Evaluation and control method for difference in long and short axis of fracture crack

Abstract

The application discloses an evaluation and control method for long-short axis difference expansion of a fracturing fracture, and comprises the following steps: obtaining working parameters and fracturing processes of a fracturing area, wherein the working parameters comprise engineering parameters and geological parameters; a physical model of a fracturing layer is established according to the working parameters and the fracturing processes, and a numerical simulation model for the long-short axis difference expansion of the fracture is established based on the physical model; the working parameters of the fracturing area are numerically simulated through the numerical simulation model, the influence of each parameter on the long-short axis difference expansion behavior difference and size is analyzed according to the numerical simulation result, and a long-short axis difference expansion prediction model is established according to the influence; the long-short axis difference expansion of the fracturing fracture is predicted according to the expansion prediction model, and the fracturing process is adjusted according to the prediction result to realize the long-short axis difference expansion control of the fracturing fracture.

Description

Technical Field

[0001] The present invention relates to the field of engineering control, and in particular to a method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracturing crack. Background Art

[0002] Controlling the expansion of hydraulic fractures is a core technical challenge facing hydraulic fracturing. Hydraulic fractures often exhibit a geometric morphology characterized by the coexistence of a main fracture and multi-scale branch fractures around the fracture. Therefore, controlling the morphology of the main fracture significantly controls the overall fracture morphology. However, three-dimensional hydraulic fractures often exhibit a narrow ellipsoidal shape, with the major and minor axes of the elliptical fracture surface often expanding differentially. Therefore, controlling the differential expansion of the major and minor axes of the elliptical main fracture is a key issue in effectively controlling the expansion of hydraulic fractures. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a method for evaluating and controlling the differential expansion of the major and minor axes of hydraulic fracturing cracks.

[0004] For shallow reservoirs where vertical geostress is less than horizontal geostress, the main fracture is horizontal with the fracture surface perpendicular to the vertical geostress. It is necessary to control the long axis of the fracture to extend along the direction of oil and gas enrichment. On this basis, the vertical well stratified fracturing plan is determined, and the horizontal well staged fracturing wellbore trajectory, fracture arrangement and parameter design based on the horizontal fractures are designed.

[0005] For deep reservoirs where vertical geostress is higher than horizontal geostress, the normal direction of the main fracturing fracture surface is perpendicular to the vertical geostress. Based on the formation structure and the location of the oil-gas producing layer, it is necessary to control the fracturing cracks to preferentially extend vertically through the layer or horizontally, that is, to control the long axis orientation of the fracturing cracks.

[0006] Technical solution: The present invention provides a method for evaluating and controlling the differential expansion of the long and short axes of fracturing cracks, comprising: obtaining the working parameters and the fracturing process of the fracturing area, wherein the working parameters include engineering parameters and geological parameters; establishing a physical model of the fracturing area according to the working parameters and the fracturing process, and establishing a numerical simulation model for the differential expansion of the long and short axes of the cracks based on the physical model; numerically simulating the working parameters of the fracturing area through the numerical simulation model; analyzing the influence of various parameters on the differential expansion behavior and size of the long and short axes of the cracks according to the numerical simulation results, and establishing a prediction model for the differential expansion of the long and short axes of the cracks according to the influence; predicting the differential expansion of the long and short axes of the fracturing cracks according to the expansion prediction model, and adjusting the fracturing process according to the prediction results to achieve control of the differential expansion of the long and short axes of the fracturing cracks.

[0007] In addition, when conducting numerical simulation, the fracturing process is also numerically simulated, and the fracture long and short axis differential expansion prediction model is updated according to the numerical simulation results of the fracturing process and the numerical simulation results of the working parameters; the fracturing process includes vertical well layered fracturing, horizontal well staged fracturing, and horizontal well staged fracturing of horizontal fractures.

[0008] In addition, a numerical simulation model for the differential expansion of the major and minor axes of cracks is established based on the physical model, including: first, constructing a numerical model by combining numerical calculation methods and physical models; the numerical calculation methods include finite discrete element, boundary element, finite difference, finite volume, material point method, and phase field method; when using the finite discrete element method, the cohesive fracture unit that characterizes the fracture characteristics of the rock is inserted between the seepage fluid-solid coupling units that characterize the coupling mechanism of the fluid and rock, and the numerical simulation model is obtained by simulating the crack expansion by disconnecting the units in sequence.

[0009] In addition, a prediction model for the differential expansion of the major and minor axes of cracks is established based on the influence, including: first, converting the engineering parameters into laboratory-scale experimental parameters using the similarity criterion, carrying out rock fracture and fracturing tests under different confining pressures in combination with the experimental parameters, and then quantifying the expansion resistance parallel or perpendicular to the crack expansion direction based on the test results. Finally, the quantified crack expansion resistance is used to construct a numerical model field variable function as the modeling basis for characterizing the prediction model for the differential expansion of the major and minor axes; and a prediction model for the differential expansion of the major and minor axes of cracks is established based on the modeling basis.

[0010] In addition, the prediction model of the differential expansion of the major and minor axes of the crack includes an engineering equal-size model or a similar-size model; in the engineering equal-size model, the model size is consistent with the actual size of the project, and the field variable function of the engineering equal-size model shown in Equation (12) is constructed by using the differential distribution characteristics of the isotropic expansion resistance;

[0011] (12)

[0012] Where, is the field variable function of the engineering equal-size model, and is the spatial coordinate in the engineering equal-size model, and It is the characteristic parameter of the crack propagation resistance field in the engineering size model, and its value is adjusted according to the actual size of the project.

[0013] In the similar size model, the difference in the expansion resistance of the major and minor axes and the difference in the numerical model and engineering geometry are combined to obtain the field variable function of the similar size model as shown in formula (13). This model is a supplement to the engineering equal size model.

[0014] (13)

[0015] Where, is a function of field variables in a model of similar size, and are the spatial coordinates of similar-sized models, 、 、 and It is the characteristic parameter of the crack propagation resistance field variable in the similar size model, and its value is adjusted according to the correlation between the actual project size and the model size.

[0016] In addition, after constructing the prediction model for the differential expansion of the length and short axes of cracks, it also includes: trial calculations of engineering parameters and geological parameters, and analysis of the differences in the behavior and size of the differential expansion of the length and short axes of cracks caused by different engineering parameters and geological parameters, and analysis of the main controlling factors and parameter sensitivity. Furthermore, based on the crack expansion laws presented in the trial calculation results and the weights of the influence of various engineering parameters and geological parameters on the differential expansion of the length and short axes of cracks, an artificial intelligence algorithm is used and trained based on the numerical simulation results to obtain a prediction model for the differential expansion of the length and short axes of cracks, compile intelligent design software for the differential expansion of the length and short axes of hydraulic fractures, and obtain a chart calculated under multi-factor conditions.

[0017] In addition, when the fracturing process is vertical well layered fracturing, adjusting the fracturing process according to the prediction results includes: according to the sensitivity of the fracturing process and engineering parameters to the balanced expansion of each reservoir and the degree of control, six levels of control are proposed corresponding to different prediction results. Level 1 control: when the spacing between multiple fractures in the fracturing is less than the preset threshold, the vertical well layered fracturing is preferably performed in layers and in sequence, and the horizontal well segmented multi-cluster fracturing is preferably performed cluster by cluster and segment by segment by continuous tubing, or the cluster spacing is appropriately increased to reach the critical cluster spacing for balanced expansion of multiple fractures; Level 2 control: based on the determination of the fracturing sequence, the displacement that is conducive to the uniform expansion of each fracture is preferred; Level 3 control: the perforation distribution that is suitable for the balanced expansion of fractures with different fracture spacing is preferred; Level 4 control: the fracturing fluid viscosity that is conducive to the uniform expansion of each fracture is preferred; Level 5 control: the fracturing fluid volume that is conducive to increasing the fracture size is preferred; Level 6 control: when the above control is completed, but some fractures do not expand after reaching the critical liquid volume, a process combining temporary plugging within the well section and within the fracture is adopted to promote the expansion of the uninitiated fractures.

