Shale hydraulic fracturing fracture height calculation method and device

Abstract

The invention provides a shale hydraulic fracturing fracture height calculation method and device, and the method comprises the steps: collecting the geological and engineering data of each rock stratum of a target well, and building a fluid-solid coupling control equation set of hydraulic fracture longitudinal extension; the crack initiation size is determined; and according to the crack initiation size and the fluid-solid coupling control equation set, the hydraulic fracturing crack height is obtained through calculation. According to the method, the longitudinal crossing effect of the hydraulic fracture under different parameters can be quantitatively evaluated, and a scientific basis is provided for prediction of the fracture height in unconventional low-permeability reservoir horizontal well staged fracturing.

Description

Technical Field

[0001] This invention belongs to the field of hydraulic fracturing technology, and specifically relates to a method and apparatus for calculating the fracture height in shale hydraulic fracturing. Background Technology

[0002] my country possesses vast shale oil and gas resources with promising exploration and development prospects. Shale reservoirs exhibit low permeability and numerous discontinuities at various scales. Efficient development of shale oil and gas resources is of practical urgency and strategic significance for ensuring national energy security. Hydraulic fracturing, as a core method of reservoir stimulation, directly determines the contact area between the fracture and the reservoir, and thus the production enhancement effect, based on the vertical extension scale of the fracture (i.e., fracture height). Currently, horizontal well staged fracturing has become a key technology for shale oil and gas development. However, due to the widespread development of bedding planes, weak surfaces, and natural fractures in shale formations, vertical fracture propagation is often inhibited, and the measured fracture height in the field is generally lower than the design expectation.

[0003] To address the influence of bedding planes on longitudinal fracture propagation, current fracturing design largely employs the fracture mechanics model proposed by Renshaw and Pollard (1997), which describes a fracture without contact and fluid injection, to estimate fracture height. Gu et al. (2003) and Weng et al. (2007) derived fracture propagation criteria for different contact angles using similar methods. Churpakov et al. (2015) further considered the influence of fluid entry into the bedding planes on fracture propagation, proposing the well-known Open-T criterion. Llanos et al. (2017) conducted experimental research on the influence of bedding planes with good permeability on fracture propagation and proposed corresponding propagation criteria. Most of these methods for calculating fracture height neglect the crucial role of fluid in hydraulic fracturing, considering only the frictional deformation of discontinuities. More importantly, these criteria only indicate whether the fracture penetrates the bedding plane, without characterizing the penetration process. Therefore, the longitudinal fracture propagation shows a continuous trend, which contradicts the actual discontinuous increase in fracture height. From a physical perspective, longitudinal cross-layer propagation of fractures is often inhibited by the difficulty in the initiation of new fractures, and the re-initiation of fractures on bedding planes is a key factor controlling fracture height. This process is influenced by multiple parameters, including geostress, rock strength, bedding plane aperture, fracturing fluid viscosity, and injection rate. Moreover, current models do not consider the physical processes of new fracture initiation, nor have they developed quantitative prediction methods that can be directly applied at the engineering scale. Summary of the Invention

[0004] This application provides a method and apparatus for calculating the fracture height in shale hydraulic fracturing, which can quantitatively evaluate the longitudinal cross-layer effect of hydraulic fractures under different parameters, and provides a scientific basis for predicting the fracture height in staged fracturing of horizontal wells in unconventional low-permeability reservoirs.

[0005] In a first aspect, embodiments of this application provide a method for calculating the height of hydraulic fracturing fractures in shale, comprising: collecting geological and engineering data of each rock stratum in the target well, establishing a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; determining the fracture initiation size; and calculating the height of hydraulic fracturing fractures based on the fracture initiation size and the set of fluid-structure interaction control equations.

[0006] This includes collecting geological and engineering data on each rock stratum in the target well, and establishing a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures, including: Collect geological and engineering data of each rock stratum for the target well. Based on the collected data, simplify and stratify the reservoir, determine the number of bedding planes, and establish an engineering-scale numerical model of the actual shale reservoir under the condition of multiple bedding planes. Establish a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures, including: establishing the rock mass elastic deformation equation and the fluid flow equation within the fracture; fluid flow includes: fluid flow along closed natural fractures and flow through open hydraulic fracture channels; use the Reynolds equation to describe the fluid motion in open hydraulic fractures, and use the pressure diffusion equation to describe the fluid flow in closed natural fractures.

