data at the gas inlet and outlet of the rock sample, and using the permeability transient solution method to calculate the permeability of the rock sample in the creep deformation stage and the deformation recovery stage respectively; Step S6, obtaining an empirical formula for the permeability evolution of the rock sample under the influence of creep deformation based on the creep deformation and permeability experimental data of the rock sample; Step S7: Based on the strain superposition principle of the Xiyuan creep model, the creep deformation increment Δε in the permeability evolution empirical formula is converted into creep Decomposed into elastic deformation increment Δε E , viscoelastic deformation increment Δε VE , viscoplastic deformation increment Δε VP The values ​​of each deformation increment are obtained from the curve drawn in step S4, and the permeability prediction formula of the rock sample at different deformation stages is further obtained; Step S8, according to the permeability evolution law in the pressure relief deformation recovery stage, respectively calculate the dynamic change data of the permeability of the rock sample in the elastic deformation of instantaneous recovery, the viscoelastic deformation of delayed recovery, and the viscoplastic deformation stage of failure to recover in the pressure relief deformation recovery stage, and respectively determine the weight coefficient a1 before the elastic deformation term, the weight coefficient a2 before the viscoelastic deformation term, and the weight coefficient a3 before the viscoplastic deformation term in the permeability evolution empirical formula; Step S9: Based on the weight coefficient values ​​of each deformation item determined in step S8, a rock permeability calculation formula is constructed to distinguish the elastic, viscoelastic, and viscoplastic deformation stages. According to the constructed rock permeability calculation formula, the permeability of the monitored rock in the elastic, viscoelastic, and viscoplastic deformation stages is predicted respectively.

2. The method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage according to claim 1, characterized in that: The specific method of performing the rock triaxial compression test in step S1 is: Step S11, selecting and preparing rock samples: Select rock blocks from the geotechnical engineering site, use coring equipment to coring the rock blocks, and process them into cylindrical rock samples with specifications of 50mm diameter × 100mm height; Step S12: installing rock samples: Apply vaseline evenly on both ends of the rock sample and wrap it with a thermoplastic tube to isolate the sample from the liquid outside the thermoplastic tube. Place the rock sample wrapped with thermoplastic tube at the center of the boss of the triaxial loading chamber base and fix it. Install the axial LVDT and circumferential deformation sensors so that the sensors are parallel to the surface of the rock sample. Connect the wires of each sensor, assemble the triaxial loading chamber, and check the air tightness of the loading chamber. Step S13, measuring the triaxial strength parameters of the rock sample: The MTS rock mechanics test system was used to conduct triaxial compression tests on rock samples under different confining pressure conditions. The confining pressure was loaded in pressure control mode and kept constant after reaching the set confining pressure value. The axial direction was loaded in displacement control mode until the rock sample was destroyed and the test was terminated. The basic mechanical parameters of rock samples are obtained through experiments, including elastic modulus, Poisson's ratio, internal friction angle, cohesion, and triaxial compression strength.

3. The method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage according to claim 2, characterized in that: The specific method for performing the rock sample creep-seepage experiment in step S2 is: Step S21, using the MTS rock mechanics testing system to conduct creep-seepage experiments on rock samples at different creep stress levels, with the axial pressure and confining pressure being loaded in a pressure control mode and kept constant after reaching a set deviatoric stress state; The gas pressure at the gas inlet and outlet of the rock sample is set to 2MPa respectively and maintained for 12 hours to make the gas inside the rock sample saturated. After saturation, the gas pressure at the gas outlet of the rock sample is set to 1MPa, so that the rock sample can seep under a gas permeability pressure difference of 1MPa. Step S22: Use the axial LVDT and the circumferential deformation sensor to monitor the axial and circumferential creep deformation data of the rock sample, and simultaneously record the attenuation of the gas pressure difference at both ends of the rock sample.

4. The method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage according to claim 3 is characterized by: The specific method of calculating the permeability using the permeability transient solution method in step S5 is: At the beginning of the experiment, the pressure difference between the upper and lower ends of the rock sample is set to P0. The fluid flows from top to bottom. During this process, the pressure at the upper end of the rock sample gradually decreases, and the pressure at the lower end gradually increases. When the flow time is t, the pressure difference between the upper and lower ends decreases to P(t). At this time, the change of the pressure difference between the upper and lower ends of the rock sample with time is described by a negative exponential function, and the expression is: P(t) = P0·e -at ; in: Combining the above expressions, the calculation formula for the transient permeability experimental data k is: Where: β is the gas compression coefficient; V is the volume of the gas chamber; P0 and P(t) are the osmotic pressure differences at the beginning and end of the permeability measurement, respectively, satisfying P(t) = P u -P d ; t is the duration of permeability measurement; A and L are the cross-sectional area and height of the rock sample, respectively.

5. The method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage according to claim 4, characterized in that: The empirical formula for permeability evolution under the influence of creep deformation obtained in step S6 is specifically: k creep =k0(1-aΔε creep ) b ; Where: k creep is the permeability under the influence of creep deformation; k0 is the initial permeability of the rock sample; Δε creep is the creep deformation increment of the rock sample; a and b are unknown coefficients.

6. The method for predicting rock permeability in the elastic-viscoelastic-viscoplastic deformation stage according to claim 5, characterized in that: The permeability prediction formula of the rock sample at different deformation stages obtained in step S7 is specifically: Where a1, a2 and a3 are the weight coefficients of each deformation term, reflecting the influence of different deformation stages on the permeability evolution.

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