[0018] In addition, when the fracturing process is horizontal well staged fracturing of horizontal fractures, the fracturing process is adjusted according to the prediction results, including:

[0019] According to the fracturing process and engineering parameters, a two-level control mechanism is proposed for the control of fracture expansion and seepage interference in horizontal wells with horizontal fractures of the same vertical depth. In the horizontal well staged fracturing of horizontal fractures, if the two fractures do not intersect, the first-level control increases the fracture spacing and reduces the displacement; if the two fractures have intersected, the second-level control increases the displacement, increases the amount of fracturing fluid, and increases the viscosity of the fracturing fluid; in the horizontal well staged fracturing of horizontal fractures of different vertical depths, if the two fractures overlap, the first-level control design is most suitable for the fracture spacing with the dominant expansion of the long axis. On this basis, the second-level control increases the displacement, increases the amount of fracturing fluid, and increases the viscosity of the fracturing fluid.

[0020] Compared with the prior art, the present invention has the following significant effects:

[0021] 1. Accuracy of the physical model in the numerical simulation method: This is specifically reflected in the use of a fracture extension mechanics criterion that is more consistent with rock fracture. Currently, most rock fracture processes are characterized by linear elastic fracture, which is inconsistent with the plastic softening fracture characteristics of the fracture process zone at the front end of the fracture in rock materials. This solves the scientific and technological challenge of accurately characterizing the fracture extension of rock materials.

[0022] 2. Numerical simulation parameter selection and modeling accuracy: Based on the on-site engineering parameters, the aforementioned rock fracture fracture extension mechanics judgment criteria, the fracture fluid flow model, the perforation pipe flow model, and the rock deformation-seepage coupling control mathematical model were used to convert engineering parameters into numerical simulation parameters, and numerical modeling was performed, achieving similarity and unity between engineering and numerical models.

[0023] 3. Applicability of engineering control using numerical simulation calculation model rules: Artificial intelligence methods are used to predict the differential expansion of the long and short axes of cracks under different engineering and geological parameters. The data volume is large, the numerical model results are highly accurate, and the feasibility of engineering control based on the numerical model results is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the process of the method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to the present invention;

[0025] Figure 2 Schematic diagram of the cohesive crack model in the fracture process zone to describe the fracture characteristics of rock materials;

[0026] Figure 3 Schematic diagram of the fracturing process and differential expansion of the major and minor axes of the fractures in the vertical well stratified fracturing of the present invention (taking the major axis parallel to the direction of maximum horizontal in-situ stress as an example);

[0027] Figure 4 Schematic diagram of the fracturing process and the differential expansion of the major and minor axes of the fractures in the staged fracturing of a horizontal well according to the present invention;

[0028] Figure 5 Schematic diagram of the fracturing process of staged fracturing of horizontal wells with vertically equal-depth horizontal fractures and the differential expansion of the major and minor axes of the fractures (taking the major axis parallel to the direction of maximum horizontal in-situ stress as an example);

[0029] Figure 6 Schematic diagram of the fracturing process of staged fracturing of horizontal wells with vertically variable-depth horizontal fractures and the differential expansion of the major and minor axes of the fractures (taking the major axis parallel to the direction of maximum horizontal in-situ stress as an example);

[0030] Figure 7 Schematic diagram of the fracturing process of staged fracturing of horizontal wells with vertically variable-depth horizontal fractures and the differential expansion of the major and minor axes of the fractures from a top view (taking the major axis parallel to the direction of maximum horizontal in-situ stress as an example);

[0031] Figure 8 Schematic diagram of a numerical simulation model for fracturing a single reservoir and a single fracture expansion according to the present invention;

[0032] Figure 9 Schematic diagram of a multi-reservoir and multi-fracture expansion fracturing numerical simulation model of the present invention;

[0033] Figure 10 Schematic diagram of the fracturing numerical simulation results of the differential expansion of the major and minor axes of a single fracture according to the present invention (taking the major axis parallel to the direction of the maximum horizontal in-situ stress as an example);

[0034] Figure 11 Schematic diagram of the fracturing numerical simulation results of the vertical well layered fracturing with different major and minor axis extension of multiple fractures (taking the major axis parallel to the direction of maximum horizontal ground stress as an example);

[0035] Figure 12 Schematic diagram of the fracturing numerical simulation results of the present invention for the differential expansion of the major and minor axes of horizontal cracks with the same minor axis in the vertical direction of the depth (taking the major axis parallel to the direction of the maximum horizontal stress as an example);

[0036] Figure 13 Schematic diagram of the fracturing numerical simulation results of the differential expansion of the major and minor axes of horizontal cracks intersecting in the same minor axis direction at the same depth according to the present invention (taking the major axis parallel to the direction of the maximum horizontal in-situ stress as an example);

[0037] Figure 14 Schematic diagram of the fracturing numerical simulation results of the present invention for the differential expansion of the major and minor axes of vertically different-depth minor-axis fractures separated from the horizontal fracture (taking the major axis parallel to the direction of the maximum horizontal in-situ stress as an example);

[0038] Figure 15 Schematic diagram of the fracturing numerical simulation results of the differential expansion of the major and minor axes of overlapping horizontal cracks with vertically different depths and minor axes according to the present invention (taking the major axis parallel to the direction of the maximum horizontal stress as an example). DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, each embodiment of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in each embodiment of the present invention, many technical details are provided to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in this application can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction. The technical solution of the application is further described in detail below with reference to the accompanying drawings.

[0040] This embodiment provides a method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture, including obtaining the working parameters and the hydraulic fracturing process of the hydraulic fracturing area, wherein the working parameters include engineering parameters and geological parameters; establishing a physical model of the hydraulic fracturing area based on the working parameters and the hydraulic fracturing process, and establishing a numerical simulation model for the differential expansion of the major and minor axes of the fracture based on the physical model; numerically simulating the working parameters of the hydraulic fracturing area using the numerical simulation model, analyzing the influence of each parameter on the differential expansion behavior and size of the major and minor axes of the fracture based on the numerical simulation results, and establishing a prediction model for the differential expansion of the major and minor axes of the fracture based on the influence; predicting the differential expansion of the major and minor axes of the hydraulic fracture using the expansion prediction model, and adjusting the hydraulic fracturing process based on the prediction results to achieve differential expansion control of the major and minor axes of the hydraulic fracture. By establishing a physical model and a numerical simulation model to obtain the laws of the major and minor axes during rock fracture, and controlling the expansion of the major and minor axes based on the laws, a judgment criterion that is more consistent with the fracture extension mechanics of rock fracture is adopted, thereby solving the scientific and technological problem of accurately characterizing the expansion of rock-like materials.

[0041] In this embodiment, the process of the evaluation and control method of the differential expansion of the major and minor axes of the fracturing crack is as follows: Figure 1 shown.

[0042] In step 1, the operating parameters of the fracturing area and the fracturing process are obtained, wherein the operating parameters include engineering parameters and geological parameters.

[0043] In this embodiment, large-scale field surveys of typical hot dry rock geothermal, unconventional oil and gas, and coalbed methane fracturing projects can be carried out. For fracturing processes such as single-layer fracturing of vertical wells, layered fracturing of vertical wells, multi-cluster fracturing of horizontal wells, and staged fracturing of horizontal fractures, geological parameters including but not limited to reservoir depth, reservoir sand body characteristics, ground stress, reservoir permeability, fracture toughness, elastic modulus, Poisson's ratio, and filtration coefficient can be determined. Process and engineering parameters including but not limited to fracturing fluid viscosity, construction displacement, total amount of fracturing fluid, number of perforations, perforation pattern, layer spacing of vertical well layered fracturing, and cluster-segment spacing of horizontal well staged fracturing can be determined. Based on the monitoring results of on-site microseismic, optical fiber, tracer, etc., the fracture morphology, geometric size, and fracture aspect ratio under different fracturing methods and different geological and engineering conditions can be determined.

[0044] Specifically, such as Figure 3-Figure 7 As shown in the figure, the fracture morphologies corresponding to the four processes of vertical well stratified fracturing, horizontal well staged fracturing, horizontal well staged fracturing of vertical horizontal fractures of the same depth, and horizontal well staged fracturing of vertical horizontal fractures of different depths are respectively shown, that is, the schematic diagram of the difference in the major and minor axis expansion of the fractures, among which, is the vertical ground stress, is the maximum horizontal ground stress, is the minimum horizontal ground stress, and the crack morphology characterization parameters include the fracture width, fracture major axis and fracture minor axis.

[0045] exist Figure 3 In the middle, it is a vertical well layered fracturing for horizontal fractures. The fractures are parallel to the horizontal stress, and the long axis of the fracturing fracture is parallel to the direction of the maximum horizontal stress.