[0007] The fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures include: Based on the collected geological and engineering data, the geological and mechanical parameters of each rock layer were determined. Based on the on-site construction discharge rate and fracturing fluid viscosity, the injection rate driving the longitudinal propagation of the fracture was calculated. The boundary conditions of the fluid-structure interaction control equations at the fracture inlet were given. The formula for calculating the injection rate driving the longitudinal propagation of the fracture is as follows:

[0008] In the formula: The two-dimensional injection rate is represented by A, and the cross-sectional area of ​​the crack is represented by A. h represents the average crack width; h represents the PKN crack height. ρ is the Poisson's ratio of the rock; G is the shear modulus of the rock; q is the flow velocity through a fracture wing; t represents the fracturing fluid viscosity; t represents the fracturing fluid injection time.

[0009] Determining the crack initiation size includes: a numerical implementation plan for determining the crack initiation size. Potential crack initiation points are determined based on stress-strength analysis, and a new crack of predetermined length d is placed at these points; Using the current stress state, the opening displacement of the precast crack is calculated, and the stress intensity factor is calculated using the displacement correlation method. The stress intensity factor is compared with the fracture toughness of the rock. If the fracture meets the nucleation criteria, the fracture is considered a newly generated fracture; otherwise, the pre-existing fracture is deleted.

[0010] Determining the crack initiation size also includes: the simulation process for determining the crack initiation size includes: A crack propagation model in a homogeneous elastic medium was constructed as a control group. Different d values ​​were used in the simulation to make the crack propagation rate and internal pressure level match the analytical solution of the control group; if the d value is greater than the threshold, the strength criterion cannot be met, and the simulation results do not match the control group results. If the numerical result remains consistent with the theoretical solution when the value of d is reduced, then the maximum value of d at this time is determined as the crack initiation size.

[0011] The calculation of hydraulic fracturing fracture height based on the fracture initiation size and the fluid-structure interaction control equations includes: embedding the determined fracture initiation size into the fluid-structure interaction control equations, numerically simulating the longitudinal propagation process of hydraulic fractures in multi-layered foliated shale, and predicting the final fracture height that the fracture can reach.

[0012] The hydraulic fracturing fracture height, calculated based on the fracture initiation size and the fluid-structure interaction control equations, includes: The fracture height is used to determine whether the fracture is in contact with the bedding plane at the current moment. If it is not in contact with the bedding plane, the stress intensity factor at the fracture tip is compared with the fracture toughness of the reservoir. If the critical condition is met, the fracture will extend vertically. If the critical condition is not met, the fracture height will remain unchanged. If the crack comes into contact with the bedding plane, it is necessary to determine whether the crack initiation process can be completed on the other side of the bedding plane and continue to propagate. When the crack moves away from the bedding plane, the unit size is gradually increased to the centimeter level to complete the longitudinal propagation process of the crack in each layer. When the net pressure at the crack tip cannot overcome the resistance to vertical propagation, longitudinal crack propagation stops, resulting in the final crack height.

[0013] Secondly, this application provides a device for calculating the height of hydraulic fracturing fractures in shale, comprising: an establishment unit for collecting geological and engineering data of each rock stratum in the target well and establishing a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; a determination unit for determining the fracture initiation size; and a calculation unit for calculating the height of hydraulic fracturing fractures based on the fracture initiation size and the set of fluid-structure interaction control equations.

[0014] Thirdly, embodiments of this application provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described above.

[0015] Fourthly, embodiments of this application provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of any of the methods described above.

[0016] The method and apparatus for calculating the fracture height in shale hydraulic fracturing according to the embodiments of this application have the following beneficial effects: This application can quantitatively evaluate the longitudinal cross-layer effect of hydraulic fractures under different parameters, and provides a scientific basis for predicting the fracture height in the staged fracturing of horizontal wells in unconventional low-permeability reservoirs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the calculation method for the fracture height in shale hydraulic fracturing according to an embodiment of this application; Figure 2 This is another flowchart illustrating the method for calculating the fracture height in shale hydraulic fracturing according to an embodiment of this application. Figure 3 Figure 1 shows the numerical simulation results of the cross-layer propagation morphology of hydraulic fractures in five sub-layers of Subsection IV of an oilfield. Figure 4 This is a schematic diagram of the structure of the device for calculating the fracture height of shale hydraulic fracturing according to an embodiment of this application. Detailed Implementation

[0018] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0019] In the following description, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The following description provides multiple embodiments of the invention, which can be substituted or combined with each other. Therefore, this application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then this application should also be considered to include embodiments containing one or more other possible combinations of features A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0020] Example 1 like Figure 1 As shown, the method for calculating the fracture height of shale hydraulic fracturing in this application includes: S101, collecting geological and engineering data of each rock layer in the target well, and establishing a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; S103, determining the fracture initiation size; S105, calculating the hydraulic fracturing fracture height based on the fracture initiation size and the set of fluid-structure interaction control equations.

