Dynamic testing method for shear slip friction coefficient and fracture permeability of rock

Abstract

The invention provides a method for dynamically testing the shear-slip friction coefficient and fracture permeability of rock. The method comprises the following steps: S1, preparing an experimental test piece according to a preset size; s2, carrying out a shear-slip friction coefficient test experiment on the experiment test piece to obtain a shear experiment rock, and calculating to obtain a shear-slip friction coefficient; s3, performing a crack permeability test experiment on the shear experiment rock, and calculating to obtain the crack dynamic permeability; and S4, obtaining a test effect of the dynamic permeability of the crack according to the shear slip friction coefficient and the dynamic permeability of the crack. According to the invention, the shear slip friction coefficient of the rock can be more accurately tested, the dynamic permeability of the shear crack can be reflected, the influence of an unstable slip starting stage and fluctuating slip after the shear failure of the rock is eliminated, and the original permeability characteristic of the shear crack surface can be accurately reflected; the effect of comprehensively and universally testing the dynamic permeability of the crack is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of experimental testing, and in particular to a dynamic testing method for rock shear-slip friction coefficient and crack permeability. Background Art

[0002] The mechanical properties of rocks are key parameters that must be obtained for the implementation of geotechnical engineering. Rock shear failure is a common type of rock failure that occurs in many geotechnical engineering projects. Its shear slip friction coefficient is a parameter that characterizes the ability of rocks to displace after shear failure. It is widely used in the analysis of geological disasters such as landslides, rock fracturing, and geotechnical engineering construction. After shear slip or tension failure of rocks, new cracks will form, new flow channels will be generated, and fluids will enter the newly generated cracks. Obtaining the permeability characteristics of the newly generated cracks is a key parameter for the later implementation of related geotechnical engineering. For example, obtaining the permeability of newly generated fracturing cracks in petroleum engineering is an important item for later production. It is an important parameter for analyzing the scope and capacity of fluid impact in geological disasters or fluid injection-induced earthquake disasters.

[0003] At present, there are a large number of documents and patents at home and abroad that disclose many equipment and methods for measuring rock shear friction coefficient and crack permeability. For example, in the document "Relationship between the sliding friction coefficient of rock and the mineral properties of rock", an inclined plane instrument for indoor experiments was developed, which uses natural crack surfaces and sawn surfaces to simulate rough and smooth discontinuous surfaces, and can measure the sliding friction coefficient of various rocks. Patent CN 108827796A discloses a test device for measuring rock shear strength and shear crack friction sliding characteristics, including an upper shear plate and a lower shear plate. The lower shear groove corresponds to the upper shear groove and can form a cylindrical accommodation space. During the test, the axial displacement and axial load changes over time can be recorded in real time, and the rock shear strength and shear crack friction sliding characteristics can be obtained at the same time. Patent CN108519293B authorizes a true triaxial rock shear seepage test device, which is connected to three groups of loading cylinders and three groups of loading plates on a hollow square frame in the three-axis direction, and connected to shear cylinders and auxiliary shear cylinders in the Z-axis direction. A seepage inlet is provided on one side of the hollow square frame in the Y-axis direction, and a seepage outlet is provided on the other side. Real-time testing of rock shear failure and seepage under triaxial stress state is realized. Patent CN110095353B authorizes an in-situ rock shear permeability performance measurement device, including: a fracturing kettle, and infiltration grooves and outfiltration grooves are arranged on its top wall and bottom wall, so as to realize the study of natural fracture shear slip permeability characteristics of rock under in-situ conditions. There are also a large number of documents and some patents such as CN106969987A, CN111220484B, CN115791451A, CN106769780B and CN106769542A, etc., which disclose or authorize some rock shear or fracture permeability measurement devices and methods. However, they are all targeted at specific devices or the data processing methods obtained cannot more accurately reflect the rock sliding friction characteristics, especially the permeability characteristics of the rock can only obtain the permeability characteristics of a certain loading stress point, and the permeability values ​​of different loading stress points need to be obtained, and the experiment needs to be repeated. Moreover, the experimental value obtained is the permeability value of the experimental fluid. If the properties of the fluid change, the experiment needs to be repeated, which leads to cumbersomeness, large workload and poor accuracy. Summary of the invention

[0004] Based on this, it is necessary to provide a dynamic testing method for rock shear slip friction coefficient and fracture permeability to address the above technical issues.

