Methods and apparatus for testing and quantitative analysis of inelastic deformation of reservoir rocks

Abstract

This application discloses a method and apparatus for testing and quantitatively analyzing inelastic deformation of reservoir rocks, relating to the field of deformation testing and quantitative analysis. The method includes: pre-treating a target rock sample and determining its initial porosity; calibrating the experimental background temperature and confining pressure based on the initial porosity, and conducting parallel experimental tests on the pre-treated target rock sample; collecting and processing experimental data during the testing process, performing microstructure analysis on the target rock sample after the test, and determining the microstructure analysis results; performing forward simulation based on a rock physical constitutive model, and determining the main controlling mechanism of inelastic deformation of the rock based on the microstructure analysis results; and quantitatively characterizing the inelastic deformation amount based on a quantitative analysis model to determine the yield stress and inelastic strain. This application can achieve accurate prediction and quantitative characterization of the main controlling deformation mechanism of inelastic deformation.

Description

Technical Field

[0001] This application relates to the field of deformation testing and quantitative analysis, and in particular to a method and apparatus for testing and quantitative analysis of inelastic deformation of reservoir rocks. Background Technology

[0002] Human underground activities (such as oil, gas, and geothermal development) often lead to surface subsidence, occasionally accompanied by induced seismic activity. Subsidence originates from reservoir compaction, driven by factors including decreased pore pressure and sedimentary rock creep. Studies have found that the compaction of sandstone reservoirs can be partially elastic (reversible) and partially inelastic (permanent). Currently, industry assessments of gas-related surface subsidence and underground stress changes primarily consider the pore elasticity effect of rocks, assuming that formation deformation is recoverable. However, numerous studies have shown that shallow sedimentary rocks undergo significant inelastic deformation under external stress disturbances. Therefore, classifying and quantifying the contributions of elastic and inelastic factors is crucial for accurately assessing stress changes and surface subsidence. Summary of the Invention

[0003] The purpose of this application is to provide a method and apparatus for testing and quantitatively analyzing the inelastic deformation of reservoir rocks, which can accurately predict and quantitatively characterize the main deformation mechanism controlling inelastic deformation.

[0004] To achieve the above objectives, this application provides the following solution:

[0005] In a first aspect, this application provides a method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks, including:

[0006] Obtain target rock samples;

[0007] The target rock sample was pretreated, and the initial porosity was determined.

[0008] Based on the initial porosity, the experimental background temperature and confining pressure were calibrated, and the pretreated target rock samples were subjected to parallel processing experiments.

[0009] Collect and process experimental data during the experimental testing process to obtain processed experimental data;

[0010] Microstructural analysis was performed on the target rock sample after experimental testing to determine the results of the microstructural analysis; the results of the microstructural analysis included the crack density distribution in the axial compression direction;

[0011] Forward modeling was performed based on a rock physical constitutive model, and the main controlling mechanism of inelastic deformation of the rock was determined based on the microstructure analysis results; the rock physical constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust.

[0012] The quantitative analysis model is used to quantitatively characterize the inelastic deformation to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope to the intrinsic control relationship corresponding to the master control mechanism. The envelope is determined based on the stress state corresponding to different inelastic strains according to the processed experimental data.

[0013] In one embodiment, the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust includes: intergranular pressure solution, stress corrosion cracking, and intergranular sliding.

[0014] The mathematical expression for the constitutive model corresponding to interparticle pressure solution is:

[0015] ;

[0016] ;

[0017] ;

[0018] The mathematical expression for the constitutive model corresponding to stress corrosion cracking is:

[0019] ;

[0020] The mathematical expression for the constitutive model corresponding to interparticle sliding is:

[0021] ;

[0022] in, To achieve effective axial stress in macroscopic terms The axial strain rate caused by pressure solution controlled by dissolution under the action of dissolution; These are geometric constants; The average particle diameter; The quartz dissolution rate coefficient; The volume of quartz is the molar volume. The coordination number of the particles; It is the gas constant; Absolute temperature; For particle shape factor; For geometric constants in the range of 0.8-1; For instantaneous aggregate porosity; This is a factor that considers the influence of grain boundary structure on the grain boundary dissolution rate; Let be the geochemical dissolution rate constant of an unstressed solid under reference fluid pressure; The crack velocity of quartz; The pre-exponential factor is a constant describing the catalytic reaction of water molecules; The activation enthalpy, as determined experimentally, describes the energy barrier that the crack propagation reaction must overcome under the catalytic pathway of water molecules. , which is a geometric factor, is a parameter describing the degree to which the geometry of the crack tip affects the reaction rate; It is a type I stress intensity factor; The proportion of Si-O bonds hydrolyzed by water molecules; is a pre-exponential factor, a constant describing the catalytic reaction associated with hydroxide ions; The activation enthalpy, as determined experimentally, describes the energy barrier that the crack propagation reaction must overcome under the hydroxide ion catalytic pathway. is a geometric factor that describes the effect of the crack tip geometry on the reaction rate under the hydroxide ion pathway. The proportion of Si-O bonds hydrolyzed by hydroxyl ions; The differential stress at which intergranular sliding begins and leads to expansion; Effective stress; is the coefficient of friction.