[0021] This application can quantitatively evaluate the longitudinal cross-layer effect of hydraulic fractures under different parameters, and provides a scientific basis for predicting the fracture height in the staged fracturing of horizontal wells in unconventional low-permeability reservoirs.

[0022] Example 2 like Figure 2As shown, the method for calculating the fracture height in shale hydraulic fracturing according to this application includes: Step S1: Collect geological and engineering data of each rock stratum for the target well.

[0023] Geological and engineering data include reservoir thickness H and rock layer elastic modulus. Poisson's ratio and fracture toughness Minimum horizontal principal stress Vertical stress , layering surface opening coefficient of friction The fracturing fluid viscosity is μ, the injection rate is Q0, and the subscript i represents different layers.

[0024] Step S2: Based on the data from Step S1, the reservoir is reasonably simplified and layered to determine the number of bedding planes and to establish an engineering-scale numerical model of the actual shale reservoir under the condition of multiple bedding planes.

[0025] Step S3: Establish the fluid-structure interaction control equations for the longitudinal propagation of hydraulic cracks.

[0026] In this step, the elastic deformation equation of the rock mass and the fluid flow equation within the fracture are established. The fluid flow is mainly divided into two cases: one is the flow of fluid along closed natural fractures; the other is the flow through open hydraulic fracture channels. The Reynolds equation is used to describe the fluid motion in open hydraulic fractures, and the pressure diffusion equation is used to describe the fluid flow in closed natural fractures. At the same time, the hydraulic fractures follow the I-II mixed propagation criterion.

[0027] Step S4: Based on the data obtained in step S1, determine the geological and mechanical parameters of each rock layer, and calculate the injection rate that drives the longitudinal propagation of the fracture based on the on-site construction discharge rate and fracturing fluid viscosity, and give the boundary conditions of the fluid-structure interaction control equation set at the fracture inlet.

[0028] In this step, the formula for calculating the injection rate driving the longitudinal propagation of the fracture is:

[0029] In the formula: For the two-dimensional injection rate, m 2 / s; A is the cross-sectional area of ​​the crack, m 2 ; h is the average crack width, in meters; h is the PKN crack height, in meters. G is the Poisson's ratio of the rock; G is the shear modulus of the rock, Pa; q is the flow velocity through a fracture flange, m. 3 / min, ; t is the fracturing fluid viscosity, Pa·s; t is the fracturing fluid injection time, s.

[0030] Step S5: Based on the physical mechanism that hydraulic fractures must simultaneously satisfy strength and toughness criteria to initiate at the bedding plane, a fracture nucleation size (FNS) is proposed to provide a criterion for fracture initiation at the bedding plane, and a numerical implementation scheme for determining the FNS is established.

[0031] In this step, the strength and toughness dual criteria proposed by Leguillon (2002) are used as the basis for judging crack initiation. On the other side of the bedding plane different from the crack, there is a small crack surface of size d, and the stress level is... It must exceed the rock material strength T, stress intensity factor K Ⅰ It must also exceed the fracture toughness K of the rock. ⅠC .

[0032] The numerical implementation scheme for FNS is determined as follows: potential initiation points are identified based on stress-intensity analysis, and a new crack of predetermined length d is placed at these points; the opening displacement of the pre-existing crack is calculated using the current stress state, and the stress intensity factor is calculated using the displacement correlation method; these stress intensity factors are compared with the fracture toughness of the rock, and if they meet the crack nucleation criteria, the crack is considered a newly generated crack; otherwise, the pre-existing crack is deleted.

[0033] Step S6: Based on the analytical solution of the propagation rate of hydraulic fractures in homogeneous rock mass and the numerical results obtained in step S5, determine whether the value of FNS is reasonable, and determine the size of FNS as the initial condition of the fluid-structure interaction control equation set.

