Method and device for quantitatively evaluating brittleness of deep coal rock gas reservoir

Abstract

The invention discloses a method and a device for quantitatively evaluating the brittleness of a deep coal-rock gas reservoir. The method comprises the following steps: establishing a rock compressibility coefficient curve according to a rock core of a deep coal-rock gas target reservoir section; determining brittle-plastic critical confining pressure according to the rock compressibility coefficient, and establishing an offset curve according to the rock compressibility coefficient curve; calculating contribution values of rock brittleness under different confining pressures according to the offset curve; calculating a rock brittleness index according to the contribution value of rock brittleness; and determining an evaluation result of the deep coal rock gas reservoir by combining the rock brittleness index according to a preset grading standard.

Description

Technical Field

[0001] This article relates to the field of oil and gas engineering technology, and in particular to a method and apparatus for quantitatively evaluating the brittleness of deep coal and gas reservoirs. Background Technology

[0002] Unconventional shale gas and coal gas exploration have also made significant strides into deeper formations, with deep and ultra-deep natural gas exploration becoming the main battleground for energy exploration. The formation of complex fracture networks in reservoirs through large-scale volumetric fracturing is crucial for the efficient development of coal gas. Rock brittleness is key to the formation of fracture networks during volumetric fracturing, playing a critical role in optimizing and improving fracturing technology. Rock brittleness is influenced by factors such as rock mineral composition, rock mechanical properties, the degree of initial microfracture development, and reservoir depth. The relationships between these factors are complex, especially given the significant variations in rock mechanical parameters in deep coal gas reservoirs, which increases the difficulty of assessing rock brittleness in deep coal gas reservoirs.

[0003] Therefore, how to develop a brittleness evaluation method that assesses the influence of rock mechanical parameters on deep coal and gas reservoirs, and provide an important basis for evaluating the resource potential of deep coal and gas and reservoir stimulation, is an urgent problem to be solved. Summary of the Invention

[0004] This application provides a method and apparatus for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs. Based on the construction of an offset curve, this application can calculate the contribution value of rock brittleness under different confining pressures, and then determine the brittleness index of the rock to quantitatively evaluate the brittleness of deep coal-rock gas reservoirs.

[0005] In a first aspect, this application provides a method for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, the method comprising:

[0006] Establish rock compressibility curves based on core samples from target deep coal-rock gas reservoir sections;

[0007] The critical confining pressure for brittle-plastic compression is determined based on the rock compressibility coefficient curve, and an offset curve is established using the critical confining pressure for brittle-plastic compression.

[0008] The contribution value of rock brittleness under different confining pressures is calculated based on the aforementioned bias curve;

[0009] The rock brittleness index is calculated based on the contribution value of the rock brittleness.

[0010] The brittleness evaluation results of deep coal-gas reservoirs are determined based on the pre-set grading standards and the rock brittleness index.

[0011] Optionally, establishing the rock compressibility curve based on core samples from the target deep coal-gas reservoir section includes:

[0012] Cores were obtained from the target deep coal-rock gas reservoir section, and the obtained cores were standardized.

[0013] Compression tests were conducted on the standardized rock cores to obtain stress-strain curve data of the rock cores under different confining pressures.

[0014] Based on the stress-strain curve data of the rock core under different confining pressures, a rock compressibility coefficient curve was established.

[0015] Optionally, establishing the rock compressibility curve based on the stress-strain curve data of the rock core under different confining pressures includes:

[0016] Obtain stress-strain curve data of rock cores under different confining pressures;

[0017] For different confining pressures, the slope at the beginning of core compression and the slope when the core enters the yielding stage from the end of the elastic stage are determined according to the stress-strain curves.

[0018] Calculate the rock compressibility coefficient under different confining pressures based on the slope;

[0019] Based on multiple confining pressures and the corresponding compressibility coefficients, a rock compressibility coefficient curve is established.

