Rock mechanical property evaluation method based on crack initiation-expansion-fracture network index and related device

Abstract

The invention discloses a rock mechanical property evaluation method based on crack initiation-expansion-fracture network indexes and a related device, and relates to the field of rock mechanics, the method comprises the following steps: respectively carrying out Brazilian splitting, fracture toughness and triaxial compression experiments on a target rock sample; obtaining a tensile strength value, a fracture toughness value and a mechanical deformation parameter of the target rock sample; calculating a crack initiation index, a crack propagation index and a crack network mode index based on the tensile strength value, the fracture toughness value and the mechanical deformation parameter; the crack initiation index is calculated based on tensile strength value normalization, the crack propagation index is calculated based on fracture toughness value normalization, and the crack network mode index is calculated based on mechanical deformation parameter normalization; and according to the crack initiation index, the crack propagation index and the crack network mode index, based on a preset evaluation standard, performing crack initiation-propagation-crack network ternary comprehensive quantitative evaluation on the mechanical properties of the target rock sample. The evaluation accuracy of the rock mechanical property can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rock mechanics, in particular to a rock mechanics property evaluation method based on cracking-expansion-fracture network index and related device. BACKGROUND

[0002] With the continuous growth of global oil and gas demand, the status of unconventional natural gas is increasingly prominent, among which shale gas as a representative is expected to become an important replacement energy in the future. However, shale reservoirs generally have strong anisotropy and tightness, complex lithology, and must be fractured to form industrial capacity. Reservoir fracturability is a key indicator for shale gas development. Brittle characteristics affect fracturing quality, but a single brittleness index is insufficient under complex geological conditions. The fracturability index that comprehensively considers stress factors such as brittleness and fracture toughness also has limitations, and it is difficult to realize logging interpretation and continuous characterization of heterogeneous reservoirs, and the evaluation results often contradict the fracturing effect. At present, there is still a lack of a unified and effective evaluation method for rock fracturability.

[0003] However, shale brittleness index and fracturability index are constructed based on the mathematical weight fitting of mechanical properties, fabric, reservoir environment and other factors, and can only effectively evaluate the fracturability of local intervals. Reservoir fracturability needs to pay more attention to fracture initiation (tensile strength), expansion capacity (fracture toughness) and expansion path (mechanical properties and stress conditions). Therefore, developing a novel, accurate and reliable rock mechanics property evaluation method has become an urgent need to promote the development of shale oil and gas engineering, and will also provide stronger theoretical and technical support for the entire rock engineering field. SUMMARY

[0004] The purpose of the present application is to provide a rock mechanics property evaluation method based on cracking-expansion-fracture network index and related device, which can improve the evaluation accuracy of rock mechanics properties.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions: In a first aspect, the present application provides a rock mechanics property evaluation method based on cracking-expansion-fracture network index, comprising: performing Brazilian splitting experiment, fracture toughness experiment and triaxial compression experiment on the target rock sample respectively to obtain the tensile strength value, fracture toughness value and mechanical deformation parameter of the target rock sample; based on the tensile strength value, fracture toughness value and mechanical deformation parameter, calculating a crack initiation index, a crack expansion index and a crack network mode index; wherein the crack initiation index is calculated based on the normalization of the tensile strength value, the crack expansion index is calculated based on the normalization of the fracture toughness value, and the crack network mode index is calculated based on the normalization of the mechanical deformation parameter; Based on the calculated crack initiation index, crack propagation index, and crack network pattern index, and based on the preset evaluation criteria, the mechanical properties of the target rock sample are comprehensively and quantitatively evaluated using a three-dimensional approach of crack initiation, propagation, and crack network.

[0006] Secondly, this application provides a rock mechanical property evaluation device based on the crack initiation-propagation-fracture network index, characterized in that it includes: The parameter acquisition module is used to perform Brazilian splitting test, fracture toughness test and triaxial compression test on the target rock sample to obtain the tensile strength value, fracture toughness value and mechanical deformation parameters of the target rock sample. The index calculation module is used to calculate the crack initiation index, crack propagation index, and crack network pattern index based on the tensile strength value, fracture toughness value, and mechanical deformation parameters. The crack initiation index is calculated based on the normalized tensile strength value, the crack propagation index is calculated based on the normalized fracture toughness value, and the crack network pattern index is calculated based on the normalized mechanical deformation parameters. The evaluation module is used to perform a three-dimensional quantitative evaluation of the mechanical properties of the target rock sample based on the calculated crack initiation index, crack propagation index, and crack network pattern index, and on a preset evaluation standard.