[0005] A method for dynamic testing of rock shear sliding friction coefficient and crack permeability comprises the following steps:

[0006] Step S1, preparing an experimental specimen according to a preset size;

[0007] Step S2, performing a shear-slip friction coefficient test experiment on the experimental specimen to obtain a shear test rock and calculate the shear-slip friction coefficient;

[0008] Step S3, performing a fracture permeability test experiment on the shear test rock to calculate the fracture dynamic permeability;

[0009] Step S4, obtaining a test result of the fracture dynamic permeability according to the shear slip friction coefficient and the fracture dynamic permeability.

[0010] In one embodiment, step S2 comprises:

[0011] Step S21, the experimental specimen is subjected to a shear-slip friction coefficient test experiment to obtain a shear test rock;

[0012] Step S22, collecting the horizontal displacement, horizontal shear force and axial stress during the experiment, and calculating the shear slip friction coefficient according to the horizontal displacement, the horizontal shear force and the axial stress.

[0013] In one embodiment, step S22 includes:

[0014] The shear slip friction coefficient is calculated according to the following formula:

[0015]

[0016] Among them, μ represents the shear sliding friction coefficient, f represents the sliding horizontal shear force, S represents the rock shear surface area, and F represents the axial stress.

[0017] In one embodiment, step S3 comprises:

[0018] Step S31, performing a roughness scan on the rock in the shear test to calculate the theoretical permeability of the fracture;

[0019] Step S32, restoring the shear test rock according to a preset size to obtain a restored test rock;

[0020] Step S33, performing a fracture permeability test experiment on the recovery test rock under multiple axial stresses;

[0021] Step S34, collecting the pressure and flow rate of the fluid at the fracture during the experiment, and calculating the hydraulic permeability according to the pressure and flow rate of the fluid;

[0022] Step S35, calculating the dynamic permeability of the fracture according to the theoretical permeability of the fracture and the hydraulic permeability.

[0023] In one embodiment, step S31 includes:

[0024] Step S311, obtaining a closed shear fracture surface, obtaining a contour line at the fracture according to the closed shear fracture surface, and calculating an average opening of the contour line at the fracture;

[0025] Step S312, calculating the fracture theoretical permeability according to the average aperture:

[0026]

[0027] Among them, K η represents the theoretical permeability of the fracture, and η represents the average opening.

[0028] In one embodiment, step S311 includes:

[0029] Acquire a closed shear crack surface, perform a roughness scan on the closed shear crack surface, and obtain a scanning coordinate of the crack surface;

[0030] Taking the scanning coordinate spacing as the interval, along the width direction of the closed shear crack surface, the crack width is divided into several contour lines parallel to the crack length direction at equal intervals along the crack width direction to obtain the crack contour line;

[0031] Calculate the roughness of the contour line at each crack:

[0032]

[0033] Among them, Z j represents the roughness of the jth contour line, L represents the length of the contour line at the crack, n represents the number of points in the length direction of the contour line at the jth crack, i represents the i-th point in the length direction of the jth crack contour line, y i+1 represents the y coordinate of the i+1 point in the length direction of the contour line at the jth crack, y i represents the y-axis coordinate of the i-th point on the crack contour line, x i+1 represents the x-coordinate of the i+1 point in the length direction of the contour line at the jth crack, x i represents the x-axis coordinate of the i-th point on the crack contour line;

[0034] Calculate the contour opening at the jth crack based on the rough contour opening:

[0035] η j =|Z′ j +Z″ j |

[0036] Among them, η j represents the contour opening at the jth crack, Z' j Indicates the rough opening of the jth contour line of the unclosed upper shear crack surface, Z″ j It represents the rough opening of the jth contour line of the unclosed lower shear crack surface;

[0037] Calculate the average opening of the contour lines at the crack:

[0038]

[0039] Where η represents the average opening of the contour line at the crack, j represents the contour line at the jth crack, and η j represents the opening of the contour line at the jth crack, and l represents the total number of contour lines at the crack.

[0040] In one embodiment, step S34 includes:

[0041] The pressure and flow rate of the fluid at the fracture during the experiment were collected, and the average flow rate of the fracture under different axial stresses was calculated based on the flow rate of the fluid:

[0042]

[0043] Where Q represents the average flow rate of the crack, P 出口 represents the crack outlet pressure, P 入口 represents the crack entrance pressure, Q 出口 represents the fracture outlet flow rate;

[0044] Calculate the equivalent hydraulic opening under different axial stresses according to the pressure of the fluid:

[0045] P 入口 -P 出口 =A1Q+A2Q 2

[0046]

[0047] Among them, P 出口 represents the crack outlet pressure, P 入口 represents the fracture entrance pressure, A1 and A2 represent the fitting coefficients, Q represents the average fracture flow rate, e represents the equivalent hydraulic opening, μ1 represents the fluid viscosity, and W represents the fracture width;

[0048] The hydraulic permeability under different axial stresses is calculated based on the equivalent hydraulic opening:

[0049]

[0050] Among them, K represents the hydraulic permeability and e represents the equivalent hydraulic opening.

