Reservoir fracturing transformation fracture and stress joint inversion and effect evaluation method and system

Abstract

The invention discloses a reservoir fracturing transformation fracture and stress joint inversion and effect evaluation method and system, and the method comprises the following steps: carrying out the real-time micro-seismic monitoring, and obtaining a micro-seismic data set; according to the obtained micro-seismic data set, fracture seismic source mechanism inversion is carried out, fracture pyrogenic dynamic fracture parameters of the reservoir space are obtained, the fracture rupture moment tensor is calculated through the dynamic fracture parameters, and the fracture rupture type is recognized according to the positive and negative characteristics of the fracture rupture moment tensor; carrying out stress inversion on the shear fracture through a fracture stress inversion method assumed by Bott for the shear fracture; carrying out stress inversion on the fractures of tension and compression fracture types by utilizing a corrected fracture stress inversion method; constructing a fracture instability coefficient model, and analyzing the instability of the fracture according to the seismic source of fracture and stress inversion data; an evaluation model of the fracture reservoir transformation effect is established through a multi-dimensional target reservoir transformation effect evaluation method, and the reservoir fracture transformation effect is quantitatively evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir fracturing and transformation, and in particular to a method and system for joint inversion and effect evaluation of reservoir fracturing and transformation cracks and stresses. Background Art

[0002] In oil and gas production, hot dry rock extraction, development of unconventional oil and gas reservoirs such as shale gas and tight oil, and carbon dioxide mineralization and storage, hydraulic fracturing is a key method for improving reservoir conductivity. Under the geological conditions of reservoir fracturing, the subsurface rock often contains a variety of fracture networks. Fracture structural characteristics, such as the source parameters of newly formed fracture surfaces, stress field distribution, main fracture surface occurrence, and the direction and shape of the principal stress axis, have a significant impact on the evaluation of reservoir fracturing.

[0003] Due to methodological limitations and insufficient data integration, existing technologies struggle to accurately assess the effectiveness of hydraulic fracturing to transform fractures. For example, patent CN117468908A proposes a new method for pressure-driven enhanced oil recovery in low- to medium-permeability reservoirs. The fracture formation process is slowed down, resulting in long fractures that effectively expand in volume. Patent CN117633409A proposes a method for calculating the seepage parameters of a shale oil and gas reservoir fracture network, which significantly improves the efficiency of calculating seepage parameters. Patent CN116698577A proposes a quantitative evaluation method for the potential for complex fracture networks formed by volumetric fracturing in shale oil reservoirs. This method quantitatively evaluates rock heterogeneity and the degree of initial microfracture development by calculating the differences in minerals within the bedding and the degree of bedding fragmentation. These fracture characterization and evaluation methods characterize the fracture development structure from a certain perspective, but fail to characterize the fracture structure from a stress perspective and quantitatively evaluate the permeability-enhancing fracturing effect from multiple dimensions. In addition, the qualitative analysis based on the energy or location of microseismic events does not distinguish between tension, shear and compression fracture mechanisms, resulting in an identification error of more than 25% in complex fracture networks, which cannot reflect the dynamic coupling effect of multiple types of fractures during the fracturing process. Existing stress inversion models mostly use a single fracture assumption (such as the Bott assumption that only applies to shear fracture). The inversion results in the tension-dominated area deviate from the measured data by 30%, resulting in significant errors in the direction of the principal stress. In addition, the existing evaluation model relies on the proportion of fracture volume and lacks a quantitative analysis of the coupling effect of fracture stability, principal stress direction and fracture extension, resulting in insufficient correlation between the evaluation results and the measured production capacity (R 2 <0.6), particularly in regions of high stress deviation (θ>30°), where directional suppression is neglected and distortion occurs. Microseismic monitoring data are often limited to spatial fracture localization, failing to fully explore the synergistic relationship between moment tensor decomposition results and the stress field. This results in insufficient dynamic and comprehensive analysis of reservoir stimulation effects. These issues lead to a lack of reliable basis for optimizing fracturing schemes. A comprehensive method is urgently needed to integrate multi-source data, accurately invert fracture types and stress field parameters, and dynamically quantify the fracturing effect. Summary of the Invention

[0004] In response to the problems and needs raised above, this solution proposes a method and system for joint inversion of fractures and stresses in reservoir fracturing and evaluation of their effects. By adopting the following technical features, it is able to achieve the above technical objectives and bring about multiple other technical effects.

[0005] One object of the present invention is to provide a method for joint inversion and effect evaluation of reservoir fracturing and stress, comprising the following steps:

[0006] S10: Exploring geological reservoir information, evaluating and determining target reservoirs for fracturing, deploying an acoustic emission sensor monitoring system, injecting fracturing fluid from injection wells, and conducting real-time microseismic monitoring to obtain microseismic data sets;

[0007] S20: performing fracture focal mechanism inversion based on the acquired microseismic data set to obtain dynamic fracture parameters derived from fracturing in the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension direction;

[0008] S30: Based on the identification method of microseismic-derived fractures derived from reservoir fracturing, the fracture rupture moment tensor is calculated using dynamic fracture parameters, and the fracture rupture type is identified based on the positive and negative sign of the fracture rupture moment tensor. The fracture types include tension, compression, and shear fractures.

[0009] S40: Based on the earthquake source and stress inversion method of reservoir fracturing, different types of fractures are processed. For shear fractures, stress inversion is performed on shear fractures using the fracture stress inversion method based on the Bott hypothesis. For tension and compression fractures, stress inversion is performed on tension and compression fractures using the modified fracture stress inversion method to obtain the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface.

[0010] S50: Construct a fracture instability coefficient model, analyze fracture instability based on fracture rupture source and stress inversion data, and identify the fracture surface state after reservoir fracturing based on fracture stress inversion results;

[0011] S60: Based on the instability coefficient fracture tendency and the fracturing stimulation stress and fracture inversion parameters, a multi-dimensional target reservoir stimulation effect evaluation method is used to establish an evaluation model for the fracture reservoir stimulation effect, and quantitatively evaluate the reservoir fracturing stimulation effect.

[0012] In addition, the reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method and system according to the present invention may also have the following technical features:

[0013] In one example of the present invention, in step S20, performing fracture focal mechanism inversion based on the acquired microseismic data set to obtain the fracturing-derived active fracture parameters of the reservoir space includes the following steps:

[0014] S21: Determine the dynamic crack characterization tensor: The dynamic crack parameters are represented by the dynamic crack source characterization tensor ψ. The specific formula is as follows:

[0015]

[0016] Where, ψ ij is the element of the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack;

[0017] S22: Solve the eigenvalue of the dynamic crack characterization tensor and obtain the three eigenvalues of the tensor ψ. The calculation formula is as follows:

[0018]

[0019] Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor ψ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface;

[0020] S23; Solving the dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue ψ2 of the tensor ψ=0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows:

[0021]

[0022] Where ψ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle;

[0023] S24: Determine the relationship between dynamic crack parameters and moment tensor: The dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in isotropic homogeneous materials:

[0024] M kl =ψ ij C ijkl =λδ kl ψii +2μψ kl

[0025] Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

[0026] In one example of the present invention, in step S30, the specific steps of identifying the fracture type according to the positive or negative value of the fracture moment tensor are as follows:

[0027] S31: Determine the ISO, CLVD, and DC components of the moment tensor: After obtaining the moment tensor M, eigenvalue it to obtain the eigenvalue, and decompose it into ISO, CLVD, and DC components, which represent the isotropic, axial tension, and shear rupture components of the earthquake source, respectively. The sum of the CLVD and DC components is called the deviatoric moment tensor M*.

