Quantitative evaluation method for shale brittleness based on bedding characteristics

Abstract

The invention discloses a quantitative evaluation method for shale brittleness based on bedding characteristics, and relates to the field of petroleum and natural gas engineering, in particular to the quantitative evaluation method for the shale brittleness based on the bedding characteristics in the exploration and development process, and the quantitative evaluation method comprises the following steps: taking a rock sample from shale at a target layer to obtain the maximum Young modulus of a block; calculating a macroscopic brittleness index; processing the rock sample into a cuboid rock block for a nanoindentation experiment, calculating an interlayer heterogeneous coefficient between two corresponding adjacent probes according to mechanical parameters at the same transverse position between stratums so as to obtain a microscopic brittleness index, and calculating the total brittleness index of the rock by combining the microscopic brittleness index with the macroscopic brittleness index; microcosmic rock mechanics experimental data between different stratums of shale are tested on the basis of nanoindentation for the first time, heterogeneity between different stratums is quantitatively calculated, quantitative evaluation of shale rock microscopic brittleness is achieved, and compared with a conventional macroscopic evaluation method, quantitative evaluation is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas engineering, in particular to a quantitative evaluation method of shale brittleness based on bedding characteristics in the process of exploration and development. BACKGROUND

[0002] Large-scale horizontal well volume fracturing is a key technology to realize the scale benefit development of shale gas reservoirs, forms a complex multi-scale fracture network, creates a man-made gas reservoir in the reservoir, and changes the fluid seepage field, which is the core of shale gas volume development. Among them, the brittleness of rock is a key factor affecting whether a complex fracture network can be formed by volume fracturing, and is also the basis for volume fracturing optimization design. Compared with foreign shale gas reservoirs, through downhole coring, it is found that the shale has strong heterogeneity, complex mineral composition, and obvious bedding development. At present, the method for evaluating rock brittleness mainly relies on quantitative calculation of mineral composition and rock mechanical parameters.

[0003] (1) Patent application No. 201910757761.4, a shale brittleness evaluation method based on mechanical heterogeneity, which determines the mineral component deviation coefficient according to the mineral composition of shale; determines the dynamic Young's modulus and dynamic Poisson's ratio of various minerals; according to the dynamic Young's modulus and dynamic Poisson's ratio of various minerals, the estimated Young's modulus and estimated Poisson's ratio of the reservoir are determined by using the component model, and the linear fitting is obtained by linear fitting. The linear fitting formula for calculating the corresponding fitting Young's modulus and fitting Poisson's ratio from the dynamic Young's modulus and dynamic Poisson's ratio, and the brittleness coefficient is calculated.

[0004] (2) Patent application No. 202510063185.9, a method, device, equipment, medium and product for evaluating the brittleness of unconventional oil and gas reservoirs, which obtains stress-strain data of a target unconventional oil and gas reservoir core sample obtained in a uniaxial compression or triaxial compression test; determines the peak strain of the target unconventional oil and gas reservoir core sample under uniaxial compression or triaxial compression according to the stress-strain data; determines the peak strain of the target unconventional oil and gas reservoir core sample based on the peak strain; and determines the rock brittleness value of the target unconventional oil and gas reservoir based on the peak strain and the peak total energy.

[0005] (3) Patent application No. 202310971924.5, a shale brittleness evaluation method and device based on element analysis, which studies the relationship between minerals and element content, finds out the sensitive elements of different minerals, establishes an element and mineral conversion model, calculates the brittleness index, and classifies according to the shale gas reservoir brittleness classification standard.

[0006] The research results have not yet evaluated the shale gas reservoir rock brittleness from the comprehensive influence of the bedding characteristics and the bedding rock mechanics characteristics from the macroscopic and microscopic angles of the brittleness influence of the shale gas reservoir. Therefore, it is necessary to propose a new method, which is consistent with the bedding development characteristics of the shale gas reservoir, and the evaluation result is more applicable, and further provides a basis for the reservoir reconstruction scheme design. SUMMARY

[0007] The purpose of the present application is to provide a bedding characteristic based quantitative evaluation method of shale brittleness, which overcomes the disadvantages that only the rock macroscopic mechanical parameters or the mineral composition evaluation are used without considering the microscopic mechanical difference influence between the beddings which are the core factors influencing the shale brittleness.