[0051] In one embodiment, step S35 includes:

[0052] The fracture surface compression coefficient is calculated based on the hydraulic permeability and axial stress:

[0053]

[0054] Where K represents hydraulic permeability, K η represents the theoretical permeability of the fracture, e represents the equivalent hydraulic opening, C f represents the crack surface compression coefficient, σ represents the axial stress;

[0055] A scatter plot is made with axial stress as the horizontal axis and the corresponding crack surface compression coefficient value as the vertical axis. The scatter plot is fitted using a quadratic nonlinear relationship, and the shear crack surface compression coefficient C' is obtained according to the following formula f

[0056] C' f =B1σ+B2σ 2 +B3

[0057] Among them, C' f represents the compression coefficient of the shear crack surface, B1, B2, B3 represent the fitting coefficients, and σ represents the axial stress;

[0058] The dynamic permeability of the fracture is calculated based on the theoretical permeability of the fracture and the shear fracture surface compression coefficient:

[0059]

[0060] Where FP represents the dynamic permeability of the fracture, K η represents the theoretical permeability of the fracture, e represents the equivalent hydraulic opening, C f represents the compression coefficient of the shear crack surface, and σ represents the axial stress.

[0061] Compared with the prior art, the advantages and beneficial effects of the present invention are: the present invention provides a rock shear sliding friction coefficient and crack permeability dynamic test method, which can more accurately test the rock shear sliding friction coefficient and the dynamic permeability of the shear crack. Among them, the rock shear sliding friction coefficient test provides a more accurate test data selection and determination method, which can better reflect the stable sliding characteristics of the rock after shearing, eliminate the influence of the unstable sliding start-up stage and the fluctuating sliding after the rock shear failure, and better reflect the sliding friction characteristics of the shear rock. At the same time, the present invention includes a dynamic test method for the permeability of the roughness of the shear fracture surface and unstable nonlinear seepage, and provides a shear fracture surface roughness, fracture surface opening and fracture theoretical permeability test method. The method can accurately reflect the original permeability characteristics of the shear fracture surface. The hydraulic permeability test focuses on the nonlinear flow law of the fluid and can better reflect the actual seepage capacity of the fluid in the fracture. At the same time, a dynamic representation method for the compression coefficient of the shear fracture surface is established, which is combined with the theoretical permeability and hydraulic permeability test method to reflect the permeability characteristics under different fracture closure stresses, and has the effect of comprehensively and universally testing the dynamic permeability of the fracture. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A schematic diagram of a process for a dynamic test method of rock shear-slip friction coefficient and fracture permeability in one embodiment;

[0063] Figure 2 is a schematic diagram of the slope of horizontal shear force changing with horizontal displacement in one embodiment;

[0064] Figure 3 A schematic diagram of a closed shear crack surface in one embodiment;

[0065] Figure 4 A schematic diagram of scattered points in one embodiment with the number of times the contour line opening value range appears as the vertical coordinate;

[0066] Figure 5 It is a schematic diagram of scattered points in one embodiment, with the axial stress as the horizontal coordinate and the corresponding shear crack surface compression coefficient as the vertical coordinate. DETAILED DESCRIPTION

[0067] Before describing the specific embodiments of the present invention, the overall concept of the present invention is described as follows:

[0068] The present invention is mainly developed for testing the permeability of rock fractures. Currently, the specific devices or data processing methods obtained cannot more accurately reflect the rock sliding friction characteristics. In particular, the permeability characteristics of the rock can only be obtained at a certain loading stress point. It is necessary to obtain the permeability values ​​of different loading stress points, and the experiment needs to be repeated. Moreover, the experimental value obtained is the permeability value of the experimental fluid. If the fluid properties change, the experiment needs to be repeated, which leads to cumbersomeness, large workload and poor accuracy.