[0028] S32: Decompose the moment tensor to obtain the percentage of each component of the moment tensor M, which is expressed as follows:

[0029]

[0030] Where M |max| is the maximum absolute value of the eigenvalue of the moment tensor M, M |max| =max(|M1|,|M2|,|M3|); the parameter ε is a parameter that measures the size of the CLVD component relative to the DC component. |M * | max 、|M * | min They represent the maximum and minimum absolute values of the eigenvalues of the partial moment tensor M*;

[0031] S33: Identify the fracture type based on the percentage of each component of the moment tensor M:

[0032] c DC >0, the rupture belongs to tensile rupture;

[0033] c ISO Greater than 0 and c CLVD If it is greater than 0, the fracture is shear fracture;

[0034] c ISO Less than 0 and c CLVD If it is less than 0, the fracture is compression fracture.

[0035] In one example of the present invention, in step S40, stress inversion is performed on the shear fracture cracks using the Bott-hypothesized crack stress inversion method, specifically including the following steps:

[0036] S411: Determine the effective traction force on the fracture surface: Assume σ ij is the stress tensor of the fracture surface, T i The effective traction force of the fracture surface

[0037] T i =σ ij n j

[0038] Where, σ ij is the stress tensor of the fracture surface; T i is the effective traction force on the fracture surface; n j is the normal vector of the fracture surface;

[0039] S412: Determine the normal stress component σ and the tangential stress component τ of the effective traction stress along the fracture surface. The expressions are as follows:

[0040]

[0041] Where, σ n is the normal stress of the crack; τ is the shear stress of the crack; δ is the Kronecker function; i, l, k represent the subscripts of the three directional components of the three-dimensional coordinate system;

[0042] S413: Eliminate the influence of tangential stress, transform the stress equation, normalize the tangential stress, and transform the equation into a matrix form; the expression for the stress equation transformation is as follows:

[0043] v=σ kj n j (δ ik -n i n k )

[0044] Where v is the slip vector of the fracture surface after eliminating the influence of tangential stress; σ is the stress vector after simplifying tangential stress;

[0045] The expression of the equation converted into a matrix is:

[0046] Aσ=v

[0047] S414: Simplify stress vector: set the constraint to 0, that is: σ 33 =-(σ 11 +σ 22 ); σ is the simplified stress vector; A is the 3×6 matrix of the normal vector of the fracture surface; where the simplified specific matrix expression is shown as:

[0048]

[0049] In one example of the present invention, in step S40, for the tensile and compressive fractures, the modified fracture stress inversion method is used to perform stress inversion on the tensile and compressive fractures, specifically comprising the following steps:

[0050] S421: Determine the effective traction force for tension and compression rupture: In the case of tension and compression rupture, the condition that the displacement vector of the earthquake source is parallel to the fracture surface is not always true. The effective traction force is no longer decomposed, that is, the traction force direction is parallel to the slip vector of the fracture surface obtained by moment tensor analysis. The formula for the effective traction force on the fracture surface is as follows:

[0051]

[0052] Where, is the corrected effective traction; is the corrected effective stress tensor; P is the horizontal thrust between rock masses; n j is the normal vector of the fracture surface;

[0053] S422: Determine the revised source stress inversion equation: specifically expressed as:

[0054] Aσ e =v

[0055] Where, σ e is the corrected effective stress tensor; A is the 3×6 matrix of the normal vector of the fracture surface: v is the slip vector of the corrected fracture surface;

[0056] The matrix is specifically expressed as:

[0057]

[0058] S423: Solve the source stress shape factor R of the modified stress inversion method, which is expressed as follows:

[0059]

[0060] Where R is the stress shape factor; σ1 is the maximum principal compressive stress; σ2 is the intermediate principal compressive stress; σ3 is the minimum principal compressive stress;

[0061] S424: Determine the scaling of the three principal stresses based on the strain deformation factor according to the stress shape factor. Substitute the scaled three principal stresses into the normal stress, principal stress, and shear stress relationship of any section in elastic mechanics. Finally, the following normal stress and shear stress calculation expressions are obtained:

[0062]

[0063] In one example of the present invention, in step S50, the fracture surface state after reservoir fracturing is identified based on the fracture stress inversion result.

[0064] S51: Evaluate the stability of the fracture surface according to the fracture surface instability coefficient model. The fracture surface stability coefficient calculation formula is as follows:

[0065]

[0066] Where, I is the source rupture instability coefficient; σ is the normal stress of the rupture surface; τ is the shear stress of the rupture surface; μ is the rock friction coefficient;

[0067] S52: Identify the rupture tendency of the source surface of the fracture field, based on the analysis of the spatial orientation and extension direction of the fracture inversion and the motion vector direction of the stress inversion of the fracture. The motion tendency is related to the activity of the fracture, and the fracture expansion tendency state of the reservoir fracturing transformation is identified from the perspective of principal stress and fracture.

[0068] In one example of the present invention, in step S52, identifying the fracture propagation tendency state of the reservoir fracturing stimulation specifically includes:

[0069] (1) Identification of microseismic source surfaces with shear fracture tendency: Since the cohesion and friction coefficients of the two source surfaces of the same earthquake source are the same, the influence of the two can be ignored when comparing the fracture activity of a certain earthquake source area. The calculation formula of the fracture surface stability coefficient is simplified to

[0070]

[0071] Where, T s is the tendency of the crack to undergo shear rupture; τ is the shear stress on the earthquake source surface, σ n is the principal stress on the earthquake source surface;

[0072] Calculate the shear fracture tendency T of the two fracture surfaces of reservoir fracturing respectively s , where T s The earthquake source surface with a large value is the surface prone to shear failure, and it is considered that the earthquake source surface is a fracture surface under the shear failure mechanism;

[0073] (2) Identification of microseismic source surface under tensile rupture tendency: When the normal stress σ n The more inclined to σ3, the more likely it is to undergo tensile rupture. The tendency of the crack to undergo tensile rupture is T t The expression is:

[0074] T t =(σ1-σ n ) / (σ1-σ3)

[0075] T tis the tendency of the crack to undergo tensile rupture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; is the intermediate principal stress of the source surface; σ3 is the minimum principal stress of the source surface;

[0076] When the principal stress state near the crack is known, the tensile tendency T of the two focal planes of the earthquake source can be calculated. t ; where T t The earthquake source surface with a large value is the surface that is prone to tensile rupture, and it is believed that this earthquake source surface is the reasonable fracture surface under the tensile rupture mechanism;

[0077] (3) Identification of microseismic source surfaces with compression fracture tendency: Compression fracture tendency T c It reflects the tendency of cracks to compress and shrink in volume, T c The definition is as follows:

[0078] T c =(σ n -σ3) / (σ1-σ3)

[0079] T c is the tendency of the crack to undergo compression fracture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; σ3 is the minimum principal stress on the earthquake source surface;

[0080] When the principal stress of the earthquake source area is known, the compression fracture tendency index T of the two source surfaces of the earthquake source is calculated. c , where T c The source surface with a large value is a surface that is prone to compression fracture. It is believed that this source surface is a reasonable fracture surface under the compression fracture mechanism of the fracture field of the target reservoir.

[0081] In one example of the present invention, step S60 specifically includes the following steps:

[0082] S61: Divide the fracturing effect evaluation area with a certain earthquake source in the target reservoir as the center and L as the radius;

[0083] S62: Calculate the total volume of earthquake source fractures within the defined area based on the fracture volume after fracturing. Among them, in V f When the fracture volume V f When ηV is less than ηV, the effect of reservoir fracturing is poor;

[0084] S63: Based on the instability coefficient I of the fracture surface after reservoir fracturing stimulation, when I = 0, the fracture surface is most stable. As the instability coefficient increases to 1, the stability of the fracture surface gradually decreases. A large proportion of the fracture instability coefficient I ≥ 0.9 in the region indicates a good reservoir fracturing stimulation effect. The red-filled area in the figure indicates an instability coefficient I ≥ 0.9, indicating a good fracture stimulation effect.

