Method for constructing shale oil horizontal well hydraulic fracture extension model

Abstract

The present application provides a kind of shale oil horizontal well hydraulic fracture extension model construction method, comprising: step 1: establishing simulation single fracture extension mathematical model;Step 2: according to displacement discontinuity method, establish fracture induced stress field model;Step 3: according to the model of step 1 and step 2, establish simulation multi-fracture extension form of multi-cluster fracture extension mathematical model;Step 4: establish the hydraulic fracture extension mathematical model considering natural fracture;Step 5: the model obtained in step 3 is combined with the model obtained in step 4, that is, the required multi-cluster hydraulic fracture extension model considering the influence of bedding can be obtained.The shale oil horizontal well hydraulic fracture extension model construction method uses the above model to analyze the influence of different parameters on the extension of fracture height, determines the law and main control factors of fracture height extension;By simulating the influence of vertical bedding on the extension of fracture height, the influence degree of bedding on fracture height is determined, suggestions are put forward for fracturing technology and optimization is carried out on construction parameters.

Description

Technical Field

[0001] This invention relates to the field of shale gas development technology, and in particular to a method for constructing a hydraulic fracture extension model for shale oil horizontal wells. Background Technology

[0002] Due to the limitations imposed by the large scale, complex formations, and lack of transparency in hydraulic fracturing projects, numerical simulation has become a common method for studying hydraulic fracturing technology. Currently, with the continuous expansion of oil and gas resource development in low-permeability tight reservoirs, extensive and in-depth research has been conducted on methods for enhancing production in these reservoirs through fracturing. Practice has proven that hydraulic fracturing is a suitable technology for enhancing production in low-permeability tight reservoirs. To study the mechanism of hydraulic fracturing in enhancing production in low-permeability tight reservoirs, it is necessary to conduct simulation analysis and numerical characterization of the fracture propagation process.

[0003] Characterizing the initiation and propagation of hydraulic fracturing fractures requires considering both the actual scale of the geomechanical model and the local natural defects and evolution patterns within the rock mass. While there are existing studies on the interaction between hydraulic and natural fractures, predicting the final morphology of artificial fractures resulting from this interaction, deep shale presents several distinct challenges compared to shallow shale, such as complex triaxial stress, high stress levels, high rock mechanical strength, nonlinear deformation, poor development and closure of natural fractures, and stress sensitivity. Therefore, there are currently no studies specifically analyzing fractures in deep shale.

[0004] Chinese patent application CN202010968797.X discloses a method for predicting the height of hydraulic fractures in vertical wells of shale formations. The method includes: S1, establishing an influencing index system for the height of hydraulic fractures in shale formations, comprising multiple influencing indices; S2, establishing a hydraulic fracturing model for shale formations; S3, calculating the height of hydraulic fractures in shale formations using the extended finite element method; S4, conducting Latin hypercube sampling within the value range of each influencing index and calculating the height of hydraulic fractures in shale formations under combined conditions of each influencing index; and S5, establishing a prediction model for the height of hydraulic fractures in shale formations based on the multivariate adaptive regression spline method, thereby predicting the height of hydraulic fractures in shale formations.

[0005] Chinese patent application CN201810247278.7 discloses a method for predicting the propagation of hydraulically driven fractures in shale, comprising the following steps: (i) calculating the normal, tangential, and effective stresses of the diagonal fractures under external stress and water pressure; (ii) obtaining the strain energy density function based on the fracture type; (iii) obtaining the strain energy density factor based on the strain energy density function; (iv) determining the fracture propagation direction and angle based on the strain energy density criterion; and (v) obtaining the influence of bedding, natural fractures, etc., on the propagation direction of hydraulically driven fractures through numerical simulation, thereby predicting the propagation of fractures under hydraulic pressure in shale.

[0006] Chinese patent application CN202110004168.X discloses an evaluation method and assessment model for the permeability of fractured shale, and a method for constructing the model. The assessment model uses the total permeability K of the shale reservoir to evaluate the permeability of fractured shale, which is calculated using a shale permeability assessment model. The construction method includes the following steps: S1, deriving the permeability expression of the shale matrix based on a hybrid fractal unit model and Darcy's law; S2, establishing a fractal characteristic expression model for the aperture and length of natural fractures based on fractal theory; S3, deriving the permeability expression of natural fractures based on the model in step S2 and the cubic law; S4, deriving the permeability expression of the overall shale reservoir based on the permeability expressions of the shale matrix and natural fractures.

[0007] The existing technologies described above are quite different from the present invention and have failed to solve the technical problem we want to solve. Therefore, we have invented a new method for constructing a hydraulic fracture extension model for shale oil horizontal wells. Summary of the Invention

[0008] The purpose of this invention is to provide a method for constructing a hydraulic fracture propagation model for shale oil horizontal wells that considers the influence of bedding, and to use it for fracture analysis.

[0009] The objective of this invention can be achieved through the following technical measures: a method for constructing a hydraulic fracture propagation model for shale oil horizontal wells, the method comprising:

[0010] Step 1: Establish a mathematical model to simulate the propagation of a single crack;

[0011] Step 2: Establish a crack-induced stress field model based on the displacement discontinuity method;

[0012] Step 3: Based on the models in Step 1 and Step 2, establish a mathematical model for simulating the multi-crack extension morphology.

[0013] Step 4: Establish a mathematical model for the propagation of hydraulic fractures that takes into account natural fractures;

[0014] Step 5: Combine the model obtained in Step 3 with the model obtained in Step 4 to obtain the multi-cluster hydraulic fracture propagation model that takes into account the influence of stratification.

[0015] The objective of this invention can also be achieved through the following technical measures:

[0016] In step 1, the mathematical model for single fracture propagation includes a wellbore fluid flow model, a fracture fluid flow model, and a fracture propagation criterion.

[0017] In step 1, the wellbore fluid flow model is established as follows:

[0018] Based on Kirchoff's first and second laws, the relationship between the frictional resistance along the wellbore and the frictional resistance of the perforation hole is calculated, the wellbore pressure drop equation is derived, and the wellbore fluid flow equation is established.

