Method, device, medium and equipment for determining effective stress coefficient of rock
By taking multiple rock samples with similar physical parameters from the same rock and conducting compressive strength tests under both pore pressure-free and pore pressure-containing conditions, and combining the Mohr-Coulomb strength criterion to calculate the effective stress coefficient of the rock, the problem of large errors in existing technologies has been solved, and rapid and accurate measurement of the effective stress coefficient of rock has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-11
- Publication Date
- 2026-03-24
AI Technical Summary
The effective stress coefficient of rock determined by measuring or calculating the volumetric compressibility coefficient and skeleton compressibility coefficient of rock core in existing technologies is prone to errors.
By taking multiple rock samples with similar physical parameters from the same rock, compressive strength tests were conducted under both pore pressure-free and pore pressure-containing conditions. The cohesion and internal friction angle of the rock samples were calculated using the Mohr-Coulomb strength criterion, and the effective stress coefficient of the rock was determined in combination with the experimental data.
It enables rapid and accurate measurement of the effective stress coefficient of rocks, reduces errors, and is suitable for measuring rocks with good permeability such as sandstone and coal.
Smart Images
Figure CN115683881B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of rock mechanics parameter measurement, and particularly relates to a method and device for determining the effective stress coefficient of rock, a medium and equipment. BACKGROUND
[0002] In 1923, Karl Terzaghi, an Austrian soil mechanic in the United States, proposed the effective stress principle when studying the mechanical properties of water-saturated soil. In the subsequent development, the principle has become an important theory in soil mechanics. In 1941, M.A. Biot found that the low-permeability porous medium was not suitable for applying the effective stress principle proposed by Terzaghi when studying the triaxial compression mechanics of rock, and further proposed a modified effective stress principle, that is, the effective stress is equal to the total stress minus the equivalent pore pressure. The equivalent pore pressure is equal to the product of the equivalent coefficient and the pore pressure, and the equivalent coefficient is between 0 and 1. The equivalent coefficient is also called the Biot coefficient.
[0003] The effective stress coefficient is an important parameter for determining the size of the effective stress in soil mechanics and rock mechanics. After the effective stress theory is proposed and developed, it is widely used in rock mechanics analysis. In the process of analyzing the deformation and failure of rock materials, it is considered that the failure of rock is mainly controlled by the effective stress, and the size of the effective stress is directly related to the effective stress coefficient, so the effective stress coefficient also becomes a key parameter in rock mechanics calculation. At present, the effective stress coefficient is obtained by drainage experiment method, wave speed dynamic calculation method, pore compression experiment method, etc. According to the physical meaning of the effective stress coefficient, the effective stress coefficient is calculated by measuring or calculating the bulk compression coefficient and the skeleton compression coefficient of the core. The main disadvantage is that the skeleton compression coefficient of the core is difficult to accurately measure or calculate, resulting in a certain error in the calculation result of the effective stress coefficient. SUMMARY
[0004] The purpose of the present application is to provide a method and device for determining the effective stress coefficient of rock, a medium and equipment, so as to solve the problem that the effective stress coefficient determined by measuring or calculating the bulk compression coefficient and the skeleton compression coefficient of the core is prone to error in the prior art.
[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:
[0006] The present application provides a method for determining the effective stress coefficient of rock, comprising:
[0007] Taking multiple rock samples with similar physical parameters on the same rock as the experimental group;
[0008] Several rock samples were selected from the experimental group and placed under different confining pressures in a pore-free state to determine their compressive strength.
[0009] Establish a rectangular coordinate system for confining pressure and compressive strength. Fit the data measured under pore pressure-free conditions into a straight line in the rectangular coordinate system, and calculate the cohesion and internal friction angle of the rock sample according to the Mohr-Coulomb strength criterion.
[0010] Several rock samples were selected from the experimental group and placed under different confining pressures under pore pressure to determine the compressive strength of the rock samples.