[0007] Thirdly, this application provides a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the rock mechanical property evaluation method based on the fracture initiation-propagation-fracture network index as described in any one of the above.

[0008] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements one of the rock mechanical property evaluation methods based on the crack initiation-propagation-fracture network index described above.

[0009] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application provides a method and related apparatus for evaluating the mechanical properties of rocks based on crack initiation-propagation-crack network indices. By conducting Brazilian splitting, fracture toughness and triaxial compression tests on target rock samples, key mechanical parameters are obtained, and crack initiation, propagation and network pattern indices are calculated based on these parameters. Finally, a comprehensive quantitative evaluation is performed according to preset standards, which effectively solves the problem that existing evaluation methods are difficult to accurately assess the mechanical properties of rocks. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is an application environment diagram of a rock mechanical property evaluation method based on the crack initiation-propagation-fracture network index in one embodiment of this application; Figure 2 A schematic flowchart illustrating a rock mechanical property evaluation method based on the crack initiation-propagation-fracture network index provided in an embodiment of this application; Figure 3 This is a diagram showing the tensile strength and FCI variation of each oil layer in the Gulong Shale case provided in an embodiment of this application; Figure 4 Fracture toughness of each oil layer provided in an embodiment of this application and FGI Change diagram; Figure 5 This is a schematic diagram of different deformation element crack network patterns provided in an embodiment of this application; Figure 6 The deformation modulus of different oil layers in well rc1 is provided in one embodiment of this application; Figure 7 A comparison diagram of the deformation modulus of different wells in the same oil layer provided as an embodiment of this application; Figure 8 The deformation modulus of each oil layer provided in an embodiment of this application and FMI Schematic diagram; Figure 9 A schematic diagram of a three-level evaluation framework for mechanical deformation initiation, propagation, and fracture network of the Gulong Shale provided in an embodiment of this application; Figure 10 Four mechanical model analysis diagrams of the shale in the Gulong area provided in one embodiment of this application; Figure 11 A schematic diagram of the functional modules of a rock mechanical property evaluation device based on the crack initiation-propagation-fracture network index provided in an embodiment of this application; Figure 12 This is a schematic diagram of the structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] Mechanical properties are the core determinant of fracturing effectiveness. Domestic and international research shows that the mechanical behavior of shale is closely related to its mineral composition, porosity, and bedding characteristics. Generally, higher porosity or more developed bedding results in lower compressive strength. Furthermore, as a typical anisotropic material, shale exhibits significant differences in its mechanical response across different load directions. To accurately describe this characteristic, domestic scholars have established various nonlinear and anisotropic mechanical models to simulate the deformation and failure of shale under different stress conditions, providing crucial theoretical support for hydraulic fracturing and drilling engineering design. Regarding fracture propagation, domestic scholars have systematically analyzed the fracture propagation path and mechanical behavior of shale under different fracturing modes through a combination of experiments and numerical simulations, and constructed corresponding predictive models, laying a theoretical foundation for optimizing fracturing schemes and improving oil recovery.

[0014] Therefore, the purpose of this application is to provide a method and related apparatus for evaluating rock mechanical properties based on the crack initiation-propagation-crack network index, which can improve the accuracy of rock mechanical property evaluation.

[0015] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] This application provides a method for evaluating rock mechanical properties based on the crack initiation-propagation-fracture network index, which can be applied to, for example... Figure 1 In the application environment shown, terminal 102 communicates with server 104 via a network. A data storage system can store the data that server 104 needs to process. The data storage system can be set up independently, integrated into server 104, or placed in the cloud or on another server.