[0019] In step 1, the wellbore fluid flow model is as follows:

[0020]

[0021] In the formula: p cf,i Let C be the frictional resistance of the wellbore in the i-th fracture. cf x is the coefficient of friction. j Let Q be the distance from fracture j to the wellbore heel. w,j Let Q be the fluid flow rate remaining after passing through j fractures, D be the horizontal wellbore diameter, and Q be the fluid flow rate remaining after passing through j fractures. T Q represents the total fluid injection volume. k Let be the fluid injection volume for the k-th crack.

[0022] In step 1, the method for establishing the fluid flow model within the crack is as follows:

[0023] Based on the theory of flat plate flow, the pressure drop equation for fluid flow within a fracture is derived; based on the law of conservation of mass, the expression for the relationship between fluid pressure and fracture width within a fracture is derived; and the finite difference method is used for discretization to establish a fluid flow model within the fracture.

[0024] In step 1, the pressure drop equation for the fracture fluid flow is:

[0025]

[0026] In the formula: q is the fluid flow rate, p is the fluid pressure, and w f Where is the maximum width of the crack cross section, u is the fluid shear displacement, and h is the height of the crack in the flat plate.

[0027] The relationship between fluid pressure within the crack and crack width is as follows:

[0028]

[0029] In the formula: w is the width of the crack at any vertical position, t is the total pumping time, and C L τ is the filtration coefficient, and τ is the time when the crack element begins to filtration.

[0030] In step 1,

[0031] Crack propagation criteria include:

[0032] The equivalent intensity factor is:

[0033]

[0034] Where: K e K is the equivalent intensity factor. Ⅰ K is a type I intensity factor. Ⅱ The strength factor is type II, and θ0 is the angle at which the crack deviates from its original extension direction.

[0035] The maximum circumferential stress criterion is expressed by the equivalent strength factor as follows:

[0036] K e ≥K Ic

[0037] In the formula, K Ic This refers to the fracture toughness of the rock mass.

[0038] In step 2, the crack-induced stress field model includes:

[0039] The stress field induced by fractures at any location in the formation is as follows:

[0040]

[0041] The displacement field at any location in the strata is:

[0042]

[0043] In the formula: The normal stress is in the x-axis direction. The normal stress is in the y-axis direction. For shear stress, G ij Shear modulus The stress boundary influence coefficient is N, where N is the number of crack elements. Let represent the displacement of the crack element in the horizontal and vertical directions. This is the displacement influence coefficient. Let be the normal displacement of the crack. This represents the tangential displacement of the crack.

[0044] In step 3, the mathematical model for the propagation of multiple fracture clusters makes the following assumptions about the rock mass:

[0045] 1) The reservoir rock is a homogeneous, isotropic, porous medium that meets the linear elasticity condition;

[0046] 2) The height of the hydraulic fracturing fracture is constant, and the cross-section in the height direction is elliptical;

[0047] 3) The influence of cracks on the propagation of hydraulic cracks is not considered;

[0048] 4) Rocks only conform to Type I and Type II fractures.

[0049] In step 3, the mathematical model for multi-cluster crack propagation makes the following assumptions about the fluid:

[0050] 1) Propionate transport within the fluid is not considered;

[0051] 2) The fluid is an incompressible Newtonian fluid and is filled with cracks;

[0052] 3) The fluid flows in a one-dimensional laminar flow within the crack, and follows Cat er filtration;

[0053] 4) Changes in mechanical properties caused by the physicochemical interaction between the fluid and the reservoir rock are not considered.

[0054] In step 4, the mathematical model for hydraulic fracture propagation considers hydraulic fractures opening along natural fractures, hydraulic fractures shearing along natural fractures, and hydraulic fractures penetrating natural fractures.

[0055] In step 4, the hydraulic fractures open along the natural fractures:

[0056] p = σ n

[0057] In the formula: p is the pressure inside the natural fracture, σ n This represents the normal stress acting on the surface of the natural crack.

[0058] In step 4, the hydraulic fracture extends shear along the natural fracture:

[0059]

[0060] In the formula: σ H For the maximum horizontal principal stress, σ h Let β be the minimum principal stress at horizontal, and K be the approximation angle. f τ is the friction coefficient of the natural fracture surface, τ0 is the cohesion of the rock, and p σ This represents the maximum fluid pressure within the crack before shear failure due to a natural crack.

[0061] In step 4, the hydraulic fracture penetrates the natural fracture:

[0062] σ r1 =T0

[0063] In the formula: σ r1 denoted as , where is the maximum principal stress at different points on the surface of the natural crack, r is the distance between the location on the natural crack and the crack tip, and T0 is the tensile strength of the natural crack.

[0064] |τ n |<τ0+K f (σ n -p0)

[0065] In the formula: τ n σ is the shear force acting on the surface of the natural crack. n This represents the normal stress acting on the surface of the natural crack.

[0066] In step 5, a mathematical model for the extension of multiple hydraulic fractures is constructed to simulate the influence of different parameters on the fracture height; the parameters include the number of bedding planes, Young's modulus of the rock, vertical principal stress difference, fracture toughness, and tensile strength.

[0067] The method for constructing a hydraulic fracture extension model for shale oil horizontal wells in this invention considers the influence of bedding in deep shale to establish a multi-cluster hydraulic fracture extension model. Using this model, the influence of different parameters on fracture height extension is analyzed, clarifying the laws and main controlling factors of fracture height extension. By simulating the vertical bedding effect on fracture height extension, the degree of influence of bedding on fracture height is clarified, suggestions for fracturing technology are proposed, and construction parameters are optimized. The beneficial effects of the method for constructing a hydraulic fracture extension model for shale oil horizontal wells in this invention are:

[0068] (1) This invention considers the influence of bedding in deep shale to establish a multi-cluster hydraulic fracture extension model. The above model is used to analyze the influence of different parameters on fracture height extension, and the law and main controlling factors of fracture height extension are clarified.