[0046] exist Figure 4 In the middle, it is for staged fracturing of horizontal wells, the cracks are parallel to the vertical stress, and the long axis of the fracturing cracks is parallel to the vertical stress;

[0047] exist Figure 5 In the horizontal well staged fracturing, the horizontal fractures at the same vertical depth are parallel to the horizontal stress, and the long axis of the fracture is parallel to the direction of the maximum horizontal stress. In addition, under this fracturing process, the fractures are at the same depth and there are three positional relationships between the fractures: separation, tangency, and intersection.

[0048] exist Figure 6 In the horizontal well staged fracturing, the fractures are parallel to the horizontal stress, and the long axis of the fractures is parallel to the direction of the maximum horizontal stress. In addition, under this fracturing technology, the fractures are at different depths, and there are three positional relationships between the fractures: separation, tangency, and intersection.

[0049] Figure 7 yes Figure 6 A top view of Figure 7In the horizontal well staged fracturing, the fractures are parallel to the horizontal stress, and the long axis of the fractures is parallel to the direction of the maximum horizontal stress. In addition, under this fracturing technology, the fractures are at different depths, and there are three positional relationships between the fractures: separation, tangency, and intersection.

[0050] In step 2, a physical model of the fracturing area is established according to the working parameters and the fracturing process, and a numerical simulation model is established for the differential expansion of the major and minor axes of the fractures based on the physical model.

[0051] Design physical mechanics and physical simulation experiments to develop a method to characterize the effects of different process, engineering, and geomechanical parameters on the differential propagation of the major and minor axes of fractures. First, determine rock composition, microstructure, and rock mechanical parameters (including but not limited to tension, tension-shear, compression-shear, elastic, and plastic parameters). Then, conduct rock fracture tests with confining pressure perpendicular and parallel to the direction of fracture propagation to determine the rock's resistance to fracture propagation in each confining pressure direction. Directions with high resistance are more likely to form the minor axis of the fracture. Secondly, in-situ cores, outcrops and similar samples of the project are taken to design and carry out true triaxial fracturing physical simulation tests under the influence of different processes, engineering and geological conditions. Typical processes such as "vertical well (layered) fracturing, horizontal well segmented (multi-cluster within a segment) fracturing" are preferred, as are typical geological and engineering parameters such as "confining pressure, permeability, injection rate, fracturing fluid viscosity, and fracturing fluid volume". At the same time, taking into account the similarity criteria between experiments and engineering, crack monitoring and characterization methods including but not limited to microseismic, fiber Bragg grating, and digital image correlation are adopted to preliminarily determine the influence of different processes, engineering and geological parameters on crack morphology and differential expansion of major and minor axes, which serves as the basis for constructing a numerical simulation physical model.

[0052] Physical models include but are not limited to rock fracture models, fluid flow models in fractures during fracturing, perforation tube flow models during fracturing, and mathematical models for rock deformation-seepage coupling control;

[0053] Specifically, the rock fracture model: Based on the rock information of optical and acoustic monitoring, the fracture characteristics of rock materials are characterized and the cohesive crack model of the fracture process zone is used for characterization. The characteristics of rock plastic fracture include cohesive tensile strength , dissipated energy , fracture energy , cumulative dissipated energy , critical cumulative dissipated energy , cohesive tensile strength As shown in formula (1),

[0054] =(3 ) / [ ] (1)

[0055] Where: is the initial load for the development of cohesive cracks in the fracture process zone; S is the span of the three-point bending test specimen; B is the specimen thickness; H is the specimen width; is the length of the prefabricated crack;

[0056] Cohesive tensile strength in the fracture process zone The complete opening degree of cohesive crack per unit length in the fracture process zone (critical opening displacement) (corresponding to the complete development of the fracture process zone) is a model parameter in the fracture model. Specifically, Figure 2 As shown in the figure, it illustrates the model of cohesive cracks in the fracture process zone that describes the fracture characteristics of rock materials. Figure 2 ① is the evolution curve of the correlation between the cohesive force and the crack opening degree in the fracture process zone per unit length, which characterizes the softening process of the cohesive crack per unit length in the fracture process zone: The critical cohesive tensile strength for softening cohesive cracks is when the cohesive tensile strength changes from achieve When , the fracture process zone begins to develop and the cohesive cracks begin to open; It is the full opening degree of the cohesive crack per unit length during the softening process. When the opening displacement of the softened cohesive crack reaches When the unit length cohesive crack is fully developed to form a real crack surface. When the unit length cohesive crack is in the softening stage and has not yet fully opened - The integrated area under the curve is the dissipated energy , and the unit length cohesive crack from the beginning of softening to the formation of the real crack surface - The integral area under the curve is the fracture energy of the cohesive crack Specifically, Figure 2 ② in the figure is the overall development process of cohesive cracks in the fracture process zone, where is the length of the cohesive crack in the softened fracture process zone, and L is the length of the fully developed cohesive crack in the fracture process zone. , critical opening displacement The three parameters of the fracture process zone length L can be directly measured by the test. In the cohesion-crack opening displacement constitutive relationship determined based on the fracture model, the dissipated energy of the unit length cohesive crack in the fracture process zone is in the softening stage and has not yet fully opened. Passable Characterization

[0057] (2)

[0058] Where, is the crack opening degree in the fracture process zone per unit length, Open for the cracks The crack cohesion under the state is the differential operator;

[0059] The fracture energy of the unit length cohesive crack from the beginning of softening to the formation of the real fracture surface in the fracture process zone , as shown in the formula express;

[0060] (3)

[0061] Where, is the full opening of cohesive cracks per unit length in the fracture process zone, Open for the cracks The crack cohesion under the state To calculate the crack opening;

[0062] Cumulative dissipated energy during the softening process of cohesive cracks in the fracture process zone , as expressed in formula (4).

[0063] (4)

[0064] Where, is the dissipated energy, is the cohesive crack length in the softened fracture process zone, is the calculated length of the cohesive crack in the fracture process zone;

[0065] Critical cumulative dissipated energy during the softening process of cohesive cracks in the fracture process zone , as expressed in formula (5).

[0066] (5)

[0067] Where, is the dissipated energy, and L is the length of the fully developed cohesive crack in the fracture process zone.

[0068] Constructing a model for fluid flow within fractures during fracturing: When the fracture process zone is fully developed, cohesive fractures evolve into macroscopic fractures, forming two fracture planes. During hydraulic fracturing, interstitial flow occurs between the two fracture planes. Within the cohesive fracture model that has evolved into a macroscopic fracture, interstitial flow exhibits two mechanical behaviors: tangential flow, where the fluid flows along the fracture propagation direction. By determining the fluid mechanics parameters, the fluid flow characteristics in that direction (steady-state vs. unsteady-state flow, uniform vs. non-uniform flow, laminar vs. turbulent flow, rotational vs. irrotational flow, etc.) are determined; and normal flow, where fluid loss occurs perpendicular to the fracture plane.

[0069] Specifically,

[0070] Tangential flow, the fluid flows along the crack expansion direction, which conforms to the Newtonian fluid model, as shown in Equation (6);

[0071] (6)

[0072] Where: is the displacement; is the fluid pressure; is the flow coefficient; is the fluid viscosity;

[0073] Normal flow, filtration occurs perpendicular to the fracture surface, as shown in formula (7);

[0074] (7)

[0075] Wherein, subscripts t, b and i represent the upper surface, lower surface and crack of the crack respectively, q is the filtration rate, p is the fluid pressure, and c is the filtration coefficient;

[0076] Construction of perforation pipe flow model during fracturing: During the fracturing process, pipe flow often occurs in the wellbore and perforations. First, the fluid flow characteristics (flow type and fluid properties) are determined, and based on the conservation of mass, momentum and energy, the controlling equation (continuity equation, Navier-Stokes equation or energy equation) is selected. The model is further simplified and boundary conditions are set. Finally, a numerical solution is performed and the model is verified.

[0077] Specifically, the perforation is introduced by using the method of sharing nodes between deep hole pipe flow and seepage flow, and the pipe flow model equation (8) is obtained by coupling Darcy's law, Bernoulli equation, loss coefficient equation and Blasius friction coefficient equation.

[0078] Pipe flow model equation:

[0079] (8)

[0080] Where, is the fluid pressure difference, is the fluid density, is the acceleration due to gravity, is the relative height of the fluid, is the fluid loss coefficient, is the loss coefficient in the connection direction, and V is the fluid flow rate.