[0034] In this step, the simulation process for determining the size of FNS specifically includes: constructing a crack propagation model in a homogeneous elastic medium as a control group; using different d values ​​for simulation to make the crack propagation rate and internal pressure level match the analytical solution of the control group; if the d value is too large, the strength criterion cannot be met, and the simulation results do not match the control group results; when the d value is further reduced, if the numerical results are still consistent with the theoretical solution, then the maximum d value at this time is determined as FNS.

[0035] Step S7: Boundary and initial conditions of the complete mathematical model.

[0036] The boundary conditions for the injection point are given based on the injection rate range determined in step S4, namely:

[0037] At the crack tip, both the opening and shear displacement discontinuities are 0, that is:

[0038] The opening profile near the crack tip is square root shaped, consistent with the stress singularity of linear elastic fracture mechanics at the crack tip. Simultaneously, the FNS determined in step S6 is used as the initial condition for crack re-initiation, thus completing the mathematical description of the engineering model.

[0039] Step S8: Embed the determined FNS size into the coupled model of step S3, numerically simulate the longitudinal propagation process of hydraulic fractures in multi-layered foliated shale, and predict the final fracture height that the fractures can reach.

[0040] This step includes: determining whether the fracture is in contact with the bedding plane at the current moment based on the fracture height; if it is not in contact with the bedding plane, comparing the stress intensity factor at the fracture tip with the fracture toughness of the reservoir; if the critical condition is met, the fracture will propagate vertically; if the critical condition is not met, the fracture height will remain unchanged. If the bedding plane is in contact, it is necessary to determine whether the crack initiation process can be completed on the other side of the bedding plane and continue to propagate. As the crack gradually moves away from the bedding plane, the element size is gradually increased to the centimeter level using about 50 elements, and the longitudinal propagation process of the crack in each layer is completed with fewer than 260 elements. When the net pressure at the crack tip is insufficient to overcome the resistance to vertical propagation, longitudinal crack propagation stops, resulting in the final crack height.

[0041] To address the problems in existing technologies, it is necessary to conduct theoretical research to elucidate the crack initiation mechanism on the bedding plane, provide a method for calculating the crack initiation size (FNS), propose a crack initiation criterion that takes into account both strength and toughness, more realistically reproduce the physical process of longitudinal cross-layer propagation in hydraulic fracturing, and develop a crack height prediction model with strong engineering applicability based on this.

[0042] This invention primarily addresses the issues of new fracture initiation inhibition and re-initiation during the longitudinal cross-layer propagation of hydraulic fractures, considering fluid interactions, and aims to predict the fracture height. A fluid-structure interaction equation set is established based on the rock mass elastic deformation equation, the fluid flow equation within the fracture, and the propagation criterion. This set is incorporated into a new cross-layer propagation model to determine whether a fracture will propagate before encountering a bedding plane, and the direction of propagation. Considering the contact and frictional sliding of bedding planes, the re-initiation of hydraulic fractures during cross-layer propagation is defined based on the strength-toughness dual criterion. A new fracture initiation model is established using more reasonable initiation conditions and a method for determining the fracture initiation point (FNS), simulating the re-initiation and propagation process of hydraulic fractures encountering bedding planes.

[0043] This application, based on an engineering-scale numerical model of actual shale reservoirs with multiple bedding planes, completes the numerical simulation of the entire process from fracture initiation to propagation. It considers the influence of bedding plane friction and fluid action on the re-initiation of hydraulic fractures and calculates the fracture height for longitudinal propagation. This application can quantitatively evaluate the longitudinal cross-layer effect of hydraulic fractures under different parameters, providing a scientific basis for predicting fracture height in staged fracturing of horizontal wells in unconventional low-permeability reservoirs.

[0044] Example 3 Methods for calculating fracture height in hydraulic fracturing in shale reservoirs, including Step S1: Collect geological and engineering data of each rock stratum for the target well.

[0045] Geological and engineering data include reservoir thickness H and rock layer elastic modulus. Poisson's ratio and fracture toughness Minimum horizontal principal stress Vertical stress , layering surface opening coefficient of friction The fracturing fluid viscosity is μ, the injection rate is Q0, and the subscript i represents different layers.

[0046] Step S2: Based on the data from Step S1, the reservoir is reasonably simplified and layered to determine the number of bedding planes and to establish an engineering-scale numerical model of the actual shale reservoir under the condition of multiple bedding planes.