[0020] Optionally, the rock compressibility coefficient is:

[0021] K im =K imax -K imin

[0022] In the above formula, K imax K represents the maximum slope of the elastic phase in the stress-strain curve. imin K represents the minimum slope of the elastic phase in the stress-strain curve. im is the rock compressibility coefficient.

[0023] Optionally, determining the brittle-plastic critical confining pressure based on the rock compressibility coefficient and establishing an offset curve using the rock compressibility coefficient includes:

[0024] Determine the critical confining pressure for a rock compressibility coefficient of zero based on the rock compressibility coefficient curve;

[0025] The critical confining pressure for brittle-plastic ductility is determined based on the rock compressibility coefficient.

[0026] An offset curve is established based on the determined critical confining pressure for brittle plasticity and the compressibility coefficient of the rock.

[0027] The bias curve is as follows:

[0028]

[0029] In the above formula, E im Less than or equal to E u E im E represents the confining pressure of the target formation. u For brittle-plastic critical confining pressure, K cm K is the rock compressibility coefficient when the confining pressure is zero. ig The contribution value to rock brittleness.

[0030] Optionally, calculating the rock brittleness index based on the contribution value of the rock brittleness includes:

[0031] Determine the relationship between the confining pressure of the target formation and the critical confining pressure of the brittle-plastic formation;

[0032] Based on the determined magnitude relationship, the rock brittleness index of the target stratum under the confining pressure is calculated by combining the influence value of rock mechanical parameters and the contribution value of rock brittleness.

[0033] Optionally, the rock mechanical parameters include: Young's modulus and Poisson's ratio;

[0034] The rock mechanics parameters affected by these parameters include Young's modulus and Poisson's ratio.

[0035] Optionally, the Young's modulus influence value is:

[0036]

[0037] The Poisson's ratio influence value is:

[0038]

[0039] In the above formula, E max E represents the maximum Young's modulus of the coal and rock in the block. min E represents the minimum Young's modulus of the coal and rock in the block. i E represents the Young's modulus of the coal and rock in the target block. iq V represents the influence value of Young's modulus. max V represents the maximum Poisson's ratio of the coal and rock in the block. min V represents the minimum Poisson's ratio for the coal and rock blocks. i V represents the Poisson's ratio of the coal and rock in the target block. iq This represents the influence of Poisson's ratio.

[0040] Optionally, the step of calculating the rock brittleness index under the confining pressure corresponding to the target stratum based on the determined magnitude relationship, combined with the influence value of rock mechanical parameters and the contribution value of rock brittleness, includes:

[0041] If the confining pressure of the target formation is less than or equal to the critical confining pressure of brittle plasticity E u The rock brittleness index under the confining pressure corresponding to the target stratum is:

[0042] K ip =K cm -K ig

[0043]

[0044] If the confining pressure of the target layer is greater than the critical confining pressure E for brittle-plastic strata u The rocks under confining pressure corresponding to the target stratum

[0045] The brittleness index is:

[0046]

[0047] In the above formula, BI is the fragility index, and K... ip To correct the bias value, E u The critical confining pressure is that of a brittle-plastic material.

[0048] E im It is the confining pressure of the target stratum.

[0049] Optionally, the grading criteria include:

[0050] When the brittleness index is 0.75 to 1.0, the reservoir brittleness level is Class I;

[0051] When the brittleness index is 0.50 to 0.75, the reservoir brittleness level is Class II;

[0052] When the brittleness index is 0.25 to 0.50, the reservoir brittleness level is Class III;

[0053] When the brittleness index is 0 to 0.25, the reservoir brittleness level is Class VI.

[0054] Secondly, embodiments of the present invention also provide an apparatus for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs. The apparatus includes a memory and a processor. The memory is used to store a program for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, and the processor is used to read and execute the program for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, and to execute the method described in any of the above embodiments.

[0055] Thirdly, embodiments of the present invention also provide a computer-readable storage medium storing a data processing program, wherein the data processing program is executed by a processor using any one of the above embodiments as a method for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs.