[0017] The terminal 102 can be, but is not limited to, various desktop computers, laptops, smartphones, tablets, IoT devices, and portable wearable devices. IoT devices can include smart speakers, smart TVs, smart air conditioners, and smart in-vehicle devices. Portable wearable devices can include smartwatches, smart bracelets, and head-mounted devices. The server 104 can be implemented using a standalone server or a server cluster composed of multiple servers, or it can be a cloud server.

[0018] In one exemplary embodiment, such as Figure 2As shown, a method for evaluating rock mechanical properties based on the crack initiation-propagation-crack network index is provided. This method is executed by computer equipment, specifically by a terminal or server alone, or by both a terminal and a server. In this embodiment, the method is applied to... Figure 1 Taking server 104 as an example, the explanation includes the following steps 1 to 3. Wherein: Step 1: Perform Brazilian splitting test, fracture toughness test and triaxial compression test on the target rock sample to obtain the tensile strength value, fracture toughness value and mechanical deformation parameters of the target rock sample; Step 2: Based on the tensile strength value, fracture toughness value, and mechanical deformation parameters, calculate the crack initiation index, crack propagation index, and crack network pattern index; wherein, the crack initiation index is calculated based on the normalized tensile strength value, the crack propagation index is calculated based on the normalized fracture toughness value, and the crack network pattern index is calculated based on the normalized mechanical deformation parameters. Step 3: Based on the calculated crack initiation index, crack propagation index, and crack network pattern index, and using preset evaluation criteria, perform a three-dimensional comprehensive quantitative evaluation of the mechanical properties of the target rock sample, considering crack initiation, propagation, and crack network.

[0019] In this embodiment, the mechanical properties of the Gulong Shale in the test area are analyzed. Based on the Brazilian splitting test, the tensile strength of the target rock sample in the test area is obtained to quantitatively evaluate the crack initiation level of the rock; based on the fracture toughness test, the fracture toughness of the target rock sample in the test area is obtained to quantitatively evaluate the crack propagation of the rock; based on the triaxial compression test, the mechanical deformation modulus of the target rock sample is obtained. E F Quantitative evaluation of rock fracture network patterns yields parameters including compressive strength, cohesion, internal friction angle, stress-strain curve, Young's modulus, and Poisson's ratio.

[0020] In some embodiments, when performing steps 1-3, the specific steps may be as follows: Specifically, step 1 includes the following steps: S11: Obtain target rock samples from the test area and determine their bulk density; each rock sample has the same height and thickness. Under the same experimental conditions, rock mechanics experiments were conducted on 101 target rock samples from the test area. S12: Determine the tensile strength of the target rock sample based on the Brazilian splitting test; determine the fracture toughness of the target rock sample based on the fracture toughness test; determine the stress-strain curve of the target rock sample based on the triaxial compression test; and determine the mechanical parameters of the target rock sample using the rock stress-strain curve; the mechanical parameters include Young's modulus, Poisson's ratio, and compressive strength, etc.

[0021] Specifically, step 2 includes the following steps: The tensile strength of the target rock sample was determined based on the Brazilian splitting test, and a crack initiation index was established based on the tensile strength value. FCI .

[0022] The fracture toughness value of the target rock sample was determined based on fracture toughness experiments, and a crack propagation index was established based on the fracture toughness value. FGI .

[0023] The mechanical parameters of the target rock sample were determined based on triaxial compression tests. These parameters included Young's modulus, Poisson's ratio, and compressive strength. A coupled mechanical deformation modulus of Young's modulus and differential stress coefficient was constructed. E F And establish crack network model indicators FMI .

[0024] Among them, such as Figure 9 As shown, a crack initiation index is defined based on the tensile strength values ​​tested in each oil layer. FCI The calculation formula can be as follows: ; in, T The tensile strength of the oil layer containing the target rock sample in the test area. T max It is the maximum tensile strength in the oil reservoir of the test area. T min This represents the minimum tensile strength in the oil reservoir of the test area. A higher fracture initiation index indicates a higher level of fracture initiation relative to other oil reservoirs, and consequently, a lower tensile strength.