[0047] The horizontal bedding planes of shale reservoirs are relatively dense. In the numerical simulation of hydraulic fracturing, in order to improve the calculation efficiency, the horizontal bedding planes are simplified by an equivalent method. According to well logging data and rock mechanics test results, this simplification is feasible.

[0048] Step S3: Establish the fluid-structure interaction control equations for the longitudinal propagation of hydraulic cracks.

[0049] (1) In the global Cartesian coordinate system, the elastic equation for the equilibrium between cracks is:

[0050] In the formula: Let be a point in two-dimensional space, t be time; ds be the differential of the crack length; w and v be the aperture and relative slip on the crack surface, respectively (discontinuity of normal and shear displacement); l r The length of the crack is given by the subscript r, which indicates the crack branch number. Normal stress, shear stress The number of locations where all crack surfaces separate is zero; and These are the normal and shear stress components generated by far-field stress, respectively; G ij It is a supersingular Green's function.

[0051] (2) As the injection pressure increases, the fluid entering the closed natural fractures in the reservoir causes mechanical expansion, thereby changing the hydraulic aperture of the fractures. It is assumed that the evolution of the hydraulic aperture follows a nonlinear spring model:

[0052] In the formula: The initial hydraulic aperture of the closed fracture is in meters (m). The elastic crack compressibility coefficient is a small constant with a value of 10. −6 ~10 −8 / Pa; The shear expansion coefficient, in meters, is specified in the input data file.

[0053] Based on mass continuity, the pressure diffusion equation is used to describe the fluid flow in a closed natural fracture:

[0054] In the formula,

[0055] (3) Use the Reynolds equation to describe the fluid motion of an open hydraulic fracture:

[0056] In the formula: s is the local coordinate along the crack path; The hydraulic pore size is generated by the microstructure of the crack surface. For fluid dynamic viscosity; The fluid pressure in the crack.

[0057] With a constant injection rate, the global mass conservation equation is:

[0058] In the formula: Q0 is the injection rate, m 3 / s;l f Let be the fluid filling length of each crack, in meters (m).

[0059] (4) Fluid fronts in fractures, including open hydraulic fractures and closed natural fractures, can be affected by the flux at the fluid front. and opening degree Find:

[0060] In the formula: flux is defined according to Poiseuille's law as follows:

[0061] (5) The magnitudes of the stress intensity factors in Mode I and Mode II at the fracture tip were determined using a displacement correlation method. The propagation of hydraulic fractures in the mixed mode follows two criteria:

[0062] In the formula, θ is the deflection angle of the current crack line; K I and K II These are the stress intensity factors for Type I and Type II cracks, respectively; K IC It is a type I (tensile) fracture toughness.

[0063] Step S4: Based on the data obtained in step S1, determine the geological and mechanical parameters of each rock layer, and calculate the injection rate that drives the longitudinal propagation of the fracture based on the on-site construction discharge rate and fracturing fluid viscosity, and give the boundary conditions of the fluid-structure interaction control equation set at the fracture inlet.

[0064] In this step, the formula for calculating the injection rate driving the longitudinal propagation of the fracture is:

[0065] In the formula: For the two-dimensional injection rate, m 2 / s; A is the cross-sectional area of ​​the crack, m 2 ; h is the average crack width, in meters; h is the PKN crack height, in meters. G is the Poisson's ratio of the rock; G is the shear modulus of the rock, Pa; q is the flow velocity through a fracture flange, m. 3 / min, ; t is the fracturing fluid viscosity, Pa·s; t is the fracturing fluid injection time, s.

[0066] Based on the analytical solution of the PKN model, the cross-sectional area of ​​the crack can be calculated using the following formula:

[0067] Assuming no fracturing fluid loss within the fracture, the fracture width at the wellbore can be calculated using the following formula:

[0068] Step S5: Based on the physical mechanism that hydraulic fractures must simultaneously satisfy strength and toughness criteria to initiate at the bedding plane, a fracture nucleation size (FNS) is proposed to provide a criterion for fracture initiation at the bedding plane, and a numerical implementation scheme for determining the FNS is established.

[0069] In this step, the strength and toughness dual criteria proposed by Leguillon (2002) are used as the basis for judging crack initiation. On the other side of the bedding plane different from the crack, there is a small crack surface of size d, and the stress level is... It must exceed the rock material strength T, stress intensity factor K Ⅰ It must also exceed the fracture toughness K of the rock. ⅠC .