[0069] Therefore, the present invention proposes a dynamic test method for rock shear-slip friction coefficient and fracture permeability. After obtaining the prepared experimental specimen, the shear-slip friction coefficient is tested by a shear-slip friction coefficient test experiment to obtain the shear-slip friction coefficient, and the fracture dynamic permeability is tested by a fracture permeability test experiment to obtain the fracture dynamic permeability, and then the test result of the fracture dynamic permeability is obtained through this data. The shear-slip friction coefficient and fracture permeability can be tested more accurately and universally.

[0070] After introducing the overall concept of the present invention, in order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0071] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in one or more embodiments of this specification should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in one or more embodiments of this specification do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0072] In one embodiment, Figure 1 As shown, a dynamic testing method for rock shear sliding friction coefficient and fracture permeability is provided, comprising the following steps:

[0073] Step S1, preparing an experimental specimen according to a preset size.

[0074] Specifically, the experimental specimens are prepared according to the preset size. For example, a rectangular rock specimen with the size of 12 cm × 8 cm × 5 cm in length × width × height is prepared, and the six end faces are polished smooth. At the same time, the rock specimen is required to have no obvious natural or artificial cracks.

[0075] Step S2, performing a shear-slip friction coefficient test experiment on the experimental specimen to obtain a shear experimental rock and calculate the shear-slip friction coefficient.

[0076] Specifically, by conducting a shear-slip friction coefficient test experiment, a shear test rock can be obtained, and the shear-slip friction coefficient can be calculated by acquiring experimental data during the experiment.

[0077] On this basis, step S2 includes:

[0078] Step S21, the experimental specimen is subjected to a shear-slip friction coefficient test experiment to obtain a shear test rock;

[0079] Step S22, collecting the horizontal displacement, horizontal shear force and axial stress during the experiment, and calculating the shear slip friction coefficient according to the horizontal displacement, the horizontal shear force and the axial stress.

[0080] Specifically, a shear-slip friction coefficient test experiment is carried out on the experimental specimen, and data such as horizontal displacement, horizontal shear force, and axial stress during the experiment are collected, and the shear-slip friction coefficient is calculated using the experimental data.

[0081] On this basis, step S22 includes:

[0082] The shear slip friction coefficient is calculated according to the following formula:

[0083]

[0084] Among them, μ represents the shear sliding friction coefficient, f represents the sliding horizontal shear force, S represents the rock shear surface area, and F represents the axial stress.

[0085] Specifically, the shear slip friction coefficient μ is calculated using the formula, where f is the sliding horizontal shear force, F is the corresponding axial stress during stable sliding, and S is the rock shear surface area. Among them, f is obtained by the following method: a horizontal shear force versus horizontal displacement curve is drawn with the horizontal shear force as the vertical axis and the horizontal displacement as the horizontal axis, and a slope graph of the horizontal shear force versus horizontal displacement is drawn on the curve graph. When three consecutive slope values ​​are approximately equal to 0, the corresponding horizontal shear force value is taken as the f value, and the corresponding F value is the axial force. Figure 2 For example, take 4 consecutive points with slopes close to 0 to draw a slope graph. The initial slope is 1, then becomes 0.01, and then the slopes of 3 consecutive points are close to 0. After the 4th point, the slope is 0.25. The subsequent data have certain changes, but the slopes fluctuate around 0. The corresponding sliding horizontal shear force is 91KN, the corresponding axial force F is 5KN, and the rock shear surface area S is 0.0096 square meters. Using the formula, the shear slip friction coefficient μ is 0.17471.

[0086] Step S3, performing a fracture permeability test experiment on the shear test rock to calculate the fracture dynamic permeability.

[0087] Specifically, a fracture permeability test experiment is carried out on the shear test rock, multiple experimental data are collected during the process, and the dynamic permeability of the fracture is calculated through the experimental data.

[0088] On this basis, step S3 includes:

[0089] Step S31, performing a roughness scan on the rock in the shear test to calculate the theoretical permeability of the fracture;

[0090] Step S32, restoring the shear test rock according to a preset size to obtain a restored test rock;

[0091] Step S33, performing a fracture permeability test experiment on the recovery test rock under multiple axial stresses;

[0092] Step S34, collecting the pressure and flow rate of the fluid at the fracture during the experiment, and calculating the hydraulic permeability according to the pressure and flow rate of the fluid;

[0093] Step S35, calculating the dynamic permeability of the fracture according to the theoretical permeability of the fracture and the hydraulic permeability.