[0025] Based on the fracture toughness strength values ​​tested in each oil layer, a crack propagation index is defined. FGI The calculation formula can be as follows: ; in, K The fracture toughness of the oil layer containing the target rock sample in the test area. K max It has the highest fracture toughness in the oil reservoir of the test area. K min This represents the minimum fracture toughness in the oil reservoir of the test area. A larger fracture propagation index indicates a higher level of fracture propagation relative to other oil reservoirs, and correspondingly lower fracture toughness.

[0026] Mechanical deformation modulus based on tests of each oil layer E F Define shale fracture network model index FMI The calculation formula can be as follows: ; in, E F The mechanical deformation modulus of the oil layer containing the target rock sample in the test area. E Fmax It is the maximum mechanical deformation modulus in the oil layer of the test area. E Fmin It is the minimum mechanical deformation modulus in the oil layer of the test area.

[0027] Specifically, based on the study of the control mechanism of rock fracture modes by inherent mechanical properties and external stress conditions, a mechanical modulus describing the differences in rock fracture modes is constructed using Young's mode parameters and differential stress coefficients: ; The mechanical modulus based on the construction needs to satisfy three conditions, given by the following formula.

[0028] ; ; ; Using a trial function: ; in, The first principal stress, It is the third principal stress, and > , , k The differential stress coefficient is when Young's modulus E The larger the coefficient of differential stress, the greater the coefficient of differential stress. k The larger the value, the greater the mechanical modulus. E F The larger the mechanical modulus, the easier it is for a single high-angle crack to develop after the rock fractures, and the easier the crack propagates; conversely, the smaller the mechanical modulus, the easier it is for the rock to develop a single high-angle crack. E F Smaller mechanical modulus values ​​make it easier for dispersed, intersecting cracks to form a network, and the cracks are less likely to propagate; however, when the mechanical modulus is smaller... E F When the rock is very small, it undergoes plastic deformation and is not prone to cracking.

[0029] Specifically, step 3 includes the following steps: Based on crack initiation index FCI Shale is classified into high-tension and low-tension types. Average fracture initiation index. FCI Average >60% is called low-tension shale. Rocks are prone to cracks or micro-fractures under tension, which affect the reservoir channels and flow of oil and gas. FCIAverage If the rock has a density of less than 60%, it is called high-tension shale, and the formation of cracks will be suppressed.

[0030] Based on crack propagation index FGI Shale is classified into high-toughness and low-toughness categories. Average fracture propagation index. FGI Average Rocks with a toughness ratio greater than 60% are called low-toughness shale, and the cracks formed by rock fractures are prone to propagation. FGI Average Rocks with a crack thickness of less than 60% are called high-toughness shale. The propagation of cracks is effectively suppressed, and the rock can resist large external forces without excessive fracturing.

[0031] Mechanical deformation modulus obtained based on mechanical parameters at different strata E F Shale deformation characteristics are divided into three deformation modes (such as...) Figure 3 Deformation mode I is the deformation modulus. E F <10GPa, characterized by indistinct macroscopic rock fracturing, small crack aperture, and weak crack-forming ability; Deformation Mode II, with a deformation modulus between 10GPa and < E F <15GPa, under stress load, strain is easily dispersed, leading to dispersed fracture and the formation of complex low-angle fracture networks; Deformation mode III, deformation modulus E F >15GPa, strain concentration, easy to develop high-angle through-crack network cracks.

[0032] Based on the fracture network pattern index FMI Shale is classified into low-modulus, medium-modulus, and high-modulus types. FMI <30% is called low-modulus shale, which is not easy to form through-cracks or has a weak ability to form cracks; 30% < FMI <45%, it is called medium-modulus shale, strain is easily dispersed, it develops dispersed fractures, and it is easy to form complex fracture networks; FMI Rocks with a density greater than 45% are called high-modulus shale, which are prone to developing large-aperture through-cracks and have a strong crack-forming ability.

[0033] Finally, taking into account the three relative evaluation indicators, a three-dimensional index method for evaluating the mechanical properties of rocks was constructed to evaluate shale at different strata in the test area.