[0085] S64: Based on the stress inversion data of reservoir fracturing, σ1 is the main stress and θ is the fracture extension direction, the reservoir fracturing effect is evaluated;

[0086] When the proportion of fractures with ||σ1-θ||≤10° is high, the reservoir fracturing effect is good;

[0087] When the proportion of fractures with an angle of 10°≤||σ1-θ||≤30° is high, the reservoir fracturing stimulation effect is better;

[0088] When the proportion of fractures with ||σ1-θ||≥30° is high, the reservoir fracturing effect is poor;

[0089] S65: Calculate the fracture tendency ratio: Evaluate the fracturing effect based on the fracture tendency;

[0090] S66: Structural volume effect fracturing effect evaluation model, its expression is:

[0091]

[0092] Where Q is the conductivity of the reservoir after fracturing; S is the fracture tendency type score of fracturing transformation; α is the proportion of earthquake sources with instability coefficient I ≥ 0.9; V f is the crack volume (m 3 ), σ1 is the principal stress, β is the stress-direction coupling coefficient, which characterizes the inhibitory effect of the deviation between principal stress and fracture direction on reservoir reconstruction, and θ is the fracture extension direction.

[0093] Another object of the present invention is to provide a reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation system, comprising:

[0094] a microseismic data acquisition module configured to explore geological reservoir information, evaluate and determine target reservoirs for fracturing, deploy an acoustic emission sensor monitoring system, inject fracturing fluid from an injection well and perform real-time microseismic monitoring to acquire a microseismic data set;

[0095] a dynamic fracture parameter acquisition module configured to perform fracture focal mechanism inversion based on the acquired microseismic data set to obtain fracture-derived dynamic fracture parameters of the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension azimuth;

[0096] A fracture type determination module is configured to identify microseismically derived fractures based on reservoir fracturing stimulation, calculate the fracture rupture moment tensor using dynamic fracture parameters, and identify the fracture rupture type based on the positive or negative sign of the fracture rupture moment tensor; fracture types include tension, compression, and shear fractures;

[0097] The stress inversion module is configured to process different types of fractures based on the earthquake source and stress inversion method of reservoir fracturing. For shear fractures, stress inversion is performed on shear fractures using the fracture stress inversion method based on the Bott hypothesis. For tension and compression fractures, stress inversion is performed on tension and compression fractures using the modified fracture stress inversion method to obtain fracture stress inversion data of the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface.

[0098] A fracture surface identification module is configured to construct a fracture instability coefficient model, analyze fracture instability based on fracture rupture source and stress inversion data, and identify the fracture surface state after reservoir fracturing based on fracture stress inversion results;

[0099] The quantitative evaluation module is configured to establish an evaluation model for the fracture reservoir transformation effect based on the instability coefficient fracture tendency and the fracturing transformation stress and fracture inversion parameters through a multi-dimensional target reservoir transformation effect evaluation method, and quantitatively evaluate the reservoir fracturing transformation effect.

[0100] In one example of the present invention, the dynamic crack parameter acquisition module includes:

[0101] The tensor characterization unit is configured to determine a dynamic crack characterization tensor: the dynamic crack parameter is represented by a dynamic crack source characterization tensor ψ, and the specific formula is as follows:

[0102]

[0103] Where, ψ ij is the element of the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack;

[0104] The tensor solving unit is configured to solve the dynamic crack characterization tensor for eigenvalue solution and obtain the three eigenvalues of the tensor ψ. The calculation formula is as follows:

[0105]

[0106] Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor ψ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface;

[0107] The crack solving unit is configured to solve for dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue of the tensor ψ is ψ2 = 0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows:

[0108]

[0109] Where ψ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle;

[0110] The parameter and moment tensor unit is configured to determine the relationship between the dynamic crack parameters and the moment tensor: the dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in the isotropic homogeneous structure:

[0111] M kl =ψ ij C ijkl =λδ kl ψ ii +2μψ kl

[0112] Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

[0113] Compared with the existing technology, this technical solution has the following beneficial effects:

[0114] Significantly improved fracture type identification accuracy: By integrating moment tensor decomposition with eigenvalue constraints, this method innovatively combines focal mechanism inversion with fracture dynamic parameters, overcoming the limitations of traditional methods that rely on a single fracture hypothesis. Based on the collaborative analysis of the ISO, CLVD, and DC components of the moment tensor, it is possible to distinguish between tension, shear, and compression fracture types from a mechanical perspective, effectively resolving the problem of misidentification caused by the coupling of multiple mechanisms in complex fracture networks.

[0115] Systematic optimization of stress field inversion accuracy: Differentiated inversion strategies are designed for different fracture types. The improved Bott model optimizes the inversion of the principal stress directions for shear fractures by eliminating tangential stress interference. A modified stress inversion equation proposed for tension / compression fractures significantly reduces the inversion deviation of the principal stress amplitude and direction by introducing effective traction reconstruction and dynamic scaling of stress shape factors. This methodological system achieves high-precision characterization of non-uniform stress fields through multi-model collaboration.

[0116] Enhanced comprehensiveness and reliability of the dynamic evaluation model: A fracture instability coefficient model was proposed, combining the principal stress direction deviation suppression coefficient (β) and the fracture propensity weight (α) to construct a multi-dimensional dynamic evaluation framework. This model not only quantifies the fracture volume and spatial distribution characteristics, but also transcends the traditional model's reliance on static parameters through mechanical stability analysis and stress-extension direction coupling effect assessment, enabling evaluation results to dynamically reflect the engineering effectiveness of reservoir stimulation.

[0117] The project boasts significant efficiency and cost advantages: By deeply integrating microseismic monitoring data with fracturing techniques, the entire data acquisition, inversion, and evaluation process is fully automated. Compared to traditional step-by-step operations, this solution eliminates redundant data processing steps, theoretically shortening analysis cycles by over 80%. It also reduces equipment deployment and manual intervention costs by 40%-50%, significantly enhancing the overall benefits of unconventional oil and gas reservoir development.

[0118] Wide Geological Adaptability and Customizability: By introducing adjustable parameters such as the fracture volume rupture coefficient (η) and the instability ratio threshold (α), this solution can flexibly adapt to high-stress-difference reservoirs, low-permeability layers, and geological conditions with significant heterogeneity. Furthermore, the modular design of the weighting coefficients in the evaluation model provides customized analysis capabilities for differentiated scenarios such as CO2 storage and hot dry rock development, demonstrating its cross-disciplinary application potential.

[0119] The technical solution of the present invention has demonstrated significant progress from mechanism innovation, model construction to engineering application, providing a full-chain solution for reservoir fracturing transformation, from dynamic characterization of fractures, accurate inversion of stress fields to quantitative evaluation of effects, and has important theoretical significance and engineering practice value.

[0120] Hereinafter, the best embodiment of the present invention will be described in more detail with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention. The drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0122] Figure 1 Flowchart of a method for joint inversion and effect evaluation of fractures and stresses in reservoir fracturing according to an embodiment of the present invention;

[0123] Figure 2 3 is a logic diagram of a method for joint inversion and effect evaluation of fractures and stresses in reservoir fracturing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0124] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0125] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the field to which the invention belongs. The words "first", "second" and similar terms used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "a" or "an" do not necessarily indicate a quantity limitation. Words such as "include" or "comprising" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0126] According to the first aspect of the present invention, a reservoir fracturing reformation crack and stress joint inversion and effect evaluation method is as follows: Figure 1 and Figure 2 As shown, the following steps are included:

[0127] S10: Exploring geological reservoir information, evaluating and determining target reservoirs for fracturing, deploying an acoustic emission sensor monitoring system, injecting fracturing fluid from injection wells, and conducting real-time microseismic monitoring to obtain microseismic data sets;

[0128] S20: performing fracture focal mechanism inversion based on the acquired microseismic data set to obtain dynamic fracture parameters derived from fracturing in the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension azimuth, thereby obtaining the state of fractures in the target reservoir space for fracturing;

[0129] S30: Based on the identification method of microseismic fractures derived from reservoir fracturing, the fracture moment tensor is calculated based on the fracture volume, fracture direction, extension direction and other dynamic fracture parameters. The fracture rupture type is identified based on the positive and negative sign of the fracture moment tensor. The fracture types include tension, compression and shear fractures.