[0081] Construction of rock deformation-seepage coupling control model: Preferably, the rock skeleton Biot effective stress model, stress balance equation (virtual work principle), continuity equation and Darcy's law are coupled to establish the rock deformation-seepage coupling control model.

[0082] Specifically, the effective stress equation:

[0083] (9)

[0084] Where: I is the identity matrix; is the effective stress; K is the proportional factor determined by surface tension and saturation; is the wetting fluid pore pressure; σ is the total stress;

[0085] Stress equilibrium equation:

[0086] (10)

[0087] in: is the effective stress of the reservoir matrix; is the matrix [1, 1, 1, 0, 0]; is the pore pressure of porous media;

[0088] R is the surface external force per unit area; is the virtual velocity field of the reservoir matrix; r is the body force per unit volume; S is the load action area; is the reservoir matrix virtual strain rate; VU is the unit volume;

[0089] Continuity equation:

[0090]

[0091] Where: is the rate of change of fluid density with time; is the net outflow of fluid.

[0092] Based on the physical model, a numerical simulation model for the differential expansion of the major and minor axes of the crack is established, including: firstly, a variety of numerical calculation methods such as finite element, discrete element, boundary element, finite difference, finite volume, material point method, phase field method, etc. are comprehensively used, and the numerical model is constructed in combination with the above physical model. Specifically, Figure 8-Figure 9 The figure shows the constructed numerical simulation models for fracturing a single reservoir with a single fracture and a multi-reservoir with multiple fractures, respectively. The model demonstrates the positional relationship between reservoirs and barriers in both the multi-reservoir and single-reservoir scenarios. Considering that two-dimensional and three-dimensional numerical simulations of rock fracturing must account for "medium heterogeneity, differences in fracture major and minor axis extension, the formation of multiple fractures and their interactions, and ease of introducing multi-field physical models," the finite discrete element method (FEM) is preferred. This method inserts "cohesive fracture units representing the fracture process zone" between "seepage fluid-solid coupling units" and simulates fracture extension by sequentially disconnecting the units. This method serves as the overall approach for numerical simulations of differential fracture major and minor axis extension.

[0093] On this basis, according to the actual process, engineering and geological conditions, dimensionless proportional dimensions are used to establish two types of fracturing numerical simulation models to characterize the expansion of single fractures and multiple fractures. For the single fracture expansion numerical model, the single fracture distribution morphology and the differential expansion characteristics of the long and short axes under the influence of engineering and geological conditions can be characterized; for the multiple fracture expansion numerical model, the geometric size characteristics of the fractures under the competitive expansion of multiple fractures and the differential expansion characteristics of the long and short axes under the influence of engineering and geological conditions can be characterized. At the same time, the mutual disturbance expansion characteristics of multiple fractures in fracturing processes such as single-layer and layered fracturing of vertical wells and segmented (multi-cluster) fracturing of horizontal wells can be characterized.

[0094] It should be noted that there are two cases for the differential expansion of the major and minor axes of the above-mentioned cracks: (1) For shallow reservoirs, the minimum principal stress appears in the vertical direction. At this time, the crack expansion direction is perpendicular to the minimum principal stress direction, and the crack expands horizontally, with the major and minor axes appearing in the horizontal direction; (2) For deep reservoirs, the minimum principal stress appears in the horizontal direction. At this time, the crack expands vertically, with the major and minor axes appearing in the vertical direction.

[0095] In order to accurately characterize the differential expansion characteristics of the long and short axes of hydraulic fractures, the numerical simulation method must cover the following four characteristics: ① Based on the physical model, the numerical model characterizes the evolution law of the long and short axis expansion resistance of the hydraulic fractures with geological and engineering factors, and constructs a characterization function. Preferably, a method with a customized non-uniform distribution field variable is used to characterize the effects of the ground stress difference coefficient and the size difference coefficient on the differential expansion of the long and short axes of the fractures, so that there are differences in the long and short axis expansion resistance of the fractures; ② It has the ability to characterize the anisotropic characteristics of the material. Through permeability anisotropy modeling, it can characterize the spatial differences in permeability in orthogonal and parallel directions such as "one-way increase, low in the middle and high on both sides, high in the middle and low on both sides" ③ “Two-dimensional and three-dimensional multi-fracture mutual interference” combined with “differential distribution of liquid with alternating expansion of multiple fractures”: based on the differential expansion of the major and minor axes of a single fracture, for the complex working conditions of multi-fracture expansion, preferably, the local finite discrete element method is used to realize the characterization of the multi-fracture expansion morphology and competition mechanism, and at the same time, the pipe flow unit nodes and the fracture units are coupled to realize the differential distribution of liquid with the alternating expansion of multiple fractures; ④ Simulation of perforation parameters: because the perforation and hydraulic fracture sizes span scales and are difficult to simulate in a 1:1 ratio, it is preferably preferred to control the flow parameters such as the number and distribution of pipe flow units, and characterize the influence of perforation parameters such as the number of perforations and perforation distribution on flow parameters such as fluid inlet friction and flow velocity.

[0096] In step 3, the working parameters of the fracturing area are numerically simulated through the numerical simulation model.

[0097] Specifically, a numerical model is first constructed by combining numerical calculation methods and the physical model; the numerical calculation methods include finite discrete element, boundary element, finite difference, finite volume, material point method, and phase field method; when using the finite discrete element method, the cohesive fracture unit characterizing the rock fracture characteristics is inserted between the seepage fluid-solid coupling unit characterizing the fluid-rock coupling mechanism, and the numerical simulation model is obtained by simulating the crack expansion by disconnecting the units in sequence.

[0098] After the numerical simulation model is established, the numerical simulation includes: numerical simulation of the effect of geological factors on the differential expansion of the major and minor axes of fractures. First, a standard condition numerical model is established based on typical field geological parameters and engineering parameters. On this basis, the control variable method is used to carry out numerical simulation of the influence of rock mechanics parameters (including but not limited to Poisson's ratio, elastic modulus, fracture toughness, etc.) and geological parameters (including but not limited to ground stress, permeability, reservoir-interlayer depth, fracture spacing, and reservoir-interlayer sand body characteristics) on the differential expansion of the major and minor axes of fractures.

[0099] The numerical simulation of the effect of engineering parameters on the differential expansion of the length and short axes of fractures is based on the standard condition numerical model and adopts the control variable method to carry out numerical simulation of the influence of engineering parameters including but not limited to perforation method, fracturing fluid properties (viscosity, type and filtration coefficient), displacement, fluid volume, etc. on the differential expansion of the length and short axes of fractures.

[0100] In step 4, the influence of various parameters on the difference in expansion behavior and size of the crack major and minor axes is analyzed based on the numerical simulation results, and a prediction model for the difference in expansion of the crack major and minor axes is established based on the influence.

[0101] In this embodiment, the influence of various parameters on the difference in expansion behavior and size of the long and short axes of the cracks is analyzed according to the results of numerical simulation, including: parameter sensitivity and main controlling factor analysis. Based on the results of numerical simulation, for the law of the difference in expansion of the long and short axes of the cracks, the influence of geological and engineering parameters on the difference in expansion of the long and short axes of the hydraulic fractures can be classified from the two aspects of monotonic change of crack size and nonlinear change of crack size. Furthermore, based on the influence of parameters on the difference in expansion behavior and size of the long and short axes of the cracks, the main controlling factor and parameter sensitivity analysis are performed.

[0102] The main controlling factor of the major and minor axis differential expansion is the "root factor" that determines the difference in crack expansion behavior in the major and minor axis directions. It is not equivalent to the parameter sensitivity that affects the major and minor axis dimensions of the crack. The control strength of the crack major and minor axis expansion behavior can be determined based on each parameter.

[0103] Parameter sensitivity refers to the effect of parameter changes on crack size changes based on the overall law of crack expansion determined by the main controlling factors. Generally speaking, it can be regarded as "branch and leaf factors". Non-main controlling factors can have a stronger effect on crack size than main controlling factors. For example, the "branch and leaf volume" can be larger than the "roots", but the growth law of the entire tree is determined by the roots.

[0104] All kinds of geological parameters and engineering parameters are sensitive parameters that further affect the size of the major and minor axes based on the main controlling factors that determine the orientation of the major and minor axes. The crack size change rate / influence factor change rate is used as the influencing factor. The specific statistical method is as follows:

[0105] Crack size change rate = |crack size 2 - crack size 1| / crack size 1;

[0106] Parameter change rate = |parameter2-parameter1| / parameter1;

[0107] Impact factor = crack size change rate / parameter change rate.