[0011] The effective stress coefficient of the rock sample was calculated using the calculated cohesion, internal friction angle, and data measured under pore pressure conditions, and then determined using the Mohr-Coulomb strength criterion. The arithmetic mean of the effective stress coefficients from multiple rock samples was taken to determine the effective stress coefficient of the rock. The expression for the effective stress coefficient of the rock sample is as follows:
[0012]
[0013]
[0014] In the formula: α is the effective stress coefficient of the rock sample, σ 3P σ is the confining pressure measured under pore pressure conditions. 1P P is the compressive strength measured under pore pressure conditions. P φ represents pore pressure, C represents rock sample cohesion, and φ represents internal friction angle.
[0015] Furthermore, it also includes the sampling method for rock samples: at least ten cylindrical standard rock core samples are drilled in the same direction on the same rock, and the physical parameters of density, sound wave velocity, porosity and permeability of each rock sample are measured. At least six rock samples with similar physical parameters are selected as the experimental group.
[0016] Furthermore, it also includes a saturation treatment method for rock samples before the experiment: each rock sample selected as the experimental group is added to the same fluid under vacuum and soaked until the rock sample fully absorbs the fluid and reaches saturation. The fluid is white oil, NaCl aqueous solution or KCl aqueous solution with viscosity.
[0017] Furthermore, it also includes experimental methods for determining the compressive strength of rock samples under pore pressure-free conditions:
[0018] 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure.
[0019] 2) After the confining pressure is increased to the set value, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is the compressive strength of the rock sample.
[0020] 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
[0021] Furthermore, it also includes experimental methods for determining the compressive strength of rock samples under pore pressure conditions:
[0022] 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure.
[0023] 2) After the confining pressure is raised to the set value, the pore fluid is delivered to the rock sample through the pore pressure pump to apply the set pore pressure, and the confining pressure and pore pressure are kept constant. At this time, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is recorded as the compressive strength of the rock sample.
[0024] 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
[0025] Furthermore, the pore fluid used by the pore pressure pump to apply pore pressure to the rock sample is the same fluid as the soaking fluid used to saturate the rock sample.
[0026] Furthermore, the expression for the effective stress coefficient of the rock is as follows: in, Let n be the effective stress coefficient of the rock, and n be a constant.
[0027] Based on the above-described method for determining the effective stress coefficient of rocks, this invention also provides an analytical apparatus for the method, comprising:
[0028] The first processing unit is used to obtain multiple rock samples with similar physical parameters from the same rock as experimental groups;
[0029] The second processing unit is used to select several rock samples from the experimental group and place them under different confining pressure conditions in a pore-free state to determine the compressive strength of the rock samples, and to determine the confining pressure σ3 and compressive strength σ1 of the rock samples.
[0030] The third processing unit is used to establish a rectangular coordinate system of confining pressure and compressive strength, and to fit the data determined under the condition of no pore pressure into a straight line in the rectangular coordinate system. Based on the Mohr-Coulomb strength criterion, the cohesion C and internal friction angle φ of the rock sample are determined by calculation.
[0031] The fourth processing unit is used to select several rock samples from the experimental group again, place them under different confining pressures while maintaining pore pressure, determine the compressive strength of the rock samples, and determine the confining pressure σ of the rock samples. 3P and compressive strength σ 1P ;
[0032] The fifth processing unit is used to calculate the effective stress coefficient α of the rock sample under pore pressure by using the calculated cohesion C, internal friction angle φ, and data determined under pore pressure conditions through the Mohr-Coulomb strength criterion, and to calculate the effective stress coefficient of the rock by taking the arithmetic mean of the effective stress coefficient α of multiple rock samples.
[0033] Based on the above-described method for determining the effective stress coefficient of rocks, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described method for determining the effective stress coefficient of rocks.
[0034] Based on the above-described method for determining the effective stress coefficient of rocks, the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the above-described method for determining the effective stress coefficient of rocks.
[0035] The present invention, by adopting the above technical solution, has the following beneficial effects:
[0036] Based on the principle that the failure of rock materials, as porous media, is controlled by the effective stress acting on the skeleton, this invention uses rock samples taken from the same core with similar physical parameters, which can be considered to have essentially the same mechanical parameters. The confining pressure applied and the compressive strength obtained in conventional mechanical experiments are both total stresses. When no pore pressure is applied, this total stress is the effective stress. Therefore, the cohesion and internal friction angle of the rock sample are first determined by the experimental data without pore pressure and the Mohr-Coulomb strength criterion. Then, the effective stress coefficient of the rock is calculated and determined by the experimental data after applying pore pressure. The principle is clear, the experimental process and data processing method are simple, and it can achieve rapid and accurate measurement of the effective stress coefficient of rock. Attached Figure Description
[0037] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:
[0038] Figure 1 This is a schematic diagram illustrating the effective stress coefficient measurement principle of an effective stress coefficient determination method provided in an embodiment of the present invention. Detailed Implementation
[0039] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.