[0094] Specifically, the shear test rock is taken out, the roughness of the shear fracture surface is scanned, and the theoretical permeability of the fracture is calculated. The shear test rock is restored to before failure, and the fluid pressure and flow rate of the fracture inlet / outlet are collected under multiple axial stresses to calculate the hydraulic permeability; based on the theoretical permeability and hydraulic permeability of the fracture, the fracture compression coefficient is calculated, and further, the dynamic permeability of the fracture is calculated.

[0095] Taking five axial stresses of 0.5, 1, 3, 5 and 10 MPa as examples, the fracture permeability experiment was carried out, and the fracture inlet / outlet fluid pressure and flow rate were collected at the same time, as shown in Table 1.

[0096] Table 1. Data collected from crack permeability experiments

[0097]

[0098]

[0099] On this basis, step S31 includes:

[0100] Step S311, obtaining a closed shear fracture surface, obtaining a contour line at the fracture according to the closed shear fracture surface, and calculating an average opening of the contour line at the fracture;

[0101] Step S312, calculating the fracture theoretical permeability according to the average aperture:

[0102]

[0103] Among them, K η represents the theoretical permeability of the fracture, and η represents the average opening.

[0104] Specifically, the shear test rock is taken out, the closed shear fracture surface is obtained through the shear test rock, the contour line at the fracture is obtained according to the closed shear fracture surface, the average opening of the contour line at the fracture is calculated, and then the theoretical permeability of the fracture is calculated through the average opening.

[0105] On this basis, step S311 includes:

[0106] Acquire a closed shear crack surface, perform a roughness scan on the closed shear crack surface, and obtain a scanning coordinate of the crack surface;

[0107] Taking the scanning coordinate spacing as the interval, along the width direction of the closed shear crack surface, the crack width is divided into several contour lines parallel to the crack length direction at equal intervals along the crack width direction to obtain the crack contour line;

[0108] Calculate the roughness of the contour line at each crack:

[0109]

[0110] Among them, Z j represents the roughness of the jth contour line, L represents the length of the contour line at the crack, n represents the number of points in the length direction of the contour line at the jth crack, i represents the i-th point in the length direction of the jth crack contour line, y i+1 represents the y coordinate of the i+1 point in the length direction of the contour line at the jth crack, y i represents the y-axis coordinate of the i-th point on the crack contour line, x i+1 represents the x-coordinate of the i+1 point in the length direction of the contour line at the jth crack, x i represents the x-axis coordinate of the i-th point on the crack contour line;

[0111] Calculate the contour opening at the jth crack based on the rough contour opening:

[0112] η j =|Z′ j +Z″ j |

[0113] Among them, η j represents the contour opening at the jth crack, Z' j Indicates the rough opening of the jth contour line of the unclosed upper shear crack surface, Z″ j It represents the rough opening of the jth contour line of the unclosed lower shear crack surface;

[0114] Calculate the average opening of the contour lines at the crack:

[0115]

[0116] Where η represents the average opening of the contour line at the crack, j represents the contour line at the jth crack, and η j represents the opening of the contour line at the jth crack, and l represents the total number of contour lines at the crack.

[0117] Specifically, the shear test rock is taken out, and two closed shear fracture surfaces of the shear test rock are scanned using a three-dimensional optical morphology measurement scanner, such as Figure 3 As shown, the coordinates of the points on the closed shear crack surface are obtained. Then, along the width direction of the closed shear crack surface, the crack width is divided into several crack contour lines parallel to the crack length direction at equal intervals along the width direction of the closed shear crack surface, with the scanning coordinate spacing as the interval, and the formula is used. Calculate the roughness Z' of the jth contour line of each closed shear crack surface j , Z j". Further, using the formula η j =(Z' j +Z j "|, calculate the contour opening η of a single crack corresponding to two closed shear crack surfaces j , where x i is the x-axis coordinate on the crack contour line, y i For x i The corresponding y-axis coordinate, L crack contour length, Z j is the roughness opening of the jth contour line, Z' j is the rough opening of the jth contour line of the unclosed upper shear crack surface, Z j "The rough opening of the jth contour line of the unclosed shear crack surface, η j is the opening of the jth contour line of the closed shear crack surface.

[0118] A scatter plot is made with the crack contour opening as the horizontal axis and the number of times each contour opening value range appears as the vertical axis, and the normal distribution function is used to fit the scatter plot. According to the fitting formula The average opening of the shear fracture surface is obtained, where δ is the mean square error and η is the average opening of the shear fracture surface.

