Coal reservoir brittleness index calculation method and coal seam geological engineering sweet spot range depicting method

Abstract

The invention belongs to the technical field of ore bed coal seam data analysis and processing, and relates to a coal reservoir brittleness index calculation method and a coal seam geological engineering dessert range depicting method, which comprise the following steps: obtaining a stress-strain curve of a deep coal seam core; obtaining the brittleness value, Young modulus and Poisson's ratio of the coal core according to the stress-strain curve; respectively determining correlation coefficients between the brittleness value and the Young modulus and between the brittleness value and the Poisson's ratio, and obtaining a rock mechanics adaptive factor according to the correlation coefficients; and obtaining the brittleness index of the coal reservoir according to the Young modulus, the Poisson's ratio and the rock mechanics adaptive factor. According to the method, deep coal seam brittleness index space distribution prediction is achieved, the prediction result is well matched with the drilling result, and deep coal seam well location deployment in the Ordos basin is effectively supported.

Description

Technical Field

[0001] The invention relates to a method for calculating a coal reservoir brittleness index and a method for characterizing a coal seam geological engineering sweet spot range, and belongs to the technical field of ore seam coal seam data analysis and processing. Background Art

[0002] After years of development, China's coalbed methane has initially achieved a breakthrough in exploration and development from shallow to medium and deep layers. The Ordos Basin is rich in deep coalbed methane resources and is an important strategic successor resource for increasing natural gas reserves and production. However, the permeability of deep coal seams is usually low, which seriously limits the efficiency of coalbed methane development. Therefore, deep coalbed methane development needs to rely on reservoir transformation technology such as fracturing to increase permeability to improve mining efficiency. Studies have shown that coal seam brittleness is one of the key factors affecting the effect of deep coal seam fracturing transformation. Coal seams with higher brittleness are more likely to form fracture networks during hydraulic fracturing, thereby increasing the release of coalbed methane and increasing production. Therefore, it is urgent to conduct research on deep coal seam brittleness seismic prediction methods to improve the accuracy of coal seam geological engineering sweet spot characterization, so as to achieve the effective scale utilization of deep coalbed methane resources. Summary of the invention

[0003] In view of the above problems, the purpose of the present invention is to provide a method for calculating the brittleness index of coal reservoirs and a method for characterizing the range of coal seam geological engineering sweet spots, which realizes the prediction of the spatial distribution of the brittleness index of deep coal seams. The prediction results are in good agreement with the drilling results, which effectively supports the deployment of deep coal seam wells in the Ordos Basin.

[0004] To achieve the above-mentioned purpose, the present invention proposes the following technical scheme: a method for calculating the brittleness index of a coal reservoir, comprising the following steps: obtaining a stress-strain curve of a coal core of a deep coal seam; obtaining a brittleness value, Young's modulus and Poisson's ratio of the coal core according to the stress-strain curve; respectively determining the correlation coefficients between the brittleness value and the Young's modulus and the Poisson's ratio, and obtaining a rock mechanics adaptive factor according to the correlation coefficients; obtaining a coal reservoir brittleness index according to the Young's modulus, Poisson's ratio and the rock mechanics adaptive factor.

[0005] Furthermore, the calculation formula of the brittleness value is:

[0006] in, is the plastic strain value of the coal core, is the stress drop rate after coal core failure, is the stress drop after the coal core is destroyed, is stress, is the strain, c is the starting point of coal core crushing, b is the starting point of coal core plastic deformation, and d is the ending point of coal core crushing; the Young's modulus is the slope of the elastic section of the stress-strain curve; the Poisson's ratio is the ratio of the axial strain to the radial strain of the coal core.

[0007] Furthermore, the correlation coefficient between the brittleness value and Young's modulus is The calculation formula is:

[0008] Correlation coefficient between the fragility value and Poisson's ratio The calculation formula is:

[0009] in, is the coal core brittleness value of the sample point, is the average value of coal core brittleness of all sample points, is the Young's modulus of the coal core at the sample point, is the average value of Young's modulus of coal core at all sample points, is the Poisson's ratio of the coal core at the sample point, It is the average value of the Poisson's ratio of the coal core of all sample points.