[0056] Compared with related technologies, this application provides a method and apparatus for quantitatively evaluating the brittleness of deep coal-gas reservoirs. The method includes: establishing a rock compressibility coefficient curve for a core sample from a target deep coal-gas reservoir section; determining the critical confining pressure at which the rock compressibility coefficient is zero, and establishing an offset curve using the critical confining pressure; calculating the contribution value of rock brittleness under different confining pressures based on the offset curve; calculating a rock brittleness index based on the contribution value of rock brittleness; and determining the evaluation result based on a grading standard and the rock brittleness index. This application, based on the constructed offset curve, can calculate the contribution value of rock brittleness under different confining pressures, and thus determine the rock brittleness index, thereby quantitatively evaluating the brittleness of deep coal-gas reservoirs.

[0057] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0058] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0059] Figure 1 This is a flowchart illustrating a method for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs according to an embodiment of this application.

[0060] Figure 2 This is a schematic diagram of an apparatus for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs according to an embodiment of this application;

[0061] Figure 3 Here are some exemplary embodiments of the compressibility curves of reservoir samples from well WS1 under different confining pressures.

[0062] Figure 4 The graph shows the compressibility coefficient curves of reservoir samples from well WS2 under different confining pressures in some exemplary embodiments. Detailed Implementation

[0063] This application describes several embodiments, but these descriptions are exemplary and not restrictive, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0064] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application may also be combined with any conventional features or elements to form a unique inventive scheme as defined by the claims. Any feature or element of any embodiment may also be combined with features or elements from other inventive schemes to form another unique inventive scheme as defined by the claims. Therefore, it should be understood that any feature shown and / or discussed in this application may be implemented individually or in any suitable combination. Therefore, the embodiments are not limited except by the limitations imposed by the appended claims and their equivalents. Furthermore, various modifications and changes may be made within the scope of the appended claims.

[0065] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation of the claims. Moreover, the claims concerning the method and / or process should not be limited to the steps performed in the written order, and those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0066] Domestic and international scholars have conducted extensive research on the evaluation and characterization of rock brittleness, and the main methods currently used are as follows:

[0067] (1) Zhao Zhihong et al. (Zhao Zhihong, Zhao Yuhang, Guo Jianchun et al. A method for evaluating the brittleness of shale based on mechanical heterogeneity, patent number: CN201910757761.4). This method determines the mineral component deviation coefficient based on the mineral composition of shale; determines the dynamic Young's modulus and dynamic Poisson's ratio of various minerals; and determines the estimated Young's modulus and estimated Poisson's ratio of the reservoir based on the dynamic Young's modulus and dynamic Poisson's ratio of various minerals using a component model. Through linear fitting, the corresponding fitted Young's modulus and fitted Poisson's ratio are obtained, and the brittleness coefficient is calculated.

[0068] (2) Yi Qinfan et al. (Yi Qinfan, Zhu Haihua, Zhang Benjian et al. A method for evaluating the brittleness of continental shale oil reservoirs, patent number: CN202210135674.7). This method mainly involves collecting rock samples from the target layer, conducting core mineral composition and composition tests and mineral crystal morphology analysis, and further defining a brittleness index to quantitatively evaluate the brittleness of shale oil reservoirs by comprehensively considering factors such as mineral content, crystal form and occurrence.

[0069] (3) Zhou Lihong et al. (Zhou Lihong, Liu Xuewei, Fu Daqi et al. Evaluation and application of factors affecting the fracturability of continental shale oil rocks - taking Kong 2 section of Cangdong Depression as an example [J]. China Petroleum Exploration, 2019, 24(5):670-678) By comprehensively considering the three factors of rock brittleness, natural fractures and geostress, a fracture network index model was established to conduct qualitative analysis and quantitative characterization of the typical continental shale oil rock fracturability of Kong 2 section of Cangdong Depression in Dagang exploration area, and further optimized the horizontal well perforation parameters and fracturing construction parameters.

[0070] The above method (1) takes into account the influence of mineral and mechanical properties, but its scope is limited. For different blocks, the standard needs to be changed, and it does not have good universality.