[0040] Current methods for determining the effective stress coefficient often suffer from errors due to the difficulty in accurately measuring or calculating the core's skeletal compressibility. This invention provides a method for determining the effective stress coefficient of rocks. By using rock samples taken from the same core with similar physical parameters, their mechanical parameters are considered essentially the same. Conventional mechanical experiments are used to determine the confining pressure and compressive strength applied to the rock sample, both of which represent the total stress. Since this total stress is the effective stress when no pore pressure is applied, the cohesion and internal friction angle of the rock sample are first determined using experimental data without pore pressure and the Mohr-Coulomb strength criterion. Then, the effective principal stress expression of the Mohr-Coulomb strength criterion is derived from the experimental data after applying pore pressure, thereby determining the effective stress coefficient of the rock. This method enables rapid and accurate measurement of the effective stress coefficient of rocks.
[0041] The present invention will be described in detail below through embodiments.
[0042] Embodiments
[0043] This invention provides a method for determining the effective stress coefficient of rocks, comprising:
[0044] Multiple rock samples with similar physical parameters were taken from the same rock to form an experimental group;
[0045] Several rock samples were selected from the experimental group and placed under different confining pressures in a pore-free state to determine their compressive strength.
[0046] Establish a rectangular coordinate system for confining pressure and compressive strength. Fit the data measured under pore pressure-free conditions into a straight line in the rectangular coordinate system, and calculate the cohesion and internal friction angle of the rock sample according to the Mohr-Coulomb strength criterion.
[0047] Several rock samples were selected from the experimental group and placed under different confining pressures under pore pressure to determine the compressive strength of the rock samples.
[0048] The effective stress coefficient of the rock sample was calculated using the calculated cohesion, internal friction angle, and data measured under pore pressure conditions, and then determined using the Mohr-Coulomb strength criterion. The arithmetic mean of the effective stress coefficients from multiple rock samples was taken to determine the effective stress coefficient of the rock. The expression for the effective stress coefficient of the rock sample is as follows:
[0049]
[0050]
[0051] In the formula: α is the effective stress coefficient of the rock sample, σ 3P σ is the confining pressure measured under pore pressure conditions. 1P P is the compressive strength measured under pore pressure conditions. P φ represents pore pressure, C represents rock sample cohesion, and φ represents internal friction angle.
[0052] Specifically, the derivation steps of the expression for the effective stress coefficient of the rock sample are as follows:
[0053] The effective principal stress expression for the Mohr-Coulomb strength criterion is:
[0054]
[0055] σ′1=σ1-αP p ;
[0056] σ′3=σ3-αP p ;
[0057] In the formula: σ′1 is the effective stress of the compressive strength, σ′3 is the effective stress of the confining pressure, σ1 is the compressive strength measured under the condition of no pore pressure, σ3 is the confining pressure measured under the condition of no pore pressure, and P P denoted as pore pressure, α as effective stress coefficient of rock sample, C as cohesion of rock sample, and φ as internal friction angle.
[0058] Due to the pore pressure P in the state of no pore pressure P=0, that is, in the effective principal stress expression of the Mohr-Coulomb strength criterion, σ′1=σ1, σ′3=σ3. By selecting several rock samples from the experimental group and placing them under different confining pressures σ3 in the absence of pore pressure, the compressive strength σ1 of the rock samples can be measured. The cohesion C and internal friction angle φ of the rock samples can then be calculated using the above formula.