[0010] Furthermore, the adaptive factor The calculation formula is as follows:

[0011] in, is the correlation coefficient between the brittleness value and Young's modulus, is the correlation coefficient between the brittleness value and Poisson's ratio.

[0012] Furthermore, the coal reservoir brittleness index The calculation formula is as follows:

[0013] Where E is Young's modulus, is the minimum value of Young's modulus, is the maximum value of Young's modulus, v is the Poisson's ratio, is the minimum value of Poisson's ratio, is the maximum value of Poisson's ratio.

[0014] The present invention also discloses a method for characterizing the range of coal seam geological engineering sweet spots, comprising: collecting pre-stack CRP gather data and seismic wave velocity data of the study area; performing pre-stack inversion on the pre-stack CRP gather data and seismic wave velocity data, and obtaining a three-dimensional spatial data volume of Young's modulus and Poisson's ratio based on the inversion result of the pre-stack inversion; using any of the coal reservoir brittleness index calculation methods as described in the above to obtain the coal reservoir brittleness index. ; Based on the three-dimensional data of Young's modulus and Poisson's ratio, combined with the coal reservoir brittleness index , obtain the three-dimensional spatial data body of coal seam brittleness in the study area; based on the three-dimensional spatial data body of coal seam brittleness in the study area and combined with the seismic analysis layer, extract the deep coal seam brittleness index distribution plan map; based on the deep coal seam brittleness index distribution plan map and combined with the planar distribution map of coal seam thickness and gas content, identify the coal seam geological engineering sweet spot range.

[0015] Furthermore, a method for obtaining a three-dimensional spatial data body of Young's modulus and Poisson's ratio based on the inversion result of the pre-stack inversion is as follows: establishing a reflection coefficient equation for pre-stack inversion; establishing a relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves; establishing a relationship between Young's modulus, Poisson's ratio and reflection coefficient based on the reflection coefficient equation and the relationship; solving the relationship between Young's modulus, Poisson's ratio and reflection coefficient based on the Bayesian inversion theory in combination with the expression of the seismic angle gather; and obtaining a three-dimensional spatial data body of Young's modulus and Poisson's ratio in combination with the iterative equation based on the solution result.

[0016] Further, the reflection coefficient equation is:

[0017] The relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves is:

[0018]

[0019] Where, E is Young's modulus; is Poisson's ratio; is the longitudinal velocity of seismic waves, is the seismic shear wave velocity; is the seismic wave density.

[0020] Further, the relationship between the Young's modulus, Poisson's ratio and reflection coefficient is as follows:

[0021] in, is the reflection coefficient, is the incident angle, is the Young’s modulus variable; is the Poisson's ratio variable; is the density variable; .

[0022] Furthermore, the method of obtaining the three-dimensional spatial data volume of Young's modulus and Poisson's ratio by combining the iterative equation is: Based on the convolution model, the seismic angle gather is expressed as: ; Based on Bayesian inversion theory, we get:

[0023] Where: , ,

[0024]

[0025] The Young's modulus and Poisson's ratio are obtained by solving the iterative equation, which is:

[0026] in, The incident angle is seismic gathers, m is the model parameter, is the seismic wavelet, G is the Jacobi matrix associated with R and m, is the model parameter disturbance term, is the residual between the seismic data and the synthetic seismic record, Indicates data error, is the variance of the model parameter disturbance, is the prior information, Indicates the number of iterations.