[0071] The above method (2) evaluates reservoir brittleness based solely on mineral composition and morphology.

[0072] The theoretical model established by the above method (3) has a large error, making it difficult to promote and apply, and its accuracy needs to be improved.

[0073] Since none of the three typical methods mentioned above take into account the characteristics of deep coal-rock gas reservoirs and fail to consider the brittleness evaluation under the influence of deep reservoir stress on rock mechanical parameters, the inventors have proposed a new brittleness evaluation method for deep coal-rock gas reservoirs based on analysis and research. This method provides an important basis for the evaluation of deep coal-rock gas resource potential and reservoir stimulation.

[0074] This invention provides a method for quantitatively evaluating the brittleness of deep coal and gas reservoirs, such as... Figure 1 As shown, the method includes steps S100-S140:

[0075] S100: Establish rock compressibility curves based on core samples from the target deep coal-rock gas reservoir section;

[0076] S110: Determine the critical confining pressure for brittle-plastic compression based on the rock compressibility coefficient, and establish an offset curve based on the rock compressibility coefficient curve;

[0077] S120: Calculate the contribution value of rock brittleness under different confining pressures based on the aforementioned bias curve;

[0078] S130: Calculate the rock brittleness index based on the contribution value of the rock brittleness;

[0079] S140: The evaluation results of deep coal and gas reservoirs are determined based on the pre-set grading standards and the rock brittleness index.

[0080] In one exemplary embodiment, establishing the rock compressibility curve of a core sample from a deep coal-gas target reservoir section includes:

[0081] The first step is to obtain core samples from the target deep coal-rock gas reservoir and to standardize the obtained core samples.

[0082] In this step, after obtaining the core of the target deep coal-gas reservoir section, the core is cut into rock samples of a certain size as required, such as standard rock samples with a diameter of 2.5cm and a length of 5cm. The standard rock samples are then placed in a 100℃ oven to dry to constant weight.

[0083] The second step is to conduct a compression test on the standardized rock core to obtain stress-strain curve data of the rock core under different confining pressures.

[0084] The third step is to obtain stress-strain curve data of the rock core under different confining pressures and establish the rock compressibility coefficient curve.

[0085] In one exemplary embodiment, obtaining stress-strain curve data of rock cores under different confining pressures and establishing a rock compressibility coefficient curve includes:

[0086] The first step is to obtain the stress curves of the rock core under different confining pressures;

[0087] The second step is to determine the slope when the core begins to compress and the slope when the core enters the yielding stage after the elastic stage, based on the stress curve, for different confining pressures.

[0088] The third step is to calculate the compressibility coefficient under different confining pressures based on the slope.

[0089] For different confining pressures, the calculation formulas for the slope at the beginning of core compression and the slope at the end of the elastic stage and the beginning of the yielding stage are determined based on the stress curves as follows:

[0090] K im =K imax -K imin (1)

[0091] Where: K imax K represents the maximum slope of the elastic phase in the stress-strain curve during the compression experiment. imin K represents the minimum slope of the elastic phase in the stress-strain curve during the compression experiment. im The compression factor is 1.

[0092] Step 4: Establish the rock compressibility curve based on multiple confining pressures and the corresponding compressibility coefficients.

[0093] Based on the third step, multiple pairs of confining pressures and their corresponding compressibility coefficients can be obtained. These pairs of confining pressures and their corresponding compressibility coefficients are then used to fit a rock compressibility coefficient curve, as shown below. Figure 3 and Figure 4 As shown.

[0094] In one exemplary embodiment, determining the critical confining pressure of brittle-plastic compression coefficient zero for the rock and establishing a bias curve using the critical confining pressure includes:

[0095] The first step is to determine the confining pressure corresponding to the zero compressibility of the rock based on the rock compressibility curve, and take this confining pressure as the critical confining pressure for brittle-plastic brittleness.

[0096] The second step is to calculate the contribution value of rock brittleness under the corresponding confining pressure based on the critical brittle-plastic confining pressure and the offset curve.