[0023] In one embodiment, the target rock sample after experimental testing is subjected to microstructure analysis to determine the microstructure analysis results, specifically including:

[0024] After the target rock sample was dried following the experimental test, it was immersed in colored epoxy resin for shaping and then placed in a vacuum coating machine for resin injection.

[0025] After resin injection, the target rock sample was wire-cut and thin sections were prepared in the direction of compression parallel to the z-axis. EDX analysis was performed using a ZEISS Gemini 450 scanning electron microscope in backscattered electron mode to identify mineral composition. After SEM imaging, microstructure analysis was performed, and the crack density distribution of the sample in the axial compression direction was statistically analyzed to obtain the microstructure analysis results.

[0026] In one embodiment, obtaining a target rock sample specifically includes:

[0027] The rock sample was processed using a wire cutting machine to obtain a cylindrical sample.

[0028] The processed sample was identified as the target rock sample.

[0029] In one embodiment, the target rock sample is pretreated to determine its initial porosity, specifically including:

[0030] The processed samples were dried, vacuumed, saturated with water, and allowed to stand for equilibrium. The pore volume was determined based on the difference in rock sample quality before and after drying.

[0031] Based on pore volume, using Determine the initial porosity; where, Initial porosity; Pore ​​volume; The volume of the rock.

[0032] In one embodiment, the experimental background temperature and confining pressure are calibrated based on the initial porosity, and parallel processing tests are performed on the pretreated target rock samples, specifically including:

[0033] Based on the well depth, rock sample density, and geothermal gradient of the target rock sample, determine the effective confining pressure and design temperature required for the experiment;

[0034] Based on the initial porosity and the effective confining pressure and design temperature required for the experiment, the experimental background temperature and confining pressure are calibrated.

[0035] Under experimental background temperature and confining pressure, the pretreated target rock sample was subjected to vacuum treatment and parallel experimental testing; the experimental testing was the testing of inelastic strain components under moderate strain; the moderate strain range was 0.3%-1.5%.

[0036] In one embodiment, the experimental testing of parallel processing specifically includes:

[0037] The pretreated target rock samples were subjected to hydrostatic pressure and deviatoric stress cyclic loading-unloading experiments, and simultaneously acoustic emission experiments were conducted. Specifically, the confining pressure was stepped-loaded and unloaded at a constant pressurization rate until the constant design confining pressure was reached, and then unloading was stopped and maintained. Then, differential stress disturbance was performed, and while maintaining a constant confining pressure, the sample was subjected to differential stress cyclic loading-unloading at a constant strain rate in the axial direction until strain softening or rock fracture phenomena were observed in the pretreated target rock samples, and then the process was stopped.

[0038] The pretreated target rock samples were subjected to inelastic deformation strain rate dependence tests; wherein, the inelastic deformation strain rate dependence tests were conducted by performing triaxial experiments with constant strain rates ranging from low to high; the range of constant strain rates was 10. -3 s -1 Up to 10 -7 s -1 .

[0039] In one embodiment, experimental data is collected and processed during the experimental testing process to obtain processed experimental data, specifically including:

[0040] Experimental data during the experimental testing process is collected based on a preset recording rate; the preset recording rate is obtained by correcting for different axial loading rates; wherein, during the static water loading stage, the collected experimental data includes: internal axial load, confining pressure, pore pressure, pore fluid volume change, sample temperature, and axial displacement signal data.

[0041] Data on the strain rate of the target rock sample are acquired using a radial displacement hoop sensor installed in the middle and an axial displacement sensor installed at the top. The acquired experimental data include axial strain, radial strain, total porosity reduction, and peak stress. Axial strain includes the principal stress along the axial direction. The rate of change of length occurs in the direction; radial strain includes the confining pressure perpendicular to the axial direction. The rate of change of diameter in the direction of change;

[0042] Determine the average effective stress-porosity reduction or volumetric strain cross plot based on the collected experimental data;

[0043] In the strain rate dependence test of inelastic deformation, the influencing factors and deformation mechanisms of inelastic deformation of rock are integrated to obtain different strain rates.

[0044] Based on different strain rates, and by combining the mean effective stress-porosity reduction or volumetric strain cross-plots, the processed experimental data are obtained.

[0045] In one embodiment, the expression corresponding to the average effective stress is:

[0046] ;

[0047] The expression corresponding to the volumetric strain is:

[0048] ;

[0049] in, The average effective stress; It is the axial principal stress; For confining pressure; Pore ​​pressure; For volumetric strain; For axial strain; For radial strain.

[0050] Secondly, this application provides a device for testing and quantitatively analyzing the inelastic deformation of reservoir rocks, comprising:

[0051] The acquisition module is used to acquire target rock samples;

[0052] A pretreatment module is used to pretreat the target rock sample and determine the initial porosity;

[0053] The experimental module is used to calibrate the experimental background temperature and confining pressure based on the initial porosity, and to perform parallel experimental tests on the pretreated target rock samples.

[0054] The data acquisition and processing module is used to acquire and process experimental data during the experimental testing process to obtain processed experimental data.

