Shale brittleness index calculation method, system, equipment and medium

Abstract

The invention belongs to the technical field of exploration, and provides a shale brittleness index calculation method, system, equipment and medium, and the method comprises the steps: collecting a shale sample, applying stress to construct a stress-strain curve, and obtaining data such as total strain, Young modulus and peak strain from the stress-strain curve; and determining normalized maximum and minimum boundary data of the strain, the Young modulus and the peak strain at the same time. And respectively calculating the plastic deformation of the shale in the compaction section and the crack growth section, the plastic deformation in the linear section and the shale fracture difficulty degree by using different data. The average value of the plastic deformation of the shale in the compaction section and the crack growth section, the plastic deformation of the shale in the linear section and the shale fracture difficulty degree is used as the shale brittleness index. The method can accurately evaluate the brittleness of the shale.

Description

Technical Field

[0001] This disclosure belongs to the field of exploration technology, and in particular relates to a method, system, equipment and medium for calculating the brittleness index of shale. Background Technology

[0002] Shale gas reservoirs are typical unconventional natural gas reservoirs with low permeability and low porosity, accounting for a large proportion of my country's oil and gas resources. However, their development is costly and difficult, and their unique reservoir characteristics dictate that fracturing and stimulation must be carried out to improve oil and gas flow conditions in order to achieve effective extraction.

[0003] The "brittleness index" can characterize the ease with which fractures form in rocks during fracturing, and can also reflect the complexity of fractures formed after reservoir fracturing. It has now become an important parameter for describing the fracturability of shale reservoirs and a necessary evaluation indicator for selecting high-quality shale.

[0004] Current mainstream methods for calculating shale brittleness index are divided into mineral brittleness index and mechanical brittleness index. Incomplete statistics show that there are over 40 methods for determining shale brittleness index. Even so, discussions, controversies, and research regarding shale brittleness index determination have never ceased, mainly for two reasons: firstly, the definition is unclear, and secondly, the boundaries are ambiguous. Currently, there is an urgent need for a widely accepted calculation method to standardize the determination process.

[0005] For example:

[0006] V. Hucka used the ratio of recoverable strain to total strain to represent the brittleness index of shale, and its specific calculation is based on the attached... Figure 1 As shown, a straight line parallel to the loading linear segment GF is drawn through the rupture peak point E, intersecting the X-axis at AD. OA is considered as irreversible deformation, and AD is considered as recoverable deformation. The calculation formula is as follows:

[0007]

[0008] Where B1 is the brittleness index, dimensionless; εr is the recoverable strain or elastic strain, dimensionless; and εtot is the total strain, dimensionless. However, this method has two shortcomings: first, because it does not consider the intrinsic cohesion of shale, it cannot reflect the characteristic of shale being prone to fracture under stress; second, the calculation of recoverable strain is inaccurate, and it does not fully consider irrecoverable strain.

[0009] CN111271055A, "Method, Apparatus and Equipment for Determining the Brittleness Index of Shale", discloses a method, apparatus and equipment for determining the brittleness index of shale. However, it sets too many brittleness indices in the calculation process. The calculation of the brittleness index of shale is not a simple summation of several data. Various intrinsic parameters of shale should be considered comprehensively. At the same time, confining pressure, as one of the basic conditions of rock mechanics experiments, has already taken into account the influence of confining pressure when obtaining mechanical data. It should not be considered as an influencing factor separately.

[0010] In summary, existing technologies suffer from low accuracy in calculating the brittleness index of shale. Summary of the Invention

[0011] To address the aforementioned issues, this disclosure provides a method, system, equipment, and medium for calculating the shale brittleness index. The method involves collecting shale samples and applying stress to construct stress-strain curves, acquiring various relevant and boundary data, and then calculating the plastic deformation and fracturing shale at different stages. The average value of these values ​​is used as the shale brittleness index. This approach more accurately reflects the shale's susceptibility to stress-induced fracturing, provides more accurate calculations of recoverable strain, comprehensively considers various intrinsic shale parameters, and does not treat confining pressure as a sole influencing factor, thereby improving the accuracy and rationality of calculating the shale brittleness index.