[0108] The larger the impact factor, the higher the sensitivity to the influence of the major and minor axes of the crack.

[0109] A prediction model for the differential expansion of the major and minor axes of cracks is established based on the influence. Specifically, the prediction model for the differential expansion of the major and minor axes of cracks is first converted into laboratory-scale experimental parameters using the similarity criterion, and rock fracture and fracturing tests under different confining pressures are further carried out. Then, the expansion resistance parallel / perpendicular to the crack expansion direction is quantified based on the experimental results. Finally, the quantified crack expansion resistance is used to construct a numerical model field variable function as the modeling basis for characterizing the differential expansion prediction model of the major and minor axes; a prediction model for the differential expansion of the major and minor axes of cracks is established based on the modeling basis.

[0110] In this embodiment, the modeling basis includes a chart (the chart is the variation pattern of the major axis, minor axis and major-minor axis ratio of the crack under different geological and engineering parameters). In view of the problem that the major and minor axes of the cracks vary strongly nonlinearly under the influence of multiple factors such as geological parameters and engineering parameters, and it is difficult to accurately predict the crack expansion size using traditional mathematical statistical models, "artificial intelligence deep learning" methods including but not limited to linear regression models, logistic regression models, decision tree models, support vector machines (SVM) models, neural network models and ensemble learning are used to train based on numerical simulation results to obtain a prediction model for the differential expansion of the major and minor axes of the cracks, and to compile intelligent design software for the differential expansion of the major and minor axes of the fracturing cracks. This chart optimization software can predict the size of the fracturing cracks by changing the engineering, geological and mechanical parameters to obtain a calculation chart under multi-factor conditions.

[0111] In the embodiment, the established crack long-short axis difference extension prediction model includes an engineering scale model or a similar size model.

[0112] In the engineering scale model, the model size is consistent with the actual engineering size, and a field variable function of the engineering scale model is constructed using the difference distribution characteristics of the extension resistance in each direction, as shown in formula (12).

[0113] (12)

[0114] In the formula, is the field variable function of the engineering scale model, and is the spatial coordinate in the engineering scale model, and is a characteristic parameter of the crack extension resistance field variable in the engineering scale model, and the numerical value is adjusted according to the actual engineering size.

[0115] In the similar size model, the long-short axis extension resistance difference and the model-engineering geometric difference are combined to obtain a field variable function of the similar size model, as shown in formula (13), which is a supplement to the engineering scale model.

[0116] (13)

[0117] In the formula, is the field variable function of the similar size model, and is the spatial coordinate of the similar size model, , , and is a characteristic parameter of the crack extension resistance field variable in the similar size model, and the numerical value is adjusted according to the correlation between the actual engineering size and the model size.

[0118] After constructing the crack long-short axis difference extension prediction model, the following steps are further included: trial calculation of engineering parameters and geological parameters, analysis of the influence of different engineering and parameters on the crack long-short axis difference extension behavior and size, main control factor and parameter sensitivity analysis, further, based on the crack extension law presented by a large number of trial calculation results and the influence weight of each engineering parameter and geological parameter on the crack long-short axis difference extension, an artificial intelligence algorithm is used to train based on the numerical simulation results to obtain the crack long-short axis difference extension prediction model, an intelligent design software for fracturing crack long-short axis difference extension is compiled, and a calculation chart under multiple factor conditions is obtained. The chart optimization software can predict the fracturing crack size by changing the engineering parameters, geological parameters and mechanical parameters.

[0119] In addition, in this embodiment, when performing numerical simulation, the fracturing process is also numerically simulated, and the extended prediction model is updated according to the numerical simulation results of the fracturing process and the numerical simulation results of the working parameters. The fracturing process includes: vertical well layered fracturing, horizontal well staged fracturing, horizontal well staged fracturing of horizontal fractures, etc. In this embodiment, the numerical simulation results of the fracturing process are as follows: Figure 10-15 As shown, in Figure 10-15 In the simulation, the numerical simulation results are presented through the fracturing crack cloud map. The cloud map shows the major and minor axis information, which can more clearly grasp the major and minor axis expansion rules under different processes. Figure 10-15 They are the numerical simulation results of the fracturing with the difference of the long and short axes of a single fracture, the vertical well stratification (such as Figure 11 The numerical simulation results of the differential expansion of the long and short axes of multiple fractures (middle layers 1, 2, and 3), the differential expansion of the long and short axes of horizontal fractures separated in the direction of the short axis at the same vertical depth, the differential expansion of horizontal fractures intersecting in the direction of the short axis at the same vertical depth, the differential expansion of horizontal fractures separated in the direction of the short axis at different vertical depths, and the differential expansion of horizontal fractures overlapping in the direction of the short axis at different vertical depths are all taken as examples when the long axis is parallel to the direction of the maximum horizontal stress.

[0120] In step 5, the differential expansion of the major and minor axes of the fracturing cracks is predicted according to the expansion prediction model, and the fracturing process is adjusted according to the prediction result to achieve the control of the differential expansion of the major and minor axes of the fracturing cracks.

[0121] When the process is vertical well stratified fracturing, the fracturing process is adjusted according to the prediction results, including: according to the sensitivity of the fracturing process and engineering parameters to the balanced expansion of each reservoir and the degree of control, six levels of control are proposed corresponding to different prediction results. The first level of control is: when the spacing between multiple fractures in the fracturing is small, the vertical well stratified fracturing is preferably performed in layers and in sequence, and the horizontal well segmented multi-cluster fracturing is preferably performed cluster by cluster and segment by segment by continuous tubing drag, or the cluster spacing is appropriately increased to reach the critical cluster spacing for balanced expansion of multiple fractures; the second level of control is: based on the determination of the fracturing sequence, the displacement is preferably preferred to be conducive to the uniform expansion of each fracture; the third level of control is: preferably the perforation distribution suitable for the balanced expansion of fractures with different fracture spacings, for example, the number of perforations can be appropriately reduced in the high permeability zone; the fourth level of control is: preferably the fracturing fluid viscosity is conducive to the uniform expansion of each fracture; the fifth level of control is: preferably the fracturing fluid volume is conducive to increasing the fracture size;

[0122] Sixth-level regulation: When the above regulation is completed, but the partially fractured cracks do not expand after reaching the critical fluid volume, a process combining temporary plugging within the well section and within the fracture can be used to promote the expansion of the uninitiated cracks.

[0123] In this embodiment, the implementation process is as follows:

[0124] Firstly, numerical simulation analysis is carried out for layered fracturing of vertical wells. Based on the numerical simulation model of different extension of long and short axes of single fracturing fracture, different numbers of "cohesion fracture elements representing fracture process zone" are inserted between "seepage fluid-structure coupling elements" at different positions in the numerical simulation model to realize parallel extension of multiple fracturing fractures under different process conditions and study the mutual influence characteristics of parallel extension of multiple fracturing fractures under different construction process conditions, including but not limited to stress field and rock mechanics behavior (stress redistribution, change of stress intensity factor at crack tip, change of rock failure mode, etc.), fracture morphology and extension characteristics (fracture length and width, fracture tortuosity, complexity of fracture network, etc.), fluid flow and fracturing effect (non-uniform distribution of fracturing fluid, migration and settlement of proppant, filtration characteristics, reservoir reconstruction volume, etc.) and the like.

[0125] Based on the numerical simulation model, numerical simulation of the influence of geological factors on the mutual interference of parallel extension of multiple fracturing fractures is carried out. Firstly, according to typical field process, geological and engineering parameters, a standard condition numerical simulation model is established. On this basis, the control variable method is adopted to carry out numerical simulation of the influence of rock mechanics parameters (including but not limited to Poisson's ratio, elastic modulus, fracture toughness, etc.) and geological parameters (including but not limited to stress, permeability, reservoir and barrier layer depth, fracture spacing, sand body characteristics of reservoir and barrier layer) on the mutual interference of parallel extension of multiple fracturing fractures. The affected change characteristics include but are not limited to stress field and rock mechanics behavior (stress redistribution, change of stress intensity factor at crack tip, change of rock failure mode, etc.), fracture morphology and extension characteristics (fracture length and width, fracture tortuosity, complexity of fracture network, etc.), fluid flow and fracturing effect (non-uniform distribution of fracturing fluid, migration and settlement of proppant, filtration characteristics, reservoir reconstruction volume, etc.) and the like.