[0034] This application also provides an example, as follows: The Songliao Basin is one of the world's richest continental sandstone-type oil and gas basins. The Daqing Gulong shale oil is a typical continental shale oil, with oil flows observed from the edge to the center of the Gulong Depression in the Songliao Basin; high yields have been achieved in interbedded, layered, and pure shale types; the lower part of the Lower Cretaceous Qing 2 Member to the Qing 1 Member is oil-bearing throughout, indicating enormous shale oil resource potential. However, due to the complex bedding structure and mineral composition of the Gulong shale, and its low permeability, the fracture network may be uneven, leading to significant differences in fracturing effectiveness and affecting oil production and development efficiency.

[0035] Evaluation of the rock mechanical properties of shale in the Gulong area based on the three-dimensional index of initiation-propagation-fracture network.

[0036] First, rock samples were obtained from all oil layers in the Gulong area (Q1-Q9). Based on the core samples, triaxial compression tests, tensile strength tests, and fracture toughness tests were conducted. A total of 101 samples were tested, and key mechanical parameters such as Young's modulus, Poisson's ratio, compressive strength, tensile strength, and fracture toughness were obtained.

[0037] 1) Evaluation of crack initiation index: Tensile strength of rock is an important parameter describing crack initiation. The lower the tensile strength, the easier it is for cracks to initiate, and vice versa. Twenty-six Brazilian splitting tests were conducted on layers Q1 to Q9. The tensile strength was generally distributed between 2 MPa and 10.4 MPa, with significant differences in tensile strength distribution among different layers.

[0038] Based on crack initiation index FCI Evaluate the differences in relative crack initiation degree among layers Q1-Q9 (e.g.) Figure 3 The tensile strength distribution within layers Q1-Q3, Q6, and Q9 is uniform, but the strength is relatively low. FCI If the overall index is greater than 50%, cracking is likely to occur; Q4 ( FCI Between 0-80%), Q5 ( FCI Between 30% and 85% and Q8 FCI The tensile strength distribution of shale layers (between 40% and 80%) is dispersed, reflecting the significant heterogeneity of the shale. Average fracture initiation index... FCI Average >60%, is called low-tension shale, which is prone to cracking and is mainly distributed in the Q1-Q3, Q6, Q7 and Q9 layers; FCI Average <60% is called high-tension shale, which is not easy to crack and is mainly distributed in the Q4, Q5 and Q8 layers.

[0039] 2) Evaluation of crack propagation index: Fracture toughness is an important parameter characterizing the propagation of rock fractures; the lower the strength, the easier the fracture propagates, and vice versa. Twelve tests were conducted on the fracture toughness (perpendicular to bedding direction) of shale to obtain the fracture toughness of each well.

[0040] Based on crack propagation index FGI Evaluate the differences in relative crack initiation degree among layers Q1-Q9 ( Figure 4 The overall average crack propagation index of each layer FGI Average >60% of the rock is classified as low-toughness shale, meaning that fractures tend to propagate easily after initiation. In contrast, the average fracture propagation index of layers Q2 and Q4-Q9 is significantly higher. FGI Average >80%, Q1 ( FGI Average =62.38%) and Q3 ( FGI Average =60%) The average crack propagation index of the strata is relatively low.

[0041] 3) Evaluation of crack mode indicators: 3.1 Classification of Shale Mechanical Deformation Modes: Obtain the mechanical deformation modulus based on the mechanical parameters of different layers. E F Shale deformation characteristics can be divided into three deformation models ( Figure 5 Deformation mode I is the deformation modulus. E F <10GPa, characterized by indistinct macroscopic rock fracturing, small crack aperture, and weak crack-forming ability; Deformation Mode II, with a deformation modulus between 10GPa and < E F <15GPa, under stress load, strain is easily dispersed, leading to dispersed fracture and the formation of complex low-angle fracture networks; Deformation mode III, deformation modulus E F >15GPa, strain concentration, easy to develop high-angle through-crack network cracks.

