A method for evaluating the dilatancy potential of a porous medium based on scanning electron microscope images

Abstract

A method for evaluating the shear dilatation potential of loose porous media based on scanning electron microscopy (SEM) images is proposed. This method employs SEM experiments to analyze the particle distribution characteristics in the SEM images, calculates the sorting coefficient and coordination number of the particle packing, and quantitatively evaluates the influence of particle non-uniformity and particle non-contact on the shear dilatation potential of actual loose porous media by establishing mathematical relationships. This method provides a rapid, accurate, and streamlined numerical representation of the shear dilatation potential of loose porous media, saving significant manpower, material resources, and time, and providing a theoretical basis for assessing the stimulation potential of loose oil and gas reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil drilling technology and reservoir stimulation technology, specifically relating to a method for evaluating the shear dilatation potential of loose porous media based on scanning electron microscopy images. Background Technology

[0002] During unconventional oil and gas extraction, reservoir rocks are exposed to rapidly changing temperature and pore pressure fields, easily inducing dynamic changes in geostress. Complex stress, temperature, and seepage environments significantly impact reservoir rock deformation. Deformation of an object under effective stress can be categorized into volume changes and shape changes. For ideal solid materials, volume changes are caused by isotropic stress and generally exhibit elastic properties, while shape changes are caused by stress eccentricity and generally exhibit plastic deformation. Loose oil and gas reservoir frameworks, as typical granular porous media, differ from ideal solid materials. Besides elastic volume changes caused by isotropic compression, stress eccentricity also causes volume changes, known as shear dilatation. Shear dilatation, also called shear expansion, refers to the phenomenon where porous media experience tumbling and overturning of sand grains under shear stress, leading to an increase in volume. At higher magnifications, loose oil and gas reservoir rocks reveal brecciated particles with distinct edges and full contact. The particles are closely packed together, forming an interlocking structure, indicating that they can release a certain shear dilatation potential under shear stress conditions. This shear dilatation potential directly reflects the potential of reservoir rocks to be artificially modified under ideal conditions.

[0003] However, current research on the dilatation potential of porous media is scarce, and most studies focus on experimental and numerical simulations of rock dilatation, lacking quantitative evaluation techniques and methods for rock dilatation at the microscopic and mesoscopic scales. On the one hand, due to the significant differences between real underground rocks and ideal particle packings, traditional particle packing theory cannot be directly applied to study the dilatation potential of underground reservoir rocks; the degree of non-uniformity of rock particles and insufficient contact between particles must be considered. On the other hand, dilatation experiments and numerical simulations require substantial human, material, and financial resources, making them less than ideal for field personnel and researchers. How to quickly, accurately, and systematically obtain the dilatation potential of porous media, thereby providing reference values ​​and comparative verification for indoor experimental research and fluid-structure interaction numerical simulations, is a pressing problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating the shear dilatation potential of porous media based on scanning electron microscopy images.

[0005] The technical solution adopted in this invention is:

[0006] A method for evaluating the shear dilatation potential of porous media, characterized by comprising the following steps:

[0007] Step 1: Define the shear dilatation potential of porous media. Shear dilatation potential refers to the maximum increase in volume of a porous media under shear dilatation.

[0008] Step 2: Establish a mathematical model of the shear dilatation potential (SDP) of a two-dimensional circular particle pack with uniform diameter. 2D =(S max -S0) / S0=(16R 2 -16R 2 sinα0) / (16R 2 sinα0)=(1-sinα0) / sinα0, draw the initial alignment angle α0 and shear dilatation potential SDP of a two-dimensional circular particle pack with equal diameter. 2D Relationship diagram;

[0009] Step 3: Introduce particle non-uniformity correction coefficient A and particle non-contact correction coefficient B to characterize the effects of particle size and particle contact on shear dilatation potential, respectively. The corrected shear dilatation potential SDP is then calculated. 2D校正 =SDP 2D ×A×B=AB(1-sinα0) / sinα0;

[0010] Step 4: Obtain the initial alignment angle α0. Randomly select m cross-sections of the loose porous medium sample for electron microscopy scanning experiments, and successively calculate the initial alignment angle α of the particle packing in the electron microscopy image of the k-th (1≤k≤m) cross-section. k0 Then, calculate the average value α0 of the initial alignment angle of the particle packing in the electron micrographs of all m cross sections;