[0012] The method for calculating the shale brittleness index in this invention:

[0013] This invention is achieved through the following technical solution:

[0014] A method for calculating the brittleness index of shale, characterized by comprising:

[0015] Collect shale samples, apply stress to the shale samples, and construct stress-strain curves based on the strain of the shale samples;

[0016] The total strain, Young's modulus, peak strain, and peak stress of the shale sample were obtained from the stress-strain curve.

[0017] Obtain the strain normalized maximum boundary, strain normalized minimum boundary, Young's modulus normalized maximum boundary, Young's modulus normalized minimum boundary, peak strain normalized maximum boundary, and peak strain normalized minimum boundary data for shale samples.

[0018] The plastic deformation of shale in the compaction and fracture growth sections is calculated using peak stress, total strain, normalized minimum strain boundary, and normalized maximum strain boundary. The plastic deformation of shale in the linear segment of the stress-strain curve is calculated using Young's modulus, normalized maximum Young's modulus boundary, and normalized minimum Young's modulus boundary. The ease of shale fracture is calculated using peak strain normalized maximum boundary, peak strain, and peak strain normalized minimum boundary.

[0019] The average values ​​of plastic deformation in the compaction and fracture growth sections of shale, plastic deformation in the linear section, and the ease of shale fracture are used as the shale brittleness index.

[0020] Furthermore,

[0021] The brittleness index of the shale is:

[0022]

[0023] Where, σ max X represents the peak stress of the shale sample; 2min X is the strain-normalized minimum boundary for the shale sample; 2max The normalized maximum boundary value for strain of the shale sample is E; E is the Young's modulus of the shale sample; E max E represents the normalized maximum boundary of the Young's modulus of the shale sample. min ε is the normalized minimum boundary of the Young's modulus of the shale sample; ε is the peak strain of the shale sample; ε min The normalized minimum boundary for the peak strain of the shale sample; ε max Eε represents the maximum normalized peak strain boundary of the shale sample. tot The total strain of the shale sample;

[0024] This refers to the plastic deformation of shale in the compaction and crack growth stages;

[0025] (EE min ) / (E max -E min () represents the plastic deformation of shale in the linear segment of the stress-strain curve;

[0026] (ε max -ε) / (ε max -ε min () represents the ease or difficulty of fracturing shale.

[0027] Furthermore,

[0028] The Young's modulus is:

[0029]

[0030] Where E is the Young's modulus of the shale sample; Δσ is the axial increment of the shale sample; Δε a The axial strain increment of the shale sample.

[0031] Furthermore,

[0032] The maximum and minimum strain normalization boundaries of the shale samples are determined by statistical analysis of test results from major global shale gas reservoirs, or by statistical analysis of strain magnitude in the shale gas block where the shale samples are located.

[0033] Furthermore,

[0034] The normalized maximum boundary, normalized minimum boundary, normalized maximum boundary, and normalized minimum boundary of the peak strain of the shale samples were determined by statistical analysis of test results from major shale gas reservoirs worldwide.

[0035] Furthermore,

[0036] The collected shale samples include:

[0037] At the same depth, drill no fewer than three parallel samples from the shale core. The diameter of the samples should be controlled at 25 mm ± 1.5 mm, and the aspect ratio of the samples should be 2.0 to 2.5.

[0038] Furthermore,

[0039] The strain data of the shale mechanical test sample in the triaxial rock mechanics experiment were obtained by recording the strain gauges of the rock mechanics instrument, and the maximum value of the data is the peak strain of the shale mechanical test sample.

[0040] A system for calculating the brittleness index of shale, characterized in that it includes:

[0041] The testing module is used to collect shale samples, apply stress to the shale samples, and construct stress-strain curves based on the strain of the shale samples.

[0042] The data acquisition module is used to obtain the total strain, Young's modulus, peak strain, and peak stress of the shale sample based on the stress-strain curve.