[0042] 3.2 Differences in mechanical deformation modes of shale at different strata: Figure 6 The rock mechanical deformation characteristics of different strata in the same well (RC1) are described. From the figure, Q2 and Q7... E F Generally less than 10 GPa, fracture network model index FMI <30%, classified as low-modulus shale, is not prone to forming through-cracks or has weak crack-forming ability; Q9 E F Between 10GPa and 15GPa, 30% < FMI<45%, classified as intermediate-mode shale, exhibits easily dispersed strain, develops dispersed fractures, and readily forms complex fracture networks; for Q1, Q3, Q4, Q5, Q6, and Q8, E F Generally greater than 15 GPa, belonging to mechanical deformation mode III. FMI Rocks with a density greater than 45% are called high-modulus shale, which are prone to developing large-aperture through-cracks and have a strong crack-forming ability.

[0043] from Figure 7 It can be seen that different wells at the same stratum E F and FMI The distribution characteristics show significant differences, indicating that the study area is highly heterogeneous; the fracture development and deformation models I, II and III are for the Q1, Q3, Q5 and Q6 layers; the fracture development and deformation models I and II are for the Q2 layer; the fracture network models II and III are for the Q4 and Q9 layers; the fracture network models I and III are for the Q7 layer; and the fracture network model III is for the Q8 layer.

[0044] from Figure 8 It can be seen that by obtaining data from different wells at the same stratigraphic level... E F and FMI Average value, for horizontal comparison, for Q2 (low-modulus shale). FMI Average =16.69%<30%, E FAverage =6.61GPa<10GPa, belonging to deformation mode I, not easy to form through cracks or weak crack-forming ability; for Q1, Q3 and Q6 (intermediate mode shale). E FAverage Between 10 GPa and 15 GPa, FMI Average Between 30% and 45%, it belongs to deformation mode II and is prone to forming fracture network characteristics; for Q4, Q5, Q7, Q8, and Q9 (high-modulus shale). E FAverage >15GPa, FMI Average >45% belong to deformation mode III, which is prone to developing high-angle through cracks.

[0045] 4) Evaluation of the differences in mechanical properties among the oil layers of the Gulong Shale: like Figure 10 As shown, based on the mechanical properties of different wells and oil layers in the Gulong Shale, the mechanical properties of the Gulong Shale are divided into four types: low tensile-low toughness-low model (Q2), low tensile-low toughness-medium model (Q1, Q3, Q6), low tensile-low toughness-high model (Q7, Q9), and high tensile-low toughness-high model (Q4, Q5, Q8).

[0046] The Q2 layer (low tensile strength, low toughness, low model) is mostly developed in the shallow reservoir section of the Gulong area, with moderate bedding cementation. Low tensile strength and low fracture toughness together reduce the difficulty of fracture initiation and propagation. The low deformation modulus corresponds to mechanical deformation mode I, and the macroscopic fracture characteristics of the rock are not significant, often forming a network of microcracks with small apertures and poor connectivity. Enhancing the conductivity of microcracks and promoting competitive propagation of multiple fractures are needed to achieve the desired effect.

[0047] Layers Q1, Q3, and Q6 (low tensile-low toughness-medium model) exhibit shale fractures that are prone to initiation and propagation, with moderate deformation modulus (deformation mode II). They also show low-angle intersecting fractures and no obvious macroscopically penetrating main fractures. Development can induce the propagation of branch fractures, increasing the complexity of the fracture network.

[0048] The Q7 and Q9 layers (low tensile-low toughness-high model) are the core sections of high-quality shale reservoirs in the Gulong area. They are mostly thick-layered high-quality reservoirs with good intra-layer homogeneity. Fractures are easy to initiate and propagate, with high deformation modulus (deformation mode III). They are prone to forming large-aperture, high-angle continuous main fractures, accompanied by branch fractures, resulting in a high degree of fracture network complexity.

[0049] In the Q4, Q5, and Q8 layers (high tensile strength-low toughness-high model), the high tensile strength increases the difficulty of crack initiation (low crack density), and the low fracture toughness promotes rapid crack propagation after initiation; it has a high deformation modulus (deformation mode III), which easily forms longitudinally penetrating extended cracks.