[0011] Step 5: Obtain the particle non-uniformity correction coefficient A, and establish the relationship between the particle sorting coefficient S and the particle non-uniformity correction coefficient A. The relationship between S and A conforms to the exponential function A = M. S-1 (S≥1), M is the coefficient to be determined;

[0012] Step Six: Obtain the particle non-contact correction coefficient B. Estimate the particle non-contact correction coefficient B using the coordination number N of the particle packing; Particle non-contact correction coefficient B = (NN) min ) / (N max -N min ), where N min and N max These are the minimum coordination number and the maximum coordination number, respectively.

[0013] Step 7: Substitute the values ​​of the initial arrangement angle α0, particle non-uniformity correction coefficient A, and particle non-contact correction coefficient B into the SDP. 2D校正 =SDP 2D×A×B=AB(1-sinα0) / sinα0, calculate the true shear dilatation potential of the loose porous medium.

[0014] In step one, for a three-dimensional spherical particle pack, the shear dilatation potential is represented by SDP. 3D =(V max -V0) / V0, where V max V0 represents the maximum volume that the three-dimensional spherical particle pack can reach under dilatation, and V0 represents the initial volume of the three-dimensional spherical particle pack without dilatation.

[0015] In step one, for a two-dimensional circular particle pack, the shear dilatation potential is represented by SDP. 2D =(S max -S0) / S0, where S max S0 represents the maximum area that a two-dimensional circular particle pack can achieve under dilatation, and S0 represents the initial area of ​​the two-dimensional circular particle pack without dilatation.

[0016] In step two, taking a 3×3 arrangement of equal-diameter two-dimensional circular particle piles with radius R as an example, the area of ​​the parallelogram enclosed by connecting the centers of all the circles around the particle pile with straight lines is defined as the effective area of ​​the particle pile.

[0017] In step two, if the initial arrangement angle of the particle pack is α0, then the initial effective area of ​​the particle pack is S0 = 4R × 4Rsinα0 = 16R 2 sinα0; When the arrangement angle of the particle pack is 90°, the area is at its maximum, which is S. max =4R×4R=16R 2 ;

[0018] In step two, the initial arrangement angle α0 ranges from 60° to 90°.

[0019] In step four, an image with a magnification of X times is obtained, and the number of particles in the image is guaranteed to be no less than 10.

[0020] In step four, when analyzing the electron microscope image of the k-th (1≤k≤m) cross-section, the positions of the quartz particles are identified, and the circumcircle of all quartz particles is drawn. The centers of the circumcircle of the particles in contact with each other are connected to form particle packing groups A1, A2...A1. n The particle packing group A was measured. i In (1≤i≤n), the angle α between the line connecting the centers of each circle and the positive direction of the horizontal line is... i1 α i2 ……α ij (j represents particle packing group A) iCalculate the average of all included angles in the electron microscope image (number of particles - 1). This average value is the initial arrangement angle α of the particle packing in the electron microscope image of the k-th (1≤k≤m) cross-section. k0 .

[0021] In step five, the sorting coefficient is expressed as: Where d 75 and d 25 These are the particle size divisions corresponding to 75% and 25% of the cumulative mass on the cumulative mass distribution curve, respectively.

[0022] In step five, S and A conform to the exponential function A = M. S-1 When S≥1 and the particle sorting coefficient is 1, the particle non-uniformity correction coefficient A is 1; when the sorting coefficient is 1.34, the correction coefficient is 0.5; when the sorting coefficient is +∞, the correction coefficient is 0.

[0023] In step five, when a small circle of equal diameter is precisely embedded in a large circle of equal diameter, half of the particles cannot exert the shear dilation effect. Therefore, the particle non-uniformity correction coefficient in this case is 0.5, while the corresponding sorting coefficient S is 1.34.