[0059] The confining pressure σ is measured separately under pore pressure conditions. 3P and compressive strength σ 1P The confining pressure σ can be determined using the effective principal stress expression of the Mohr-Coulomb strength criterion. 3P and compressive strength σ 1P The effective stress expression is:
[0060] σ′1=σ 1p -αP p ;
[0061] σ′3=σ 3p -αP p ;
[0062] The calculated cohesion C, internal friction angle φ, and data measured under pore pressure were substituted into the effective principal stress expression of the Mohr-Coulomb strength criterion, and the following assumptions were made: The reconstructable effective principal stress expression is: σ 1P -αP P =(σ 3P -αP P )σ′3K 2 +2CK;
[0063] The expression for the effective principal stress of the reconstructed rock sample is derived to establish the expression for the effective stress coefficient:
[0064]
[0065] Based on the expression for the effective stress coefficient of rock samples, multiple compressive strength data measured under pore pressure conditions are substituted into the expression for the effective stress coefficient to calculate the corresponding effective stress coefficients α1, α2, ... α. n The effective stress coefficient of the rock is obtained by taking the arithmetic mean of multiple calculated effective stress coefficients, and the expression for taking the arithmetic mean of multiple effective stress coefficients is as follows:
[0066]
[0067] in, Let n be the effective stress coefficient of the rock, and n be a constant.
[0068] Furthermore, the method for sampling rock samples includes drilling at least ten cylindrical standard core samples from the same rock along the same direction, and measuring the physical parameters of each sample, including density, acoustic velocity, porosity, and permeability. From these, at least six rock samples with similar physical parameters are selected as the experimental group. Preferably, during the rock sample collection process, the diameter of the collected rock samples is approximately 25 mm, and the length is approximately 50 mm.
[0069] Furthermore, the method also includes a saturation treatment for rock samples before the experiment: each rock sample selected as part of the experimental group is immersed in the same fluid under vacuum until it fully absorbs the fluid and reaches saturation. Specifically, during the saturation process, the rock samples must first be evacuated, and then a sufficient amount of fluid is added to them under vacuum. Preferably, the immersion time is two hours to allow the rock samples to fully absorb the fluid. Additionally, depending on the testing requirements, the fluid is white oil, NaCl aqueous solution, or KCl aqueous solution with a certain viscosity, etc.
[0070] Furthermore, it also includes experimental methods for determining the compressive strength of rock samples under pore pressure-free conditions:
[0071] 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure.
[0072] 2) After the confining pressure is increased to the set value, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is the compressive strength of the rock sample.
[0073] 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
[0074] Since the Mohr-Coulomb strength criterion is only used to describe shear failure of rock materials, it is necessary to ensure that the failure mode of the rock sample is shear failure in the experiment in order to improve the accuracy of the effective stress coefficient calculation.
[0075] As mentioned above, taking three rock samples as an example, the compressive strength test of the three rock samples was carried out under confining pressures of 10MPa, 20MPa and 30MPa respectively. The compressive strength of the rock samples under different confining pressures without pore pressure was determined, and the compressive strength σ1 corresponding to different confining pressures σ3 was obtained.
[0076] Furthermore, it also includes experimental methods for determining the compressive strength of rock samples under pore pressure conditions:
[0077] 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure.
[0078] 2) After the confining pressure is raised to the set value, the pore fluid is delivered to the rock sample through the pore pressure pump to apply the set pore pressure, and the confining pressure and pore pressure are kept constant. At this time, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is recorded as the compressive strength of the rock sample.
[0079] 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
[0080] Since the Mohr-Coulomb strength criterion is only used to describe shear failure of rock materials, it is necessary to ensure that the failure mode of the rock sample is shear failure in the experiment in order to improve the accuracy of the effective stress coefficient calculation.
[0081] As mentioned above, taking three other rock samples as examples, compressive strength tests were conducted on the three rock samples under confining pressures of 10 MPa, 20 MPa, and 30 MPa, respectively. During the tests, the same fluid as when the rock samples were saturated was used to apply a pore pressure of 5 MPa to the rock samples. The compressive strength of the rock samples under different confining pressures with pore pressure was measured, and the compressive strength σ under different confining pressures was obtained. 3P Corresponding compressive strength σ 1P Furthermore, by substituting the measured data into the expression for the effective stress coefficient and calculating, the corresponding effective stress coefficients α1, α2, and α3 are obtained. The effective stress coefficients of the three rock samples are then taken as an arithmetic mean to obtain the effective stress coefficient of the rock. The expression for taking the arithmetic mean of the effective stress coefficients of the three rock samples is as follows:
[0082] Furthermore, the pore fluid used by the pore pressure pump to apply pore pressure to the rock sample is the same fluid as the soaking fluid used to saturate the rock sample.