[0119] Taking 1mm interval as an example, the crack width is divided into 80 contour lines parallel to the crack length direction along the crack width direction, and then the formula is used Calculate the rough opening Z' of the jth contour line of the upper and lower shear crack surfaces j , Z″ j , further, using the formula η j =|Z' j +Z″ j |, calculate the single contour opening η corresponding to the two closed shear crack surfaces j The calculation results are shown in Table 2.

[0120] Table 2 Opening calculation results

[0121]

[0122]

[0123]

[0124] A scatter plot is made with the crack contour opening as the horizontal axis and the number of times each contour opening value range appears as the vertical axis. This time, it is divided into 10 ranges, namely: 0-0.2, 0.2-0.4, 0.4-0.6, 0.6-0.8, 0.8-1.0, 1.0-1.2, 1.2-1.4, 1.4-1.6, 1.6-1.8 and 1.8-2.0. Further, the normal distribution function is used to fit the scatter plot, such as Figure 4 As shown, according to the normal distribution formula After fitting, the formula is The average opening η of the shear fracture surface is obtained to be 1.27835.

[0125] Using formula Calculate the theoretical fracture permeability K η It is 0.13618156.

[0126] On this basis, step S34 includes:

[0127] The pressure and flow rate of the fluid at the fracture during the experiment were collected, and the average flow rate of the fracture under different axial stresses was calculated based on the flow rate of the fluid:

[0128]

[0129] Where Q represents the average flow rate of the crack, P 出口 represents the crack outlet pressure, P 入口 represents the crack entrance pressure, Q 出口 represents the fracture outlet flow rate;

[0130] Calculate the equivalent hydraulic opening under different axial stresses according to the pressure of the fluid:

[0131] P 入口 -P 出口 =A1Q+A2Q 2

[0132]

[0133] Among them, P 出口 represents the crack outlet pressure, P 入口 represents the fracture entrance pressure, A1 and A2 represent the fitting coefficients, Q represents the average fracture flow rate, e represents the equivalent hydraulic opening, μ1 represents the fluid viscosity, and W represents the fracture width;

[0134] The hydraulic permeability under different axial stresses is calculated based on the equivalent hydraulic opening:

[0135]

[0136] Among them, K represents the hydraulic permeability and e represents the equivalent hydraulic opening.

[0137] Specifically, the formula Calculate the average flow rate Q of the crack under different axial stresses,

[0138] Using formula P 入口 -P 出口 =A1Q+A2Q 2, calculate the equivalent hydraulic opening e under different axial stresses, where W is the crack width, μ1 is the experimental fluid viscosity, and A1 is the fitting coefficient.

[0139] The average flow rate Q of the cracks at five axial stresses of 0.5, 1, 3, 5 and 10 MPa is calculated, and the calculation results are shown in Table 1 above.

[0140] The equivalent hydraulic opening e under five axial stresses of 0.5, 1, 3, 5 and 10 MPa is calculated, and the calculation results are shown in Table 1 above.

[0141] On this basis, step S35 includes:

[0142] Calculating a shear fracture surface compression coefficient based on the hydraulic permeability and the axial stress;

[0143] The dynamic permeability of the fracture is calculated based on the theoretical permeability of the fracture and the shear fracture surface compression coefficient:

[0144]

[0145] Where K represents hydraulic permeability, K η represents the theoretical permeability of the fracture, e represents the equivalent hydraulic opening, C f represents the compression coefficient of the shear crack surface, and σ represents the axial stress.

[0146] Specifically, the formula Take five or more different axial stresses σ and the corresponding hydraulic permeability K to calculate five different C f With axial stress σ as the horizontal coordinate, the corresponding C f The value is used as the vertical axis to draw a scatter plot, and the quadratic nonlinear relationship is used to fit the scatter plot. According to the fitting formula C' f =B1σ+B2σ 2 +B3 to obtain the shear crack surface compression coefficient C' f .

[0147] Take five axial stresses of 0.5, 1, 3, 5 and 10 MPa and the corresponding hydraulic permeability K to calculate five different C f The values ​​are shown in Table 3. With the axial stress σ as the horizontal coordinate, the corresponding C f The value is used as the vertical axis to draw a scatter plot, and the quadratic nonlinear relationship is used to fit the scatter plot, such as Figure 5 As shown, we can get B1 = -0.4608, B2 = 0.0347, B3 = 1.041, and the fitting formula is C' f =0.0347σ 2 -0.4608σ+1.041.