[0069] (2) This invention clarifies the influence of bedding on the height of cracks by simulating the vertical extension of the bedding in the vertical direction, and makes suggestions on the fracturing process and optimizes the construction parameters. Attached Figure Description

[0070] Figure 1 This is a physical model diagram of the multi-fracture extension in the horizontal well segmented fracturing of this invention;

[0071] Figure 2 This is a schematic diagram of the crack morphology in the crack propagation model of the present invention;

[0072] Figure 3 This is a schematic diagram of a two-dimensional displacement discontinuous crack unit in this invention;

[0073] Figure 4 This is a schematic diagram of the crack being divided into multiple unit bodies in this invention;

[0074] Figure 5This is a schematic diagram of the force on the crack unit body in this invention;

[0075] Figure 6 This is a schematic diagram illustrating the mass conservation of the crack unit in this invention;

[0076] Figure 7 This is a schematic diagram of the flow rate and pressure distribution in a horizontal well with multiple fractures in this invention;

[0077] Figure 8 This is a schematic diagram illustrating the interference between natural cracks and hydraulic cracks in this invention.

[0078] Figure 9 This is a schematic diagram of a hydraulic crack penetrating a natural crack in this invention;

[0079] Figure 10 This is a schematic diagram illustrating the relationship between the number of layers and the seam height in a specific embodiment of the present invention;

[0080] Figure 11 This is a graph showing the relationship between vertical stress difference and seam height in a specific embodiment of the present invention.

[0081] Figure 12 This is a graph showing the relationship between fracture toughness and fracture height in a specific embodiment of the present invention.

[0082] Figure 13 This is a graph showing the relationship between Young's modulus and seam height in a specific embodiment of the present invention;

[0083] Figure 14 This is a graph showing the relationship between tensile strength and seam height in a specific embodiment of the present invention;

[0084] Figure 15 This is a flowchart of a specific embodiment of the method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to the present invention. Detailed Implementation

[0085] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0086] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0087] like Figure 15 As shown, Figure 15 This is a flowchart illustrating a specific embodiment of the method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to the present invention. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to the present invention includes the following steps:

[0088] Step 1: Establish a mathematical model to simulate the propagation of a single crack;

[0089] The mathematical model for single fracture propagation includes a wellbore fluid flow model, a fracture fluid flow model, and a fracture propagation criterion.

[0090] The method for establishing the fluid flow model within the crack is as follows:

[0091] Based on the theory of flat plate flow, the pressure drop equation for fluid flow in a fracture is derived; based on the law of conservation of mass, the expression for the relationship between fluid pressure and fracture width in a fracture is derived; and the fluid flow model in a fracture is established by discretization using the finite difference method.

[0092] The method for establishing a wellbore fluid flow model is as follows:

[0093] Based on Kirchoff's first and second laws, the relationship between the frictional resistance along the wellbore and the frictional resistance of the perforation hole is calculated, the wellbore pressure drop equation is derived, and the wellbore fluid flow equation is established.

[0094] The pressure drop equation for the fluid flow in the crack is:

[0095]

[0096] In the formula: q is the fluid flow rate, p is the fluid pressure, and w f Where is the maximum width of the crack cross section, u is the fluid shear displacement, and h is the height of the crack in the flat plate.

[0097] The relationship between fluid pressure within the crack and crack width is as follows:

[0098]

[0099] In the formula: w is the width of the crack at any vertical position, t is the total pumping time, and C L The filtration coefficient is τ, and the filtration time of the crack element is the time when filtration begins.

[0100] The wellbore fluid flow model is as follows:

[0101]

[0102] In the formula: p cf,i Let C be the frictional resistance of the wellbore in the i-th fracture. cf x is the coefficient of friction. j Let Q be the distance from fracture j to the wellbore heel. w,jLet Q be the fluid flow rate remaining after passing through j fractures, D be the horizontal wellbore diameter, and Q be the fluid flow rate remaining after passing through j fractures. T Q represents the total fluid injection volume. k Let be the fluid injection volume for the k-th crack;

[0103] Crack propagation criteria include:

[0104] The equivalent intensity factor is:

[0105]

[0106] Where: K e K is the equivalent intensity factor. Ⅰ K is a type I intensity factor. Ⅱ The strength factor is type II, and θ0 is the angle at which the crack deviates from its original extension direction.

[0107] The maximum circumferential stress criterion is expressed by the equivalent strength factor as follows:

[0108] K e ≥K Ic

[0109] In the formula, K Ic This refers to the fracture toughness of the rock mass.

[0110] Step 2: Establish a crack-induced stress field model based on the displacement discontinuity method; the crack-induced stress field model includes:

[0111] The stress field induced by fractures at any location in the formation is as follows:

[0112]

[0113] The displacement field at any location in the strata is:

[0114]

[0115] In the formula: The normal stress is in the x-axis direction. The normal stress is in the y-axis direction. For shear stress, G ij Shear modulus The stress boundary influence coefficient is N, where N is the number of crack elements. Let represent the displacement of the crack element in the horizontal and vertical directions. This is the displacement influence coefficient. Let be the normal displacement of the crack. This represents the tangential displacement of the crack.

[0116] Step 3: Based on the models in Step 1 and Step 2, establish a mathematical model for simulating the multi-crack extension morphology.

[0117] The mathematical model for the propagation of multiple fracture clusters makes the following assumptions about the rock mass:

[0118] 1) The reservoir rock is a homogeneous, isotropic, porous medium that meets the linear elasticity condition;

[0119] 2) The height of the hydraulic fracturing fracture is constant, and the cross-section in the height direction is elliptical;

[0120] 3) The influence of cracks on the propagation of hydraulic cracks is not considered;

[0121] 4) Rocks only conform to Type I and Type II fractures.

[0122] The mathematical model for multi-cluster crack propagation makes the following assumptions about the fluid:

[0123] 1) Propionate transport within the fluid is not considered;

[0124] 2) The fluid is an incompressible Newtonian fluid and is filled with cracks;

[0125] 3) The fluid flows in a one-dimensional laminar flow within the crack, and follows Cat er filtration;

[0126] 4) Changes in mechanical properties caused by the physicochemical interaction between the fluid and the reservoir rock are not considered.

[0127] Step 4: Establish a mathematical model for the propagation of hydraulic fractures that takes into account natural fractures;

[0128] The mathematical model for hydraulic fracture propagation considers hydraulic fractures opening along natural fractures, hydraulic fractures shearing along natural fractures, and hydraulic fractures penetrating natural fractures.