[0008] The bedding characteristic based quantitative evaluation method of shale brittleness comprises the following steps: 1) The target layer shale is sampled, the mechanical parameters of the rock sample are measured, the rock mechanics parameter Young's mode basic data of the target layer are collected, the maximum Young's modulus of the block is obtained, and the macroscopic brittleness index is calculated; 2) The rock sample is processed into a cuboid rock block for nanoindentation experiment, wherein the probe arrangement of the nanoindentation experiment follows the experiment with the bedding as the interface, the microscopic mechanical parameters of different positions in different beddings are obtained, the mechanical difference between the beddings is characterized, then the interlayer heterogeneity coefficient between the corresponding adjacent two probes is calculated according to the mechanical parameters of the same horizontal position between the beddings, and the overall interlayer heterogeneity coefficient of the adjacent two layers is further calculated; 3) The overall interlayer heterogeneity coefficient between different beddings is obtained from the overall interlayer heterogeneity coefficient of the adjacent two layers, and the microscopic brittleness index is obtained, the total brittleness index of the rock is calculated by combining the macroscopic brittleness index, and the rock brittleness grade is divided according to the value, when 0<total brittleness index≤0.30, the brittleness is poor, and the grade is III type reservoir; when 0.30<total brittleness index≤0.60, the brittleness is moderate, and the grade is II type reservoir; when 0.60<total brittleness index≤1, the brittleness is good, and the grade is I type reservoir.

[0009] Preferably, the obtained rock sample is cored in step 1), and is made into a standard cylindrical core; Then, the mechanical parameter measurement of the standard cylindrical core is carried out, specifically: the triaxial rock mechanics test system is used to measure the Young's modulus of the core; The macroscopic brittleness index is calculated by using the measured core Young's modulus and the maximum Young's modulus of the block, and the calculation formula is as follows: In the formula, E s is the measured Young's modulus, MPa; E maxB1 is a macroscopic brittleness index, dimensionless.

[0010] Preferably, the rock sample is sampled and made into a cuboid rock block in step 2), wherein the cutting direction is one side parallel to the bedding direction and the other side perpendicular to the bedding direction; The cuboid rock block is subjected to nanoindentation experiment, in which a plurality of probes are arranged at the same interval in the same bedding to measure the Young's modulus of the target position, and a corresponding number of probes are arranged according to the number of beddings in the direction perpendicular to the bedding; The Young's modulus of the same transverse position of the adjacent two beddings is calculated to obtain the interlayer heterogeneity coefficient, and the calculation formula is as follows: In the formula, Eij is the Young's modulus of the i-th row and the j-th column, MPa, wherein i is the transverse direction, j is the vertical direction, and m ij is the Young's modulus of the i-th row and the j-th column, MPa, wherein i is the transverse direction, j is the vertical direction, and m ij is the interlayer heterogeneity coefficient, dimensionless.

[0011] Preferably, the calculation formula of the overall interlayer heterogeneity coefficient is as follows: In the formula, K is the overall interlayer heterogeneity coefficient corresponding to adjacent layers, dimensionless. j is the overall interlayer heterogeneity coefficient corresponding to adjacent layers, dimensionless.

[0012] Preferably, the calculation formula of the micro-brittleness index is as follows: In the formula, G is the average interlayer heterogeneity coefficient, dimensionless; B2 is the micro-brittleness index, dimensionless.

[0013] Preferably, the calculation formula of the total brittleness index is as follows: In the formula, BI is the total brittleness index, dimensionless.

[0014] Compared with the prior art, the present application has the following effects: The present application firstly innovatively calculates the heterogeneity between different beddings based on the micro-rock mechanics experimental data of shale between different beddings obtained by nanoindentation test, realizes quantitative evaluation of the micro-brittleness of shale rock, and further improves the conventional macroscopic evaluation method.

[0015] Compared with the conventional evaluation method, the present application overcomes the disadvantages of only using the overall macro-mechanical parameters or mineral composition for evaluation without considering the influence of the core factor of the micro-mechanical difference between the beddings on the brittleness of shale.

[0016] The present application evaluates the overall brittleness of rock from the perspective of the difference between the microscopic mechanical characteristics and the macroscopic mechanical characteristics of the bedding. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Schematic diagram for measuring the Young's modulus position of the nanoindentation experiment probe.