[0148] Table 3 Calculation results of shear crack surface compression coefficient

[0149] Serial number Axial stress (MPa) Hydraulic permeability K <![CDATA[Fracture theory permeability K η > <![CDATA[Shearing crack surface compression coefficient C f > 1 0.5 0.0208 0.1361816 1.2516232 2 1 0.0833 0.1361816 0.1637135 3 3 0.7500 0.1361816 -0.189565 4 5 2.0833 0.1361816 -0.181849 5 10 8.3333 0.1361816 -0.137134

[0150] Using formula The dynamic permeability of fractures under different stress environments can be obtained

[0151] Step S4, obtaining a test result of the fracture dynamic permeability according to the shear slip friction coefficient and the fracture dynamic permeability.

[0152] Specifically, the test results are obtained according to the shear-slip friction coefficient and the dynamic permeability of the fracture in accordance with the preset test requirements.

[0153] The present invention provides a rock shear sliding friction coefficient and crack permeability dynamic test method, which can more accurately test the rock shear sliding friction coefficient and the dynamic permeability of the shear crack. The rock shear sliding friction coefficient test provides a more accurate test data selection and determination method, which can better reflect the stable sliding characteristics of the rock after shearing, eliminate the influence of the unstable sliding start-up stage and the fluctuating sliding after the rock shear failure, and better reflect the sliding friction characteristics of the shear rock. At the same time, the present invention includes a dynamic test method for the permeability of the roughness of the shear fracture surface and unstable nonlinear seepage, and provides a shear fracture surface roughness, fracture surface opening and fracture theoretical permeability test method. The method can accurately reflect the original permeability characteristics of the shear fracture surface. The hydraulic permeability test focuses on the nonlinear flow law of the fluid and can better reflect the actual seepage capacity of the fluid in the fracture. At the same time, a dynamic representation method for the compression coefficient of the shear fracture surface is established. Combined with the theoretical permeability and hydraulic permeability test methods, it can reflect the permeability characteristics under different fracture closure stresses, and has the effect of comprehensively and universally testing the dynamic permeability of the fracture.

[0154] It should be noted that some embodiments of the present invention are described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the above embodiments and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0155] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0156] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0157] Where specific details have been set forth to describe exemplary embodiments of the present invention, it will be apparent to those skilled in the art that embodiments of the present invention may be implemented without these specific details or with variations thereto. Therefore, these descriptions should be considered illustrative rather than restrictive. Although the present invention has been described in conjunction with specific embodiments of the present invention, many replacements, modifications, and variations of these embodiments will be apparent to those of ordinary skill in the art based on the foregoing description.

[0158] The embodiments of the present invention are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the present invention.

Claims

1. A dynamic testing method for rock shear sliding friction coefficient and crack permeability, characterized in that: include: Step S1, preparing an experimental specimen according to a preset size; Step S2, performing a shear-slip friction coefficient test experiment on the experimental specimen to obtain a shear test rock and calculate the shear-slip friction coefficient; Step S3, performing a fracture permeability test experiment on the shear test rock to calculate the fracture dynamic permeability; Step S4, obtaining a test result of the fracture dynamic permeability according to the shear slip friction coefficient and the fracture dynamic permeability.

2. A rock shear sliding friction coefficient and crack permeability dynamic testing method according to claim 1, characterized in that: The step S2 comprises: Step S21, the experimental specimen is subjected to a shear-slip friction coefficient test experiment to obtain a shear test rock; Step S22, collecting the horizontal displacement, horizontal shear force and axial stress during the experiment, and calculating the shear slip friction coefficient according to the horizontal displacement, the horizontal shear force and the axial stress.

3. A rock shear sliding friction coefficient and crack permeability dynamic testing method according to claim 2, characterized in that: The step S22 comprises: The shear slip friction coefficient is calculated according to the following formula: Among them, μ represents the shear sliding friction coefficient, f represents the sliding horizontal shear force, S represents the rock shear surface area, and F represents the axial stress.

4. The method for dynamic testing of rock shear sliding friction coefficient and crack permeability according to claim 2, characterized in that: The step S3 comprises: Step S31, performing a roughness scan on the rock in the shear test to calculate the theoretical permeability of the fracture; Step S32, restoring the shear test rock according to a preset size to obtain a restored test rock; Step S33, performing a fracture permeability test experiment on the recovery test rock under multiple axial stresses; Step S34, collecting the pressure and flow rate of the fluid at the fracture during the experiment, and calculating the hydraulic permeability according to the pressure and flow rate of the fluid; Step S35, calculating the dynamic permeability of the fracture according to the theoretical permeability of the fracture and the hydraulic permeability.