[0129] Hydraulic fissures open along natural cracks:

[0130] p = σ n

[0131] In the formula: p is the pressure inside the natural fracture, σ n This refers to the normal stress acting on the surface of a natural crack;

[0132] Hydraulic fractures extend along natural fractures in a shearing manner:

[0133]

[0134] In the formula: σ H For the maximum horizontal principal stress, σ h Let β be the minimum principal stress at horizontal, and K be the approximation angle. f τ is the friction coefficient of the natural fracture surface, τ0 is the cohesion of the rock, and p σ The maximum fluid pressure within the crack before shear failure of the natural crack;

[0135] Hydraulic cracks penetrate natural cracks:

[0136] σ r1 =T0

[0137] In the formula: σ r1 denoted as , where is the maximum principal stress at different points on the surface of the natural crack, r is the distance between the location on the natural crack and the crack tip, and T0 is the tensile strength of the natural crack.

[0138] |τ n |<τ0+K f (σ n -p0)

[0139] In the formula: τ n σ is the shear force acting on the surface of the natural crack. n This represents the normal stress acting on the surface of the natural crack.

[0140] Step 5: Combine the model obtained in Step 3 with the model obtained in Step 4 to obtain the multi-cluster hydraulic fracture propagation model that takes into account the influence of stratification.

[0141] A mathematical model for the extension of multiple hydraulic fractures was constructed to simulate the influence of different parameters on fracture height. The parameters include bedding number, Young's modulus of rock, vertical principal stress difference, fracture toughness, and tensile strength.

[0142] The following are several specific embodiments of the application of the present invention.

[0143] Example 1

[0144] Multi-fracture propagation is a highly complex physical process involving multiple coexisting and interfering factors. Essentially, it is a coupling of four fundamental mechanical processes: (1) stress interference between multiple hydraulic fractures; (2) flow of fracturing fluid within the wellbore and fractures, with hydraulic pressure causing deformation of the surrounding rock; (3) fluid loss along the fracture walls; and (4) fracture extension at the fracture tips. Additionally, issues such as wellbore friction, perforation friction, and flow distribution within the multi-fracture wellbore need to be considered. Figure 1 As shown, multiple fractures simultaneously initiate and extend in a horizontal well, thus establishing a physical model for multi-fracture extension. The simulation of the extension process needs to comprehensively consider the combined effects of multiple factors, such as stress interference from multiple fractures, fluid flow, fracturing fluid loss, and fracture tip extension, to establish a corresponding model to simulate the multi-fracture extension morphology. This provides an effective means to study the multi-fracture extension law and optimize construction parameters.

[0145] The following section first introduces the process of establishing a mathematical model for the propagation of multiple crack clusters:

[0146] Generally, in hydraulic fracturing of tight oil and gas reservoirs, the fracture length is much greater than the fracture height, and the assumptions made about the fracture in the PKN model form the basis for the fluid flow model within the fracture. For example... Figure 2As shown, basic assumptions are made for the rock mass and fluid in the model.

[0147] The following assumptions are made about the rock mass:

[0148] 1) The reservoir rock is a homogeneous, isotropic, porous medium that meets the linear elasticity condition;

[0149] 2) The height of the hydraulic fracturing fracture is constant, and the cross-section in the height direction is elliptical;

[0150] 3) The influence of cracks on the propagation of hydraulic cracks is not considered;

[0151] 4) Rocks only conform to Type I and Type II fractures.

[0152] The following assumptions are made regarding the fluid:

[0153] 1) Propionate transport within the fluid is not considered;

[0154] 2) The fluid is an incompressible Newtonian fluid and is filled with cracks;

[0155] 3) The fluid flows in a one-dimensional laminar flow within the crack, obeying Cater filtration;

[0156] 4) Changes in mechanical properties caused by the physicochemical interaction between the fluid and the reservoir rock are not considered.

[0157] Step 1: Establish a mathematical model to simulate the propagation of a single crack

[0158] The mathematical model for single fracture propagation includes the fluid flow model within the fracture, the fluid flow model in the wellbore, and the fracture propagation criterion.

[0159] Establish a fluid flow model within the crack

[0160] The fluid flow model within a fracture mainly studies the flow pattern of fluid within each fracture. This includes calculating the pressure drop generated by the flow within the fracture and deriving the relationship between the fluid flow rate and the fracture width using the law of conservation of mass, in order to solve for the fluid pressure and the geometric dimensions of the fracture.

[0161] The establishment process is as follows: Based on the flat plate flow theory, the pressure drop equation of fluid flow in the crack is derived; based on the law of conservation of mass, the expression of the relationship between fluid pressure and crack width in the crack is derived; the finite difference method is used for discretization to establish the fluid flow model in the crack.

[0162] The pressure drop equation for fluid flow in the crack is:

[0163]

[0164] In the formula: q is the fluid flow rate, p is the fluid pressure, and w fWhere is the maximum width of the crack cross section, u is the fluid shear displacement, and h is the height of the crack in the flat plate.

[0165] The above equation shows that, considering filtration loss, the fluid entering the fracture will not only increase the fracture width and length, but also some of the fluid will be filtered out into the formation along the wall. The remaining fluid flow rate is necessarily related to the fracture width and the fluid pressure change along the fracture length. All three of these are unknowns. To facilitate calculation, it is necessary to further reduce the variables in the solution process.

[0166] The relationship between fluid pressure within the crack and crack width is as follows:

[0167]

[0168] In the formula: w is the width of the crack at any vertical position, t is the total pumping time, and C L τ is the filtration coefficient, and τ is the time when the crack element begins to filtration.

[0169] The above equation is the mass balance equation, which, based on the law of conservation of mass, derives the relationship between fluid flow rate, fracture width, and fluid loss rate. In actual fracturing processes, the total volume of fracturing fluid entering the fracture within a given time is known. For example... Figure 6 As shown, the mass of fracturing fluid in a fracture micro-unit over a certain period of time varies. First, the left side represents fluid entering the micro-unit, and the right side represents fluid exiting the micro-unit. Second, there is also fracturing fluid loss on both sides of the fracture, which can be calculated using the loss rate. Finally, the entire fracture micro-unit undergoes a volume change.