[0126] Based on the numerical simulation model, numerical simulation of the influence of engineering parameters on the differential extension of long and short axes of fractures is carried out. Based on the calibration of the numerical simulation model under typical conditions, the control variable method is adopted to carry out numerical simulation of the influence of engineering factors including but not limited to perforation method, number of perforations, fracturing fluid properties (viscosity, type and filtration coefficient), displacement, liquid volume and the like on the mutual interference of parallel extension of multiple fracturing fractures. The affected change characteristics include but are not limited to stress field and rock mechanics behavior (stress redistribution, change of stress intensity factor at crack tip, change of rock failure mode, etc.), fracture morphology and extension characteristics (fracture length and width, fracture tortuosity, complexity of fracture network, etc.), fluid flow and fracturing effect (non-uniform distribution of fracturing fluid, migration and settlement of proppant, filtration characteristics, reservoir reconstruction volume, etc.) and the like.

[0127] The parameter sensitivity and main controlling factors were analyzed based on the numerical simulation results. Based on the numerical simulation results of the mutual interference and expansion of multiple parallel hydraulic fractures, priority was given to the influence of construction technology, engineering and geological parameters on the changes in the major and minor axis dimensions of multiple hydraulic fractures, the mutual interference between multiple fractures (inhibition and promotion of expansion), and the main controlling factors and parameter sensitivity analysis were performed.

[0128] Specifically, the analysis is conducted through calculation charts. The control variable method is adopted. Based on the numerical model calculation results, the long and short axis dimensions of multiple fractures under the influence of multiple factors such as different fracturing processes, geological parameters and engineering parameters are statistically analyzed. For example, in vertical well stratified fracturing, other arbitrary parameters are kept unchanged, and only the numerical model displacement is changed. The long and short axis dimensions and the long and short axis ratios of the fractures in the upper, middle and lower layers are statistically analyzed to obtain calculation charts under multiple factors including but not limited to ground stress, permeability, displacement, fracture spacing, liquid volume, and number of reservoirs. Other parameters are calculated in sequence according to the above steps.

[0129] Finally, the expansion difference between the long and short axes of the fracture is predicted according to the expansion prediction model, and the fracturing process is adjusted according to the prediction results to achieve the control of the expansion difference between the long and short axes of the fracture.

[0130] In this embodiment, adjusting vertical well stratified fracturing based on prediction results includes, first, deriving a control mechanism for the parallel expansion and interference of multiple fractures based on the numerical simulation results of the aforementioned fracturing process, geological parameters, and engineering parameters, and further formulating a process optimization plan based on the control mechanism. Preferably, in vertical well stratified fracturing and horizontal well segmented multi-cluster multi-fracture fracturing, to ensure balanced expansion of multiple fractures, the dual mechanism of "interference between small fracture spacing to inhibit fracture expansion + disturbance to increase net pressure driving force" should be considered, and graded control should be performed based on conditions such as fracturing sequence, displacement, perforation, fracturing fluid viscosity, fluid volume, and temporary plugging process: Level 1 control: When the spacing between multiple fractures in the fracturing is small, the dual mechanism of "interference between small fracture spacing to inhibit fracture expansion + disturbance to increase net pressure driving force" is complex, and vertical well stratified fracturing is preferably performed in layers and sequentially, while horizontal well segmented multi-cluster fracturing is preferably performed cluster by cluster and segment by segment using coiled tubing, or the cluster spacing should be appropriately increased to achieve the critical cluster spacing for balanced expansion of multiple fractures. Secondary control: Based on the determined fracturing sequence, the flow rate is optimized to promote uniform expansion of all fractures. Third-level control: The perforation distribution is optimized to achieve balanced expansion of fractures with varying fracture spacing. For example, the number of perforations can be appropriately reduced in high-permeability areas. Fourth-level control: The viscosity of the fracturing fluid is optimized to promote uniform expansion of all fractures. Fifth-level control: The volume of the fracturing fluid is optimized to increase fracture size. Sixth-level control: When the above control measures are completed but some fractures do not expand after reaching the critical fluid volume, a combination of intra-well and intra-fracture temporary plugging can be used to promote expansion of uninitiated fractures. Specific fracturing process optimization methods can be adjusted in real time based on the parallel expansion and interference characteristics of multiple fractures under different conditions.

[0131] Preferably, in this embodiment, in a vertical well stratified fracturing scenario, the geological parameters and engineering parameters of the sandstone reservoir are: reservoir depth of 820-1100m, reservoir thickness of 3m, vertical in-situ stress of 18-21MPa, minimum horizontal in-situ stress of 19-21MPa, maximum horizontal in-situ stress of 24-26MPa, permeability of 7-20mD, porosity of 0.28-0.31, elastic modulus of 3.95-4.68GPa, Poisson's ratio of 0.18-0.22, fracture toughness of 0.35-0.4MPa·m 0.5 The geological and mechanical parameters of the upper and lower layers are as follows: depth 820-1100m, vertical ground stress 18-21MPa, minimum horizontal ground stress 19-21MPa, maximum horizontal ground stress 24-26MPa, permeability 7-20mD, porosity 0.28-0.31, elastic modulus 3.95-4.68GPa, Poisson's ratio 0.18-0.22, fracture toughness 0.35-0.4MPa·m 0.5 First, due to the small spacing between vertical well reservoirs, the dual mechanism of "interference between small fractures to inhibit fracture expansion + disturbance to increase net pressure driving force" is complex, so it is preferred to use layered fracturing as the first-level regulation; secondly, it is preferred to use 8m high-pressure fracturing, which is conducive to the uniform expansion of each layer of fractures. 3 / min or more as the second-level regulation; secondly, the balanced perforation distribution with the number of perforations of 8-8-8 is preferred as the third-level regulation, and the number of perforations is appropriately reduced in the high permeability layer; further, the fracturing fluid viscosity of 40mPa·s is preferred as the fourth-level regulation; thirdly, the viscosity of the fracturing fluid greater than 300m 3 The fifth-level regulation is to pump in a certain amount of fracturing fluid; finally, the sixth-level regulation is to use a process combining temporary plugging within the well section and within the fracture to promote the expansion of uninitiated fractures.

[0132] When the process is horizontal well staged fracturing of horizontal fractures, adjusting the fracturing process according to the prediction results includes: proposing a two-level regulation for the horizontal well staged fracture expansion and seepage interference control mechanism of the horizontal fractures according to the fracturing process and engineering parameters in response to different prediction results. In the horizontal well staged fracturing of horizontal fractures with the same vertical depth, if the two fractures intersect, the first-level regulation needs to increase the fracture spacing and reduce the displacement; if the two fractures have already intersected, the second-level regulation needs to increase the displacement, increase the fracturing fluid volume, and increase the fracturing fluid viscosity; in the horizontal well staged fracturing of horizontal fractures with different vertical depths, if the two fractures overlap, the first-level regulation needs to design the fracture spacing most suitable for the long axis advantage expansion. On this basis, the second-level regulation needs to increase the displacement, increase the fracturing fluid volume, and increase the fracturing fluid viscosity.

[0133] In this embodiment, the implementation process is as follows:

[0134] Firstly, a numerical simulation analysis is conducted on the horizontal well segmented fracturing of horizontal fractures. Based on the numerical simulation model of the differential expansion of the long and short axes of a single fracture, the "cohesive fracture unit representing the fracture process zone" is inserted into the "between the seepage fluid-solid coupling units" in the same reservoir in the model, and injection points are set at a specified distance in the horizontal direction. The area between the two injection points is a fracture section, thereby realizing the horizontal fracture expansion numerical modeling of the horizontal well segmented (multi-cluster) fracturing of horizontal fractures. It should be noted that the model includes the segmented (multi-cluster) fracturing of horizontal wells with the same vertical depth and the vertical different depth. For horizontal well segmented (multi-cluster) fracturing, if the vertical depth is the same, that is, in the same reservoir, the multiple fracturing segments (clusters) are on the same horizontal plane; if the vertical depth is different, that is, in the same reservoir, the multiple fracturing segments (clusters) are on different horizontal planes; further, the impact of the differential expansion of the major and minor axes of horizontal fractures in segmented horizontal wells under different construction technologies, geological and engineering conditions is analyzed; preferably, the focus is on analyzing the expansion characteristics of horizontal fractures in different segments and different clusters within a segment, and the horizontal fracture plane seepage interference is analyzed, including but not limited to the horizontal fracture expansion plane seepage interference characteristics and the horizontal fracture drainage plane seepage interference characteristics.