[0055] The microstructure analysis module is used to perform microstructure analysis on target rock samples after experimental testing and to determine the microstructure analysis results; the microstructure analysis results include: the crack density distribution in the axial compression direction;

[0056] The main control mechanism determination module is used to perform forward modeling based on the rock physical constitutive model and determine the main control mechanism of rock inelastic deformation based on the microstructure analysis results; the rock physical constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust.

[0057] The quantitative analysis module is used to quantitatively characterize the inelastic deformation based on the quantitative analysis model to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope to the parameters corresponding to the main control mechanism. The envelope is determined based on the stress state corresponding to different inelastic strains from the processed experimental data.

[0058] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0059] This application provides a method and apparatus for testing and quantitatively analyzing the inelastic deformation of reservoir rocks. The method involves pre-treating the target rock sample and determining its initial porosity; calibrating the experimental background temperature and confining pressure based on the initial porosity; conducting parallel experimental tests on the pre-treated target rock sample; collecting and processing experimental data during the testing process; performing microstructural analysis on the target rock sample after the tests to determine the microstructural analysis results; performing forward simulation based on a rock physical constitutive model and determining the main controlling mechanism of inelastic deformation based on the microstructural analysis results; and quantitatively characterizing the inelastic deformation amount based on a quantitative analysis model to determine the yield stress and inelastic strain. This application, based on parallel experimental testing and combined with rock microstructural analysis, clarifies the inelastic deformation mechanism of sedimentary rocks and conducts quantitative characterization, thereby achieving accurate prediction and quantitative characterization of the main controlling deformation mechanism of inelastic deformation. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a schematic diagram of a typical stress-strain curve under uniaxial stress (compression);

[0062] Figure 2 A flowchart of a method for testing and quantitatively analyzing inelastic deformation of reservoir rocks;

[0063] Figure 3 Flowchart for inelastic deformation testing and quantitative characterization;

[0064] Figure 4 A graph showing the relationship between porosity reduction and average effective stress during triaxial hydrostatic cyclic loading-unloading.

[0065] Figure 5 The graph shows the relationship between inelastic deformation and time dependence under different axial strain rates.

[0066] Figure 6 This is a schematic diagram of the crack density distribution along the axial compression direction;

[0067] Figure 7 This is a schematic diagram showing the relationship between inelastic deformation and differential stress-mean effective stress.

[0068] Figure 8 This is a structural diagram of a device for testing and quantitatively analyzing the inelastic deformation of reservoir rocks. Detailed Implementation

[0069] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0070] Currently, the main testing method for inelastic deformation of rocks is based on the traditional triaxial compression test, using typical stress-strain curves under uniaxial stress (compression), such as... Figure 1 As shown, the constitutive relations characterize most rocks. Figure 1The constitutive curve in the figure can be roughly divided into the following stages: Stage 1 is the "work hardening" stage (OA segment), where the stress-strain curve shows an upward bending trend, indicating that as stress increases, the strain growth rate slows down, and the rock hardens with increasing stress (work). From a microscopic perspective, the bending of the OA segment is caused by the closure of many microcracks in the natural rock under stress; Stage 2 is the linear elastic stage (AB segment), where the slope of AB (i.e., the effective Young's modulus of the rock) is determined by the elastic constant of the solid rock material and the porosity contained therein; Stage 3 is the strain "softening stage" (BC segment), where the stress-strain curve deviates from a straight line again. At this time, the inelastic deformation of the rock begins to appear significantly, and the inelastic volumetric strain increases, that is, the rock hardens. The rock expansion phenomenon shows that as strain increases, the strain growth rate also accelerates. Stage four is the curve after rock failure (section CD). When loading a rock sample with a conventional press, once the rock's strength (point C) is reached, the sample's load-bearing capacity decreases, strain accelerates, and most of the elastic energy stored in the press is released, resulting in violent failure of the sample at point C. The curve before rock failure is obtained. Later, using the concept of controlled fracture proposed by Cook (1965) and Wawersik and Fairhurst (1970) and the electro-hydraulic closed-loop servo control motor, the curve after rock failure is obtained. Stage five is the stage where the macroscopic fracture of the rock is completed and the fracture surface is formed (section DE). Its stress-strain curve represents the frictional sliding of the rock along both sides of the fracture surface. In current geomechanical model studies, inelastic deformation is generally considered to correspond to the strain in segment BC. However, studies have found that a large number of inelastic deformation components also exist under moderate strain in segment AB. However, the testing of inelastic deformation in this stage, as well as targeted discrimination and quantitative characterization techniques, are still immature. To fill this gap, this application provides a detailed description of the testing and quantitative characterization methods for inelastic deformation of rock samples from gas storage facilities.

[0071] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0072] In one exemplary embodiment, such as Figure 2 As shown, a method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks is provided, including:

[0073] Step 100: Obtain the target rock sample.

[0074] Obtaining the target rock sample specifically includes:

[0075] The rock sample was processed using a wire cutting machine to obtain a cylindrical sample; the processed sample was then identified as the target rock sample.

[0076] Step 200: Pre-treat the target rock sample and determine the initial porosity.

[0077] This includes pre-processing the target rock sample and determining its initial porosity, specifically including:

[0078] The processed samples were dried, vacuum-absorbed, water-saturated, and allowed to settle to equilibrate. The pore volume was determined based on the mass difference of the rock samples before and after drying. Based on the pore volume, [the following method was used]. Determine the initial porosity; where, Initial porosity; Pore ​​volume; The volume of the rock.