[0097] The bias curve is as follows:

[0098]

[0099] In the formula: E im E represents the confining pressure of the target layer. u For brittle-plastic critical confining pressure, K cm K is the core compressibility coefficient when the confining pressure is zero. ig The contribution value to rock brittleness.

[0100] In this example, only a few compressibility coefficients under confining pressures can be obtained experimentally, such as those under mechanical conditions like 5 MPa and 10 MPa. Because conducting experiments is time-consuming and yields limited data, only a few sets of data are available. However, by fitting an offset curve to these sets of mechanical experimental data, the compressibility coefficients under mechanical conditions like 12 MPa and 13 MPa, which were not previously tested, can be calculated. This offset curve represents the contribution of rock brittleness to the compressibility of the rock.

[0101] In one exemplary embodiment, the rock mechanical parameters include Young's modulus and Poisson's ratio; the influence values ​​of the rock mechanical parameters include Young's modulus influence value and Poisson's ratio influence value.

[0102] In one exemplary embodiment, the Young's modulus influence value is:

[0103]

[0104] The Poisson's ratio influence value is:

[0105]

[0106] In the above formula, E max E represents the maximum Young's modulus of the coal and rock in the block. min E represents the minimum Young's modulus of the coal and rock in the block. i E represents the Young's modulus of the coal and rock in the target block. iq V represents the influence value of Young's modulus. max V represents the maximum Poisson's ratio of the coal and rock in the block. min V represents the minimum Poisson's ratio for the coal and rock blocks. i V represents the Poisson's ratio of the coal and rock in the target block. iq The values ​​represent the influence of Poisson's ratio. Specifically, the maximum and minimum values ​​of Young's modulus, Poisson's ratio, and Young's modulus of the coal and rock in the block are obtained through core testing experiments conducted on the same block, yielding the maximum and minimum values ​​of Young's modulus and Poisson's ratio for the measured area.

[0107] In one exemplary embodiment, calculating the rock brittleness index based on the contribution value of the rock brittleness includes:

[0108] The first step is to determine the relationship between the confining pressure of the target stratum and the critical confining pressure of the brittle-plastic layer;

[0109] The second step is to calculate the rock brittleness index under confining pressure in the target stratum based on different relationships and the influence values ​​of mechanical parameters.

[0110] In one exemplary embodiment, calculating the rock brittleness index under confining pressure at the target stratum based on different relationships and in conjunction with the influence values ​​of mechanical parameters includes:

[0111] If the confining pressure of the target layer is less than or equal to E u The rock brittleness index is:

[0112] K ip =K cm -K ig (5)

[0113]

[0114] If the confining pressure at the target stratum is greater than E u The rock brittleness index is:

[0115]

[0116] Where: K ip The bias value is dimensionless; BI is the fragility index, which is also dimensionless.

[0117] In one exemplary embodiment, rock brittleness is classified into four levels based on the brittleness index, with higher levels indicating better compressibility of the reservoir rock, in the order I>II>III>VI. The classification criteria include:

[0118] When the brittleness index is 0.75 to 1.0, the reservoir brittleness level is Class I;

[0119] When the brittleness index is 0.50 to 0.75, the reservoir brittleness level is Class II;

[0120] When the brittleness index is 0.25 to 0.50, the reservoir brittleness level is Class III;

[0121] When the brittleness index is 0 to 0.25, the reservoir brittleness level is Class VI.

[0122] The quantitative evaluation method for the brittleness of deep coal and gas reservoirs implemented in this embodiment has the following technical advantages:

[0123] First, the influence of deep coal and gas rock mechanical parameters on rock brittleness was quantified, which is an improvement over conventional qualitative evaluation methods.

[0124] Second, by utilizing the contribution of mechanical parameters to rock brittleness and combining them with the critical confining pressure for brittleness and plasticity, a new rock brittleness index is defined to achieve quantitative evaluation and classification of the brittleness magnitude of the target evaluation reservoir under different confining pressure conditions.