[0024] In step five, the three (S,A) coordinate values ​​(1,1), (1.34,0.5), and (+∞,0) are substituted into A = M. S-1 (S≥1), therefore the relationship between S and A is A=0.13 S-1 ;

[0025] In step six, the coordination number N is calculated by inversely based on the relationship between coordination number and porosity. The relationship between coordination number and porosity is N = [0.1193 - sqrt(0.01724Φ - 0.00425)] / 0.00862 or N = (10.968Φ - 6.527) / [0.414(Φ - 1)].

[0026] In step six, porosity is obtained through electron microscope images. Porosity is the ratio of the sum of the areas of all circumcircles to the field of view of the electron microscope.

[0027] In step six, for an actual particle packing, the minimum coordination number N min =6, maximum coordination number N max =12.

[0028] The beneficial effects of this invention are:

[0029] This method employs scanning electron microscopy (SEM) experiments to analyze the distribution characteristics of particles in SEM images, calculates the sorting coefficient and coordination number of particle packings, and quantitatively evaluates the influence of particle non-uniformity and particle non-contact on the shear dilatation potential of actual loose porous media by establishing mathematical relationships. It provides a rapid, accurate, and streamlined numerical value for the shear dilatation potential of loose porous media, saving significant manpower, material resources, and time, and providing a theoretical basis for assessing the stimulation potential of loose oil and gas reservoirs. Attached Figure Description

[0030] Figure 1 A flowchart of a method for evaluating the shear dilatation potential of porous media based on scanning electron microscopy images;

[0031] Figure 2 Two-dimensional particle packing state diagrams under different arrangement angles in a loose porous medium;

[0032] Figure 3 A graph showing the relationship between the initial alignment angle and the dilatation potential of a two-dimensional circular particle pack of equal diameter.

[0033] Figure 4 This is an electron microscope image at 320x magnification of a cross section of a loose oil and gas reservoir rock.

[0034] Figure 5 A two-dimensional particle packing diagram showing the state of particles when a small circle of equal diameter is perfectly embedded within a large circle of equal diameter.

[0035] Figure 6 A representative volume unit of a two-dimensional particle packing body in which a smaller circle of equal diameter is perfectly embedded within a larger circle of equal diameter;

[0036] Figure 7 A cumulative mass percentage curve when a smaller circle of equal diameter is perfectly embedded within a larger circle of equal diameter.

[0037] Figure 8 The curve showing the relationship between the particle sorting coefficient S and the particle non-uniformity correction coefficient A;

[0038] Figure 9 This is a curve showing the cumulative mass percentage of particle deposits in a cross section of a loose oil and gas reservoir rock. Detailed Implementation

[0039] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0040] Example 1:

[0041] like Figure 1 As shown, a method for evaluating the shear dilatation potential of porous media based on scanning electron microscopy images is characterized by comprising the following steps:

[0042] Step 1: Define the shear dilatation potential of porous media. Shear dilatation potential refers to the maximum increase in volume of a porous media under shear dilatation. Figure 2 As shown, the initial state of the loose porous medium is assumed to be... Figure 2 (b) then the maximum volume of porous media under shear dilatation can reach Figure 2 (c), then from Figure 2 (b) to Figure 2 (c) The maximum increase in volume that occurs is Figure 2 (b) shows the shear dilatation potential of the porous medium.

[0043] Step 2: Establish a mathematical model of the shear dilatation potential of a two-dimensional circular particle pack with uniform diameter. Figure 2 (b) shows a porous medium with an initial alignment angle of α0 and a shear dilatation potential of SDP. 2D =(S max -S0) / S0=(16R 2 -16R 2 sinα0) / (16R 2 sinα0)=(1-sinα0) / sinα0, where the radius of the circular particle is R; for example Figure 3 As shown, the initial alignment angle α0 and shear dilatation potential SDP of a two-dimensional circular particle pack of equal diameter are plotted. 2D Relationship diagram;

[0044] Step 3: Introduce particle non-uniformity correction coefficient A and particle non-contact correction coefficient B to characterize the effects of particle size and particle contact on shear dilatation potential, respectively. The corrected shear dilatation potential SDP is then calculated. 2D校正 =SDP 2D ×A×B=AB(1-sinα0) / sinα0;