[0043] Obtain the strain normalized maximum boundary, strain normalized minimum boundary, Young's modulus normalized maximum boundary, Young's modulus normalized minimum boundary, peak strain normalized maximum boundary, and peak strain normalized minimum boundary data for shale samples.

[0044] The calculation module is used to calculate the plastic deformation of shale in the compaction and fracture growth stages using peak stress, total strain, normalized minimum boundary of strain, and normalized maximum boundary of strain; to calculate the plastic deformation of shale in the linear segment of the stress-strain curve using Young's modulus, normalized maximum boundary of Young's modulus, and normalized minimum boundary of Young's modulus; and to calculate the ease of shale fracture using normalized maximum boundary of peak strain, peak strain, and normalized minimum boundary of peak strain.

[0045] The average values ​​of plastic deformation in the compaction and fracture growth sections of shale, plastic deformation in the linear section, and the ease of shale fracture are used as the shale brittleness index.

[0046] Compared with the prior art, this disclosure has the following advantages:

[0047] This invention considers the intrinsic cohesion of shale. By acquiring various data, such as the normalized maximum boundary of strain, the normalized minimum boundary of strain, the normalized maximum boundary of Young's modulus, the normalized minimum boundary of Young's modulus, the normalized maximum boundary of peak strain, and the normalized minimum boundary of peak strain, this invention calculates the plastic deformation and fracturing shale at different stages. This more accurately reflects the stress-induced fracturing characteristics of shale and provides a more accurate calculation of recoverable strain. Furthermore, by comprehensively considering various intrinsic shale parameters and not treating confining pressure as a separate influencing factor, the accuracy and rationality of the calculation are improved, resulting in a more precise shale brittleness index.

[0048] Other features and advantages of this disclosure will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the disclosure. The objects and other advantages of this disclosure may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A schematic diagram of the method of the present invention is shown;

[0051] Figure 2 The stress-strain curve is shown. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0053] Currently, most accidents are caused by the combined effects of dust, gas, and static electricity; in other words, an accident is often caused by the accumulation of several errors or deficiencies. Dust electrostatic explosions are a matter of probability. The more probabilistic factors present, the higher the risk of a dust explosion. When these probabilistic factors accumulate to a certain level, a simple process deviation or operational error may trigger a dust explosion in the silo. Currently, there is a lack of methods for assessing and calculating the risk of dust electrostatic explosion accidents in silos.

[0054] Therefore, it is necessary to study a method for calculating and assessing the risk of electrostatic explosion of dust in silos, so as to scientifically prevent the occurrence of electrostatic explosion accidents of dust in silos. This is of great significance for improving product quality and ensuring safe production.

[0055] Based on this, such as Figure 1 A schematic diagram of the method according to the present invention is shown. The technical concept of the present invention is as follows:

[0056] Triaxial rock mechanics experiments were conducted on multiple shale samples from target wells within the geological region to determine peak stress, total strain, strain normalized minimum boundary, strain normalized maximum boundary, Young's modulus normalized minimum boundary, Young's modulus, Young's modulus normalized maximum boundary, peak strain normalized minimum boundary, peak strain, and peak strain normalized maximum boundary.

[0057] Based on triaxial rock mechanics experiments of shale formations, the peak stress, strain normalized minimum boundary, strain normalized maximum boundary, Young's modulus normalized minimum boundary, Young's modulus, Young's modulus normalized maximum boundary, peak strain normalized minimum boundary, peak strain, and peak strain normalized maximum boundary were determined, and the brittleness index of shale formations was calculated.

[0058] The following are the specific execution steps of this invention:

[0059] 1. Step 1: Obtain the total strain, Young's modulus and peak strain of the shale sample.

[0060] Specifically, the total strain, Young's modulus, and peak strain were obtained through triaxial rock mechanics experiments. Stress-strain curves of the shale mechanical test samples were obtained through these experiments, including... Figure 2 The OD value represents the total strain of the shale mechanical test sample.

[0061] To more accurately and comprehensively determine the brittleness index of shale, multiple shale samples can be prepared from the target well. At the same depth, no fewer than three parallel samples should be drilled from the shale core, with a diameter controlled at 25 mm ± 1.5 mm and an aspect ratio of 2.0 to 2.5.