[0170] The above equation reflects the relationship between fluid pressure and crack width. Since this equation is a partial differential equation, it is generally difficult to obtain an analytical solution and requires numerical methods. This invention uses the finite difference method to discretize the equation and simultaneously combines it with a crack-induced stress field model to solve for the fluid pressure and crack width within the crack.

[0171] The fluid flow model within the fracture requires initial and boundary conditions to be applied and solved. At the start of the multi-fracture extension pumping program, the initial time is recorded as 0. It is assumed that the initial fracture azimuth angle (the angle between the fracture and the horizontal wellbore) is 90°. The initial fracture length, fracture width, and initial net pressure are solved using a system of equations.

[0172] At the hydraulic fracture inlet: the total displacement remains constant at Q during fracturing. T The fluid flow rate entering through the i-th crack is Q. i For a single crack:

[0173]

[0174] For multiple cracks:

[0175]

[0176] In the formula: Q i —The fluid flow rate entering the i-th crack, m 3 / min;

[0177] m — Total number of fracture clusters, dimensionless;

[0178] Q T —Total displacement of the crack, m 3 / min.

[0179] At the tip of the hydraulic fracture: if the fracture width is 0, then:

[0180] w f (l f ,t)=0

[0181] In the formula: l f — The distance the crack extends to its tip, in meters.

[0182] Establish a wellbore fluid flow model

[0183] Due to the diverse injection methods and flow regimes of fluids in the wellbore, calculating frictional resistance along the well is quite complex. We only consider fluid injection from the tubing, where the fluid flow in the wellbore satisfies Kirchoff's first and second laws. This section primarily addresses the pressure drop (wellbore friction) caused by the fluid flow in the wellbore.

[0184] The process of establishing the wellbore fluid flow model is as follows:

[0185] Based on Kirchoff's first and second laws, the relationship between the frictional resistance along the wellbore and the frictional resistance of the perforation hole is calculated, the wellbore pressure drop equation is derived, and the wellbore fluid flow equation is established.

[0186] like Figure 7 As shown, neglecting the wellbore storage effect, the total fluid injection volume should be the sum of the fluid flow rates entering each fracture, which is the law of conservation of mass.

[0187]

[0188] Kirchoff's second law describes the pressure balance relationship of fluids in a wellbore, namely, the pressure at the root of a horizontal well is equal to the sum of the pressure drop due to wellbore friction on the fracture, the perforation friction, and the pressure at the first unit cell at the fracture inlet. When there are m fractures extending simultaneously, there are m pressure balance equations:

[0189] p0 = p w,i +p pf,i +p cf,i(i = 1, 2, ..., m)

[0190] Where: p0——fluid pressure at the root of the horizontal well, MPa;

[0191] p w, i — Fluid pressure at the inlet of the i-th fracture, MPa;

[0192] p pf,i —Frictional resistance of the i-th fracture perforation, MPa;

[0193] p cf,i — Wellbore friction of the i-th fracture, MPa.

[0194] The formula for calculating the friction of the perforation is:

[0195]

[0196] In the formula: ρ s — Fracturing fluid density, kg / m³ 3 ;

[0197] n p,i —The number of perforations in the i-th crack, dimensionless;

[0198] d p,i —Diameter of the i-th perforation hole, in meters;

[0199] C d,i —Correction coefficient for the i-th crack aperture, m

[0200]

[0201] Perforation friction is largely affected by the orifice diameter; when the orifice diameter decreases, perforation friction increases rapidly.

[0202] Wellbore friction is proportional to the fracture spacing. The pressure drop of each fracture on the horizontal wellbore is calculated using the following formula: This formula is the fluid flow model in the wellbore.

[0203]

[0204] In the formula: p cf,i —This represents the frictional resistance of the wellbore in the i-th fracture.

[0205] C cf —Friction coefficient, Pa·s / m 4 ;

[0206] x j — The distance from fracture j to the wellbore heel, in meters;

[0207] Q w,j —The remaining fluid flow rate after passing through j cracks, m3 / min;

[0208] D – Diameter of the horizontal wellbore, in meters.

[0209] Q T This represents the total fluid injection volume.

[0210] Q k Let m be the fluid injection volume for the k-th fracture. 3 / min.

[0211] Simultaneously, the entire flow system must satisfy the law of conservation of mass, that is, the volume of fluid entering is equal to the sum of the volume of fluid stored inside each fracture and the volume of fluid lost into the formation. The overall mass conservation equation for the entire system is:

[0212]

[0213] In the above content, formula (3) is the fluid flow model in the wellbore, and the other contents are the solution process of the model.

[0214] Establish a fracture propagation criterion during hydraulic fracturing based on the principle of maximum circumferential stress.

[0215] The fracture propagation criterion during hydraulic fracturing is one of the core issues in multi-fracture propagation models. The propagation criterion needs to address two questions: under what conditions does fracture propagate and in what direction does it propagate? Currently, there are many theories for judging rock fractures, with representative ones including the maximum tensile stress theory, the maximum circumferential stress theory, the maximum energy release rate theory, and the strain energy density factor theory. Different criteria require different parameters; for computational convenience, the maximum circumferential stress theory is adopted as the propagation criterion.

[0216] The equivalent intensity factor is:

[0217]

[0218] Where: K e K is the equivalent intensity factor. Ⅰ K is a type I intensity factor. Ⅱ The strength factor is type II, and θ0 is the angle at which the crack deviates from its original extension direction.

[0219] The maximum circumferential stress criterion is expressed by the equivalent strength factor as follows:

[0220] K e ≥K Ic (5)

[0221] In the formula, K Ic This refers to the fracture toughness of the rock mass.

[0222] Equation 4 is used to solve for the stress intensity factor, and Equation 5 is used for judgment. When the stress intensity factor calculated by Equation 5 is greater than the fracture toughness, the crack extends. The main determination is whether the crack will extend.

[0223] Step 2: Establish a crack-induced stress field model based on the displacement discontinuity method.