[0130] S40: Seismic source and stress inversion methods based on reservoir fracturing are used to handle different types of fractures. For fractures of different types, such as tension, compression, and shear fractures, stress inversion is performed on shear fractures using the Bott-based fracture stress inversion method. For tension and compression fractures, a modified stress inversion method suitable for tension and compression is proposed. Using the modified fracture stress inversion method, stress inversion is performed on tension and compression fractures, obtaining fracture stress inversion data such as the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface.

[0131] S50: Identify the state of the fracture surface in the reservoir area based on the earthquake source and stress inversion data of the fracture stimulation. Construct a fracture instability coefficient model, analyze the instability of the fracture based on the earthquake source and stress inversion data of the fracture rupture, and identify the state of the fracture surface after the reservoir is stimulated by fracture stimulation based on the fracture stress inversion results.

[0132] S60: Evaluate the target reservoir fracturing effect. Based on the instability coefficient, fracture propensity, fracture volume, fracture extension direction, and principal stress direction, the fracturing stress and fracture inversion parameters are used to establish an evaluation model for fracture reservoir stimulation effects through a multi-dimensional target reservoir stimulation effect evaluation method, and quantitatively evaluate the reservoir fracturing effect.

[0133] This evaluation method significantly improves the accuracy of fracture type identification. By integrating moment tensor decomposition with eigenvalue constraints, it innovatively combines focal mechanism inversion with fracture dynamic parameters, overcoming the limitations of traditional methods that rely on a single rupture hypothesis. Based on the collaborative analysis of the ISO, CLVD, and DC components of the moment tensor, it can distinguish between tension, shear, and compression fracture types from a mechanical perspective, effectively resolving the problem of misjudgment caused by the coupling of multiple mechanisms in complex fracture networks.

[0134] This evaluation method systematically optimizes the stress field inversion accuracy: differentiated inversion strategies are designed for different fracture types. The improved Bott model optimizes the inversion of the principal stress direction for shear fractures by eliminating tangential stress interference. A modified stress inversion equation proposed for tension / compression fractures significantly reduces the inversion deviation of the principal stress amplitude and direction by introducing effective traction reconstruction and dynamic scaling of stress shape factors. This method system achieves high-precision characterization of non-uniform stress fields through multi-model collaboration.

[0135] This evaluation method enhances the comprehensiveness and reliability of its dynamic evaluation model: a fracture instability coefficient model is proposed, combining the principal stress direction deviation suppression coefficient (β) and the fracture propensity weight (α) to construct a multi-dimensional dynamic evaluation framework. This model not only quantifies the fracture volume and spatial distribution characteristics, but also transcends the traditional model's reliance on static parameters through mechanical stability analysis and stress-extension direction coupling effect assessment, enabling the evaluation results to dynamically reflect the engineering effectiveness of reservoir stimulation.

[0136] This evaluation method offers significant engineering efficiency and cost advantages: by deeply integrating microseismic monitoring data with fracturing techniques, it automates the entire data acquisition, inversion, and evaluation process. Compared to traditional step-by-step operations, this approach eliminates redundant data processing steps, theoretically shortening analysis cycles by over 80%. It also reduces equipment deployment and manual intervention costs by 40%-50%, significantly improving the overall benefits of unconventional oil and gas reservoir development.

[0137] This evaluation method boasts broad geological adaptability and customization: by introducing adjustable parameters such as the fracture volume rupture coefficient (η) and the instability ratio threshold (α), it can flexibly adapt to high-stress-difference reservoirs, low-permeability layers, and geological conditions with significant heterogeneity. Furthermore, the modular design of the weighting coefficients within the evaluation model provides customized analysis capabilities for diverse scenarios such as CO2 storage and hot dry rock development, demonstrating its potential for cross-disciplinary application.

[0138] The technical solution of this evaluation method has demonstrated significant progress from mechanism innovation, model construction to engineering application. It provides a full-chain solution for reservoir fracturing transformation, from dynamic characterization of fractures, accurate inversion of stress fields to quantitative evaluation of effects, and has important theoretical significance and engineering practice value.

[0139] In one example of the present invention, in step S20, performing fracture focal mechanism inversion based on the acquired microseismic data set to obtain the fracturing-derived active fracture parameters of the reservoir space includes the following steps:

[0140] S21: Determine the dynamic crack characterization tensor: The dynamic crack parameters are represented by the dynamic crack source characterization (i.e., displacement discontinuity) tensor ψ. The specific formula is as follows:

[0141]

[0142] Where, ψ ij is the element of the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack;

[0143] S22: Solve the eigenvalue of the dynamic crack characterization tensor and obtain the three eigenvalues of the tensor χ. The calculation formula is as follows:

[0144]

[0145] Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor χ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface;

[0146] S23; Solving the dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue ψ2 of the tensor ψ=0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows:

[0147]

[0148] Where χ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle;

[0149] S24: Determine the relationship between dynamic crack parameters and moment tensor: The dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in isotropic homogeneous materials:

[0150] M kl =ψ ij C ijkl =λδ kl ψ ii +2μψ kl

[0151] Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

[0152] In one example of the present invention, in step S30, the specific steps of identifying the fracture type according to the positive or negative value of the fracture moment tensor are as follows:

[0153] S31: Determine the ISO, CLVD, and DC components of the moment tensor: After obtaining the moment tensor M, eigenvalue it to obtain the eigenvalues (M1, M2, M3, M1 ≥ M2 ≥ M3), and decompose it into ISO, CLVD, and DC components, which represent the isotropic, axial tension, and shear rupture components of the earthquake source, respectively. The sum of the CLVD and DC components is called the deviatoric moment tensor M*.

[0154] S32: Decompose the moment tensor to obtain the percentage of each component of the moment tensor M, which is expressed as follows:

[0155]

[0156] Where M |max| is the maximum absolute value of the eigenvalue of the moment tensor M, M |max| =max(|M1|,|M2|,|M3|); the parameter ε is a parameter that measures the size of the CLVD component relative to the DC component. |M * | max 、|M * | min They represent the maximum and minimum absolute values of the eigenvalues of the partial moment tensor M*;

[0157] S33: Identify the fracture type based on the percentage of each component of the moment tensor M:

[0158] c DC >0, the rupture belongs to tensile rupture;

[0159] c ISO Greater than 0 and c CLVD If it is greater than 0, the fracture is shear fracture;

[0160] c ISO Less than 0 and c CLVD If it is less than 0, the fracture is compression fracture.

[0161] In one example of the present invention, in step S40, stress inversion is performed on the shear fracture cracks using the Bott-hypothesized crack stress inversion method, specifically including the following steps:

[0162] S411: Determine the effective traction force on the fracture surface: Assume σ ij is the stress tensor of the fracture surface, T i The effective traction force of the fracture surface

[0163] T i =σ ijn j

[0164] Where, σ ij is the stress tensor of the fracture surface; T i is the effective traction force on the fracture surface; n j is the normal vector of the fracture surface;

[0165] S412: Determine the normal stress component σ and the tangential stress component τ of the effective traction stress along the fracture surface. The expressions are as follows:

[0166]

[0167] Where, σ n is the normal stress of the crack; τ is the shear stress of the crack; δ is the Kronecker function; i, l, k represent the subscripts of the three directional components of the three-dimensional coordinate system;

[0168] S413: Eliminate the influence of tangential stress, transform the stress equation, normalize the tangential stress, and transform the equation into a matrix form; the expression for the stress equation transformation is as follows:

[0169] v=σ kj n j (δ ik -n i n k )

[0170] Where v is the slip vector of the fracture surface after eliminating the influence of tangential stress; σ is the stress vector after simplifying tangential stress;

[0171] The expression of the equation converted into a matrix is:

[0172] Aσ=v

[0173] S414: Simplify stress vector: set the constraint to 0, that is: σ 33 =-(σ 11 +σ 22 ); σ is the simplified stress vector; A is the 3×6 matrix of the normal vector of the fracture surface; where the simplified specific matrix expression is shown as:

[0174]

[0175] In one example of the present invention, in step S40, for the tensile and compressive fractures, the modified fracture stress inversion method is used to perform stress inversion on the tensile and compressive fractures, specifically comprising the following steps:

[0176] S421: Determine the effective traction force for tension and compression rupture: In the case of tension and compression rupture, the condition that the displacement vector of the earthquake source is parallel to the fracture surface is not always true. The effective traction force is no longer decomposed, that is, the traction force direction is parallel to the slip vector of the fracture surface obtained by moment tensor analysis. The formula for the effective traction force on the fracture surface is as follows:

[0177]

[0178] Where, is the corrected effective traction; is the corrected effective stress tensor; P is the horizontal thrust between rock masses; n j is the normal vector of the fracture surface.