[0062] The Young's modulus of the shale mechanical experimental sample can be calculated using the following formula based on experimental data:

[0063]

[0064] Where E is the Young's modulus of the shale sample, MPa; Δσ is the axial increment of the shale sample, MPa; Δε a The axial strain increment of the shale sample is dimensionless.

[0065] The strain data of the shale mechanical test sample in the triaxial rock mechanics test can be recorded by the strain gauge of the rock mechanics instrument, and the maximum value is the peak strain of the shale mechanical test sample.

[0066] 2. Step Two: Determine the maximum and minimum normalized strain boundaries of the shale sample.

[0067] Since there are many shale gas blocks globally, the maximum and minimum normalized strain boundaries of the shale samples are determined by statistical analysis of test results from major global shale gas reservoirs, or they can be redefined based on statistical results of strain magnitude in the shale gas block where the shale sample is located.

[0068] Following the principle that the larger the sample size, the more accurate the maximum and minimum normalization boundaries of the shale sample strain will be, strain data of shale samples should be obtained as much as possible when collecting statistical sample information.

[0069] 3. Step 3: Determine the maximum and minimum boundaries of the normalized Young's modulus, the maximum boundary of the normalized peak strain, and the minimum boundary of the normalized peak strain for the shale sample.

[0070] The maximum and minimum normalized boundaries of Young's modulus, peak strain, and peak strain of shale samples are defined by statistical analysis of test results from major shale gas reservoirs worldwide, and also follow the principle that the larger the sample size, the more accurate the parameters obtained.

[0071] Among them, the maximum and minimum normalized strain boundaries of shale samples, the maximum and minimum normalized Young's modulus boundaries of shale samples, and the maximum and minimum normalized peak strain boundaries of shale samples are all block-specific attributes. Due to the influence of regional geology, the statistical results may differ from region to region.

[0072] 4. Step Four: Calculate the brittleness index of the shale sample.

[0073] The calculation formula is:

[0074]

[0075] Where, σmax X represents the peak stress of the shale sample, in MPa; 2min The minimum strain normalization boundary for the shale sample is %, %; X 2max is the strain normalized maximum boundary for the shale sample, %; E is the Young's modulus of the shale sample, MPa; E max The normalized maximum boundary of Young's modulus for shale samples, MPa; E min ε represents the normalized minimum boundary value of the Young's modulus of the shale sample, in MPa; ε is the peak strain of the shale sample, in MPa; ε min The peak strain normalized minimum boundary for the shale sample is given in MPa; ε max The peak strain normalized maximum boundary for the shale sample is given in MPa; Eε tot denoted as the total strain of the shale sample, in MPa.

[0076] The formula comprises three components, referred to from left to right as the first, second, and third components. The first component characterizes the plastic deformation of shale in the compaction zone (OG) and fracture growth zone (FE); the second component indirectly reflects the plastic deformation in the linear zone; and the third component quantifies the ease of shale fracture using peak strain. This algorithm integrates the two defining elements, employs a normalization method, and takes the average of the three components as the brittleness index, making it a feasible and reliable method for calculating the shale brittleness index at present.

[0077] Among them, the normalized minimum boundary of the Young's modulus of the shale sample is the minimum value among all tested Young's moduli in the geological region where the shale sample is located.

[0078] Among them, the normalized maximum boundary of the Young's modulus of the shale sample is the maximum value among all tested Young's moduli in the geological region where the shale sample is located.

[0079] The normalized minimum boundary for peak strain of shale samples is the minimum value among all tested peak strains in the geological region where the shale samples are located.

[0080] Among them, the maximum normalized boundary of peak strain for shale samples is the maximum value among all tested peak strains in the geological region where the shale samples are located.