[0045] Step 4: Obtain the initial alignment angle α0. Randomly select m cross-sections of the loose sandstone sample for electron microscopy scanning, and successively calculate the initial alignment angle α of the grain aggregates in the electron microscopy image of the k-th (1≤k≤m) cross-section. k0 Then, calculate the average value α0 of the initial alignment angle of the particle packing in the electron micrographs of all m cross sections;

[0046] Step 5: Obtain the particle non-uniformity correction coefficient A, and establish the relationship between the particle sorting coefficient S and the particle non-uniformity correction coefficient A. The relationship between S and A conforms to the exponential function A = M. S-1 (S≥1), M is the coefficient to be determined;

[0047] Step Six: Obtain the particle non-contact correction coefficient B. Estimate the particle non-contact correction coefficient B using the coordination number N of the particle packing; Particle non-contact correction coefficient B = (NN) min ) / (Nmax -N min ), where N min and N max These are the minimum coordination number and the maximum coordination number, respectively.

[0048] Step 7: Substitute the values ​​of the initial arrangement angle α0, particle non-uniformity correction coefficient A, and particle non-contact correction coefficient B into the SDP. 2D校正 =SDP 2D ×A×B=AB(1-sinα0) / sinα0, calculate the true shear dilatation potential of the loose porous medium.

[0049] In step one, for a three-dimensional spherical particle pack, the shear dilatation potential is represented by SDP. 3D =(V max -V0) / V0, where V max V0 represents the maximum volume that the three-dimensional spherical particle pack can reach under dilatation, and V0 represents the initial volume of the three-dimensional spherical particle pack without dilatation.

[0050] In step one, for a two-dimensional circular particle pack, the shear dilatation potential is represented by SDP. 2D =(S max -S0) / S0, where S max S0 represents the maximum area that a two-dimensional circular particle pack can achieve under dilatation, and S0 represents the initial area of ​​the two-dimensional circular particle pack without dilatation.

[0051] In step two, as Figure 2 As shown, taking a 3×3 arrangement of equal-diameter two-dimensional circular particles of radius R as an example, the area of ​​the parallelogram enclosed by connecting the centers of all the circles around the particle accumulation with straight lines is defined as the effective area of ​​the particle accumulation.

[0052] In step two, as Figure 2 As shown in (b), if the initial alignment angle of the particle pack is α0, then the initial effective area of ​​the particle pack is S0 = 4R × 4Rsinα0 = 16R 2 sinα0; as Figure 2 As shown in (c), when the arrangement angle of the particle pack is 90°, the area is at its maximum, S. max =4R×4R=16R 2 ;

[0053] In step two, as Figure 2 As shown, the initial arrangement angle α0 ranges from 60° to 90°.

[0054] In step four, such as Figure 4As shown, an image with a magnification of X = 320 is obtained, and the number of particles in the image is guaranteed to be no less than 10.

[0055] In step four, let m = 1 and k = 1, that is, use an electron microscope image of a cross-section to calculate the initial alignment angle α0, as shown below. Figure 4 As shown, identify the positions of the quartz particles and draw the circumcircle of all the quartz particles; connect the centers of the circumcircle circles of the particles that are in contact with each other to form particle packs A1, A2, A3, and A4, respectively. Measure the angle α between the line connecting the centers of each particle pack A1 and the positive direction of the horizontal line. 11 =56°, the angle α between the line connecting the centers of each circle in A2 and the positive direction of the horizontal line. 21 =60°, α 22 =70°, α 23 =46°, α 24 =68°, the angle α between the line connecting the centers of each circle in A3 and the positive direction of the horizontal line. 31 =74°, α 32 =40°, α 33 =64°, α 34 =53°, α 35 =62°, the angle α between the line connecting the centers of each circle in A4 and the positive direction of the horizontal line. 41 =74°, calculate the average value of all included angles in the electron microscope image, i.e., the initial arrangement angle α0 = (α 11 +α 21 +α 22 +α 23 +α 24 +α 31 +α 32 +α 33 +α 34 +α 35 +α 41 ) / 11=(56+60+70+46+68+74+40+64+53+62+74)° / 11=60.64°.

[0056] In step five, the sorting coefficient is expressed as: Where d 75 and d 25 These are the particle size distributions at 75% and 25% of the cumulative mass, respectively, on the cumulative distribution curves.