[0125] Third, this method can quantitatively evaluate any reservoir section in a well. It only requires the test results of the actual rock mechanical parameters of the downhole core, eliminating the need for extensive and costly monitoring at the mine. This solves the problem of long testing cycles and high costs at the mine. Its calculation method is accurate and reliable, and it is also applicable to the evaluation of rock brittleness in similar deep coal and gas reservoirs. It has good application prospects and can provide technical support for the advancement of deep coal and gas reservoir stimulation technology.

[0126] Secondly, embodiments of the present invention also provide a device for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, such as... Figure 2As shown, the device includes a memory 200 and a processor 210; the memory is used to store a program for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, and the processor is used to read and execute the program for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs, and to execute the method described in any of the above embodiments.

[0127] Thirdly, embodiments of the present invention also provide a computer-readable storage medium storing a data processing program, wherein the data processing program is executed by a processor using any one of the above embodiments as a method for quantitatively evaluating the brittleness of deep coal-rock gas reservoirs.

[0128] Example 1

[0129] This example demonstrates a quantitative evaluation method for the brittleness of deep coal-rock gas reservoirs. The specific implementation process is as follows:

[0130] Step 1: Obtain downhole cores of the target deep coal-rock gas reservoir section, standardize the obtained cores, and then test their rock mechanical parameters.

[0131] Step 11: Core collection and core preparation;

[0132] Core samples were taken from the target reservoirs of wells WS1 and WS2 to produce five standard rock samples each with a diameter of 2.5 cm and a length of 5 cm. The standard rock samples were dried in an oven at 100℃ until constant weight. The rock samples were treated as parallel samples and numbered as R1-R5 for well WS1 and U1-U5 for well WS2.

[0133] Step 12: Obtain mechanical parameters;

[0134] Young's modulus and Poisson's ratio of rock cores were tested using a triaxial rock mechanics testing system.

[0135] The average Young's modulus of the rock samples from well WS1 was 2301 MPa, and the average Young's modulus of the rock samples from well WS2 was 1902 MPa.

[0136] The average Poisson's ratio of the rock samples from well WS1 was 0.246, and the average Poisson's ratio of the rock samples from well WS2 was 0.302.

[0137] Step 2: Obtain stress-strain curve data of rock cores under different confining pressures and calculate the rock compressibility coefficient;

[0138] Using the stress-strain curve of the triaxial rock mechanics testing system, the slope at the beginning of the core compression and the slope at the end of the elastic stage and the beginning of the yield stage were obtained to calculate the compression coefficient. The calculation was performed using formula (1), where R1-R5 and U1-U5 were ordered from largest to smallest, and the test confining pressures were 0 MPa, 10 MPa, 15 MPa, 20 MPa and 25 MPa. The results are shown in Table 1, the mechanical parameter table.

[0139] Table 1

[0140] Name 0 MPa 10 MPa 15 MPa 20 MPa 25 MPa WS1 compressibility factor 0.135 0.037 0.007 0 0 WS2 compressibility factor 0.112 0.025 0.008 0 0

[0141] Step 3: Determine the critical confining pressure for brittle-plastic materials where the compressibility coefficient is zero;

[0142] like Figure 3 and Figure 4 As shown, 20 MPa is the critical confining pressure for evaluating the brittle-plastic reservoirs in wells WS1 and WS2.

[0143] Step 4: Determine the bias curve;

[0144] The confining pressure when the compression coefficient is zero is called the critical confining pressure of brittle plastic. The confining pressure value at this time is recorded as 20MPa. The offset curve is calculated by combining the compression coefficient when the confining pressure is zero. Thus, the offset curve can be obtained by formula (2).

[0145] then,

[0146] The offset curve for well WS1 is as follows:

[0147]

[0148] The offset curve for well WS2 is as follows:

[0149]

[0150] Step 5: Determine the influence values ​​of mechanical parameters

[0151] Different mechanical parameters have different effects on the magnitude of brittleness. Here, Young's modulus and Poisson's ratio are chosen for calculation, where E max For 13000MPa, E min For 1000MPa, V max It is 0.7, V min It is 0.1.

