CN-121994592-A - Shale brittleness index calculation method, system, equipment and medium

CN121994592ACN 121994592 ACN121994592 ACN 121994592ACN-121994592-A

Abstract

The method comprises the steps of collecting shale samples, applying stress to construct a stress-strain curve, acquiring data such as total strain, young modulus, peak strain and the like, and simultaneously determining normalized maximum and minimum boundary data of the strain, the Young modulus and the peak strain. And respectively calculating the plastic deformation of the shale in the compaction section and the crack growth section and the plastic deformation in the linear section by using different data, and the difficulty of cracking the shale. The average value of the plastic deformation of shale in the compaction section and the crack growth section, the plastic deformation in the linear section and the shale cracking difficulty is taken as the shale brittleness index. The method can accurately evaluate the brittleness of the shale.

Inventors

LIU FEI
YANG JIAN
PENG HUAN
MIN JIAN
LIU YUNTAO
GOU XINGHAO

Assignees

中国石油天然气股份有限公司

Dates

Publication Date: 20260508
Application Date: 20241107

Claims (10)

1. A method for calculating a shale brittleness index, comprising: Collecting a shale sample, applying stress to the shale sample, and constructing a stress-strain curve according to the strain of the shale sample; Acquiring total strain, young modulus, peak strain and peak stress of the shale sample according to the stress-strain curve; obtaining the data of a strain normalization maximum boundary, a strain normalization minimum boundary, a Young modulus normalization maximum boundary, a Young modulus normalization minimum boundary, a peak strain normalization maximum boundary and a peak strain normalization minimum boundary of a shale sample; Calculating plastic deformation of shale in a compaction section and a crack growth section by using peak stress, total strain, strain normalization minimum boundary and strain normalization maximum boundary, calculating plastic deformation of shale in a stress strain curve and a linear section by using Young modulus, young modulus normalization maximum boundary and Young modulus normalization minimum boundary, and calculating shale cracking difficulty by using peak strain normalization maximum boundary, peak strain and peak strain normalization minimum boundary; The average value of the plastic deformation of shale in the compaction section and the crack growth section, the plastic deformation in the linear section and the shale cracking difficulty is taken as the shale brittleness index.
2. The method for calculating a shale brittleness index as set forth in claim 1, wherein said shale brittleness index is: Wherein σ max is the peak stress of the shale sample, X 2min is the minimum boundary of the strain normalization of the shale sample, X 2max is the maximum boundary of the strain normalization of the shale sample, E is the Young's modulus of the shale sample, E max is the maximum boundary of the Young's modulus normalization of the shale sample, E min is the minimum boundary of the Young's modulus normalization of the shale sample, ε is the peak strain of the shale sample, ε min is the minimum boundary of the peak strain normalization of the shale sample, ε max is the maximum boundary of the peak strain normalization of the shale sample, and E ε tot is the total strain of the shale sample; plastic deformation of shale in a compaction section and a crack growth section; (E-E min )/(E max -E min ) is the plastic deformation of shale in the stress-strain curve, in the linear section; (ε max -ε)/(ε max -ε min ) is the ease of shale cracking.
3. The method of claim 2, wherein the young's modulus is: wherein E is the Young's modulus of the shale sample, deltaSigma is the axial increment of the shale sample, and DeltaEpsilon a is the axial strain increment of the shale sample.
4. The method of claim 1, wherein the maximum and minimum boundaries for the shale sample strain normalization are determined by statistics of global main shale gas reservoir test results or by statistics of the shale gas block strain size where the shale sample is located.
5. The method of claim 1, wherein the shale sample young's modulus normalized maximum boundary, young's modulus normalized minimum boundary, peak strain normalized maximum boundary, strain normalized minimum boundary are determined by global primary shale gas reservoir test result statistics.
6. A method of calculating a shale brittleness index as claimed in claim 1, the method is characterized in that the shale sample collection comprises the following steps: At the same depth, not less than 3 parallel samples are drilled in the shale rock core, the diameter of the samples is controlled to be 25mm plus or minus 1.5mm, and the length-diameter ratio of the samples is 2.0-2.5.
7. The method for calculating the shale brittleness index according to claim 1, wherein strain data of the shale mechanics experiment sample in a triaxial rock mechanics experiment is obtained through strain gauge recording of a rock mechanics instrument, and the maximum value is peak strain of the shale mechanics experiment sample.
8. A system for calculating a shale brittleness index, comprising: The testing module is used for collecting shale samples, applying stress to the shale samples and constructing a stress-strain curve according to the strain of the shale samples; The data acquisition module is used for acquiring total strain, young modulus, peak strain of the shale sample and peak stress of the shale sample according to the stress-strain curve; obtaining the data of a strain normalization maximum boundary, a strain normalization minimum boundary, a Young modulus normalization maximum boundary, a Young modulus normalization minimum boundary, a peak strain normalization maximum boundary and a peak strain normalization minimum boundary of a shale sample; The calculation module is used for calculating plastic deformation of shale in the compaction section and the crack growth section by utilizing peak stress, total strain, strain normalized minimum boundary and strain normalized maximum boundary; calculating the plastic deformation of shale in a stress strain curve and a linear section by using the Young modulus, the Young modulus normalized maximum boundary and the Young modulus normalized minimum boundary; The average value of the plastic deformation of shale in the compaction section and the crack growth section, the plastic deformation in the linear section and the shale cracking difficulty is taken as the shale brittleness index.
9. A shale brittleness index calculation device 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 to enable the at least one processor to perform the shale brittleness index calculation method of any of claims 1-7.
10. A computer storage medium having stored thereon executable instructions which when executed by a processor cause the processor to implement the method of any of claims 1 to 7.