[0224] Discontinuity Discontinuity Theory (DDM) is a type of indirect boundary element method, proposed by Crouch in 1976 when studying two-dimensional fractured rock mass problems. This theory was first applied to geotechnical engineering, offering a convenient solution for problems involving discontinuities. It only requires meshing and discretizing the fracture elements, unlike the direct boundary element method which requires meshing both sides of the fracture surface. Furthermore, the DDM is more accurate and faster than the finite element method or finite difference method. In the DDM, the displacement discontinuity on the fracture mesh is treated as an unknown quantity, then solved using given fracture boundary conditions. The displacement discontinuity is then used to characterize the stress and displacement fields at any location within the plane, resulting in a continuous distribution of stress and displacement within the formation plane. For the multi-fracture propagation problem in this invention's model, the stress generated after the fractures open is essentially the same as the stress experienced at the fracture boundary in geotechnical engineering; therefore, the DDM can be used to calculate the induced stress field generated by the fractures.

[0225] like Figure 3 As shown, assume there is a fracture unit cell with a length of 2a in the formation, and the displacements of the two fracture surfaces are represented by u(x,0). + ) and u(x,0 - The tangential and normal displacements between the two crack surfaces are represented by D. x and D y To express.

[0226] The induced stress field of a single crack element at any location in the plane is derived, while each crack contains many tiny crack elements, such as... Figure 4 As shown. The induced stress generated by each fracture is the resultant force of the induced stresses of all the micro-fracture units, and the displacement at any location in the formation is the superposition of the displacements generated by all the fracture units.

[0227] The crack-induced stress field model includes:

[0228] The stress field induced by fractures at any location in the formation is as follows:

[0229]

[0230] The displacement field at any location in the strata is:

[0231]

[0232] In the formula: The normal stress is in the x-axis direction. The normal stress is in the y-axis direction. For shear stress, G ij Shear modulus The stress boundary influence coefficient is N, where N is the number of crack elements. Let represent the displacement of the crack element in the horizontal and vertical directions. This is the displacement influence coefficient. Let be the normal displacement of the crack. This represents the tangential displacement of the crack.

[0233] The solution process for the above model is as follows:

[0234] Multiple crack elements exist on the crack surface, and they influence each other. Therefore, the stress field on the crack surface should satisfy the following equation, where the normal stress and shear stress can be expressed as:

[0235]

[0236] In the formula, for, for.

[0237]

[0238] In the formula: "-" in the symbol represents the lower surface of the crack, and "+" is omitted for the upper surface of the crack.

[0239] γ is the boundary influence coefficient; f is the derivative of the function f(x,y); ij =β i -β j .

[0240] The normal displacement of the crack can be calculated by combining equation (9) with the boundary conditions of the crack. and tangential displacement This allows us to determine the stress and displacement fields at any location within the formation.

[0241] Crack boundary conditions

[0242] In the discrete calculation process, each crack is divided into N crack element bodies. After performing stress analysis on each element body, the crack boundary conditions can be obtained. For example... Figure 5 As shown, each fracture element is subjected to the combined effects of fluid pressure within the fracture (fracture surface pressure and shear stress) and external stress. The external stress includes fracture-induced stress from other fracture elements, filtration-induced stress, and the in-situ stress field. The boundary conditions are as follows:

[0243]

[0244] In the formula: σ H —Maximum horizontal principal stress in the in-situ stress field, MPa;

[0245] σ h —Minimum horizontal principal stress in the in-situ stress field, MPa;

[0246] σ xy —In-situ stress shear stress, MPa;

[0247] —Normal induced stress of crack element j at element i, MPa;

[0248] —Shear-induced stress at element i in crack element j, MPa;

[0249] — The filtration-induced stress on crack element i, in MPa.

[0250] β i 'U' represents the angle between the local coordinate system and the global coordinate system, expressed in degrees.

[0251] p f ν is the fluid pressure within the fracture unit, in MPa.

[0252] As can be seen from equation (10), the fracture boundary condition is the result of the combined action of fluid pressure, fracture-induced stress, filtration-induced stress, and in-situ stress, closely linking several stresses of different natures. Therefore, the boundary condition is the key link between rock mass stress and fluid pressure. From the perspective of the significance of the fracture boundary condition, the normal stress at the fracture boundary represents the size of the fracture width. Among these stresses, analysis reveals that the fluid pressure within the fracture is the driving force for fracture extension, while the fracture-induced stress, filtration-induced stress, and in-situ stress are all resistances to fracture extension. The shear stress at the fracture boundary represents the degree of fracture deflection. Among these stresses, the fracture-induced stress is the driving force for fracture deflection, while the in-situ stress is the resistance to fracture deflection. Therefore, the fracture boundary condition can explain many physical phenomena in multi-fracture extension. For example, in multi-fracture extension, the outer fracture will deflect outward due to the action of fracture shear-induced stress.

[0253] Step 3: Based on the models in Step 1 and Step 2, establish a mathematical model for simulating the multi-crack extension morphology.

[0254] By combining the models from steps 1 and 2, the desired mathematical model for multi-cluster crack propagation can be obtained.

[0255] Step 4: Establish a mathematical model for hydraulic fracture propagation considering natural fractures.

[0256] The granular flow method, also known as the Discrete Element Method (DEM), simulates the mechanical or other properties of materials by modeling a whole composed of spherical rigid particles. Cundall et al. first proposed the concept of the DEM method, which has since developed into a complete discipline. When a hydraulic fracture encounters an intersecting natural fracture during its propagation, shear failure, faulting, and slippage of the natural fracture can significantly affect the fracture's propagation path. The hydraulic fracture may extend along the natural fracture, shear through the natural fracture, or even continue propagating through it. This section determines how the hydraulic fracture propagates when it intersects with a natural fracture.

[0257] Hydraulic cracks extend along natural cracks

[0258] like Figure 8 As shown, assuming that after the two fractures intersect but before the natural fracture opens, the fracturing fluid does not enter the natural fracture in large quantities, and the fluid pressure drop and pore pressure within the natural fracture are ignored. The pressure within the natural fracture at this time is p; therefore, p is also the fracture tip pressure of the hydraulic fracture. At this point, when the fracture pressure p is greater than the normal stress σ... n When the natural cracks that were originally closed open, they will open. The critical state for judging whether a natural crack has opened is: when a hydraulic crack intersects with a natural crack, whether the natural crack has opened.

[0259] p = σ n (11)

[0260] Hydraulic fractures extend along natural fractures.