[0079] Step 300: Based on the initial porosity, calibrate the experimental background temperature and confining pressure, and conduct parallel processing experiments on the pretreated target rock samples.

[0080] The experimental tests, which calibrated the experimental background temperature and confining pressure based on the initial porosity and performed parallel processing on the pretreated target rock samples, specifically include:

[0081] Based on the well depth, rock sample density, and geothermal gradient of the target rock sample, the effective confining pressure and design temperature required for the experiment are determined.

[0082] Based on the initial porosity and the effective confining pressure and design temperature required for the experiment, the experimental background temperature and confining pressure are calibrated.

[0083] Under the experimental background temperature and confining pressure, the pretreated target rock samples were subjected to vacuum treatment and parallel experimental testing. The experimental testing was the testing of inelastic strain components under moderate strain, which ranged from 0.3% to 1.5%.

[0084] The experimental tests of parallel processing specifically include:

[0085] The pretreated target rock samples were subjected to hydrostatic pressure and deviatoric stress cyclic loading-unloading experiments, and simultaneously acoustic emission experiments were conducted. Specifically, the confining pressure was stepped-loaded and unloaded at a constant pressurization rate until the constant design confining pressure was reached, and then unloading was stopped and maintained. Then, differential stress disturbance was performed, and while maintaining a constant confining pressure, the sample was subjected to differential stress cyclic loading-unloading at a constant strain rate in the axial direction until strain softening or rock fracture phenomena were observed in the pretreated target rock samples, and then the process was stopped.

[0086] Inelastic deformation strain rate dependence tests were performed on the pretreated target rock samples; the inelastic deformation strain rate dependence tests consisted of triaxial experiments with constant strain rates ranging from low to high; the range of constant strain rates was 10. -3 s-1 Up to 10 -7 s -1 .

[0087] Step 400: Collect and process the experimental data during the experimental testing process to obtain the processed experimental data.

[0088] This includes collecting and processing experimental data during the testing process to obtain processed experimental data, specifically including:

[0089] Experimental data during the experimental testing process are collected based on a preset recording rate. The preset recording rate is obtained by correcting different axial loading rates. Among them, during the static water loading stage, the collected experimental data include: internal axial load, confining pressure, pore pressure, pore fluid volume change, sample temperature, and axial displacement signal data.

[0090] Data on the strain rate of the target rock sample are acquired using a radial displacement hoop sensor installed in the middle and an axial displacement sensor installed at the top. The acquired experimental data include axial strain, radial strain, total porosity reduction, and peak stress. Axial strain includes the principal stress along the axial direction. The rate of change of length occurs in the direction; radial strain includes the confining pressure perpendicular to the axial direction. The rate of change of diameter in the direction of change.

[0091] Based on the collected experimental data, a cross-plot of the average effective stress-porosity reduction or volumetric strain was determined.

[0092] In the strain rate dependence test of inelastic deformation, the influencing factors and deformation mechanisms of inelastic deformation of rocks are integrated to obtain different strain rates.

[0093] Based on different strain rates, and by combining the mean effective stress-porosity reduction or volumetric strain cross-plots, the processed experimental data are obtained.

[0094] The expression corresponding to the mean effective stress is:

[0095] .

[0096] The expression for volumetric strain is:

[0097] .

[0098] in, The average effective stress; It is the axial principal stress; For confining pressure; Pore ​​pressure; For volumetric strain; For axial strain; For radial strain.

[0099] Step 500: Perform microstructural analysis on the target rock sample after experimental testing to determine the microstructural analysis results. The microstructural analysis results include the crack density distribution in the axial compression direction.

[0100] In one embodiment, the target rock sample after experimental testing is subjected to microstructure analysis to determine the microstructure analysis results, specifically including:

[0101] After the target rock samples were dried following the experimental tests, they were immersed in colored epoxy resin for shaping and then placed in a vacuum coating machine for resin injection. The resin-injected target rock samples were then wire-cut in the direction parallel to the z-axis compression loading direction to prepare rock thin sections. EDX analysis was performed using a ZEISS Gemini 450 scanning electron microscope in backscattered electron mode to identify mineral composition. After SEM imaging, microstructure analysis was performed, and the crack density distribution of the samples in the axial compression direction was statistically analyzed to obtain the microstructure analysis results.

[0102] Step 600: Perform forward modeling based on the rock physics constitutive model, and determine the controlling mechanism of inelastic deformation of the rock based on the microstructure analysis results. The rock physics constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust.

[0103] The inelastic deformation mechanisms of shallow sedimentary rocks in the Earth's crust include: intergranular pressure solution, stress corrosion cracking, and intergranular sliding.

[0104] The mathematical expression for the constitutive model corresponding to interparticle pressure solution is:

[0105] .

[0106] .

[0107] .

[0108] The mathematical expression for the constitutive model corresponding to stress corrosion cracking is:

[0109] .

[0110] The mathematical expression for the constitutive model corresponding to interparticle sliding is:

[0111] .