[0027] The technical scheme of the present invention has at least the following technical effects or advantages: the present invention realizes the prediction of the spatial distribution of the brittleness index of deep coal seams, and the prediction results of the brittleness index have a good correlation with the peak gas production of drilling, which is consistent with the understanding that the higher the coal seam brittleness index, the more conducive it is to the fracturing transformation of the coal reservoir. Based on the prediction results of the brittleness index, combined with various key geological engineering parameters such as coal seam thickness, ground stress, and fracture development density, the "double sweet spots" of geological engineering in the study area are characterized, thereby effectively supporting the deployment of deep coal seam wells in the Ordos Basin and promoting the study area to achieve integrated geological and engineering fine evaluation and increase and stabilize production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a uniaxial compression test curve diagram of a sample obtained by uniaxial compression in one embodiment of the present invention; Figure 2 is a photo of a coal core before and after a uniaxial compression test in one embodiment of the present invention, Figure 2 (a) is a photo of the coal core before the uniaxial compression test. Figure 2 (b) is a photo of the coal core after the uniaxial compression test; Figure 3 is a cross-sectional diagram of the brittleness value and elastic modulus of the coal core in one embodiment of the present invention; Figure 4 is a cross-sectional scatter plot of the brittleness value and Poisson's ratio of the coal core in one embodiment of the present invention; Figure 5 is a plan view of the brittleness index distribution of deep coal seams in the M area of ​​the Ordos Basin in one embodiment of the present invention; Figure 6 It is a plane distribution diagram of the brittleness index of deep coal seams in the M area of ​​the Ordos Basin in one embodiment of the present invention; Figure 7 It is a cross-plot of the peak gas production of deep coal seams in the M area of ​​the Ordos Basin and the BRIT of the seismically predicted coal seam brittleness in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the provision of specific embodiments is only for a better understanding of the present invention, and they should not be understood as limitations of the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0030] In order to solve the problem in the prior art that it is necessary to conduct research on the deep coal seam brittle seismic prediction method and improve the accuracy of coal seam geological engineering sweet spot characterization, the present invention proposes a coal reservoir brittleness index calculation method and a coal seam geological engineering sweet spot range characterization method, which uses the deep coal seam coal core obtained by drilling and coring in the study area to carry out rock mechanics experimental research, proposes the brittleness index of the coal core based on the experimentally obtained coal core stress-strain curve, and analyzes the relationship between elastic parameters such as Young's modulus and Poisson's ratio and coal seam brittleness. By introducing rock mechanics adaptive factors, the influence of different elastic parameters on coal rock brittleness is allocated using correlation coefficients, and then a coal seam brittleness index characterization formula based on elastic parameters is constructed. On this basis, an approximate formula for reflection coefficient based on Young's modulus, Poisson's ratio and density is derived and constructed, and the spatial distribution prediction of deep coal seam brittleness index is realized in combination with the Bayesian seismic inversion method. The prediction results are in good agreement with the drilling results, which effectively supports the deployment of deep coal seam wells in the Ordos Basin. The scheme of the present invention is described in detail below with reference to the accompanying drawings through embodiments.

[0031] Embodiment 1 This embodiment discloses a method for calculating the brittleness index of a coal reservoir, which is described by taking a deep coal seam in the M area of ​​the Ordos Basin as an example, and includes the following steps: S1 obtains the stress-strain curve of the coal core in the deep coal seam.

[0032] The stress-strain curve of rock can reflect the properties of rock. Using rock mechanics experiments to obtain rock stress-strain curves is currently the main method to obtain the brittleness of rock. Rock mechanics experiment is a method to study the physical and mechanical properties of rock under different conditions. Through experiments, information such as the strength characteristics, deformation characteristics, and brittle characteristics of rocks can be obtained. Common rock mechanics experiments include: uniaxial compression test, triaxial compression test, direct shear test, and indirect tensile test. In this embodiment, a uniaxial compression test was carried out on the coal core samples obtained by drilling in the study area. By applying unidirectional pressure to the coal core, the stress-strain curve of the coal core was obtained. The basic data and experimental results of the coal core samples are shown in Table 1. The uniaxial compression test curve of the sample obtained by uniaxial compression is shown in Table 1. Figure 1 As shown in Figure 2, the photos of coal core before and after uniaxial compression test are shown in Figure 2. Figure 2 As shown, Figure 2 (a) is a photo of the coal core before the uniaxial compression test. Figure 2 (b) is a photo of the coal core after the uniaxial compression test.