[0083] In summary, through the above steps, the effective stress coefficient can be calculated from the experimental data of the saturated compressive strength of rock samples. The principle is that, as a porous medium, the failure of rock materials is controlled by the effective stress acting on the framework. Therefore, this invention first determines the cohesion and internal friction angle of the rock sample using experimental data without pore pressure and the Mohr-Coulomb strength criterion. Then, it uses experimental data with pore pressure applied to deduce the effective principal stress expression of the Mohr-Coulomb strength criterion, thereby determining the effective stress coefficient of the rock. That is, the method for determining the effective stress coefficient of this invention, by combining the commonly used core compressive strength experimental equipment (rock mechanics testing machine) in the field of rock mechanics, has a clear principle, simple experimental process and data processing methods, and can achieve rapid and accurate measurement of the effective stress coefficient of rocks. It is suitable for determining the effective stress coefficient of sandstone, coal, and other rocks with good permeability.
[0084] Based on the above-described method for determining the effective stress coefficient of rocks, this invention also provides an analytical apparatus for the method, comprising:
[0085] The first processing unit is used to obtain multiple rock samples with similar physical parameters from the same rock as experimental groups;
[0086] The second processing unit is used to select several rock samples from the experimental group and place them under different confining pressure conditions in a pore-free state to determine the compressive strength of the rock samples, and to determine the confining pressure σ3 and compressive strength σ1 of the rock samples.
[0087] The third processing unit is used to establish a rectangular coordinate system of confining pressure and compressive strength, and to fit the data determined under the condition of no pore pressure into a straight line in the rectangular coordinate system. Based on the Mohr-Coulomb strength criterion, the cohesion C and internal friction angle φ of the rock sample are determined by calculation.
[0088] The fourth processing unit is used to select several rock samples from the experimental group again, place them under different confining pressures while maintaining pore pressure, determine the compressive strength of the rock samples, and determine the confining pressure σ of the rock samples. 3P and compressive strength σ 1P ;
[0089] The fifth processing unit is used to calculate the effective stress coefficient α of the rock sample under pore pressure by using the calculated cohesion C, internal friction angle φ, and data determined under pore pressure conditions through the Mohr-Coulomb strength criterion, and to calculate the effective stress coefficient of the rock by taking the arithmetic mean of the effective stress coefficient α of multiple rock samples.
[0090] Based on the above-described method for determining the effective stress coefficient of rocks, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described method for determining the effective stress coefficient of rocks.
[0091] Based on the above-described method for determining the effective stress coefficient of rocks, the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the above-described method for determining the effective stress coefficient of rocks.
[0092] This invention is described based on flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to specific embodiments. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing device, generate instructions for implementing the flowcharts and / or block diagrams. Figure One One or more processes and / or boxes Figure One A device that provides the functions specified in one or more boxes.
[0093] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure One One or more processes and / or boxes Figure One The function specified in one or more boxes.
[0094] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure One One or more processes and / or boxes Figure One Figure One The steps of the function specified in one or more boxes.
[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for determining the effective stress coefficient of rock, characterized in that, The method for determining the effective stress coefficient includes: Multiple rock samples with similar physical parameters were taken from the same rock to form an experimental group; Several rock samples were selected from the experimental group and placed under different confining pressures in a pore-free state to determine their compressive strength. Establish a rectangular coordinate system for confining pressure and compressive strength. Fit the data measured under pore pressure-free conditions into a straight line in the rectangular coordinate system, and calculate the cohesion and internal friction angle of the rock sample according to the Mohr-Coulomb strength criterion. Several rock samples were selected from the experimental group and placed under different confining pressures under pore pressure to determine the compressive strength of the rock samples. The effective stress coefficient of the rock sample was calculated using the calculated cohesion, internal friction angle, and data measured under pore pressure conditions, and then determined using the Mohr-Coulomb strength criterion. The arithmetic mean of the effective stress coefficients from multiple rock samples was taken to determine the effective stress coefficient of the rock. The expression for the effective stress coefficient of the rock sample is as follows: In the formula: α is the effective stress coefficient of the rock sample, σ 3P σ is the confining pressure measured under pore pressure conditions. 1P P is the compressive strength measured under pore pressure conditions. P φ represents pore pressure, C represents rock sample cohesion, and φ represents internal friction angle.