[0112] in, To achieve effective axial stress in macroscopic terms The axial strain rate caused by pressure solution controlled by dissolution under the action of dissolution; It is a geometric constant, and its value is approximately 2; The average particle diameter; The quartz dissolution rate coefficient; The volume of quartz is the molar volume. This is the particle coordination number, which takes a value of approximately 6. It is the gas constant; Absolute temperature; The particle shape factor has a value of approximately ; For geometric constants in the range of 0.8-1; For instantaneous aggregate porosity; This is a factor that considers the influence of grain boundary structure on the grain boundary dissolution rate; Let be the geochemical dissolution rate constant of an unstressed solid under reference fluid pressure; The crack velocity of quartz; The pre-exponential factor is a constant describing the catalytic reaction of water molecules; The activation enthalpy, as determined experimentally, describes the energy barrier that the crack propagation reaction must overcome under the catalytic pathway of water molecules. , which is a geometric factor, is a parameter describing the degree to which the geometry of the crack tip affects the reaction rate; It is a type I stress intensity factor; The proportion of Si-O bonds hydrolyzed by water molecules; is a pre-exponential factor, a constant describing the catalytic reaction associated with hydroxide ions; To experimentally determine the activation enthalpy, this describes the energy barrier that the crack propagation reaction needs to overcome under the hydroxide ion catalytic pathway. is a geometric factor that describes the effect of the crack tip geometry on the reaction rate under the hydroxide ion pathway. The proportion of Si-O bonds hydrolyzed by hydroxyl ions; The differential stress at which intergranular sliding begins and leads to expansion, i.e. , For effective confining pressure; Effective stress; is the coefficient of friction.

[0113] It refers to the preceding item; The activation enthalpy was determined experimentally. The geometry of the crack tip ( Indicates the relevant molecules or ions in a catalytic reaction, such as or That is, when Reference At that time, the corresponding Refers to , which corresponds to the pre-exponential factor.

[0114] Step 700: Quantitatively characterize the inelastic deformation based on the quantitative analysis model to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope to the intrinsic control relationship corresponding to the master control mechanism; the envelope is determined based on the stress state corresponding to different inelastic strains from the processed experimental data.

[0115] This application relates to an experimental testing and quantitative characterization method for the inelastic deformation of rocks caused by periodic changes in formation pressure during gas storage and extraction. Specifically, it is a method based on triaxial loading-unloading and stress relaxation experiments, combined with rock microstructure analysis, to clarify the mechanism of inelastic deformation in sedimentary rocks and conduct quantitative characterization. Figure 3 As shown. This application plays an important role in accurately assessing ground subsidence and stress field changes in industrial mining areas.

[0116] This application provides a method for testing and quantitative characterizing inelastic deformation under rock reservoir compaction, aiming to fill the gap in most current sandstone mechanics studies, which only focus on inelastic deformation developed under large compressive strain and ignore the influence of inelastic strain caused by small strain. This method enables accurate prediction and quantitative characterization of the main deformation mechanism controlling inelastic deformation in geomechanical modeling of future induced subsidence and seismic activity.

[0117] The overall technical solution flow of this application is as follows: Figure 3 Specifically, it includes the following steps:

[0118] Step (a): Use a wire cutting machine to process the rock sample. The processed sample is a cylinder with a height of about 50 mm and a diameter of about 25 mm. The sample surface should be smooth, flat and free of impurities. There should be no less than 3 samples (labeled as 1, 2, 3...).

[0119] Step (b): The sample prepared in step (a) is dried, vacuum-absorbed, water-saturated, and allowed to stand for equilibrium. The pore volume is obtained by measuring the difference in rock sample mass before and after drying, and then calculated using the formula. The initial porosity of the sample was calculated, and based on the well depth of the sample, the density of the rock sample, and the geothermal gradient of the rock sample, the effective confining pressure and design temperature required for the experiment were calculated.

[0120] Step (c): Inelastic strain testing method under different pressure conditions: Based on the initial porosity calculation results in step (b), the experimental background temperature and confining pressure are calibrated. After loading the sample, the rock sample is vacuum-treated to test the magnitude of the inelastic strain component under moderate strain (0.3%-1.5%). First, a pure hydrostatic pressure cyclic loading-unloading experiment is carried out simultaneously with acoustic emission detection. The confining pressure is stepped-loaded and unloaded at a constant pressurization rate until the constant design confining pressure is reached, then unloading is stopped and maintained. Then, differential stress disturbance is performed, maintaining a constant confining pressure, and the sample is subjected to differential stress cyclic loading-unloading at a constant strain rate in the axial direction until strain softening or rock fracture occurs, then the experiment is stopped. During the experiment, in the hydrostatic loading stage, data such as internal axial load, confining pressure, pore pressure, pore fluid volume change, sample temperature, and axial displacement signal are recorded every 0.5s (the recording rate is adjusted according to different axial loading rates). Data on the sample strain rate are collected through a radial displacement hoop sensor installed in the middle of the sample and an axial displacement sensor installed at the top. The axial strain is mainly observed along the axial principal stress of the sample. Rate of change of length in direction ( ,in, This represents the change in axial displacement. (This refers to the initial height of the sample). Radial strain is mainly observed along the confining pressure perpendicular to the axial direction. Rate of change of diameter in direction ( ;in, This represents the radial displacement change. (Initial diameter of the sample), total porosity reduction The change in sample pore volume is expressed as the change in sample pore volume divided by the initial sample volume. The peak stress (Qpeak) is the maximum differential stress that can be withstood before strain softening behavior is observed. Hydrostatic pressure disturbance and differential stress disturbance aim to examine whether the sample exhibits anisotropy. Based on the experimental results, cross-plots of mean effective stress versus porosity reduction or volumetric strain are plotted, such as... Figure 4 As shown.