[0018] Figure 2 Comparison diagram of interlayer heterogeneity coefficients between different beddings. DETAILED DESCRIPTION

[0019] The present application will be specifically described below in combination with examples. The present application is a quantitative evaluation method for shale brittleness based on the characteristics of beddings, which comprises the following steps: 1. W is a shale gas reservoir development block, the main development layer is W1, and the downhole coring work is carried out at the target layer. The mechanical parameters of the rock sample are measured, and the macroscopic brittleness index is calculated to represent the overall brittleness. The specific content is as follows: (1) Standard core production: the obtained rock sample is cored to produce a standard cylindrical core with a diameter of 2.5 cm and a height of 5 cm, which is named XL-1-1. (2) Measurement of mechanical parameters: the triaxial rock mechanics test system is used to measure the Young's modulus of the core, and the measured Young's modulus of the core is 34108 MPa. (3) Macroscopic brittleness index: the measured Young's modulus of the core is calculated with the maximum Young's modulus of the block, and the maximum Young's modulus of the core in the block is the maximum Young's modulus of the core in the block where the coring well is located. In the formula: E s is the measured Young's modulus, MPa; E max is the maximum Young's modulus of the block, MPa; B1 is the macroscopic brittleness index, dimensionless; and the maximum Young's modulus of the rock sample in the block is 47198 MPa, and the value of the macroscopic brittleness index is 0.723.

[0020] 2. The rock sample is processed into a square rock block for nanoindentation experiment. The arrangement of the nanoindentation probe follows the experiment with the bedding as the dividing surface. The obtained microscopic mechanical parameters are the mechanical parameters of the rock sample at the same spacing position in the bedding. The mechanical performance between the layers is compared, and then the mechanical parameters of the adjacent rock samples at the same horizontal position between the layers are calculated to obtain the interlayer heterogeneity coefficient of the adjacent two layers. The specific content is as follows: (1) Rock sample production: the obtained rock sample is sampled to produce a rock block with a size of 6mm×6mm×4mm. The cutting direction is that one side is parallel to the bedding direction and the other side is perpendicular to the bedding direction. The rock sample is named XL-2-1. (2) Nanoindentation experiment: In the experiment, a total of 10 probes were arranged at the same spacing within the same stratum to measure the Young's modulus at the target location. The probes were set according to the number of strata in the direction perpendicular to the stratum. Figure 1 As shown, the rock sample prepared in this experiment has 12 bedding layers. (3) Interlayer heterogeneity coefficient: The Young's modulus at the same transverse position of two adjacent bedding layers is calculated. The Young's modulus values ​​at probes 1 to 6 of bedding layers are shown in Table 1, and the Young's modulus values ​​at probes 7 to 12 of bedding layers are shown in Table 2. The interlayer heterogeneity coefficient at each location is calculated according to formula (2) as shown in Table 3. In the formula: E ij Let m be the Young's modulus in the i-th row and j-th column, in MPa, where i is the transverse direction, representing different stratification directions, and j is the longitudinal direction, which is within the same stratification; ij is the interlayer heterogeneity coefficient, which is dimensionless; Table 1. Measurement data of Young's modulus at different locations in strata 1-6. Lamination 1 (MPa) Lamination 2 (MPa) Lamination 3 (MPa) Lamination 4 (MPa) Lamination 5 (MPa) Lamination 6 (MPa) 34576 36272 33056 33054 37713 32170 34534 36072 33039 33613 37697 32169 34291 36053 33147 33664 38059 32269 34629 36202 33470 33840 37650 32420 34043 36023 32537 33953 38048 32540 34935 36251 33388 33456 37647 32239 34212 36040 33439 33548 38178 32855 34332 35563 33362 33254 37992 32878 34392 36022 33268 33628 37847 32993 34972 35786 33492 33140 37772 32800 Table 2. Measurement data of Young's modulus at different locations in strata 7-12. Table 3. Coefficients of interlayer heterogeneity at various locations. 3. Overall interlayer heterogeneity coefficient: Using the interlayer heterogeneity coefficient calculation and combined with formula (3), the interlayer heterogeneity coefficient between each layer is calculated: Where: K j This is the overall interlayer heterogeneity coefficient corresponding to adjacent layers, dimensionless; the calculation results are attached. Figure 2 As shown.

[0021] The micro-brittleness index is obtained from the interlayer heterogeneity coefficient of each adjacent layer, and the total brittleness index is obtained by combining it with the macro-brittleness index, thereby achieving the purpose of quantitative evaluation. The specific content is as follows: (1) Microscopic brittleness index: It is obtained by using the interlayer heterogeneity coefficient and combined with formula (4) to calculate that the average interlayer heterogeneity coefficient is 0.119; G is the interlayer average heterogeneity coefficient, which is dimensionless; Combining formula (5), the micro-brittleness index is calculated to be 0.664; In the formula: B2 is the micro-brittleness index, which is dimensionless.