Description

Shale brittleness index calculation method, system, equipment and medium Technical Field The disclosure belongs to the technical field of exploration, and particularly relates to a method, a system, equipment and a medium for calculating a shale brittleness index. Background Shale gas reservoirs are typical unconventional natural gas reservoirs with low permeability and low porosity, and have great specific gravity in oil and gas resources in China. However, the development cost is high and the difficulty is high, and the special reservoir characteristics determine that the development of the reservoir has to be subjected to fracturing transformation, so that the seepage condition of the oil gas flow is improved, and the purpose of effective exploitation is achieved. The brittleness index can represent the difficulty of crack formation of the rock in the fracturing process, can reflect the complexity of the cracks formed after the fracturing of the reservoir, and is an important parameter for describing the fracturing property of the shale reservoir and a necessary evaluation index for selecting high-quality shale. The existing mainstream shale brittleness index calculation method is divided into a mineral brittleness index and a mechanical brittleness index, the data are incompletely counted, and the shale brittleness index measurement method reaches more than 40. Even so, discussions, disputes and studies on shale brittleness index determinations have never been stopped, mainly for two reasons, namely, undefined definition and undefined boundaries. There is a need for a widely accepted calculation method for unifying measurement methods. For example: Hucka expresses shale brittleness index by the ratio of recoverable strain to total strain, and is specifically calculated by intersecting a straight line parallel to loading linear section GF with X-axis at peak point E of overspray as shown in fig. 1, OA is regarded as non-recoverable deformation, AD is regarded as recoverable deformation, and the calculation formula is: Wherein B1 is a brittleness index, dimensionless, εr is a recoverable strain or an elastic strain, dimensionless, εtot is a total strain, dimensionless. However, the method has two defects, namely, the characteristic that the shale is easy to crack due to stress cannot be reflected due to the fact that the intrinsic cohesion factor of the shale is not considered, and the recoverable strain calculation is inaccurate and the unrecoverable strain is not fully considered. CN111271055A (method, device and equipment for determining brittleness index of shale) discloses a method, device and equipment for determining brittleness index of shale, but excessive brittleness index is set in the calculation process, the calculation of the brittleness index of shale is not the addition of several simple data, each shale intrinsic parameter should be comprehensively considered, meanwhile, confining pressure is taken as one of basic conditions of rock mechanics experiment, the influence of confining pressure is considered while mechanical data is obtained, and the influence is not taken as an influence factor to be considered independently. In a word, the prior art has the problem that the accuracy of calculating the shale brittleness index is not high. Disclosure of Invention In order to solve the problems, the disclosure provides a calculation method, a system, equipment and a medium for shale brittleness index, which are characterized in that a stress-strain curve is constructed by collecting shale samples and applying stress, various related data and boundary data are obtained, and further, the plastic deformation and cracking difficulty of the shale at different stages are calculated, the average value of the stress-strain curve is used as the shale brittleness index, the characteristic that the shale is easy to crack under stress can be more accurately reflected, the calculation of recoverable strain is more accurate, various shale intrinsic parameters are comprehensively considered, and the confining pressure is not used as an independent influence factor, so that the accuracy and the rationality for calculating the shale brittleness index are improved. The method for calculating the shale brittleness index comprises the following steps: the invention is realized by the following technical scheme: A method for calculating a shale brittleness index, comprising: Collecting a shale sample, applying stress to the shale sample, and constructing a stress-strain curve according to the strain of the shale sample; Acquiring total strain, young modulus, peak strain and peak stress of the shale sample according to the stress-strain curve; obtaining the data of a strain normalization maximum boundary, a strain normalization minimum boundary, a Young modulus normalization maximum boundary, a Young modulus normalization minimum boundary, a peak strain normalization maximum boundary and a peak strain normalization