[0081] The following are embodiments of the present invention:

[0082] In this embodiment, as shown in the appendix Figure 2 The stress unloading experiment was performed on the shale sample continuously loaded to point F. The stress unloading path did not rebound along FG, but rather unloaded along a path similar to FB. That is, the linear segment of loading GF is not equal to the elastic segment, and plastic deformation continues to develop from point G to point F. With the same slope as the linear segment of stress unloading FB, a straight line is drawn through the peak point E and intersects the x-axis at point C. The AC segment represents the neglected irreversible strain.

[0083] The true recoverable strain of a shale sample is calculated using the following formula, based on the unrecoverable strain and pseudo-recoverable strain of the linear segment:

[0084] ε' r =ε r -ε p =AD-AC (2)

[0085] Where, ε r ′ represents the true recoverable strain of the shale sample in the stress unloading experiment, %; ε r The spurious recoverable strain (%) of the shale sample in the stress unloading experiment; ε p The linear segment of the unrecoverable strain of the shale sample in the stress unloading experiment is %.

[0086] Based on the true recoverable strain, false recoverable strain, and unrecoverable strain of shale samples in stress unloading experiments, as well as the intrinsic cohesion and plastic strain of shale samples, the brittleness index of shale samples is calculated through parameter normalization:

[0087]

[0088] Where Xmin is the strain normalized minimum boundary of the shale sample, %; Xmax is the strain normalized maximum boundary of the shale sample, %; C is the cohesion of the shale sample, MPa; Cmin is the cohesion normalized minimum boundary of the shale sample, MPa; Cmax is the cohesion normalized maximum boundary of the shale sample, MPa; ε tot The total strain of the shale sample is %.

[0089] The normalized minimum boundary for strain of shale samples is the minimum strain among all tested strains in the geological region where the shale samples are located. The normalized maximum boundary for strain of shale samples is the maximum strain among all tested strains in the geological region where the shale samples are located. The normalized minimum boundary for cohesion of shale samples is the minimum cohesion among all tested cohesions in the geological region where the shale samples are located. The normalized maximum boundary for cohesion of shale samples is the maximum cohesion among all tested cohesions in the geological region where the shale samples are located.

[0090] Considering the complexity and large errors in testing the intrinsic cohesion of shale in practical applications, this invention uses peak strain instead to characterize the ease of fracture in order to ensure the universality of the method. Meanwhile, the FB curve of the sample stress unloading experiment varies with the magnitude of stress loading, meaning that point C is difficult to pinpoint accurately. However, the magnitude of plastic deformation (AC) in the linear segment directly determines the magnitude of Young's modulus of shale, and this component can be characterized by Young's modulus. Based on the above considerations, the calculation formula is transformed as follows:

[0091]

[0092] Where, σ max X represents the peak stress of the shale sample, in MPa; 2min The minimum strain normalization boundary for the shale sample is %, %; X 2max is the strain normalized maximum boundary for the shale sample, %; E is the Young's modulus of the shale sample, MPa; E max The normalized maximum boundary of Young's modulus for shale samples, MPa; E min ε represents the normalized minimum boundary value of the Young's modulus of the shale sample, in MPa; ε is the peak strain of the shale sample, in MPa; ε min The peak strain normalized minimum boundary for the shale sample is given in MPa; ε max The peak strain normalized maximum boundary for the shale sample is given in MPa; Eε tot denoted as the total strain of the shale sample, in MPa.

[0093] The following are practical application examples of this invention:

[0094] A total of 25 downhole cores from 17 shale gas wells and 5 shale formations in the Sichuan Basin were collected. The shale samples were prepared into standard cylindrical specimens with a diameter of 25 mm and an aspect ratio of 2.0–2.5. Figure 2 The stress / strain relationship curves of the samples subjected to continuous compressive load were tested using a GTS-RTR-2000 rock mechanics instrument under standard atmospheric pressure, 20℃ and no pore pressure conditions. The Young's modulus and Poisson's ratio of the linear segment of axial deformation were calculated and the peak stress and peak strain were recorded, as shown in Table 1.

[0095] Table 1. Statistical Table of Shale Mechanics Experiment Results

[0096]

[0097]

[0098] Rock mechanics experimental data of all shale rocks within the aforementioned shale gas blocks were collected. Based on the statistical results, the normalized maximum and minimum boundaries of Young's modulus, the normalized maximum and minimum boundaries of peak strain, and the normalized maximum and minimum boundaries of strain for shale samples were obtained for the shale gas blocks.