[0261] During hydraulic fracturing operations in fractured reservoirs, hydraulic fractures inevitably encounter naturally developed fracture zones. For ease of study, the actual field model is simplified. It is assumed that the hydraulic fracture intersects a natural fracture along the horizontal principal stress direction in the far field, as shown below. Figure 8 As shown. Where the approximation angle is β, σ H and σ h These are the maximum and minimum horizontal principal stresses, respectively.

[0262]

[0263] In the formula: σ H For the maximum horizontal principal stress, σ h Let β be the minimum principal stress at horizontal, and K be the approximation angle. f τ is the friction coefficient of the natural fracture surface, τ0 is the cohesion of the rock, and p σ This represents the maximum fluid pressure within the crack before shear failure due to a natural crack.

[0264] As shown in the above formula, when hydraulic fractures and natural fractures intersect, the factors determining whether the natural fractures undergo shear slip include the approach angle, the difference in horizontal principal stresses, and the friction coefficient of the natural fracture surface. Under conditions of low stress difference, low approach angle, or low friction coefficient, the natural fractures are prone to shear failure due to the influence of the hydraulic fractures. This section is used to determine whether the natural fractures undergo shear failure when hydraulic fractures intersect.

[0265] Hydraulic cracks penetrate natural cracks

[0266] When a hydraulic fracture intersects a natural fracture, the hydraulic fracture passes through the natural fracture if the stress acting on the natural fracture wall reaches the tensile strength of the rock and the natural fracture does not undergo shear slip. For example... Figure 9 As shown, assume that the hydraulic fracture encounters a moderately sized natural fracture during its extension, with an approach angle of β and a penetration angle of γ. H and σ h These are the maximum and minimum horizontal principal stresses, respectively.

[0267] If a new crack is to initiate on the wall of a natural crack, the stress acting on the wall must reach the tensile strength of the rock, that is, the maximum principal stress must be satisfied: to determine whether a hydraulic crack will penetrate a natural crack.

[0268] σ r1 =T0 (13)

[0269] In the formula: σ r1 —The maximum principal stress at different points on the surface of a natural crack.

[0270] If a hydraulic fracture penetrates a natural fracture, then in addition to satisfying the stress conditions analyzed above, the natural fracture must also not undergo shear failure under those stress conditions, i.e.

[0271] |τ n |<τ0+K f (σ n -p0) (14)

[0272] Where: τ0—rock cohesion, MPa;

[0273] K f —The coefficient of friction of natural cracks.

[0274] In the formula: p f — Fluid pressure within the fracture unit, MPa.

[0275] Step 5: Combine the model obtained in Step 3 with the model obtained in Step 4 to obtain the multi-cluster hydraulic fracture propagation model that considers the influence of stratification.

[0276] The mathematical model for hydraulic fracture propagation determines how hydraulic fractures propagate when they intersect with natural fractures. The multi-cluster fracture propagation mathematical model in step 3 is the basic model of the fractures, simulating the propagation process. Integrating the model obtained in step 3 into the model in step 4 yields the desired model. This model can be used to model the propagation process of hydraulic fractures when they intersect with natural fractures. This model can also be used to predict the influence of bedding on the propagation of hydraulic fractures along the fracture height direction.

[0277] Example 2

[0278] In a specific embodiment 2 of the present invention, the model can be built using existing commercial software. After the model is built in the software tool, the solution method has been described in detail above; the input comes from parameters obtained from previous statistical analysis of fractured wells. After solving the model, the law of fracture extension under different parameter conditions can be obtained. Based on this law, the influence of each parameter on the fracture height can be clarified, providing suggestions for the fracturing process and optimizing the construction parameters.

[0279] The input parameters include, but are not limited to, the rock Young's modulus, such as Poisson's ratio, tensile strength, fracture toughness, geostress, and natural fracture parameters (density, dip angle, dip direction, size, etc.), as shown in the table below.

[0280] Table 1. Crack Height Direction Extension Model

[0281]

[0282] The results of suture height extension simulations for 2, 4, 6, 10, and 20 bedding layers are as follows: Figure 10 As shown in the figure, as the bedding density increases, the number of bedding layers increases, and the number of bedding layers broken during the extension process also increases. Due to the opening of bedding layers and the loss of fracturing fluid into the bedding layers, the extension in the fracture height direction is restricted, and the fracture height continuously decreases with increasing bedding density, but the rate of decrease also gradually decreases.

[0283] Example 3

[0284] In a specific embodiment 3 of the present invention, using the parameters in Table 1, the results of seam height extension under vertical stress differences of 5, 10, 15, 20, and 25 MPa were simulated respectively. Figure 11 As shown in the figure, as the vertical stress difference increases, the stress acting on the bedding plane increases, the difficulty of bedding opening increases, and the fracturing fluid loss decreases. Therefore, the fracture height increases with the increase of the vertical stress difference, but the increase is relatively small.

[0285] Example 4

[0286] In a specific embodiment 4 of the present invention, the parameters in Table 1 were used to simulate fracture toughnesses of 0.2, 0.4, 0.6, 0.8, and 1 MPa·m, respectively. 0.5 The result of the lower seam height extension is as follows Figure 12 As shown in the figure, as fracture toughness increases, the energy required for crack propagation increases, thus the crack height decreases, but the effect is relatively small.

[0287] Example 5

[0288] In a specific embodiment 5 of the present invention, using the parameters in Table 1, the results of seam height elongation were simulated for Young's modulus of 10, 15, 20, 30, and 40 GPa, respectively. Figure 13 As shown in the figure, it can be seen that as Young's modulus increases, the crack height will increase slightly, but it will not break through new bedding, indicating that Young's modulus has little effect on crack height.

[0289] Example 6

[0290] In a specific embodiment 6 of the present invention, using the parameters in Table 1, the seam height elongation was simulated for tensile strengths of 4, 6, 8, 10, and 12 MPa, respectively. Figure 14 As shown in the figure, it can be seen that as the tensile strength increases, the energy required for crack propagation increases, and therefore the crack height decreases accordingly, but the impact is relatively small.