5. A rock shear sliding friction coefficient and crack permeability dynamic testing method according to claim 4, characterized in that: The step S31 comprises: Step S311, obtaining a closed shear fracture surface, obtaining a contour line at the fracture according to the closed shear fracture surface, and calculating an average opening of the contour line at the fracture; Step S312, calculating the fracture theoretical permeability according to the average aperture: Among them, K η represents the theoretical permeability of the fracture, and η represents the average opening.

6. A rock shear sliding friction coefficient and crack permeability dynamic testing method according to claim 5, characterized in that: The step S311 includes: Acquire a closed shear crack surface, perform roughness scanning on the closed shear crack surface, and obtain scanning coordinates of the closed shear crack surface; Taking the scanning coordinate spacing as the interval, along the width direction of the closed shear crack surface, the crack width is divided into a number of contour lines parallel to the crack length direction at equal intervals along the crack width direction to obtain the crack contour line; Calculate the roughness of the contour line at each crack: Among them, Z j represents the roughness of the jth contour line, L represents the length of the contour line at the crack, n represents the number of points in the length direction of the contour line at the jth crack, i represents the i-th point in the length direction of the jth crack contour line, y i+1 represents the y coordinate of the i+1 point in the length direction of the contour line at the jth crack, y i represents the y-axis coordinate of the i-th point on the crack contour line, x i+1 represents the x-coordinate of the i+1 point in the length direction of the contour line at the jth crack, x i represents the x-axis coordinate of the i-th point on the crack contour line; Calculate the contour opening at the jth crack based on the rough contour opening: η j =|From j +Z j Among them, η j represents the contour opening at the jth crack, Z' j represents the rough opening of the jth contour line of the unclosed upper shear crack surface, Z j " represents the rough opening of the jth contour line of the unclosed lower shear crack surface; Calculate the average opening of the contour lines at the crack: Where η represents the average opening of the contour line at the crack, j represents the contour line at the jth crack, and η j represents the opening of the contour line at the jth crack, and l represents the total number of contour lines at the crack.

7. A rock shear sliding friction coefficient and fracture permeability dynamic testing method according to claim 4, characterized in that: The step S34 comprises: The pressure and flow rate of the fluid at the fracture during the experiment were collected, and the average flow rate of the fracture under different axial stresses was calculated based on the flow rate of the fluid: Where Q represents the average flow rate of the crack, P 出口 represents the crack outlet pressure, P 入口 represents the crack entrance pressure, Q 出口 represents the fracture outlet flow rate; Calculate the equivalent hydraulic opening under different axial stresses according to the pressure of the fluid: P 入口 -P 出口 =A1Q+A2Q 2 Among them, P 出口 represents the crack outlet pressure, P 入口 represents the fracture entrance pressure, A1 and A2 represent the fitting coefficients, Q represents the average fracture flow rate, e represents the equivalent hydraulic opening, μ1 represents the fluid viscosity, and W represents the fracture width; According to the equivalent hydraulic opening, the hydraulic permeability under different axial stresses is calculated: Among them, K represents the hydraulic permeability and e represents the equivalent hydraulic opening.

8. A rock shear sliding friction coefficient and crack permeability dynamic testing method according to claim 5, characterized in that: The step S35 comprises: The fracture surface compression coefficient is calculated based on the hydraulic permeability and axial stress: Where K represents hydraulic permeability, K η represents the theoretical permeability of the fracture, e represents the equivalent hydraulic opening, C f represents the crack surface compression coefficient, σ represents the axial stress; A scatter plot is made with axial stress as the horizontal axis and the corresponding crack surface compression coefficient value as the vertical axis. The scatter plot is fitted using a quadratic nonlinear relationship, and the shear crack surface compression coefficient C' is obtained according to the following formula f There f =B1σ+B2σ 2 +B3 Among them, C' f represents the compression coefficient of the shear crack surface, B1, B2, B3 represent the fitting coefficients, and σ represents the axial stress; The dynamic permeability of the fracture is calculated based on the theoretical permeability of the fracture and the shear fracture surface compression coefficient: Where FP represents the dynamic permeability of the fracture, K η represents the theoretical permeability of the fracture, e represents the equivalent hydraulic opening, C f represents the compression coefficient of the shear crack surface, and σ represents the axial stress.

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