2. The method for determining the effective stress coefficient of rock according to claim 1, characterized in that, It also includes the sampling method for rock samples: at least ten cylindrical standard rock core samples are drilled in the same direction on the same rock, and the physical parameters of density, sound velocity, porosity and permeability of each rock sample are measured. At least six rock samples with similar physical parameters are selected as the experimental group.
3. The method for determining the effective stress coefficient of rock according to claim 2, characterized in that, It also includes a saturation treatment method for rock samples before the experiment: each rock sample selected as the experimental group is added to the same fluid under vacuum and soaked until the rock sample fully absorbs the fluid and reaches saturation. The fluid is white oil, NaCl aqueous solution or KCl aqueous solution with viscosity.
4. The method for determining the effective stress coefficient of rock according to claim 3, characterized in that, It also includes experimental methods for determining the compressive strength of rock samples under pore pressure-free conditions: 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure. 2) After the confining pressure is increased to the set value, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is the compressive strength of the rock sample. 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
5. The method for determining the effective stress coefficient of rock according to claim 4, characterized in that, It also includes experimental methods for determining the compressive strength of rock samples under pore pressure conditions: 1) Using a rock mechanics testing machine, the rock sample is sealed in a heat shrink sleeve and placed in the rock mechanics testing machine for compression. The confining pressure is gradually increased to the set value, and the axial load is increased simultaneously to make the axial stress proportional to the confining pressure. 2) After the confining pressure is raised to the set value, the pore fluid is delivered to the rock sample through the pore pressure pump to apply the set pore pressure, and the confining pressure and pore pressure are kept constant. At this time, the axial load is slowly increased so that the axial stress on the rock sample gradually increases until the rock sample is destroyed. The maximum axial stress on the rock sample at this time is recorded as the compressive strength of the rock sample. 3) Release the confining pressure, remove the rock sample from the rock mechanics testing machine and observe its failure mode to ensure that the rock sample has undergone shear failure. If the rock sample has not undergone shear failure, take another rock sample with similar physical parameters, saturate it and repeat steps 1)-2) until the rock sample undergoes shear failure.
6. The method for determining the effective stress coefficient of rock according to claim 5, characterized in that: The pore fluid that applies pore pressure to the rock sample using a pore pressure pump is the same fluid as the soaking fluid used to saturate the rock sample.
7. The method for determining the effective stress coefficient of rock according to claim 6, characterized in that, The expression for the effective stress coefficient of the rock is: in, Let n be the effective stress coefficient of the rock, and n be a constant.
8. An analytical apparatus, characterized in that, The analytical device includes: The first processing unit is used to obtain multiple rock samples with similar physical parameters from the same rock as experimental groups; The second processing unit is used to select several rock samples from the experimental group and place them under different confining pressure conditions in a pore-free state to determine the compressive strength of the rock samples, and to determine the confining pressure σ3 and compressive strength σ1 of the rock samples. The third processing unit is used to establish a rectangular coordinate system of confining pressure and compressive strength, and to fit the data determined under the condition of no pore pressure into a straight line in the rectangular coordinate system. Based on the Mohr-Coulomb strength criterion, the cohesion C and internal friction angle φ of the rock sample are determined by calculation. The fourth processing unit is used to select several rock samples from the experimental group again, place them under different confining pressures while maintaining pore pressure, determine the compressive strength of the rock samples, and determine the confining pressure σ of the rock samples. 3P and compressive strength σ 1P ; The fifth processing unit is used to calculate the effective stress coefficient α of the rock sample under pore pressure by using the calculated cohesion C, internal friction angle φ, and data determined under pore pressure conditions through the Mohr-Coulomb strength criterion, and to calculate the effective stress coefficient of the rock by taking the arithmetic mean of the effective stress coefficient α of multiple rock samples.
9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for determining the effective stress coefficient of rock as described in any one of claims 1-7.
10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for determining the effective stress coefficient of rock as described in any one of claims 1-7.