[0022] (2) Total brittleness index: the macroscopic brittleness index and the microscopic brittleness index are combined to calculate, and the total brittleness index is 0.693 according to formula (6); In the formula, BI is the total brittleness index, and the unit is dimensionless.

[0023] According to the value, the brittleness grade of the rock is divided, the main development layer W1 reservoir of the shale gas reservoir development block W is good in brittleness, and the grade is a class I reservoir.

[0024] The application is described in detail through the embodiments, the embodiments are only preferred embodiments of the application, do not limit the application, and are not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, and the changes and simple changes made by the person skilled in the art without departing from the technical idea and scope of the application are all within the protection scope of the technical scheme of the application.

Claims

1. A method for quantitatively evaluating shale brittleness based on stratigraphic features, characterized in that, The method comprises the following steps: 1) taking rock samples from the target layer, measuring the mechanical parameters of the rock samples by coring, collecting the basic data of the rock mechanics parameters of the target layer, obtaining the maximum Young's modulus of the block, and calculating the macroscopic brittleness index; 2) processing the rock samples into cuboid-shaped rock blocks for nanoindentation experiments, wherein the probe arrangement for nanoindentation follows the layering as the boundary surface for the experiment, the micro-mechanical parameters of different positions in different layerings are obtained to represent the mechanical differences between the layerings, then the interlayer heterogeneity coefficient between the corresponding adjacent two probes is calculated according to the mechanical parameters of the same horizontal position between the layerings, and the overall interlayer heterogeneity coefficient of the adjacent two layers is further calculated; 3) obtaining the overall interlayer heterogeneity coefficient between different layerings from the overall interlayer heterogeneity coefficient of the adjacent two layers to obtain the micro-brittleness index, calculating the total brittleness index of the rock by combining the macro-brittleness index and the micro-brittleness index, and dividing the brittleness grade of the rock according to the value, when 0<total brittleness index≤0.30, the brittleness is poor, and the grade is III type reservoir; when 0.30<total brittleness index≤0.60, the brittleness is moderate, and the grade is II type reservoir; when 0.60<total brittleness index≤1, the brittleness is good, and the grade is I type reservoir.

2. The method of quantitative evaluation of shale brittleness based on stratigraphic features according to claim 1, characterized in that, In step 1), the obtained rock sample is cored to be a standard cylindrical core; Then, the mechanical parameters of the standard cylindrical core are measured, specifically: the triaxial rock mechanics test system is used to measure the Young's modulus of the core; The macro-brittleness index is calculated by using the measured core Young's modulus and the maximum Young's modulus of the block, and the calculation formula is as follows: wherein: E s E is the measured Young's modulus, MPa; E max B1 is the macroscopic brittleness index, dimensionless.

3. The method of claim 2, wherein the method further comprises: In step 2), the obtained rock sample is sampled to be a cuboid-shaped rock block, wherein the cutting direction is that one side is parallel to the bedding direction and the other side is perpendicular to the bedding direction; The cuboid-shaped rock block is subjected to nanoindentation experiments, wherein in the experiments, multiple probes are arranged at the same interval in the same layering to measure the Young's modulus of the target position, and in the direction perpendicular to the layering, a corresponding number of probes are arranged according to the number of layerings; The interlayer heterogeneity coefficient is calculated by measuring the Young's modulus of the same horizontal position of the adjacent two layerings, and the calculation formula is as follows: wherein: E ij Eijis the Young's modulus, MPa, for the ith layer in the jth direction, where i is the cross directional, different layering direction, and j is the longitudinal direction, which is within the same layering; m ij is the interlayer heterogeneity coefficient, dimensionless.

4. The method of claim 3, wherein the method is characterized by, The calculation formula of the overall interlayer heterogeneity coefficient is as follows: wherein: K j is the overall interlayer heterogeneity coefficient corresponding to the adjacent layers, dimensionless.

5. The method of quantitative evaluation of shale brittleness based on stratigraphic features according to claim 4, characterized in that, The calculation formula of the micro-brittleness index is as follows: In the formula, G is the average interlayer heterogeneity coefficient, dimensionless; In the formula, B2 is the micro-brittleness index, dimensionless.

6. The method of quantitative evaluation of shale brittleness based on stratigraphic features according to claim 5, characterized in that, The calculation formula of the total brittleness index is as follows: In the formula, BI is the total brittleness index, dimensionless.

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