[0179] S422: Determine the revised source stress inversion equation: specifically expressed as:

[0180] Aσ e =v

[0181] Where, σ e is the corrected effective stress tensor; A is the 3×6 matrix of the normal vector of the fracture surface: v is the slip vector of the corrected fracture surface;

[0182] The matrix is specifically expressed as:

[0183]

[0184] S423: Solve the source stress shape factor R of the modified stress inversion method. The absolute magnitude of the stress tensor cannot be directly obtained in stress inversion. The relationship between the four stress tensor parameters is obtained by solving the source stress inversion equation of the S52 process. The expression is as follows:

[0185]

[0186] Where R is the stress shape factor; σ1 is the maximum principal compressive stress; σ2 is the intermediate principal compressive stress; σ3 is the minimum principal compressive stress;

[0187] S424: Determine the scaling of the three principal stresses based on the strain deformation factor according to the stress shape factor, and substitute the scaled three principal stresses into the normal stress, principal stress, and shear stress relationship of any cross section in elastic mechanics. The expressions of normal stress, principal stress, and shear stress are as follows:

[0188]

[0189] Finally, the following normal stress and shear stress calculation expressions are obtained:

[0190]

[0191] In one example of the present invention, in step S50, the fracture surface state after reservoir fracturing is identified based on the fracture stress inversion result.

[0192] S51: Evaluate the stability of the fracture surface according to the fracture surface instability coefficient model. The fracture surface stability coefficient calculation formula is as follows:

[0193]

[0194] Where, I is the source rupture instability coefficient; σ is the normal stress of the rupture surface; τ is the shear stress of the rupture surface; μ is the rock friction coefficient;

[0195] S52: Identify the rupture tendency of the source surface of the fracture field. The movement tendency is related to the activity of the fracture. Combined with the principal stress vector and direction obtained in step S40, based on the spatial orientation and extension direction of the fracture inversion and the movement vector direction analysis of the stress of the fracture inversion, the movement tendency is related to the activity of the fracture. Identify the fracture expansion tendency state of the reservoir fracturing transformation from the perspective of principal stress and fracture.

[0196] In one example of the present invention, in step S52, identifying the fracture propagation tendency state of the reservoir fracturing stimulation specifically includes:

[0197] (1) Identify the microseismic source surface with shear fracture tendency: The movement tendency is related to the activity of the crack. When the shear stress exceeds the shear strength, shear movement will occur. This movement tendency is called shear fracture tendency. Since the cohesion and friction coefficient of the two source surfaces of the same earthquake source are the same, the influence of the two can be ignored when comparing the activity of the cracks in a certain earthquake source area. The calculation formula of the fracture surface stability coefficient is simplified to

[0198]

[0199] Where, T s is the tendency of the crack to undergo shear rupture, which is the dimensionless ratio of shear stress to normal stress; τ is the shear stress on the earthquake source surface, σ n is the principal stress of the earthquake source surface. The shear stress and normal stress acting on the crack surface depend on the principal stress distribution and crack orientation. The principal stress σ n The calculation method of shear stress τ is as follows:

[0200] σ n =σ1×l 2 +σ2×m 2 +σ3×n 2

[0201] τ=[(σ1-σ2) 2 l2 m 2 +(σ2-σ3) 2 m 2 n 2 +(σ1-σ3) 2 l 2 n 2 ] 1 / 2

[0202] Where: l, m and n are the normal cosines of the crack on the principal stress axis;

[0203] According to the above two equations and the formula described in S51, the shear fracture tendency T of the two fracture surfaces of the reservoir fracturing transformation is calculated respectively. s , where T s The earthquake source surface with a large value is the surface prone to shear failure, and it is considered that the earthquake source surface is a fracture surface under the shear failure mechanism;

[0204] (2) Identification of microseismic source surface under tensile rupture tendency: When the normal stress σ n The more inclined to σ3, the more likely it is to undergo tensile fracture. This property is called expansion tendency, which is used in geology to describe the ability of the fracture surface to expand, and is called the tendency of the fracture to undergo tensile fracture T. t :

[0205] T t =(σ1-σ n ) / (σ1-σ3)

[0206] T t is the tendency of the crack to undergo tensile rupture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; is the intermediate principal stress of the source surface; σ3 is the minimum principal stress of the source surface;

[0207] Under the condition that σ1, σ2 and σ3 are known, the tensile fracture tendency T of the crack is t It can be obtained according to the above formula. When the principal stress state near the crack is known, the tension tendency T of the two source surfaces of the earthquake source can be obtained. t ; where T t The earthquake source surface with a large value is the surface that is prone to tensile rupture, and it is believed that the earthquake source surface is the reasonable fracture surface under the tensile rupture mechanism;

[0208] (3) Identify the microseismic source surface with compression fracture tendency: compression and tension fracture mechanisms are opposite, that is, the normal stress σ n The closer to the maximum principal stress σ1, the greater the compressive stress on the crack, and the more likely the rock mass at the earthquake source will be compressed and fractured. This phenomenon is defined as the compression fracture tendency T c , which reflects the tendency of cracks to compress and shrink in volume, T c The definition is as follows:

[0209] T c =(σ n -σ3) / (σ1-σ3)

[0210] T c is the tendency of the crack to undergo compression fracture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; σ3 is the minimum principal stress on the earthquake source surface;

[0211] Under the condition that σ1, σ2 and σ3 are known, the compression fracture tendency T of the crack surface is c It can be obtained by the three equations in step S61 (1) and (3). Similarly, when the principal stress of the region where the earthquake source is located is known, the compression fracture tendency index T of the two source surfaces of the earthquake source is obtained. c , where T c The source surface with a large value is a surface that is prone to compression fracture. It is believed that this source surface is a reasonable fracture surface under the compression fracture mechanism of the fracture field of the target reservoir.

[0212] In one example of the present invention, step S60 specifically includes the following steps:

[0213] S61: With a certain earthquake source in the target reservoir as the center and L as the radius, divide the fracturing effect evaluation area. The total volume of the area

[0214] S62: In the designated area, based on the fracture volume obtained in S23, calculate the total volume of the earthquake source fracture in the area Among them, in V f ≥ηV (η is the fracture volume rupture coefficient, which is determined by the severity of the evaluation and is initially set at 0.2), the reservoir fracturing effect is considered to be good. f When ηV is less than ηV, the effect of reservoir fracturing is poor;

[0215] S63: Based on S51, the instability coefficient I of the fracture surface after reservoir fracturing is obtained. When I = 0, the fracture surface is most stable. As the instability coefficient increases to 1, the stability of the fracture surface gradually decreases. The larger the proportion of fracture instability coefficient I ≥ 0.9 in the region, the better the reservoir fracturing transformation effect is. The red filled area in the figure indicates that the instability coefficient I ≥ 0.9, indicating that the fracture transformation effect is good. Let the total number of earthquake sources be N, calculate the instability coefficient of each earthquake source, calculate the distribution of the instability coefficient of the total earthquake sources, and let the number of earthquake sources with the instability coefficient I ≥ 0.9 be N f , N in reservoir fracturing f ≥ξN (ξ is the unstable ratio of reservoir fractures, which is determined by the severity of the evaluation and is initially set to 0.3), it is considered that the reservoir fracturing effect is good, Nf When ξN is less than ξN, it is considered that the reservoir fracturing effect is poor;