[0050] The evaluation results of the Gulong Shale based on the ternary index model are consistent with the actual compressibility evaluation results. Imaging logging data shows that the natural fractures and foliation fractures in the Q1-Q3 layers are poorly developed and have extremely poor connectivity. The natural fractures are mainly concentrated in the Q5, Q7, Q8, and Q9 oil layers. The mineral composition of the Q1-Q9 layers shows a vertical differentiation characteristic of being viscous at the top and brittle at the bottom. Among them, the Q1-Q2 layers have strong plasticity and poor compressibility, while the Q8-Q9 layers have high brittleness and excellent fracture propagation, making them the optimal fracturing target layers in this area.

[0051] Based on the same inventive concept, this application also provides a rock mechanical property evaluation device based on the fracture initiation-propagation-fracture network index for implementing the aforementioned rock mechanical property evaluation method based on the fracture initiation-propagation-fracture network index. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of a rock mechanical property evaluation device based on the fracture initiation-propagation-fracture network index provided below can be found in the above-described limitations of the rock mechanical property evaluation method based on the fracture initiation-propagation-fracture network index, and will not be repeated here.

[0052] In one exemplary embodiment, such as Figure 11As shown, a rock mechanical property evaluation device based on the crack initiation-propagation-fracture network index is provided, comprising: The parameter acquisition module 1101 is used to perform Brazilian splitting test, fracture toughness test and triaxial compression test on the target rock sample to obtain the tensile strength value, fracture toughness value and mechanical deformation parameters of the target rock sample. The index calculation module 1102 is used to calculate the crack initiation index, crack propagation index and crack network pattern index based on the tensile strength value, fracture toughness value and mechanical deformation parameters; wherein, the crack initiation index is calculated based on the normalized tensile strength value, the crack propagation index is calculated based on the normalized fracture toughness value, and the crack network pattern index is calculated based on the normalized mechanical deformation parameters. Evaluation module 1103 is used to perform a three-dimensional comprehensive quantitative evaluation of the mechanical properties of the target rock sample based on the calculated crack initiation index, crack propagation index, and crack network pattern index, and on a preset evaluation standard.

[0053] In one exemplary embodiment, a computer device is provided, which may be a server or a terminal, and its internal structure diagram may be as follows. Figure 12 As shown, this computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operation of the operating system and computer programs in the non-volatile storage media. The database stores rock mechanical property evaluation results. The I / O interfaces are used for information exchange between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When executed by the processor, the computer program implements a rock mechanical property evaluation method based on the fracture initiation-propagation-fracture network index.

[0054] Those skilled in the art will understand that Figure 12 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0055] In one exemplary embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0056] In one exemplary embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0057] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0058] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0059] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0060] In summary, this application has the following technical effects: This application provides a method and related apparatus for evaluating the mechanical properties of rocks based on the fracture initiation-propagation-fracture network index. For rock samples from all oil layers (Q1-Q9) in the Gulong area, triaxial compression tests, tensile strength tests, and fracture toughness tests were conducted on core samples. A total of 101 samples were tested, obtaining key mechanical parameters such as Young's modulus, Poisson's ratio, compressive strength, tensile strength, and fracture toughness. A physical model of relative tensile strength index was established based on the tensile strength value, and a physical model of relative fracture toughness index was established based on the fracture toughness value. The mechanical parameters of the target rock samples were determined according to the triaxial compression test, and a coupled mechanical deformation modulus of Young's modulus and differential stress coefficient was established. E F A physical model for the relative mechanical deformation modulus index was established. Considering three relative evaluation indices, a ternary index method for evaluating the mechanical properties of shale was constructed, encompassing initiation, propagation, and fracture network, to evaluate the mechanical properties of shale in all oil layers of the Gulong area (Q1-Q9). This application addresses the shortcomings of existing evaluation methods and provides a new technical approach for the study of rock mechanical properties.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for evaluating rock mechanical properties based on a crack initiation-propagation-network indicator, characterized by, Comprising: Brazilian split experiment, fracture toughness experiment and triaxial compression experiment are performed on the target rock sample respectively to obtain the tensile strength value, fracture toughness value and mechanical deformation parameter of the target rock sample; Based on the tensile strength value, fracture toughness value and mechanical deformation parameter, a crack initiation index, a crack propagation index and a crack network mode index are calculated; wherein the crack initiation index is calculated based on the normalization of the tensile strength value, the crack propagation index is calculated based on the normalization of the fracture toughness value, and the crack network mode index is calculated based on the normalization of the mechanical deformation parameter; According to the calculated crack initiation index, crack propagation index and crack network mode index, based on the preset evaluation standard, the mechanical properties of the target rock sample are comprehensively quantitatively evaluated in terms of crack initiation, propagation and network.

2. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 1, characterized in that, The determination process of the mechanical deformation parameter is: The stress-strain curve of the target rock sample is determined according to the triaxial compression experiment; Based on the rock stress-strain curve, the mechanical deformation parameter of the target rock sample is determined; The mechanical deformation parameter includes Young's modulus, Poisson's ratio and compressive strength.

3. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 2, characterized in that, The calculation formula of the crack initiation index is: ； wherein, T is the tensile strength of the oil formation in which the target rock sample of the test area is located, T max is the maximum tensile strength of the oil formation in the test area, T min is the minimum tensile strength of the oil formation in the test area.

4. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 3, characterized in that, The calculation formula of the crack propagation index is: ； wherein, K Kmax is the maximum fracture toughness of the target rock sample in the test zone, K max Kmax is the maximum fracture toughness of the target rock sample in the test zone, K min Kmin is the minimum fracture toughness of the target rock sample in the test zone.

5. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 4, characterized in that, The calculation formula of the crack network mode index is: ； wherein, E F is the mechanical deformation modulus value of the oil layer in which the target rock sample in the test area is located, E Fmax is the maximum mechanical deformation modulus in the oil layer of the test area, E Fmin is the minimum mechanical deformation modulus in the oil layer of the test area.

6. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 5, characterized in that, The mechanical deformation modulus value of the target rock sample in the test area is determined according to the Young's modulus and the differential stress coefficient; the calculation formula of the mechanical deformation modulus value is: ； wherein, E E is the Young's modulus, k is the differential stress coefficient.

7. The method for evaluating rock mechanical properties based on the crack initiation-propagation-network indicator according to claim 6, characterized in that, The evaluation standard specifically includes: when the average fracture initiation index is FCI Average > 60%, the target rock sample is determined to be a low-tension shale; when the average fracture initiation index is FCI Average < 60%, the target rock sample is determined to be a high-tension shale; the average fracture initiation index is FCI Average an average of the fracture initiation indices for the pieces of the target rock sample. when the average fracture propagation indicator is FGI Average > 60%, the target rock sample is determined to be a low-toughness shale; when the average fracture propagation indicator is FGI Average < 60%, the target rock sample is determined to be a high-toughness shale; the average fracture propagation indicator is FGI Average an average of the fracture propagation indicators for the pieces of the target rock sample. When 30% < the crack network pattern index When the fracture network model index is less than 45%, the target rock sample is determined to be a medium-modulus shale; when the fracture network model index... When the content is >45%, the target rock sample is identified as high-modulus shale.

8. A rock mechanical property evaluation device based on a crack initiation-propagation-network indicator, characterized by, Comprising: The parameter acquisition module is configured to perform Brazilian split experiment, fracture toughness experiment and triaxial compression experiment on the target rock sample respectively to obtain the tensile strength value, fracture toughness value and mechanical deformation parameter of the target rock sample; The index calculation module is configured to calculate a crack initiation index, a crack propagation index and a crack network mode index based on the tensile strength value, fracture toughness value and mechanical deformation parameter; wherein the crack initiation index is calculated based on the normalization of the tensile strength value, the crack propagation index is calculated based on the normalization of the fracture toughness value, and the crack network mode index is calculated based on the normalization of the mechanical deformation parameter; The evaluation module is configured to perform comprehensive quantitative evaluation on the mechanical properties of the target rock sample in terms of crack initiation, propagation and network based on the preset evaluation standard according to the calculated crack initiation index, crack propagation index and crack network mode index.

9. A computer device comprising: A memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the rock mechanical property evaluation method based on crack initiation-propagation-crack network index according to any one of claims 1-7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the rock mechanical property evaluation method based on crack initiation-propagation-crack network index according to any one of claims 1-7.

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