[0291] This invention establishes a multi-cluster hydraulic fracture extension model, considering the influence of bedding on the extension of fracture height. This model is used to analyze the extension law of deep shale hydraulic fracturing fracture height. Based on the fracturing geological parameters of each block, the model can simulate and analyze the fracture morphology formed in different blocks, identify the main controlling factors of fracture morphology and the characteristics of fractures formed in each block, and provide a basis for subsequent process parameter recommendations.

[0292] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0293] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A method for constructing a hydraulic fracture propagation model for shale oil horizontal wells, characterized in that, The method for constructing the hydraulic fracture propagation model for shale oil horizontal wells includes: Step 1: Establish a mathematical model to simulate the propagation of a single crack; Step 2: Establish a crack-induced stress field model based on the displacement discontinuity method; Step 3: Based on the models in Step 1 and Step 2, establish a mathematical model for simulating the multi-crack extension morphology. Step 4: Establish a mathematical model for the propagation of hydraulic fractures that takes into account natural fractures; Step 5: Combine the model obtained in Step 3 with the model obtained in Step 4 to obtain the multi-cluster hydraulic fracture propagation model that takes into account the influence of bedding. In step 1, the mathematical model for single fracture propagation includes a wellbore fluid flow model, a fracture fluid flow model, and a fracture propagation criterion. In step 1, the wellbore fluid flow model is established as follows: Based on Kirchoff's first and second laws, the relationship between the frictional resistance along the wellbore and the frictional resistance of the perforation hole is calculated, the wellbore pressure drop equation is derived, and the wellbore fluid flow equation is established. In step 1, the wellbore fluid flow model is as follows: （3） In the formula: Let C be the frictional resistance of the wellbore in the i-th fracture. cf x is the coefficient of friction. j Let j be the distance from the crack to the wellbore heel. Let Q be the fluid flow rate remaining after passing through j fractures, D be the horizontal wellbore diameter, and Q be the fluid flow rate remaining after passing through j fractures. T Q represents the total fluid injection volume. k Let be the fluid injection volume for the k-th crack; In step 2, the crack-induced stress field model includes: The stress field induced by fractures at any location in the formation is as follows: （6） The displacement field at any location in the strata is: （7） In the formula: The normal stress is in the x-axis direction. The normal stress is in the y-axis direction. For shear stress, Shear modulus , , , , , The stress boundary influence coefficient is N, where N is the number of crack elements. , Let represent the displacement of the crack element in the horizontal and vertical directions. , , , This is the displacement influence coefficient. Let be the normal displacement of the crack. This represents the tangential displacement of the crack.

2. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 1, characterized in that, In step 1, the method for establishing the fluid flow model within the crack is as follows: Based on the theory of flat plate flow, the pressure drop equation for fluid flow within a fracture is derived; based on the law of conservation of mass, the expression for the relationship between fluid pressure and fracture width within a fracture is derived; and the finite difference method is used for discretization to establish a fluid flow model within the fracture.

3. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 2, characterized in that, In step 1, the pressure drop equation for the fracture fluid flow is: （1） In the formula: q is the fluid flow rate, p is the fluid pressure, and w f Where is the maximum width of the crack cross section, u is the fluid shear displacement, and h is the height of the crack in the flat plate. The relationship between fluid pressure within the crack and crack width is as follows: （2） In the formula: w is the width of the crack at any vertical position, t is the total pumping time, and C L τ is the filtration coefficient, and τ is the time when the crack element begins to filtration.

4. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 1, characterized in that, In step 1, Crack propagation criteria include: The equivalent intensity factor is: （4） Where: K e K is the equivalent intensity factor. Ⅰ K is a type I intensity factor. Ⅱ It is a type II intensity factor. The angle at which the crack deviates from its original direction of extension; The maximum circumferential stress criterion is expressed by the equivalent strength factor as follows: （5） In the formula, This refers to the fracture toughness of the rock mass.

5. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 1, characterized in that, In step 3, the mathematical model for the propagation of multiple fracture clusters makes the following assumptions about the rock mass: 1) The reservoir rock is a homogeneous, isotropic, porous medium that meets the linear elasticity condition; 2) The height of the hydraulic fracturing fracture is constant, and the cross-section in the height direction is elliptical; 3) The influence of cracks on the propagation of hydraulic cracks is not considered; 4) Rocks only conform to Type I and Type II fractures.

6. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 5, characterized in that, In step 3, the mathematical model for multi-cluster crack propagation makes the following assumptions about the fluid: 1) Propionate transport within the fluid is not considered; 2) The fluid is an incompressible Newtonian fluid and is filled with cracks; 3) The fluid flows in a one-dimensional laminar flow within the crack, obeying Cater filtration; 4) Changes in mechanical properties caused by the physicochemical interaction between the fluid and the reservoir rock are not considered.

7. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 1, characterized in that, In step 4, the mathematical model for hydraulic fracture propagation considers hydraulic fractures opening along natural fractures, hydraulic fractures shearing along natural fractures, and hydraulic fractures penetrating natural fractures.

8. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 7, characterized in that, In step 4, the hydraulic fractures open along the natural fractures: （11） In the formula: p is the pressure inside the natural fracture. This represents the normal stress acting on the surface of the natural crack.

9. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 7, characterized in that, In step 4, the hydraulic fracture extends shear along the natural fracture: （12） In the formula: σ H For the maximum horizontal principal stress, σ h For the minimum principal stress in the horizontal direction, For the approximation angle, K f The coefficient of friction of the natural crack surface. For the cohesion of rocks, This represents the maximum fluid pressure within the crack before shear failure due to a natural crack.

10. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 7, characterized in that, In step 4, the hydraulic fracture penetrates the natural fracture: （13） In the formula: denoted as the maximum principal stress at different points on the wall of the natural crack, r is the distance between the location on the natural crack and the crack tip, and T0 is the tensile strength of the natural crack. （14） In the formula: The shear force acting on the surface of the natural crack. This represents the normal stress acting on the surface of the natural crack.

11. The method for constructing a hydraulic fracture propagation model for shale oil horizontal wells according to claim 1, characterized in that, In step 5, a mathematical model for the extension of multiple hydraulic fractures is constructed to simulate the influence of different parameters on the fracture height; the parameters include the number of bedding planes, Young's modulus of rock, difference in vertical principal stress, fracture toughness, and tensile strength.

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