[0033] Table 1 Coal core basic data and experimental results Sample No. Depth(m) Weight(g) Diameter(mm) Height(mm) <![CDATA[Density (g / cm 3 )]]> Uniaxial compression (MPa) 1 1360.85 33.595 24.89 47.36 1.459 23.12 2 1313.90 41.565 25.03 61.56 1.373 10.66 3 1313.30 48.496 24.92 49.41 2.013 27.33 4 1359.35 32.590 24.95 49.92 1.336 23.22 5 1313.65 52.439 25.10 46.63 2.274 18.08 S2 obtains the brittleness value, Young's modulus and Poisson's ratio of the coal core according to the stress-strain curve.

[0034] like Figure 1 As shown in the figure, the stress-strain curve of the uniaxial compression test of the sample reflects that the coal core first enters the compaction stage, i.e., the curve oa segment, under the action of unidirectional pressure. The microcracks or pores inside the coal core gradually decrease until they are closed. Under the continued action of pressure, the compacted coal core enters the elastic deformation stage, i.e., the curve ab segment. At this time, the stress and axial strain show a linear growth relationship. After reaching point b, affected by the original cracks and internal pores in the coal core, the stress of the coal core is locally concentrated, resulting in crack expansion. The cracks in the coal core gradually develop, and the curve bc segment shows plastic deformation until it reaches the stress peak point c, where the coal core breaks. After the stress peak, the stress decreases significantly, and the strain continues to increase. The curve cd segment shows brittle failure characteristics.

[0035] Studies have shown that when brittle rocks are subjected to external forces, they show a very short plastic stage on the stress-strain curve, and when the stress reaches the peak value, they will break rapidly. Therefore, when the stress-strain curve of the coal core reaches the yield point b, the smaller the plastic strain, the greater the brittleness of the coal core, and after reaching the stress peak point c, the stress intensity decreases. The relative size and absolute rate of post-peak stress drop can reflect the degree of brittleness, that is, if the strength drops rapidly to a very small value after the peak, it means that the rock is very brittle. If the strength decreases very slowly or even does not decrease after the peak, it means that the brittleness is very small. Based on this, the calculation formula for the brittleness value of the coal core is proposed as follows:

[0036] in, is the plastic strain value of the coal core, is the stress drop rate after coal core failure, is the stress drop after the coal core is destroyed, is stress, is the strain, c is the starting point of coal core crushing, b is the starting point of coal core plastic deformation, and d is the ending point of coal core crushing; Young's modulus is the slope of the elastic section of the stress-strain curve; Poisson's ratio is the ratio of the axial strain to the radial strain of the coal core.

[0037] S3 determines the correlation coefficients between the brittleness value and Young's modulus and Poisson's ratio, and obtains the rock mechanics adaptive factor based on the correlation coefficients.

[0038] Young's modulus is an important parameter in rock mechanics. It describes the ability of rock to resist deformation within the elastic range. It can be determined by calculating the slope of the elastic deformation range of the stress-strain curve, that is, by calculating the slope of the ab segment of the curve.

[0039]

[0040] in: is the change in stress during the elastic deformation stage of the coal core, and It is the change of strain during the elastic deformation stage of the coal core.

[0041] In rock mechanics, the Poisson's ratio parameter is used to describe the proportional relationship between the axial contraction and radial elongation of rocks. When an object is stretched in one direction, it will shrink in the direction perpendicular to the stretching direction. The Poisson's ratio is the ratio of the absolute value of the axial contraction strain to the radial elongation strain. Using the stress-strain curve of the coal core sample, the axial strain and radial strain of the sample are obtained, and then the Poisson's ratio of the coal core is calculated.

[0042]

[0043] in: is the axial strain value of the coal core under stress, It is the radial strain value of the coal core under stress.