[0057] In step five, S and A conform to the exponential function A = M. S-1 (S≥1), when the particle sorting coefficient is 1, the particle non-uniformity correction coefficient A is 1; when the sorting coefficient is 1.34, the correction coefficient is 0.5; when the sorting coefficient is +∞, the correction coefficient is 0.

[0058] In step five, such as Figure 5 As shown, when a small circle of equal diameter is perfectly embedded within a large circle of equal diameter, half of the particles cannot exert a shear dilatation effect. Therefore, the particle non-uniformity correction coefficient in this case is 0.5, while the corresponding sorting coefficient S is 1.34. The specific calculation process is as follows: Let the diameter of the large circle be D and the diameter of the small circle be d, then the Pythagorean theorem D is satisfied. 2 +D 2 =(D+d) 2 Thus, we get d = (2-1)D ≈ 0.41D; Figure 6 As shown, within a representative volume unit, the area of ​​the small circle is S. 小 = 4π(0.41D / 2) 2 =0.53D 2 The area of ​​the great circle is S. 大 = 3π(D / 2) 2 =2.36D 2 ;like Figure 7 As shown, the cumulative mass corresponding to a particle size of 0.41D is (0.53D). 2 ) / (0.53D 2 +2.36D 2 The cumulative mass percentage is 18.34% (assuming the density of large and small spheres is the same). When the particle size is D, the cumulative mass percentage is 100%. Assuming a linear relationship between the cumulative mass percentage and the particle size, the corresponding particle diameters d for cumulative mass percentages of 75% and 25% can be calculated. 75 =0.82D and d 25 =0.46D, therefore the sorting coefficient

[0059] In step five, such as Figure 8 As shown, substituting the three (S,A) coordinate values ​​(1,1), (1.34,0.5), and (+∞,0) into A = M S-1 (S≥1), therefore the relationship between S and A is A=0.13 S-1 ;

[0060] In step five, such as Figure 4 As shown, at a certain scaling factor (scaling does not affect the calculation of the sorting factor), the diameter of the two circles in particle pack A1 is d. 11 =80 units ("units" refers to a length measurement at a certain scaling factor), d 12 =100 units, the diameters of the 5 circles in A2 are d respectively. 21 =88 units, d 22 =93 units, d 23 =102 units, d 24 =78 units, d 25=102 units, the diameters of the 6 circles in A3 are d respectively. 31 =91 units, d 32 =66 units, d 33 =92 units, d 34 =66 units, d 35 =68 units, d 36 =88 units, the diameters of the two circles in A4 are d respectively 41 =63 units, d 42 =90 units; the cumulative mass percentage curve is calculated as follows: Figure 9 As shown, according to Figure 9 The particle diameters d for cumulative mass percentages of 75% and 25% were calculated to be d respectively. 75 =95.39 units and d 25 =79.25 units, quantifiable sorting coefficient Substitute A = 0.13 S-1 Therefore, A = 0.82;

[0061] In step six, the coordination number N is calculated by inversely based on the relationship between coordination number and porosity. The relationship between coordination number and porosity is N = [0.1193 - sqrt(0.01724Φ - 0.00425)] / 0.00862;

[0062] In step six, porosity is obtained through images. Porosity is the ratio of the sum of the areas of all circumcircles to the area of ​​the electron microscope's field of view; for example... Figure 4 As shown, at a certain scaling factor (scaling does not affect the porosity calculation), the length of the electron microscope's field of view is measured to be 466 units and the width to be 403 units. The diameter of the two circles in particle packing A1 is d. 11 =80 units, d 12 =100 units, the diameters of the 5 circles in A2 are d respectively. 21 =88 units, d 22 =93 units, d 23 =102 units, d 24 =78 units, d 25 =102 units, the diameters of the 6 circles in A3 are d respectively. 31 =91 units, d 32 =66 units, d 33 =92 units, d 34 =66 units, d 35 =68 units, d 36 =88 units, the diameters of the two circles in A4 are d respectively 41 =63 units, d 42 = 90 units; The total area of ​​all circumcircles is calculated to be 86063.15 units. 2The electron microscope field of view is 187,798 units. 2 Therefore, the porosity is 86063.15 / 187798 = 0.46; substituting Φ = 0.46 into N = [0.1193 - sqrt(0.01724Φ - 0.00425)] / 0.00862, we get the coordination number N = 6.8. Therefore, the particle non-contact correction coefficient B = (NN min ) / (N max -N min )=(6.8-6) / (12-6)=0.13;