[0152] Calculate the influence value of the mechanical parameters for each well based on the above mechanical parameters:

[0153] The Young's modulus influence value of well WS1 is 0.89, and the Poisson's ratio influence value is 0.24.

[0154] The Young's modulus influence value of well WS2 is 0.92, and the Poisson's ratio influence value is 0.34.

[0155] Step 6: Calculate the brittleness index;

[0156] The influence of each mechanical parameter on brittleness is allocated by using the bias curve and the influence value of mechanical parameters. The confining pressure of the reservoir in well WS1 is 22 MPa and the confining pressure of the reservoir in well WS2 is 17 MPa. The brittleness index of well WS1 is calculated using formula (7) and the brittleness index of well WS2 is calculated using formula (6).

[0157] The brittleness index of the reservoir section evaluated in well WS1 is 0.55, while that of well WS2 is 0.66. Therefore, the brittleness of the reservoir section evaluated in well WS2 is higher than that evaluated in well WS1.

[0158] Step 7: Evaluate reservoir brittleness according to the rock brittleness classification standard;

[0159] According to the rock brittleness classification standard, the rock brittleness of the reservoir section evaluated in wells WS1 and WS2 belongs to Class II.

[0160] In this example, firstly, downhole core samples from the target deep coal-gas reservoir section are obtained and standardized before testing their rock mechanical parameters. Secondly, stress-strain curves of the core samples under different confining pressures are acquired, the rock compressibility coefficient is calculated, and the influence of different confining pressures on the internal pore structure of the core samples is evaluated. Based on this, the critical confining pressure for brittle-plastic compressibility (where the compressibility coefficient is zero) is obtained, and an offset curve is further calculated to quantitatively characterize the contribution of different mechanical parameters to rock brittleness. Finally, using the contribution of mechanical parameters to rock brittleness and combining it with the critical confining pressure for brittle-plastic compressibility, a new rock brittleness index is defined to achieve a quantitative evaluation and classification of the brittleness magnitude of the target reservoir section under different confining pressures, thereby achieving the purpose of quantitative evaluation.

[0161] It will be understood by those skilled in the art that all or some of the steps, systems, or apparatuses disclosed above, and their functional modules / units, can be implemented as software, firmware, hardware, or suitable combinations thereof. In hardware implementations, the division between functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed collaboratively by several physical components. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit (ASIC). Such software may be distributed on a computer-readable medium, which may include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

Claims

1. A method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir, characterized by, The method comprises: establishing a rock compression coefficient curve according to a core of a deep coal rock gas target reservoir section; determining a brittle-plastic critical confining pressure according to the rock compression coefficient curve, and establishing a bias curve by using the brittle-plastic critical confining pressure; calculating a rock brittleness contribution value under different confining pressures according to the bias curve; calculating a rock brittleness index according to the rock brittleness contribution value; determining a deep coal rock gas reservoir brittleness evaluation result according to a pre-set grade division standard and the rock brittleness index.

2. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 1, characterized in that, The method of establishing a rock compression coefficient curve according to a core of a deep coal rock gas target reservoir section comprises: obtaining a core of a deep coal rock gas target reservoir section, and performing standardization processing on the obtained core; performing compression test experiments on the core after standardization processing to obtain stress-strain curve data of the core under different confining pressures; establishing a rock compression coefficient curve according to the stress-strain curve data of the core under different confining pressures.

3. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 2, characterized in that, The method of establishing a rock compression coefficient curve according to stress-strain curve data of a core under different confining pressures comprises: obtaining stress-strain curve data of the core under different confining pressures; determining, for different confining pressures, a slope at which the core starts to compress and a slope at which the core enters a yield stage from an end of an elastic stage according to the stress-strain curve; calculating rock compression coefficients corresponding to different confining pressures according to the slopes; establishing a rock compression coefficient curve according to a plurality of confining pressures and compression coefficients corresponding to the confining pressures.