[0121] The mean effective stress is calculated using formula (1):

[0122] (1)

[0123] Volumetric strain is calculated using formula (2):

[0124] (2)

[0125] based on Figure 4The data shown is used to calculate the difference between the volumetric strain at the end of each loading-unloading cycle and the initial volumetric strain. This difference represents the inelastic strain corresponding to the maximum loading stress within that cycle. The results are in... Figure 4 The center is represented by a hollow circle. Figure 4 The red and black curves in the graph represent different types of experiments performed on the two samples, respectively. Figure 4 Point C1 in the diagram represents the starting point of the nonlinear compaction portion of the two samples.

[0126] Step (d): Strain rate dependence test method for inelastic deformation of samples: This step is parallel to step (c) and aims to comprehensively understand the influencing factors and deformation mechanism of inelastic deformation of rocks. Samples with the same composition are selected, and constant strain rate triaxial tests are carried out from low to high (indoor tests are usually set to 10). -3 s -1 Up to 10 -7 s -1 ), and integrate the data to obtain different strain rates, such as Figure 5 As shown, combined with step (c), this provides an important reference for determining the deformation mechanism in the next step.

[0127] Step (e): Observing the inelastic deformation mechanism of the constrained sample based on microstructure: After the experiments in steps (c) and (d), the sample was removed from the container, dried, and then immersed in colored epoxy resin for shaping. It was then placed in a vacuum coating machine for resin injection. Subsequently, thin rock sections were prepared by wire cutting parallel to the z-axis compression loading direction. The processed samples were analyzed using a ZEISS Gemini 450 scanning electron microscope in backscattered electron (BSE) mode using EDX analysis to identify mineral composition. Microstructure analysis was performed after SEM imaging to statistically analyze the crack density distribution along the axial compression direction. Figure 6 As shown.

[0128] Step (f): Constraining the inelastic deformation mechanism of the sample based on the forward model results of the rock physics constitutive model: Previous studies have shown that the inelastic deformation mechanisms of shallow sedimentary rocks mainly include intergranular pressure solution (IPS), stress corrosion cracking (SCC), and intergranular sliding, and each mechanism has a corresponding constitutive model. Forward simulations were conducted under the corresponding experimental temperature and pressure conditions using the constitutive model corresponding to each mechanism to obtain results such as strain rate, yield stress, and peak stress. Combined with the microstructure observation results from step (e), the main mechanism of rock inelastic deformation was determined, and then the corresponding constitutive model could be selected to fit the experimental data in the next step. The criteria for determining the main controlling mechanism of rock inelastic deformation are shown in Table 1.

[0129] Table 1. Criteria for Determining the Main Controlling Mechanism of Inelastic Deformation in Rocks

[0130]

[0131] Quantitative characterization of inelastic deformation of rock: This involves summarizing the different differential stresses and average effective stresses corresponding to the same amount of inelastic deformation in experiments, where the differential stress = The average effective stress is given by formula (1), and a cross-plot is plotted. Typical results are shown below. Figure 7 As shown, different inelastic strains correspond to different stress states that form different envelopes. The first function of this diagram is to project the stress state corresponding to a new study area to obtain the deformation domain (brittle, ductile, or brittle-ductile transition) and inelastic deformation of the sample. Another function is to fit the envelope using the constitutive relation corresponding to the controlling mechanism obtained in step (f), thus obtaining accurate model parameters. The final model can then be used to predict the yield stress and inelastic strain of similar experimental samples under other temperature, pressure, and natural strain rate conditions.

[0132] like Figure 4 As shown, this application mainly uses a static water stress cycle experiment to generate a mechanical data relationship diagram of porosity reduction versus average effective stress. The specific steps are as follows:

[0133] Vertical axis (Y-axis): Average effective stress.

[0134] Horizontal axis (X-axis): Porosity reduction, i.e., the current porosity of the rock relative to its initial porosity.

[0135] Determine the amount of inelastic deformation The obtained values ​​correspond one-to-one with the average effective stress, generating a dot plot.

[0136] Figure 4 The black line represents the cyclic loading-unloading process curve, and the red line represents the sample loading process envelope under constant strain rate. By comparing the constant strain rate experiment with the cyclic loading-unloading experiment, we can verify whether there is a time-dependent damage mechanism acting on the rock sample during the cyclic loading-unloading experiment, which would cause the monotonically loaded sample to have a larger porosity change than the cyclically loaded sample under the same stress conditions.

[0137] like Figure 5 As shown, this application mainly tests the relationship between inelastic deformation and time dependence at different strain rates. The specific steps are as follows:

[0138] To quantify the inelastic deformation caused by the decrease in axial strain rate, two samples with the same well location, depth, porosity, and bedding plane were selected and subjected to constant strain rate experiments under the same confining pressure, temperature, and other conditions.