[0063] In step seven, the initial arrangement angle α0 = 60.64°, the particle non-uniformity correction coefficient A = 0.82, and the particle non-contact correction coefficient B = 0.13 are substituted into SDP. 2D校正 =AB(1-sinα0) / sinα0=0.82×0.13×(1-sin60.64°) / sin60.64°=0.016, the shear dilatation potential of the corrected loose porous medium is 0.016.

[0064] This method employs scanning electron microscopy (SEM) experiments to analyze the distribution characteristics of particles in SEM images, calculates the sorting coefficient and coordination number of particle packings, and quantitatively evaluates the influence of particle non-uniformity and particle non-contact on the shear dilatation potential of actual loose porous media by establishing mathematical relationships. It provides a rapid, accurate, and streamlined numerical value for the shear dilatation potential of loose porous media, saving significant manpower, material resources, and time, and providing a theoretical basis for assessing the stimulation potential of loose oil and gas reservoirs.

[0065] Example 2:

[0066] In this embodiment, the steps and methods for calculating the dilatation potential are the same as in Embodiment 1. The difference is that the relationship between coordination number and porosity is N = (10.968Φ - 6.527) / [0.414(Φ - 1)].

[0067] Substituting Φ = 0.46 into the equation, we get the coordination number N = 6.6. Therefore, the particle non-contact correction coefficient B = (NN) min ) / (N max -N min )=(6.6-6) / (12-6)=0.10;

[0068] Substituting the initial alignment angle α0 = 60.64°, particle non-uniformity correction coefficient A = 0.82, and particle non-contact correction coefficient B = 0.10 into SDP... 2D校正=AB(1-sinα0) / sinα0=0.82×0.10×(1-sin60.64°) / sin60.64°=0.012, the shear dilatation potential of the corrected loose porous medium is 0.012.

Claims

1. A method for evaluating the shear dilatation potential of porous media, characterized in that, Includes the following steps: Step 1: Define the shear dilatation potential of porous media. Shear dilatation potential refers to the maximum increase in volume of a porous media under shear dilatation. Step 2: Establish a mathematical model of the shear dilatation potential (SDP) of a two-dimensional circular particle pack with uniform diameter. 2D =(S max -S0) / S0=(16R 2 -16R 2 sinα0) / (16R 2 sinα0)=(1-sinα0) / sinα0, draw the initial alignment angle α0 and shear dilatation potential SDP of a two-dimensional circular particle pack with equal diameter. 2D The relationship diagram, where R is the radius of the two-dimensional circular particle pack with uniform diameter, and S max S0 represents the maximum area that a two-dimensional circular particle pack can achieve under dilatation, and S0 represents the initial area of ​​the two-dimensional circular particle pack without dilatation. Step 3: Introduce particle non-uniformity correction coefficient A and particle non-contact correction coefficient B to characterize the effects of particle size and particle contact on shear dilatation potential, respectively. The corrected shear dilatation potential SDP is then calculated. 2D校正 =SDP 2D ×A×B=AB(1-sinα0) / sinα0; Step 4: Obtain the initial alignment angle α0. Randomly select m cross-sections of the loose porous medium sample for electron microscopy scanning experiments, and successively calculate the initial alignment angle α of the particle packing in the electron microscopy image of the k-th cross-section. k0 , 1≤k≤m, and then calculate the average value α0 of the initial arrangement angle of the particle pack in the electron micrographs of all m cross sections; Step 5: Obtain the particle non-uniformity correction coefficient A, and establish the relationship between the particle sorting coefficient S and the particle non-uniformity correction coefficient A. The relationship between S and A conforms to the exponential function A = M. S-1 (S≥1), M is the coefficient to be determined; Step Six: Obtain the particle non-contact correction coefficient B, and estimate the particle non-contact correction coefficient B using the coordination number N of the particle packing; Particle non-contact correction coefficient B = (NN) min ) / (N max -N min ), where N min and N max These are the minimum coordination number and the maximum coordination number, respectively. Step 7: Substitute the values ​​of the initial arrangement angle α0, particle non-uniformity correction coefficient A, and particle non-contact correction coefficient B into the SDP. 2D校正 =SDP 2D ×A×B=AB(1-sinα0) / sinα0, calculate the true shear dilatation potential of the loose porous medium.