[0044] The brittleness value, Young's modulus and Poisson's ratio were calculated, and the correlation coefficient between the brittleness value and Young's modulus was determined. The brittleness value and Young's modulus showed a positive correlation, such as Figure 3 As shown. The correlation coefficient between the brittleness value and the Poisson's ratio is determined. The brittleness value and the Poisson's ratio show a negative correlation, as shown in Figure 4 shown.

[0045] Coal seam brittleness and Young's modulus E and Poisson's ratio There is a correlation. By calculating the correlation coefficient R, the correlation between them is quantitatively described. The correlation coefficient between the brittleness value and Young's modulus The calculation formula is:

[0046] Correlation coefficient between brittleness value and Poisson's ratio The calculation formula is:

[0047] in, is the coal core brittleness value of the sample point, is the average value of coal core brittleness of all sample points, is the Young's modulus of the coal core at the sample point, is the average value of Young's modulus of coal core at all sample points, is the Poisson's ratio of the coal core at the sample point, It is the average value of the Poisson's ratio of the coal core of all sample points.

[0048] S4 obtains the coal reservoir brittleness index based on Young's modulus, Poisson's ratio and rock mechanics adaptive factor.

[0049] The correlation strength and direction of Young's modulus and Poisson's ratio with coal seam brittleness are different, that is, there are differences in the characterization ability of coal seam brittleness. In order to describe this difference, a rock mechanics adaptive factor is constructed. , adaptive factor The calculation formula is as follows:

[0050] in, is the correlation coefficient between the brittleness value and Young's modulus, is the correlation coefficient between the brittleness value and Poisson's ratio.

[0051] Combining the rock mechanics adaptive factor, Young's modulus and Poisson's ratio parameters, the coal seam brittleness index BRIT based on elastic parameters is constructed. The calculation formula is as follows:

[0052] Where E is Young's modulus, is the minimum value of Young's modulus, is the maximum value of Young's modulus, v is the Poisson's ratio, is the minimum value of Poisson's ratio, is the maximum value of Poisson's ratio.

[0053] Coal seams in different regions or target layers have different relationships between elastic parameters and coal seam brittleness due to differences in coalification degree, microscopic components, pore structure, and overlying stratum pressure. By studying the rock mechanics experimental results of coal seams in different regions or target layers, the rock mechanics adaptive factor is calculated. , and then the elastic parameters can be used to characterize the brittleness index of the coal seam.

[0054] Embodiment 2 Based on the same inventive concept, this embodiment discloses a method for characterizing the range of a coal seam geological engineering sweet spot, comprising: S1 collects pre-stack CRP gather data and seismic wave velocity data in the study area.

[0055] S2 performs prestack inversion on the prestack CRP gather data and seismic wave velocity data, and obtains the three-dimensional spatial data volume of Young's modulus and Poisson's ratio based on the inversion results of prestack inversion; S3 uses any of the above coal reservoir brittleness index calculation methods to obtain the coal reservoir brittleness index .

[0056] S4 is based on the three-dimensional spatial data of Young's modulus and Poisson's ratio, combined with the coal reservoir brittleness index , obtain the three-dimensional spatial data of coal seam brittleness in the study area, such as Figure 5 shown.

[0057] S5 extracts the distribution plane of deep coal seam brittleness index based on the three-dimensional spatial data of coal seam brittleness in the study area and combines it with the seismic analysis horizon, such as Figure 6 shown.

[0058] S6 identifies the geological engineering sweet spot range of coal seams based on the deep coal seam brittleness index distribution plan map combined with the plan distribution map of coal seam thickness and gas content, thereby supporting the deployment of deep coal seam wells.

[0059] The method for obtaining the three-dimensional spatial data volume of Young's modulus and Poisson's ratio based on the inversion results of prestack inversion is: Prestack inversion is a relatively mature seismic data interpretation technology. Compared with traditional post-stack inversion, prestack inversion can retain more angle information and provide richer information about underground structure and fluid properties. It is widely used in oil and gas exploration and development. In order to obtain the spatial distribution data of coal seam brittleness index in this study, it is necessary to combine the prestack inversion method to obtain the Young's modulus and Poisson's ratio data. Conventional prestack inversion uses the Zoeppritz approximation formula proposed by Aki and Richards to characterize the reflection coefficient. , the equation for the reflection coefficient is:

[0060] in, is the reflection coefficient, is the incident angle, is the longitudinal velocity of seismic waves, is the seismic shear wave velocity; is the seismic wave density, ; is the density variable, is the longitudinal wave velocity variable, is the shear wave velocity variable.