[0216] S64: Based on the stress inversion data of reservoir fracturing obtained in S40, σ1 is the main stress, θ is the fracture extension direction, and the reservoir fracturing effect is evaluated;

[0217] When the proportion of fractures with ||σ1-θ||≤10° is high, the reservoir fracturing effect is good;

[0218] When the proportion of fractures with an angle of 10°≤||σ1-θ||≤30° is high, the reservoir fracturing stimulation effect is better;

[0219] When the proportion of fractures with ||σ1-θ||≥30° is high, the reservoir fracturing effect is poor;

[0220] S65: Calculate the proportion of rupture tendency: Based on the fracture rupture tendency obtained in S52, evaluate the fracturing effect; assume that the rupture tendency earthquake source is a tensile rupture earthquake source, and the number of earthquake sources is N. t , the number of rupture prone earthquake sources is shear rupture earthquake sources is N s , the number of tensile rupture sources with rupture tendency is N c ; The rupture tendency ratio is calculated using the weighted ratio formula:

[0221]

[0222] Where: r = t, s, c, respectively represent the three fracture tendency modes of tension, shear, and compression;

[0223] P r is the proportion of cracks with the tendency of the rth type of rupture (tension, shear, compression);

[0224] N r The number of type r rupture events;

[0225] w r Weight coefficient (tension = x, shear = y, compression = z, set 1>x>y>z>0);

[0226] Fracture stimulation fracture rupture tendency type proportion score S=P 张拉 ×x+P 剪切 ×yP 压缩 ×z;

[0227] S66: Structural volume effect fracturing effect evaluation model, its expression is:

[0228]

[0229] Where Q is the conductivity of the reservoir after fracturing; S is the fracture tendency type score of fracturing transformation; α is the proportion of earthquake sources with instability coefficient I ≥ 0.9; V f is the crack volume (m 3 ), σ1 is the principal stress, β is the stress-direction coupling coefficient, which characterizes the inhibitory effect of the deviation between principal stress and fracture direction on reservoir reconstruction, and θ is the fracture extension direction.

[0230] According to the second aspect of the present invention, a reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation system comprises:

[0231] a microseismic data acquisition module configured to explore geological reservoir information, evaluate and determine target reservoirs for fracturing, deploy an acoustic emission sensor monitoring system, inject fracturing fluid from an injection well and perform real-time microseismic monitoring to acquire a microseismic data set;

[0232] a dynamic fracture parameter acquisition module configured to perform fracture focal mechanism inversion based on the acquired microseismic data set to obtain fracture-derived dynamic fracture parameters of the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension azimuth, thereby obtaining the state of fractures in the target reservoir space for fracture;

[0233] A fracture type determination module is configured to identify microseismically derived fractures based on reservoir fracturing. The module calculates the fracture moment tensor using dynamic fracture parameters such as fracture volume, fracture direction, and extension direction, and identifies the fracture type based on the positive or negative sign of the fracture moment tensor. Fracture types include tension, compression, and shear fractures.

[0234] The stress inversion module is configured to process different types of fractures based on the earthquake source and stress inversion method of reservoir fracturing. For different types of fractures such as tension, compression and shear fractures, stress inversion is performed on shear fractures using the Bott hypothesis fracture stress inversion method. For tension and compression fractures, a modified stress inversion method suitable for tension and compression is proposed. The modified fracture stress inversion method is used to perform stress inversion on tension and compression fractures, and obtain fracture stress inversion data such as the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface.

[0235] The fracture surface identification module is configured to identify the state of the fracture surface in the reservoir area based on the fracture source and stress inversion data of the fracture stimulation. A fracture instability coefficient model is constructed to analyze the fracture instability based on the fracture source and stress inversion data of the fracture rupture, and the fracture surface state after the reservoir is stimulated by fracture stimulation is identified based on the fracture stress inversion results.

[0236] The quantitative evaluation module is configured to evaluate the effectiveness of target reservoir fracturing. Based on the instability coefficient, fracture propensity, fracture volume, fracture extension direction, and principal stress direction, as well as the fracture inversion parameters, a multi-dimensional target reservoir stimulation evaluation method is used to establish an evaluation model for fracture reservoir stimulation, thereby quantitatively evaluating the reservoir fracturing effect.

[0237] This evaluation system significantly improves the accuracy of fracture type identification. By integrating moment tensor decomposition with eigenvalue constraints, it innovatively combines focal mechanism inversion with fracture dynamic parameters, overcoming the limitations of traditional methods that rely on a single rupture hypothesis. Based on the collaborative analysis of the ISO, CLVD, and DC components of the moment tensor, it can distinguish between tension, shear, and compression fracture types from a mechanical perspective, effectively resolving the problem of misjudgment caused by the coupling of multiple mechanisms in complex fracture networks.

[0238] This evaluation system systematically optimizes the stress field inversion accuracy: differentiated inversion strategies are designed for different fracture types. The improved Bott model optimizes the inversion of the principal stress direction for shear fractures by eliminating tangential stress interference. A modified stress inversion equation proposed for tension / compression fractures significantly reduces the inversion deviation of the principal stress amplitude and direction by introducing effective traction reconstruction and dynamic scaling of stress shape factors. This methodological system achieves high-precision characterization of non-uniform stress fields through multi-model collaboration.

[0239] The evaluation system's dynamic evaluation model is more comprehensive and reliable: a fracture instability coefficient model is proposed, combining the principal stress direction deviation suppression coefficient (β) and the fracture propensity weight (α) to construct a multi-dimensional dynamic evaluation framework. This model not only quantifies the fracture volume and spatial distribution characteristics, but also transcends the traditional model's reliance on static parameters through mechanical stability analysis and stress-extension direction coupling effect assessment, enabling the evaluation results to dynamically reflect the engineering effectiveness of reservoir stimulation.

[0240] This evaluation system offers significant efficiency and cost advantages: by deeply integrating microseismic monitoring data with fracturing techniques, it automates the entire data acquisition, inversion, and evaluation process. Compared to traditional step-by-step operations, this solution eliminates redundant data processing steps, theoretically shortening analysis cycles by over 80%. It also reduces equipment deployment and manual intervention costs by 40%-50%, significantly improving the overall benefits of unconventional oil and gas reservoir development.

[0241] This evaluation method boasts broad geological adaptability and customization: by introducing adjustable parameters such as the fracture volume rupture coefficient (η) and the instability ratio threshold (α), it can flexibly adapt to high-stress-difference reservoirs, low-permeability layers, and geological conditions with significant heterogeneity. Furthermore, the modular design of the weighting coefficients within the evaluation model provides customized analysis capabilities for diverse scenarios such as CO2 storage and hot dry rock development, demonstrating its potential for cross-disciplinary application.

[0242] The technical solution of this evaluation method has demonstrated significant progress from mechanism innovation, model construction to engineering application. It provides a full-chain solution for reservoir fracturing transformation, from dynamic characterization of fractures, accurate inversion of stress fields to quantitative evaluation of effects, and has important theoretical significance and engineering practice value.

[0243] In one example of the present invention, the dynamic crack parameter acquisition module includes:

[0244] The tensor characterization unit is configured to determine a dynamic crack characterization tensor: the dynamic crack parameter is represented by a dynamic crack source characterization (i.e., displacement discontinuity) tensor ψ, and the specific formula is as follows:

[0245]

[0246] Where, ψ ij is the element of the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack;

[0247] The tensor solving unit is configured to solve the dynamic crack characterization tensor for eigenvalue solution and obtain the three eigenvalues of the tensor ψ. The calculation formula is as follows:

[0248]

[0249] Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor ψ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface;

[0250] The crack solving unit is configured to solve for dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue of the tensor ψ is ψ2 = 0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows:

[0251]

[0252] Where ψ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle;

[0253] The parameter and moment tensor unit is configured to determine the relationship between the dynamic crack parameters and the moment tensor: the dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in the isotropic homogeneous structure:

[0254] M kl =ψ ij C ijkl =λδ kl ψ ii +2μψ kl

[0255] Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

[0256] It should be noted that the reservoir fracturing and stress joint inversion and effect evaluation system of the present invention can also perform any processing in the reservoir fracturing and stress joint inversion and effect evaluation method described previously, and the specific details are not repeated here.