[0139] For the experimental sample, the strain rate was 10. -3 s-1 The sample was loaded until it softened and fractured, generating a stress-strain curve; for another sample of the same type, the strain rate was 10... -6 s -1 The sample is loaded until it softens and cracks, generating a stress-strain curve.

[0140] After processing the experimental data using software such as Origin and Excel, the inelastic deformation was characterized. .

[0141] in, This refers to inelastic deformation. For in 10 -6 s -1 Axial strain generated at strain rate; This represents the amount of purely elastic deformation.

[0142] In one exemplary embodiment, such as Figure 8 As shown, a device for testing and quantitatively analyzing the inelastic deformation of reservoir rocks is provided, comprising:

[0143] The acquisition module is used to acquire target rock samples.

[0144] The pretreatment module is used to pretreat the target rock sample and determine the initial porosity.

[0145] The experimental module is used to calibrate the experimental background temperature and confining pressure based on the initial porosity, and to perform parallel experimental tests on the pretreated target rock samples.

[0146] The data acquisition and processing module is used to acquire and process experimental data during the experimental testing process to obtain processed experimental data.

[0147] The microstructure analysis module is used to perform microstructure analysis on target rock samples after experimental testing and to determine the microstructure analysis results. The microstructure analysis results include the crack density distribution in the axial compression direction.

[0148] The master control mechanism determination module is used to perform forward simulation based on the rock physical constitutive model and determine the master control mechanism of rock inelastic deformation based on the microstructure analysis results; the rock physical constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust.

[0149] The quantitative analysis module is used to quantitatively characterize the inelastic deformation based on the quantitative analysis model in order to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope with parameters based on the intrinsic control relationship corresponding to the main control mechanism. The envelope is determined based on the stress state corresponding to different inelastic strains from the processed experimental data.

[0150] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0151] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks, characterized in that, include: Obtain target rock samples; The target rock sample was pretreated, and the initial porosity was determined. Based on the initial porosity, the experimental background temperature and confining pressure were calibrated, and the pretreated target rock samples were subjected to parallel processing experiments. Collect and process experimental data during the experimental testing process to obtain processed experimental data; Microstructure analysis was performed on the target rock samples after experimental testing to determine the results of the microstructure analysis. The microstructure analysis results include: the crack density distribution in the axial compression direction; Forward modeling was performed based on a rock physical constitutive model, and the main controlling mechanism of inelastic deformation of the rock was determined based on the microstructure analysis results; the rock physical constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust. The quantitative analysis model is used to quantitatively characterize the inelastic deformation to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope to the constitutive relation corresponding to the main control mechanism. The envelope is determined based on the stress state corresponding to different inelastic strains from the processed experimental data. Microstructural analysis was performed on the target rock samples after experimental testing to determine the results, specifically including: After the target rock sample was dried following the experimental test, it was immersed in colored epoxy resin for shaping and then placed in a vacuum coating machine for resin injection. For the target rock sample after resin injection, wire cutting was performed in the direction parallel to the z-axis compression loading direction to prepare rock thin sections. EDX analysis was performed using a ZEISS Gemini 450 scanning electron microscope and backscattered electron mode to identify mineral composition. After SEM imaging, microstructure analysis was performed, and the crack density distribution of the sample in the axial compression direction was statistically analyzed to obtain the microstructure analysis results. Based on the initial porosity, the experimental background temperature and confining pressure were calibrated, and parallel experimental tests were performed on the pretreated target rock samples, specifically including: Based on the well depth, rock sample density, and geothermal gradient of the target rock sample, determine the effective confining pressure and design temperature required for the experiment; Based on the initial porosity and the effective confining pressure and design temperature required for the experiment, the experimental background temperature and confining pressure are calibrated. Under experimental background temperature and confining pressure, the pretreated target rock sample was subjected to vacuum treatment and parallel experimental testing; the experimental testing was the testing of inelastic strain components under moderate strain; the moderate strain range was 0.3%-1.5%.

2. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 1, characterized in that, The inelastic deformation mechanisms of shallow sedimentary rocks in the Earth's crust include: intergranular pressure solution, stress corrosion cracking, and intergranular sliding. The mathematical expression for the constitutive model corresponding to interparticle pressure solution is: ； ； ； The mathematical expression for the constitutive model corresponding to stress corrosion cracking is: ； The mathematical expression for the constitutive model corresponding to interparticle sliding is: ； in, To achieve effective axial stress in macroscopic terms The axial strain rate caused by pressure solution controlled by dissolution under the action of dissolution; These are geometric constants; The average particle diameter; The quartz dissolution rate coefficient; The volume of quartz is the molar volume. The coordination number of the particles; It is the gas constant; Absolute temperature; For particle shape factor; For geometric constants in the range of 0.8-1; For instantaneous aggregate porosity; This is a factor that considers the influence of grain boundary structure on the grain boundary dissolution rate; Let be the geochemical dissolution rate constant of an unstressed solid under reference fluid pressure; The crack velocity of quartz; The pre-exponential factor is a constant describing the catalytic reaction of water molecules; The activation enthalpy, as determined experimentally, describes the energy barrier that the crack propagation reaction must overcome under the catalytic pathway of water molecules. , which is a geometric factor, is a parameter describing the degree to which the geometry of the crack tip affects the reaction rate; It is a type I stress intensity factor; The proportion of Si-O bonds hydrolyzed by water molecules; is a pre-exponential factor, a constant describing the catalytic reaction associated with hydroxide ions; The activation enthalpy, as determined experimentally, describes the energy barrier that the crack propagation reaction must overcome under the hydroxide ion catalytic pathway. is a geometric factor that describes the effect of the crack tip geometry on the reaction rate under the hydroxide ion pathway. The proportion of Si-O bonds hydrolyzed by hydroxyl ions; The differential stress at which intergranular sliding begins and leads to expansion; Effective stress; is the coefficient of friction.

3. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 1, characterized in that, Obtaining target rock samples specifically includes: The rock sample was processed using a wire cutting machine to obtain a cylindrical sample. The processed sample was identified as the target rock sample.

4. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 1, characterized in that, The target rock sample is pretreated to determine its initial porosity, specifically including: The processed samples were dried, vacuumed, saturated with water, and allowed to stand for equilibrium. The pore volume was determined based on the difference in rock sample quality before and after drying. Based on pore volume, using Determine the initial porosity; where, Initial porosity; Pore ​​volume; The volume of the rock.

5. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 1, characterized in that, The experimental tests of parallel processing specifically include: The pretreated target rock samples were subjected to hydrostatic pressure and deviatoric stress cyclic loading-unloading experiments, and simultaneously acoustic emission experiments were conducted. Specifically, the confining pressure was stepped-loaded and unloaded at a constant pressurization rate until the constant design confining pressure was reached, and then unloading was stopped and maintained. Then, differential stress disturbance was performed, and while maintaining a constant confining pressure, the sample was subjected to differential stress cyclic loading-unloading at a constant strain rate in the axial direction until strain softening or rock fracture phenomena were observed in the pretreated target rock samples, and then the process was stopped. The pretreated target rock samples were subjected to inelastic deformation strain rate dependence tests; wherein, the inelastic deformation strain rate dependence tests were conducted by performing triaxial experiments with constant strain rates ranging from low to high; the range of constant strain rates was 10. -3 s -1 Up to 10 -7 s -1 .

6. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 1, characterized in that, Collect and process experimental data during the experimental testing process to obtain processed experimental data, specifically including: Experimental data during the experimental testing process is collected based on a preset recording rate; the preset recording rate is obtained by correcting for different axial loading rates; wherein, during the static water loading stage, the collected experimental data includes: internal axial load, confining pressure, pore pressure, pore fluid volume change, sample temperature, and axial displacement signal data. Data on the strain rate of the target rock sample are acquired using a radial displacement hoop sensor installed in the middle and an axial displacement sensor installed at the top. The acquired experimental data include axial strain, radial strain, total porosity reduction, and peak stress. Axial strain includes the principal stress along the axial direction. The rate of change of length occurs in the direction; radial strain includes the confining pressure perpendicular to the axial direction. The rate of change of diameter in the direction of change; Determine the average effective stress-porosity reduction or volumetric strain cross plot based on the collected experimental data; In the strain rate dependence test of inelastic deformation, the influencing factors and deformation mechanisms of inelastic deformation of rock are integrated to obtain different strain rates. Based on different strain rates, and by combining the mean effective stress-porosity reduction or volumetric strain cross-plots, the processed experimental data are obtained.

7. The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks according to claim 6, characterized in that, The expression corresponding to the average effective stress is: ； The expression corresponding to the volumetric strain is: ； in, The average effective stress; It is the axial principal stress; For confining pressure; Pore ​​pressure; For volumetric strain; For axial strain; For radial strain.

8. A device for testing and quantitatively analyzing the inelastic deformation of reservoir rocks, characterized in that, The method for testing and quantitatively analyzing the inelastic deformation of reservoir rocks as described in any one of claims 1-7 is used; the apparatus for testing and quantitatively analyzing the inelastic deformation of reservoir rocks includes: The acquisition module is used to acquire target rock samples; A pretreatment module is used to pretreat the target rock sample and determine the initial porosity; The experimental module is used to calibrate the experimental background temperature and confining pressure based on the initial porosity, and to perform parallel experimental tests on the pretreated target rock samples. The data acquisition and processing module is used to acquire and process experimental data during the experimental testing process to obtain processed experimental data. The microstructure analysis module is used to perform microstructure analysis on target rock samples after experimental testing and to determine the microstructure analysis results; the microstructure analysis results include: the crack density distribution in the axial compression direction; The main control mechanism determination module is used to perform forward modeling based on the rock physical constitutive model and determine the main control mechanism of rock inelastic deformation based on the microstructure analysis results; the rock physical constitutive model is a mechanical model determined based on the inelastic deformation mechanism of shallow sedimentary rocks in the Earth's crust. The quantitative analysis module is used to quantitatively characterize the inelastic deformation based on the quantitative analysis model to determine the yield stress and inelastic strain. The quantitative analysis model is a physical simulation model determined by fitting the envelope to the constitutive relation corresponding to the master control mechanism. The envelope is determined based on the stress state corresponding to different inelastic strains from the processed experimental data.

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