2. The method for evaluating the shear dilatation potential of porous media according to claim 1, characterized in that, In step one, for a three-dimensional spherical particle pack, the shear dilatation potential is represented by SDP. 3D =(V max -V0) / V0, where V max V0 represents the maximum volume that the three-dimensional spherical particle pack can reach under dilatation, and V0 represents the initial volume of the three-dimensional spherical particle pack without dilatation. In step one, for a two-dimensional circular particle pack, the shear dilatation potential is represented by SDP. 2D =(S max -S0) / S0.

3. The method for evaluating the shear dilatation potential of porous media according to claim 1, characterized in that, In step two, taking a 3×3 arrangement of equal-diameter two-dimensional circular particle piles with radius R as an example, the area of ​​the parallelogram enclosed by connecting the centers of all the circles around the particle pile with straight lines is defined as the effective area of ​​the particle pile. In step two, if the initial arrangement angle of the particle pack is α0, then the initial effective area of ​​the particle pack is S0 = 4R × 4Rsinα0 = 16R 2 sinα0; when the arrangement angle of the particle packing is 90° o At this time, the area is at its maximum, which is S. max =4R×4R=16R 2 ; In step two, the initial arrangement angle α0 ranges from 60°. o ≤α0≤90 o .

4. The method for evaluating the shear dilatation potential of porous media according to claim 1, characterized in that, In step four, an image with a magnification of X times is obtained, and the number of particles in the image is guaranteed to be no less than 10. In step four, when analyzing the electron microscope image of the k-th cross-section, 1≤k≤m, the positions of the quartz particles are identified, and the circumcircle of all quartz particles is drawn. The centers of the circumcircle of the particles in contact with each other are connected to form particle packing groups A1, A2...A1. n The particle packing group A was measured. i The angle α between the line connecting the centers of each circle and the positive direction of the horizontal line. i1 α i2 ……α ij j represents the particle packing group A i Given the number of particles in the electron microscope (EM) image -1, where 1 ≤ i ≤ n, calculate the average of all included angles in the EM image. This average value is the initial arrangement angle α of the particle packing in the EM image of the k-th cross-section. k0 , 1≤k≤m.

5. The method for evaluating the shear dilatation potential of porous media according to claim 1, characterized in that, In step five, the sorting coefficient is expressed as: Where d 75 and d 25 These are the particle size divisions corresponding to 75% and 25% of the cumulative mass on the cumulative mass distribution curve, respectively. In step five, S and A conform to the exponential function A = M. S-1 When S≥1 and the particle sorting coefficient is 1, the particle non-uniformity correction coefficient A is 1; when the sorting coefficient is 1.34, the correction coefficient is 0.5; when the sorting coefficient is +∞, the correction coefficient is 0. In step five, when a small circle of equal diameter is precisely embedded in a large circle of equal diameter, half of the particles cannot exert the shear dilation effect. Therefore, the particle non-uniformity correction coefficient in this case is 0.5, while the corresponding sorting coefficient S is 1.

34. In step five, the three (S,A) coordinate values ​​(1,1), (1.34,0.5), and (+∞,0) are substituted into A = M. S-1 (S≥1), therefore the relationship between S and A is A=0.13 S-1 .

6. The method for evaluating the shear dilatation potential of porous media according to claim 1, characterized in that, In step six, the coordination number N is calculated by inversely based on the relationship between coordination number and porosity. The relationship between coordination number and porosity is N = [0.1193 - sqrt(0.01724Φ - 0.00425)] / 0.00862 or N = (10.968Φ - 6.527) / [0.414(Φ - 1)]. In step six, porosity is obtained through electron microscope images. Porosity is the ratio of the sum of the areas of all circumcircles to the field of view of the electron microscope. In step six, for an actual particle packing, the minimum coordination number N min =6, maximum coordination number N max =12.

Images