4. The method of quantitatively evaluating brittleness of a deep coal rock gas reservoir according to claim 3, wherein the rock compression coefficient is:

5. The method of quantitatively evaluating brittleness of a deep coal rock gas reservoir according to claim 4, wherein the method of determining a brittle-plastic critical confining pressure according to the rock compression coefficient, and establishing a bias curve by using the brittle-plastic critical confining pressure comprises: K im = K imax - K imin In the above equation, K imax is the maximum value of the slope of the elastic stage in the stress-strain curve, K imin is the minimum value of the slope of the elastic stage in the stress-strain curve, K im is the compressibility of the rock. determining a brittle-plastic critical confining pressure corresponding to a rock compression coefficient of zero according to the rock compression coefficient curve; determining a brittle-plastic critical confining pressure according to the rock compression coefficient; establishing a bias curve according to the determined brittle-plastic critical confining pressure and the rock compression coefficient; wherein the bias curve is: The method of calculating a rock brittleness index according to the rock brittleness contribution value comprises: determining a size relationship between a confining pressure of a target formation and the brittle-plastic critical confining pressure; In the above formula, E im Less than or equal to E u E im E represents the confining pressure of the target formation. u For brittle-plastic critical confining pressure, K cm K is the rock compressibility coefficient when the confining pressure is zero. ig The contribution value to rock brittleness.

6. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 4, characterized in that, calculating a rock brittleness index under a confining pressure corresponding to the target formation according to the determined size relationship, a rock mechanics parameter influence value, and a rock brittleness contribution value. The rock mechanics parameter comprises: Young's modulus and Poisson's ratio; The rock mechanics parameter influence value comprises: Young's modulus influence value and Poisson's ratio influence value.

7. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 6, characterized in that, The Young's modulus influence value is: The Poisson's ratio influence value is:

8. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 7, characterized in that, 9. The method of quantitatively evaluating brittleness of a deep coal rock gas reservoir according to claim 8, wherein the method of calculating a rock brittleness index under a confining pressure corresponding to a target formation according to the determined size relationship, a rock mechanics parameter influence value, and a rock brittleness contribution value comprises: The grade division standard comprises: In the above formula, E max is the maximum value of the Young's modulus of the coal rock in the block, E min is the minimum value of the Young's modulus of the coal rock in the block, E i is the Young's modulus of the coal rock in the target block, E iq is the Young's modulus influence value, V max is the maximum value of the Poisson's ratio of the coal rock in the block, V min is the minimum value of the Poisson's ratio of the coal rock in the block, V i is the Poisson's ratio of the coal rock in the target block, V iq is the Poisson's ratio influence value. when a brittleness index is 0.75-1.0, a reservoir brittleness grade is I; when a brittleness index is 0.50-0.75, a reservoir brittleness grade is II; If the target formation confining pressure is less than or equal to the brittle-plastic critical confining pressure E u , the rock brittleness index under the confining pressure corresponding to the target formation is: K ip = K cm - K ig If the target layer position confining pressure is greater than the brittle plastic critical confining pressure E u , the rock brittleness index under the confining pressure corresponding to the target formation is: In the above equation, BI is the brittleness index, K ip is a correction bias value, E u is the brittle-plastic critical confining pressure, E im is the confining pressure of the target formation.

10. The method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to claim 1, characterized in that, ​ ​ ​ When the brittleness index is 0.25-0.50, the reservoir brittleness grade is III; When the brittleness index is 0-0.25, the reservoir brittleness grade is VI.

11. A device for quantitatively evaluating the brittleness of a deep coal rock gas reservoir, characterized by, The device comprises a memory and a processor; the memory is used for saving a program for quantitatively evaluating the brittleness of a deep coal rock gas reservoir, and the processor is used for reading and executing the program for quantitatively evaluating the brittleness of the deep coal rock gas reservoir and executing the method according to any one of claims 1-10. 12.A computer readable storage medium, wherein a data processing program is stored on the computer readable storage medium, and the data processing program is executed by a processor to perform the method for quantitatively evaluating the brittleness of a deep coal rock gas reservoir according to any one of claims 1-10.

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