[0061] Establish the relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves; The relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves is:

[0062]

[0063] Where, E is Young's modulus; is Poisson's ratio; is the longitudinal velocity of seismic waves, is the seismic shear wave velocity; is the seismic wave density, Based on the reflection coefficient equation and relationship, the relationship between Young's modulus, Poisson's ratio and reflection coefficient is established; In order to reduce the cumulative error caused by indirect calculation, the above three formulas are combined to establish a reflection system formula based on Young's modulus, Poisson's ratio and density:

[0064] in, is the Young’s modulus variable; is the Poisson's ratio variable.

[0065] Based on the Bayesian inversion theory, the relationship between Young's modulus, Poisson's ratio and reflection coefficient is solved in combination with the expression of seismic angle gathers. Based on the solution results, the three-dimensional spatial data volume of Young's modulus and Poisson's ratio is obtained in combination with the iterative equation.

[0066] The method of obtaining the three-dimensional spatial data volume of Young's modulus and Poisson's ratio by combining the iterative equation is: Based on the convolution model, the seismic angle gather is expressed as: ; Based on Bayesian inversion theory, we get:

[0067] Where: , ,

[0068]

[0069] The Young's modulus and Poisson's ratio are obtained by solving the iterative equation. The iterative equation is:

[0070] in, The incident angle is seismic gathers, m is the model parameter, is the seismic wavelet, G is The Jacobi matrix associated with m is, is the model parameter disturbance term, is the residual between the seismic data and the synthetic seismic record, Indicates data error, is the variance of the model parameter disturbance, is the prior information, Indicates the number of iterations.

[0071] The analysis shows that the coal seam brittleness index based on seismic prediction matches well with drilling, with a coincidence rate of more than 70%, which can meet production needs. Figure 7 As shown in the figure, the predicted brittleness index has a good correlation with the peak gas production of drilling, which is consistent with the understanding that the higher the coal seam brittleness index, the more conducive it is to the fracturing transformation of the coal reservoir.

[0072] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0074] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0075] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention should be included in the protection scope of the claims of the present invention. The above content is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for calculating the brittleness index of a coal reservoir, characterized in that: The following steps are involved: Obtain stress-strain curves of coal cores in deep coal seams; Obtaining the brittleness value, Young's modulus and Poisson's ratio of the coal core according to the stress-strain curve; respectively determining the correlation coefficients between the brittleness value and Young's modulus and Poisson's ratio, and obtaining a rock mechanics adaptive factor according to the correlation coefficients; According to the Young's modulus, Poisson's ratio and rock mechanics adaptive factor, the coal reservoir brittleness index is obtained.

2. The method for calculating the coal reservoir brittleness index according to claim 1, characterized in that: The calculation formula of the brittleness value is: in, is the plastic strain value of the coal core, is the stress drop rate after coal core failure, is the stress drop after the coal core is destroyed, is stress, is the strain, c is the starting point of coal core crushing, b is the starting point of coal core plastic deformation, and d is the ending point of coal core crushing; The Young's modulus is the slope of the elastic segment of the stress-strain curve; The Poisson's ratio is the ratio of the axial strain to the radial strain of the coal core.

3. The method for calculating the coal reservoir brittleness index according to claim 1, characterized in that: Correlation coefficient between the brittleness value and Young's modulus The calculation formula is: Correlation coefficient between the fragility value and Poisson's ratio The calculation formula is: in, is the coal core brittleness value of the sample point, is the average value of coal core brittleness of all sample points, is the Young's modulus of the coal core at the sample point, is the average value of Young's modulus of coal core at all sample points, is the Poisson's ratio of the coal core at the sample point, It is the average value of the Poisson's ratio of the coal core of all sample points.