[0099] The peak strain, Young's modulus, total strain, and peak stress of shale gas well core samples from the Sichuan Basin were measured using the experimental data mentioned above. The brittleness index of shale was calculated using statistical data such as Young's modulus, peak strain, and normalized maximum and minimum strain boundaries of shale gas blocks.

[0100] The brittleness index of core samples from shale gas wells in the Sichuan Basin was calculated using the following formula, as shown in Table 2:

[0101]

[0102] Where, σ max X represents the peak stress of the shale sample, in MPa; 2min The minimum strain normalization boundary for the shale sample is %, %; X 2max is the strain normalized maximum boundary for the shale sample, %; E is the Young's modulus of the shale sample, MPa; E max The normalized maximum boundary of Young's modulus for shale samples, MPa; E min ε represents the normalized minimum boundary value of the Young's modulus of the shale sample, in MPa; ε is the peak strain of the shale sample, in MPa; ε min The peak strain normalized minimum boundary for the shale sample is given in MPa; ε max The peak strain normalized maximum boundary for the shale sample is given in MPa; Eε tot denoted as the total strain of the shale sample, in MPa.

[0103] Table 2 Calculation results of shale brittleness index

[0104]

[0105]

[0106] Based on the method of the present invention, this disclosure also provides a system corresponding to the above method, which includes:

[0107] The testing module is used to collect shale samples, apply stress to the shale samples, and construct stress-strain curves based on the strain of the shale samples.

[0108] The data acquisition module is used to obtain the total strain, Young's modulus, and peak strain of shale samples based on the stress-strain curve.

[0109] Obtain the strain normalized maximum boundary, strain normalized minimum boundary, Young's modulus normalized maximum boundary, Young's modulus normalized minimum boundary, peak strain normalized maximum boundary, and peak strain normalized minimum boundary data for shale samples.

[0110] The calculation module is used to calculate the plastic deformation of shale in the compaction and fracture growth stages using peak stress, total strain, normalized minimum boundary of strain, and normalized maximum boundary of strain; to calculate the plastic deformation of shale in the linear segment of the stress-strain curve using Young's modulus, normalized maximum boundary of Young's modulus, and normalized minimum boundary of Young's modulus; and to calculate the ease of shale fracture using normalized maximum boundary of peak strain, peak strain, and normalized minimum boundary of peak strain.

[0111] The average values ​​of plastic deformation in the compaction and fracture growth sections of shale, plastic deformation in the linear section, and the ease of shale fracture are used as the shale brittleness index.

[0112] Based on the same inventive concept as disclosed above, embodiments of this disclosure also provide an apparatus corresponding to the above method, comprising at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the above method.

[0113] It should be noted that the electrical connection between the above-mentioned units does not necessarily mean the connection between lines. The indirect connection method can be applied to the embodiments of this disclosure as long as it achieves the purpose of this disclosure.

[0114] Based on the same inventive concept, this disclosure also provides a computer storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to perform the above-described method.

[0115] Although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A method for calculating the brittleness index of shale, characterized in that, include: Collect shale samples, apply stress to the shale samples, and construct stress-strain curves based on the strain of the shale samples; The total strain, Young's modulus, peak strain, and peak stress of the shale sample were obtained from the stress-strain curve. Obtain the strain normalized maximum boundary, strain normalized minimum boundary, Young's modulus normalized maximum boundary, Young's modulus normalized minimum boundary, peak strain normalized maximum boundary, and peak strain normalized minimum boundary data for shale samples. The plastic deformation of shale in the compaction and fracture growth sections is calculated using peak stress, total strain, normalized minimum strain boundary, and normalized maximum strain boundary. The plastic deformation of shale in the linear segment of the stress-strain curve is calculated using Young's modulus, normalized maximum Young's modulus boundary, and normalized minimum Young's modulus boundary. The ease of shale fracture is calculated using peak strain normalized maximum boundary, peak strain, and peak strain normalized minimum boundary. The average values ​​of plastic deformation in the compaction and fracture growth sections of shale, plastic deformation in the linear section, and the ease of shale fracture are used as the shale brittleness index.