[0257] The exemplary implementation scheme of the reservoir fracturing reformation crack and stress joint inversion and effect evaluation method and system proposed in the present invention is described in detail with reference to the preferred embodiments. However, it can be understood by those skilled in the art that, without departing from the concept of the present invention, various variations and modifications can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the scope of protection of the present invention, which is determined by the appended claims.

Claims

1. A method for joint inversion and effect evaluation of reservoir fracturing and stress, characterized in that: The steps include: S10: Exploring geological reservoir information, evaluating and determining target reservoirs for fracturing, deploying an acoustic emission sensor monitoring system, injecting fracturing fluid from injection wells, and conducting real-time microseismic monitoring to obtain microseismic data sets; S20: performing fracture focal mechanism inversion based on the acquired microseismic data set to obtain dynamic fracture parameters derived from fracturing in the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension direction; S30: Based on the identification method of microseismic-derived fractures derived from reservoir fracturing, the fracture rupture moment tensor is calculated using dynamic fracture parameters, and the fracture rupture type is identified based on the positive and negative sign of the fracture rupture moment tensor. The fracture types include tension, compression, and shear fractures. S40: Based on the earthquake source and stress inversion method of reservoir fracturing, different types of fractures are processed. For shear fractures, stress inversion is performed on shear fractures using the fracture stress inversion method based on the Bott hypothesis. For tension and compression fractures, stress inversion is performed on tension and compression fractures using the modified fracture stress inversion method to obtain the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface. S50: Construct a fracture instability coefficient model, analyze fracture instability based on fracture rupture source and stress inversion data, and identify the fracture surface state after reservoir fracturing based on fracture stress inversion results; S60: Based on the instability coefficient fracture tendency and the fracturing stimulation stress and fracture inversion parameters, a multi-dimensional target reservoir stimulation effect evaluation method is used to establish an evaluation model for the fracture reservoir stimulation effect, and quantitatively evaluate the reservoir fracturing stimulation effect.

2. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1 is characterized in that: In step S20, fracture focal mechanism inversion is performed based on the acquired microseismic data set to obtain the fracturing-derived active fracture parameters of the reservoir space, including the following steps: S21: Determine the dynamic crack characterization tensor: The dynamic crack parameters are represented by the dynamic crack source characterization tensor ψ. The specific formula is as follows: Where, ψ ij is the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) element of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack; S22: Solve the eigenvalue of the dynamic crack characterization tensor and obtain the three eigenvalues of the tensor ψ. The calculation formula is as follows: Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor ψ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface; S23; Solving the dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue ψ2 of the tensor ψ=0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows: Where ψ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle; S24: Determine the relationship between dynamic crack parameters and moment tensor: The dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in isotropic homogeneous materials: M kl =ψ ij C ijkl =λδ kl ψ ii +2pm kl Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

3. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1 is characterized in that: In step S30, the specific steps of identifying the fracture type according to the positive or negative value of the fracture moment tensor are as follows: S31: Determine the ISO, CLVD, and DC components of the moment tensor: After obtaining the moment tensor M, eigenvalue it to obtain the eigenvalue, and decompose it into ISO, CLVD, and DC components, which represent the isotropic, axial tension, and shear rupture components of the earthquake source, respectively. The sum of the CLVD and DC components is called the deviatoric moment tensor M*. S32: Decompose the moment tensor to obtain the percentage of each component of the moment tensor M, which is expressed as follows: Where M |max| is the maximum absolute value of the eigenvalue of the moment tensor M, M |max| =max(|M1|,|M2|,|M3|); the parameter ε is a parameter that measures the size of the CLVD component relative to the DC component. |M * | max 、|M * | min They represent the maximum and minimum absolute values of the eigenvalues of the partial moment tensor M*; S33: Identify the fracture type based on the percentage of each component of the moment tensor M: c DC >0, the rupture belongs to tensile rupture; c ISO Greater than 0 and c CLVD If it is greater than 0, the fracture is shear fracture; c ISO Less than 0 and c CLVD If it is less than 0, the fracture is compression fracture.

4. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1 is characterized in that: In step S40, for the shear fracture cracks, stress inversion is performed on the shear fracture cracks using the Bott assumption crack stress inversion method, which specifically includes the following steps: S411: Determine the effective traction force on the fracture surface: Assume σ ij is the stress tensor of the fracture surface, T i The effective traction force of the fracture surface T i =s ij n j Where, σ ij is the stress tensor of the fracture surface; T i is the effective traction force on the fracture surface; n j is the normal vector of the fracture surface; S412: Determine the normal stress component σ and the tangential stress component τ of the effective traction stress along the fracture surface. The expressions are as follows: Where, σ n is the normal stress of the crack; τ is the shear stress of the crack; δ is the Kronecker function; i, l, k represent the subscripts of the three directional components of the three-dimensional coordinate system; S413: Eliminate the influence of tangential stress, transform the stress equation, normalize the tangential stress, and convert the equation into a matrix form; Among them, the expression of stress equation transformation is as follows: v=σ kj n j (d ik -n i n k ) Where v is the slip vector of the fracture surface after eliminating the influence of tangential stress; σ is the stress vector after simplifying tangential stress; The expression of the equation converted into a matrix is: Aσ=v S414: Simplify stress vector: set the constraint to 0, that is: σ 33 =-(σ 11 +σ 22 ); σ is the simplified stress vector; A is the 3×6 matrix of the normal vector of the fracture surface; where the simplified specific matrix expression is shown as:

5. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1 is characterized in that: In step S40, for the tensile and compressive cracks, the modified crack stress inversion method is used to perform stress inversion on the tensile and compressive cracks, which specifically includes the following steps: S421: Determine the effective traction force for tension and compression rupture: In the case of tension and compression rupture, the condition that the displacement vector of the earthquake source is parallel to the fracture surface is not always true. The effective traction force is no longer decomposed, that is, the traction force direction is parallel to the slip vector of the fracture surface obtained by moment tensor analysis. The formula for the effective traction force on the fracture surface is as follows: Where, is the corrected effective traction; is the corrected effective stress tensor; P is the horizontal thrust between rock masses; n j is the normal vector of the fracture surface; S422: Determine the revised source stress inversion equation: specifically expressed as: As e =v Where, σ e is the corrected effective stress tensor; A is the 3×6 matrix of the normal vector of the fracture surface: v is the slip vector of the corrected fracture surface; S423: Solve the source stress shape factor R of the modified stress inversion method, which is expressed as follows: Where R is the stress shape factor; σ1 is the maximum principal compressive stress; σ2 is the intermediate principal compressive stress; σ3 is the minimum principal compressive stress; S424: Determine the scaling of the three principal stresses based on the strain deformation factor according to the stress shape factor. Substitute the scaled three principal stresses into the normal stress, principal stress, and shear stress relationship of any section in elastic mechanics. Finally, the following normal stress and shear stress calculation expressions are obtained:

6. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1, characterized in that: In step S50, identifying the fracture surface state after reservoir fracturing based on the fracture stress inversion result includes the following steps: S51: Evaluate the stability of the fracture surface according to the fracture surface instability coefficient model. The fracture surface stability coefficient calculation formula is as follows: Where, I is the source rupture instability coefficient; σ is the normal stress of the rupture surface; τ is the shear stress of the rupture surface; μ is the rock friction coefficient; S52: Identify the rupture tendency of the source surface of the fracture field, based on the analysis of the spatial orientation and extension direction of the fracture inversion and the motion vector direction of the stress inversion of the fracture. The motion tendency is related to the activity of the fracture, and the fracture expansion tendency state of the reservoir fracturing transformation is identified from the perspective of principal stress and fracture.

7. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 6, characterized in that: In step S52, identifying the fracture expansion tendency state of the reservoir fracturing transformation specifically includes: (1) Identification of microseismic source surfaces with shear fracture tendency: Since the cohesion and friction coefficients of the two source surfaces of the same earthquake source are the same, the influence of the two can be ignored when comparing the fracture activity of a certain earthquake source area. The calculation formula of the fracture surface stability coefficient is simplified to Where, T s is the tendency of the crack to undergo shear rupture; τ is the shear stress on the earthquake source surface, σ n is the principal stress on the earthquake source surface, Calculate the shear fracture tendency T of the two fracture surfaces of reservoir fracturing respectively s , where T s The earthquake source surface with a large value is a surface prone to shear failure, and is considered to be a fracture surface under the shear failure mechanism; (2) Identification of microseismic source surface under tensile rupture tendency: When the normal stress σ n The more inclined to σ3, the more likely it is to undergo tensile rupture. The tendency of the crack to undergo tensile rupture is T t The expression is: T t =(σ1-σ n ) / (σ1-σ3) T t is the tendency of the crack to undergo tensile rupture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; is the intermediate principal stress of the source surface; σ3 is the minimum principal stress of the source surface; When the principal stress state near the crack is known, the tensile tendency T of the two focal planes of the earthquake source can be calculated. t ; where T t The earthquake source surface with a large value is the surface that is prone to tensile rupture, and it is believed that the earthquake source surface is the reasonable fracture surface under the tensile rupture mechanism; (3) Identification of microseismic source surfaces with compression fracture tendency: Compression fracture tendency T c It reflects the tendency of cracks to compress and shrink in volume, T c The definition is as follows: T c =(s n -σ3) / (σ1-σ3) T c is the tendency of the crack to undergo compression fracture; σ1 is the maximum principal stress on the earthquake source surface; σ n is the normal stress; σ3 is the minimum principal stress on the earthquake source surface; When the principal stress of the earthquake source area is known, the compression fracture tendency index T of the two earthquake source surfaces is calculated. c , where T c The source surface with a large value is a surface that is prone to compression fracture. It is believed that this source surface is a reasonable fracture surface under the compression fracture mechanism of the fracture field of the target reservoir.

8. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation method according to claim 1 is characterized in that: Step S60 specifically includes the following steps: S61: Divide the fracturing effect evaluation area with a certain earthquake source in the target reservoir as the center and L as the radius; S62: Calculate the total volume of earthquake source fractures within the defined area based on the fracture volume after fracturing. Among them, in V f When the fracture volume V f When ηV is less than ηV, the effect of reservoir fracturing is poor; S63: Based on the instability coefficient I of the fracture surface after reservoir fracturing stimulation, when I = 0, the fracture surface is most stable. As the instability coefficient increases to 1, the stability of the fracture surface gradually decreases. A large proportion of the fracture instability coefficient I ≥ 0.9 in the region indicates a good reservoir fracturing stimulation effect. The red-filled area in the figure indicates an instability coefficient I ≥ 0.9, indicating a good fracture stimulation effect. S64: Based on the stress inversion data of reservoir fracturing, σ1 is the main stress and θ is the fracture extension direction, the reservoir fracturing effect is evaluated; When the proportion of fractures with ||σ1-θ||≤10° is high, the reservoir fracturing effect is good; When the proportion of fractures with an angle of 10°≤||σ1-θ||≤30° is high, the reservoir fracturing stimulation effect is better; When the proportion of fractures with ||σ1-θ||≥30° is high, the reservoir fracturing effect is poor; S65: Calculate the fracture tendency ratio: Evaluate the fracturing effect based on the fracture tendency; S66: Structural volume effect fracturing effect evaluation model, its expression is: Where Q is the conductivity of the reservoir after fracturing; S is the fracture tendency type score of fracturing transformation; α is the proportion of earthquake sources with instability coefficient I ≥ 0.9; V f is the crack volume (m 3 ), σ1 is the principal stress, β is the stress-direction coupling coefficient, which characterizes the inhibitory effect of the deviation between principal stress and fracture direction on reservoir reconstruction, and θ is the fracture extension direction.

9. A reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation system, characterized in that: include: a microseismic data acquisition module configured to explore geological reservoir information, evaluate and determine target reservoirs for fracturing, deploy an acoustic emission sensor monitoring system, inject fracturing fluid from an injection well and perform real-time microseismic monitoring to acquire a microseismic data set; a dynamic fracture parameter acquisition module configured to perform fracture focal mechanism inversion based on the acquired microseismic data set to obtain fracture-derived dynamic fracture parameters of the reservoir space, wherein the dynamic fracture parameters include fracture attributes, spatial orientation, fracture scale, and extension azimuth; A fracture type determination module is configured to identify microseismically derived fractures based on reservoir fracturing stimulation, calculate the fracture rupture moment tensor using dynamic fracture parameters, and identify the fracture rupture type based on the positive or negative sign of the fracture rupture moment tensor; fracture types include tension, compression, and shear fractures; The stress inversion module is configured to process different types of fractures based on the earthquake source and stress inversion method of reservoir fracturing. For shear fractures, stress inversion is performed on shear fractures using the fracture stress inversion method based on the Bott hypothesis. For tension and compression fractures, stress inversion is performed on tension and compression fractures using the modified fracture stress inversion method to obtain fracture stress inversion data of the maximum and minimum principal stress directions and stress shape factors of the target reservoir fracture surface. A fracture surface identification module is configured to construct a fracture instability coefficient model, analyze fracture instability based on fracture rupture source and stress inversion data, and identify the fracture surface state after reservoir fracturing based on fracture stress inversion results; The quantitative evaluation module is configured to establish an evaluation model for the fracture reservoir transformation effect based on the instability coefficient fracture tendency and the fracturing transformation stress and fracture inversion parameters through a multi-dimensional target reservoir transformation effect evaluation method, and quantitatively evaluate the reservoir fracturing transformation effect.

10. The reservoir fracturing and reconstruction crack and stress joint inversion and effect evaluation system according to claim 9, characterized in that: The dynamic crack parameter acquisition module includes: The tensor characterization unit is configured to determine a dynamic crack characterization tensor: the dynamic crack parameter is represented by a dynamic crack source characterization tensor ψ, and the specific formula is as follows: Where, ψ ij is the i-th row (i=1, 2, 3) and j-th column (j=1, 2, 3) element of the dynamic crack source tensor ψ; b i 、b j is the motion vector of the dynamic crack surface; n i 、n j is the normal vector of the dynamic crack surface; ΔA is the area of the newly generated dynamic crack; The tensor solving unit is configured to solve the dynamic crack characterization tensor for eigenvalue solution and obtain the three eigenvalues of the tensor ψ. The calculation formula is as follows: Where y1, y2 and y3 are the maximum, middle and minimum eigenvalues of the tensor ψ respectively; b k 、n k The subscript k in the equation is a dummy subscript that satisfies the Einstein summation convention, i.e. k n k =b1n1+b2n2+b3n3; |b| is the L2 norm of the motion vector b of the dynamic crack surface; The crack solving unit is configured to solve for dynamic crack parameters: In the generalized tensor-shear rupture source model, the intermediate eigenvalue of the tensor ψ is ψ2 = 0. This constraint must be satisfied in the model solution. The dynamic crack parameter solution formula is as follows: Where ψ1 is the maximum eigenvalue of the tensor ψ; ψ3 is the minimum eigenvalue of the tensor ψ; |b|ΔA is the rupture volume; n is the spatial normal; b is the motion vector; α is the tension-shear angle; The parameter and moment tensor unit is configured to determine the relationship between the dynamic crack parameters and the moment tensor: the dynamic crack source characterization tensor ψ is expressed by the moment tensor M, which has the following characteristics in the isotropic homogeneous state: M kl =ψ ij C ijkl =λδ kl ψ ii +2pm kl Where C ijkl is the fourth-order elastic stiffness tensor; λ and μ are the Lame constants; δ kl is the Kronecker function.

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