4. The method for calculating the coal reservoir brittleness index according to claim 3, characterized in that: The adaptive factor The calculation formula is as follows: in, is the correlation coefficient between the brittleness value and Young's modulus, is the correlation coefficient between the brittleness value and Poisson's ratio.

5. The method for calculating the coal reservoir brittleness index according to claim 4, characterized in that: The coal reservoir brittleness index The calculation formula is as follows: Where E is Young's modulus, is the minimum value of Young's modulus, is the maximum value of Young's modulus, v is the Poisson's ratio, is the minimum value of Poisson's ratio, is the maximum value of Poisson's ratio.

6. A method for characterizing the range of coal seam geological engineering sweet spots, characterized in that: include: Collect pre-stack CRP gather data and seismic wave velocity data in the study area; Performing prestack inversion on the prestack CRP gather data and seismic wave velocity data, and obtaining a three-dimensional spatial data volume of Young's modulus and Poisson's ratio based on the inversion result of the prestack inversion; The coal reservoir brittleness index is obtained by using the coal reservoir brittleness index calculation method as described in any one of claims 1 to 5. ; According to the three-dimensional spatial data of Young's modulus and Poisson's ratio, combined with the coal reservoir brittleness index , obtain the three-dimensional spatial data volume of coal seam brittleness in the study area; Based on the three-dimensional spatial data volume of coal seam brittleness in the study area and combined with the seismic analysis horizon, a distribution plane map of deep coal seam brittleness index is extracted; Based on the deep coal seam brittleness index distribution plan map, combined with the plan distribution map of coal seam thickness and gas content, the coal seam geological engineering sweet spot range is identified.

7. The method for characterizing the sweet spot range of coal seam geological engineering according to claim 6, characterized in that: The method for obtaining the three-dimensional spatial data volume of Young's modulus and Poisson's ratio based on the inversion results of the prestack inversion is: Establish the reflection coefficient equation for prestack inversion; Establish the relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves; Based on the reflection coefficient equation and the relationship, a relationship between Young's modulus, Poisson's ratio and reflection coefficient is established; Based on the Bayesian inversion theory, the relationship between Young's modulus, Poisson's ratio and reflection coefficient is solved in combination with the expression of seismic angle gathers; Based on the solution results, the three-dimensional spatial data of Young's modulus and Poisson's ratio are obtained by combining the iterative equation.

8. The method for characterizing the sweet spot range of coal seam geology engineering according to claim 7, characterized in that: The reflection coefficient equation is: The relationship between Young's modulus, Poisson's ratio and the velocity and density of seismic longitudinal and transverse waves is: Where, E is Young's modulus; is Poisson's ratio; is the longitudinal velocity of seismic waves, is the seismic shear wave velocity; is the seismic wave density.

9. The method for characterizing the sweet spot range of coal seam geological engineering according to claim 8, characterized in that: The relationship between Young's modulus, Poisson's ratio and reflection coefficient is as follows: in, is the reflection coefficient, is the incident angle, is the Young’s modulus variable; is the Poisson's ratio variable; is the density variable; .

10. The method for characterizing the sweet spot range of coal seam geological engineering according to claim 9, characterized in that: The method of obtaining the three-dimensional spatial data volume of Young's modulus and Poisson's ratio by combining the iterative equation is: Based on the convolution model, the seismic angle gather is expressed as: ； Based on Bayesian inversion theory, we get: Where: ， ， The Young's modulus and Poisson's ratio are obtained by solving the iterative equation, which is: in, The incident angle is seismic gathers, m is the model parameter, is the seismic wavelet, G is The Jacobi matrix associated with m is, is the model parameter disturbance term, is the residual between the seismic data and the synthetic seismic record, Indicates data error, is the variance of the model parameter disturbance, is the prior information, Indicates the number of iterations.

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