2. The method for calculating the brittleness index of shale according to claim 1, characterized in that, The brittleness index of the shale is: Where, σ max X represents the peak stress of the shale sample; 2min X is the strain-normalized minimum boundary for the shale sample; 2max The normalized maximum boundary value for strain of the shale sample is E; E is the Young's modulus of the shale sample; E max E represents the normalized maximum boundary of the Young's modulus of the shale sample. min ε is the normalized minimum boundary of the Young's modulus of the shale sample; ε is the peak strain of the shale sample; ε min The normalized minimum boundary for the peak strain of the shale sample; ε max Eε represents the maximum normalized peak strain boundary of the shale sample. tot The total strain of the shale sample; This refers to the plastic deformation of shale in the compaction and crack growth stages; (EE min ) / (E max -E min () represents the plastic deformation of shale in the linear segment of the stress-strain curve; (ε max -ε) / (ε max -ε min The degree of difficulty in fracturing shale is indicated by the number of shale rocks.

3. The method for calculating the brittleness index of shale according to claim 2, characterized in that, The Young's modulus is: Where E is the Young's modulus of the shale sample; Δσ is the axial increment of the shale sample; Δε a The axial strain increment of the shale sample.

4. The method for calculating the brittleness index of shale according to claim 1, characterized in that, The maximum and minimum strain normalization boundaries of the shale samples are determined by statistical analysis of test results from major global shale gas reservoirs, or by statistical analysis of strain magnitude in the shale gas block where the shale samples are located.

5. The method for calculating the brittleness index of shale according to claim 1, characterized in that, The normalized maximum boundary, normalized minimum boundary, normalized maximum boundary, and normalized minimum boundary of the peak strain of the shale samples were determined by statistical analysis of test results from major shale gas reservoirs worldwide.

6. The method for calculating the brittleness index of shale according to claim 1, characterized in that, The collected shale samples include: At the same depth, drill no fewer than three parallel samples from the shale core. The diameter of the samples should be controlled at 25 mm ± 1.5 mm, and the aspect ratio of the samples should be 2.0 to 2.

5.

7. The method for calculating the brittleness index of shale according to claim 1, characterized in that, The strain data of the shale mechanical test sample in the triaxial rock mechanics experiment were obtained by recording the strain gauges of the rock mechanics instrument, and the maximum value of the data is the peak strain of the shale mechanical test sample.

8. A system for calculating the brittleness index of shale, characterized in that, include: The testing module is used to collect shale samples, apply stress to the shale samples, and construct stress-strain curves based on the strain of the shale samples. The data acquisition module is used to obtain the total strain, Young's modulus, peak strain, and peak stress of the shale sample based on the stress-strain curve. Obtain the strain normalized maximum boundary, strain normalized minimum boundary, Young's modulus normalized maximum boundary, Young's modulus normalized minimum boundary, peak strain normalized maximum boundary, and peak strain normalized minimum boundary data for shale samples. The calculation module is used to calculate the plastic deformation of shale in the compaction and fracture growth stages using peak stress, total strain, normalized minimum boundary of strain, and normalized maximum boundary of strain; to calculate the plastic deformation of shale in the linear segment of the stress-strain curve using Young's modulus, normalized maximum boundary of Young's modulus, and normalized minimum boundary of Young's modulus; and to calculate the ease of shale fracture using normalized maximum boundary of peak strain, peak strain, and normalized minimum boundary of peak strain. The average values ​​of plastic deformation in the compaction and fracture growth sections of shale, plastic deformation in the linear section, and the ease of shale fracture are used as the shale brittleness index.

9. A device for calculating the brittleness index of shale, comprising: At least one processor; And a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the method for calculating the shale brittleness index as described in any one of claims 1 to 7.

10. A computer storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to perform the method of any one of claims 1 to 7.

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