[0135] The effect of fracture spacing on the expansion of horizontal cracks in segmented (multiple clusters within a segment) hydraulic fracturing of horizontal wells is studied based on a numerical simulation model: injection points are set at different intervals in the horizontal wellbore direction, and different spacings between the two injection points are used to simulate different fracture spacings (two hydraulic fractures are separated, tangent, or intersecting). Then, the effect of different fracture spacings on the expansion of horizontal cracks in segmented (multiple clusters within a segment) hydraulic fracturing of horizontal wells, horizontal fracture expansion, and seepage interference on the drainage plane (including but not limited to pore pressure) can be studied.

[0136] Based on the numerical simulation model, the control variable method is adopted to carry out numerical simulation analysis of the influence of engineering parameters including but not limited to fracturing fluid properties (viscosity, type and loss coefficient), displacement, fluid volume, etc. on the expansion of horizontal cracks in horizontal well segmentation (multiple clusters within a segment) fracturing, and to carry out numerical simulation analysis of horizontal crack expansion in horizontal well segmentation (multiple clusters within a segment) and seepage interference in the drainage and production plane (including but not limited to pore pressure).

[0137] Based on the numerical simulation model and using the control variable method, we conduct numerical simulation analysis on the influence of geological parameters (including but not limited to Poisson's ratio, elastic modulus, fracture toughness, etc.) and geological parameters (including but not limited to ground stress, permeability, reservoir barrier depth, fracture spacing, and reservoir barrier sand body characteristics) on the expansion of horizontal cracks in horizontal well segmentation (multiple clusters within a segment) fracturing, and conduct numerical simulation analysis on the expansion of horizontal cracks in horizontal well segmentation (multiple clusters within a segment) and the seepage interference in the drainage plane (including but not limited to pore pressure).

[0138] The parameter sensitivity and main controlling factors were analyzed based on the numerical simulation results. Based on the numerical simulation results of horizontal crack expansion in segmented (multiple clusters within a segment) horizontal well fracturing, priority was given to the influence of fracturing technology (including but not limited to fracture spacing, etc.), engineering parameters and geological parameters on horizontal crack expansion in segmented (multiple clusters within a segment) horizontal well fracturing, as well as the influence of horizontal crack expansion and seepage interference in the drainage plane (including but not limited to pore pressure), and the main controlling factors and parameter sensitivity analysis were performed.

[0139] Specifically, the analysis is conducted through calculation charts. The control variable method is adopted. Based on the numerical model calculation results, the long and short axis dimensions of multiple fractures under the influence of multiple factors such as different fracturing processes, geological parameters and engineering parameters are statistically analyzed. For example, in the horizontal well staged fracturing of horizontal fractures, any other parameters are kept unchanged, and only the numerical model displacement is changed. The long and short axis dimensions and the long and short axis ratio of the horizontal fractures in the horizontal well stage (multiple clusters within a stage), the pore pressure distribution of the fractures, etc. are statistically analyzed. The calculation chart is obtained under the conditions of multiple factors including but not limited to fracture spacing, ground stress, permeability, displacement, liquid volume, and number of reservoirs. Other conditions are carried out in sequence according to the above steps.

[0140] Adjusting horizontal well staged fracturing based on the prediction results includes: first, numerically simulating the fracture propagation of horizontal fractures in horizontal well stages (multiple clusters within a stage) based on the aforementioned fracturing process, geological parameters, and engineering parameters, to derive a control mechanism for fracture propagation and seepage interference in horizontal well stages (multiple clusters within a stage). Furthermore, a process optimization plan is developed based on this control mechanism. Preferably, in horizontal well staged fracturing (multiple clusters within a stage) with horizontal fractures at the same vertical depth, if two fractures intersect, the effective fracturing scale is limited. Therefore, primary control measures must address the issue of fracture intersection, such as increasing the fracture spacing and reducing the flow rate, to effectively prevent the two fractures from intersecting and increase the fracturing scale. If the two fractures already intersect, secondary control measures must address the issue of increasing the fracturing scale, such as increasing the flow rate, increasing the amount of fracturing fluid, and increasing the viscosity of the fracturing fluid, to effectively increase the scale of the intersecting fractures. Optimally, in staged fracturing (multiple clusters within a stage) of horizontal wells with vertically varying depths, if two fractures overlap, there will be strong interfracture interference between them. This characteristic effectively increases the major axis size. Therefore, primary control must address the challenge of increasing the major axis, such as designing the optimal fracture spacing for the expansion of the major axis. Based on this, secondary control must address the challenge of increasing the fracturing scale, such as increasing the displacement, fracturing fluid volume, and fracturing fluid viscosity. Specific fracturing process optimization methods can be implemented in real time based on the parallel expansion and interference characteristics of multiple fractures under different conditions.

[0141] Preferably, in this embodiment, in a horizontal well staged fracturing scenario, the geological parameters and engineering parameters of the sandstone reservoir are: reservoir depth of 820-1100m, reservoir thickness of 10m, vertical in-situ stress of 18-21MPa, minimum horizontal in-situ stress of 19-21MPa, maximum horizontal in-situ stress of 24-26MPa, permeability of 7-15mD, porosity of 0.28-0.31, elastic modulus of 3.95-4.68GPa, Poisson's ratio of 0.18-0.22, fracture toughness of 0.35-0.4MPa·m 0.5 The geological and mechanical parameters of the upper and lower layers are as follows: the thickness of the layer is 3m, the depth is 820-1100m, the vertical ground stress is 18-21MPa, the minimum horizontal ground stress is 19-21MPa, the maximum horizontal ground stress is 24-26MPa, the permeability is 1-7mD, the porosity is 0.02-0.14, the elastic modulus is 10-15GPa, the Poisson's ratio is 0.18-0.22, and the fracture toughness is 0.35-0.4MPa·m 0.5 First, in the horizontal well staged fracturing of horizontal fractures with the same vertical depth, in order to avoid the intersection of short axes, it is preferred to have a segment spacing of ≥100m and a 4m 3 / min displacement is used as the first-level control parameter. If two fractures have already intersected, the size of the intersecting fracture is dominant, and 50m is preferred. 3 / min displacement, ≥500m 3 The fracturing fluid volume is used as the secondary control parameter. For staged fracturing of horizontal wells with vertically different-depth horizontal fractures, it is necessary to enhance the overlap of the two fractures to increase the long axis of the fractures. Therefore, the interval between the two fractures is preferably 80-110m as the primary control parameter. Furthermore, the fracture size is dominant, so 50m is preferred. 3 / min displacement, ≥500m 3 The fracturing fluid volume and fracturing fluid viscosity ≥40 mPa·s are used as secondary controls.

[0142] The above-described embodiments are merely descriptions of the embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture, characterized in that: include: Obtaining operating parameters and fracturing processes in a fracturing area, wherein the operating parameters include engineering parameters and geological parameters; Establishing a physical model of the fracturing area according to the working parameters and the fracturing process, and establishing a numerical simulation model for the differential expansion of the major and minor axes of the fractures based on the physical model; Performing numerical simulation on working parameters of the fracturing area by using the numerical simulation model; Based on the numerical simulation results, the influence of various parameters on the difference in the expansion behavior and size of the cracks' major and minor axes was analyzed, and a prediction model for the difference in the expansion of the cracks' major and minor axes was established based on the influence. Predicting the differential expansion of the major and minor axes of the fracturing cracks according to the expansion prediction model, and adjusting the fracturing process according to the prediction results to achieve differential expansion control of the major and minor axes of the fracturing cracks; The method of establishing a prediction model for the difference in the major and minor axis expansion of cracks based on the influence includes: First, the engineering parameters are converted into laboratory-scale test parameters using similarity criteria. Combined with the test parameters, rock fracture and fracturing tests were carried out under different confining pressures. Then, based on the test results, the expansion resistance parallel to or perpendicular to the crack expansion direction is quantified. Finally, the quantified crack propagation resistance is used to construct the field variable function of the numerical model, which serves as the basis for the modeling of the major-minor axis differential propagation prediction model. Establishing a prediction model for the differential expansion of the major and minor axes of cracks based on the modeling basis; The prediction model for the difference in the major and minor axis expansion of the crack includes an engineering equal-size model or a similar-size model; In the engineering equal-size model, the model size is consistent with the actual size of the project, and the field variable function of the engineering equal-size model shown in formula (12) is constructed by using the difference distribution characteristics of the isotropic expansion resistance; (12)， Where, is the field variable function of the engineering equal-size model, and is the spatial coordinate in the engineering equal-size model, and It is the characteristic parameter of the crack propagation resistance field in the engineering size model, and its value is adjusted according to the actual size of the project. In the similar size model, the difference in the expansion resistance of the major and minor axes and the difference in the numerical model and engineering geometry are combined to obtain the field variable function of the similar size model as shown in formula (13). This model is a supplement to the engineering equal size model. (13)， Where, is a function of field variables in a model of similar size, and are the spatial coordinates of similar-sized models, 、 、 and It is the characteristic parameter of the crack propagation resistance field variable in the similar size model, and its value is adjusted according to the correlation between the actual project size and the model size.

2. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 1, characterized in that: The method further comprises: When performing the numerical simulation, the fracturing process is also numerically simulated, and the extended prediction model is updated according to the numerical simulation results of the fracturing process and the numerical simulation results of the working parameters; The fracturing process includes vertical well stratified fracturing, horizontal well staged fracturing, and horizontal well staged fracturing of horizontal fractures.

3. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 1, characterized in that: Establish a physical model of the fracturing area based on operating parameters and fracturing technology, including: Establish rock fracture model, fluid flow model in fracture during fracturing, perforation tube flow model during fracturing, and rock deformation-seepage coupling control mathematical model; Rock fracture model: Based on the rock information of optical and acoustic monitoring, the characteristics of rock plastic fracture are characterized and the cohesive crack model of the fracture process zone is used for characterization. The characteristics of rock plastic fracture include cohesive tensile strength , dissipated energy , fracture energy , cumulative dissipated energy , critical cumulative dissipated energy , Cohesive tensile strength Specifically as shown in formula (1), =(3 ) / [ ] (1)， Where: is the initial load for the development of cohesive cracks in the fracture process zone; S is the span of the three-point bending test specimen; B is the thickness of the specimen; H is the width of the specimen; is the length of the prefabricated crack; The dissipated energy of the unit length cohesive crack in the fracture process zone is in the softening stage and has not yet fully opened. , as shown in formula (2), （2）， Where: is the crack opening degree in the fracture process zone per unit length; is the crack cohesion; is the differential operator; The fracture energy of the unit length cohesive crack from the beginning of softening to the formation of the real fracture surface in the fracture process zone , as shown in the formula express; （3）， Where: is the full opening of cohesive cracks per unit length in the fracture process zone; Cumulative dissipated energy during the softening process of cohesive cracks in the fracture process zone , as expressed in formula (4); （4）， Where: is the cohesive crack length in the softened fracture process zone; is the length of the cohesive crack in the calculated fracture process zone; Critical cumulative dissipated energy during the softening process of cohesive cracks in the fracture process zone , as expressed in formula (5); （5）， Where: L is the fully developed length of the fault process zone; The fluid flow model in the fracture during the fracturing process includes: Tangential flow, the fluid flows along the crack expansion direction, which conforms to the Newtonian fluid model, as shown in Equation (6); (6)， Where: is the displacement; is the fluid pressure; is the flow coefficient; is the fluid viscosity; Normal flow, the fluid is lost perpendicular to the fracture surface, as shown in formula (7); (7)， Where: subscripts t, b and i represent the upper surface, lower surface and crack, respectively; q is the filtration rate; p is the fluid pressure; c is the filtration coefficient; The perforation pipe flow model in the fracturing process includes: introducing perforation by using the method of sharing nodes between deep hole pipe flow and seepage flow, and coupling Darcy's law, Bernoulli equation, loss coefficient equation and Blasius friction coefficient equation to obtain the pipe flow model equation as shown in Equation (8); Pipe flow model equation: （8）， Where: is the fluid pressure difference; is the fluid density is the acceleration due to gravity; is the relative height of the fluid; is the fluid loss coefficient; is the connection direction loss coefficient; V is the fluid flow rate; The rock deformation-seepage coupling control mathematical model includes: effective stress equation, stress balance equation, continuity equation and Darcy's law; The effective stress equation is as follows (9): （9）， Where: I is the unit matrix; is the effective stress; K is a proportional factor determined by surface tension and saturation; is the wetting fluid pore pressure; σ is the total stress; The stress balance equation is as follows (10): (10)， in: is the effective stress of the reservoir matrix; is the matrix [1, 1, 1, 0, 0]; is the pore pressure of porous media; R is the surface external force per unit area; is the virtual velocity field of the reservoir matrix; r is the physical force per unit volume; S is the load acting area; is the reservoir matrix virtual strain rate; VU is the unit volume; The continuity equation is as follows (11): (11)， Where: is the rate of change of fluid density with time; is the net outflow of fluid.

4. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 1, characterized in that: A numerical simulation model for the differential expansion of the major and minor axes of the crack is established based on the physical model, including: Firstly, a numerical model is constructed by combining the numerical calculation method and the physical model; The numerical calculation methods include finite discrete element, boundary element, finite difference, finite volume, material point method and phase field method; When using the finite discrete element method, the cohesive fracture unit that characterizes the rock fracture characteristics is inserted between the seepage fluid-solid coupling units that characterize the fluid-rock coupling mechanism, and the numerical simulation model is obtained by disconnecting the units in sequence to simulate the fracture extension.

5. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 1, characterized in that: After constructing the prediction model of the difference between the major and minor axes of cracks, it also includes: Calculate the engineering parameters and geological parameters, analyze the influence of different engineering parameters and geological parameters on the difference in the expansion behavior and size of the crack major and minor axes, and conduct the main control factors and parameter sensitivity analysis. Furthermore, based on the crack propagation law presented by the trial calculation results and the weights of the influence of various engineering parameters and geological parameters on the differential propagation of the major and minor axes of the cracks, an artificial intelligence algorithm was used and trained based on the numerical simulation results to obtain a prediction model for the differential propagation of the major and minor axes of the cracks. An intelligent design software for the differential expansion of the major and minor axes of hydraulic fractures was compiled to obtain a calculation chart under multi-factor conditions.

6. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 2, characterized in that: When the fracturing process is vertical well stratified fracturing, adjusting the fracturing process according to the prediction results includes: According to the fracturing technology and engineering parameters on the sensitivity of each reservoir's balanced expansion and the degree of control, six levels of control are proposed corresponding to different prediction results. Level 1 control: When the spacing between multiple fractures is less than the preset threshold, vertical well stratified fracturing is performed in layers and in sequence, while horizontal well staged multi-cluster fracturing is performed cluster by cluster and stage by stage using coiled tubing, or the cluster spacing is appropriately increased to reach the critical cluster spacing for balanced expansion of multiple fractures. Secondary regulation: Based on the determined fracturing sequence, select the displacement that is conducive to the uniform expansion of each fracture; Three-level control: select the perforation distribution suitable for balanced crack expansion at different crack spacing; Four-level control: select the fracturing fluid viscosity that is conducive to the uniform expansion of each fracture; Five-level control: select the amount of fracturing fluid that is conducive to increasing the crack size; Six-level regulation: When the regulation of levels 1 to 5 is completed, but the fractures do not expand after reaching the critical fluid volume, a process combining temporary plugging within the well section and within the fracture is used to promote the expansion of the uninitiated fractures.

7. The method for evaluating and controlling the differential expansion of the major and minor axes of a hydraulic fracture according to claim 2, characterized in that: When the fracturing process is horizontal well staged fracturing of horizontal fractures, adjusting the fracturing process according to the prediction results includes: According to the fracturing technology and engineering parameters, the horizontal well segmented fracture expansion and seepage interference control mechanism of horizontal fractures is proposed according to different prediction results. In the staged fracturing of horizontal wells with horizontal fractures at the same vertical depth, if the two fractures do not intersect, the first-level control increases the fracture spacing and reduces the displacement; if the two fractures have intersected, the second-level control increases the displacement, increases the amount of fracturing fluid, and increases the viscosity of the fracturing fluid; In the staged fracturing of horizontal wells with vertically varying depths of horizontal fractures, if two fractures overlap, the first-level control design is most suitable for the fracture spacing with the dominant long axis expansion. On this basis, the second-level control increases the displacement, the amount of fracturing fluid, and the viscosity of the fracturing fluid.

Images