[0070] The numerical implementation scheme for FNS is determined as follows: potential initiation points are identified based on stress-intensity analysis, and a new crack of predetermined length d is placed at these points; the opening displacement of the pre-existing crack is calculated using the current stress state, and the stress intensity factor is calculated using the displacement correlation method; these stress intensity factors are compared with the fracture toughness of the rock, and if they meet the crack nucleation criteria, the crack is considered a newly generated crack; otherwise, the pre-existing crack is deleted.

[0071] Step S6: Based on the analytical solution of the propagation rate of hydraulic fractures in homogeneous rock mass and the numerical results obtained in step S5, determine whether the value of FNS is reasonable, and determine the size of FNS as the initial condition of the fluid-structure interaction control equation set.

[0072] In this step, the simulation process for determining the size of FNS specifically includes: constructing a crack propagation model in a homogeneous elastic medium as a control group; simulating with different d values ​​to ensure that the crack propagation rate and internal pressure level match the analytical solution of the control group; if the d value is too large, the strength criterion cannot be met, and the simulation results do not match the control group results; when the d value is further reduced, if the numerical results still maintain consistency with the theoretical solution, then the maximum d value at this point is determined as FNS. The simulation reveals that FNS is not an inherent parameter of the material, but a parameter that dynamically adjusts with changes in material properties and stress conditions, exhibiting a functional relationship, namely:

[0073] In the formula: It is horizontal stress; Vertical stress; Tensile strength.

[0074] Step S7: Boundary and initial conditions of the complete mathematical model.

[0075] The boundary conditions for the injection point are given based on the injection rate range determined in step S4, namely:

[0076] At the crack tip, both the opening and shear displacement discontinuities are 0, that is:

[0077] The opening profile near the crack tip is square root shaped, consistent with the stress singularity of linear elastic fracture mechanics at the crack tip. Simultaneously, the FNS determined in step S6 is used as the initial condition for crack re-initiation, thus completing the mathematical description of the engineering model.

[0078] Step S8: Embed the determined FNS size into the coupled model of step S3, numerically simulate the longitudinal propagation process of hydraulic fractures in multi-layered foliated shale, and predict the final fracture height that the fractures can reach.

[0079] This step includes: determining whether the fracture is in contact with the bedding plane at the current moment based on the fracture height; if it is not in contact with the bedding plane, comparing the stress intensity factor at the fracture tip with the fracture toughness of the reservoir; if the critical condition is met, the fracture extends vertically; if the critical condition is not met, the fracture height remains unchanged; if it is in contact with the bedding plane, it is necessary to determine whether the fracture initiation process can be completed on the other side of the bedding plane and continue to extend; as the fracture gradually moves away from the bedding plane, the element size is gradually increased to the centimeter level using approximately 50 elements, and the longitudinal extension process of the fracture within each layer is completed with fewer than 260 elements; when the net pressure at the fracture tip is insufficient to overcome the resistance to vertical extension, the longitudinal extension of the fracture stops, and the final fracture height is obtained.

[0080] For the fifth sub-layer of the IV section of a certain oilfield, the calculation method for hydraulic fracturing fracture height in shale reservoirs proposed in this application was used to calculate the fracturing fracture height, including the following implementation steps: Geological and engineering data of well HY7 in a certain oilfield were collected, as shown in Table 1: Table 1. Engineering and geological data of the 5th sub-layer in the IV section of Jiangsu Oilfield

[0081] Based on the characteristics of geostress distribution, the original five sub-layers were finely divided into six sub-layers, and a total of 24 bedding planes were laid out using a simplified method. The fracturing fluid viscosity was 0.01 Pa·s. The injection displacement Q0 in the field was generally 12-18 m³ / s. 3 / min, the longitudinal propagation injection rate of the driving fracture is calculated according to the formula for calculating the longitudinal propagation injection rate of the driving fracture. =10 -4 m 2 / s.

[0082] To determine the size of the crack NS (fractional stress scalar propagation), numerical simulations were conducted with d = 1 mm, 3 mm, 5 mm, and 10 mm, and the results were compared with analytical solutions for crack propagation in homogeneous elastic media. The results show that when... =10 -4 m 2 When the value is 3 mm, the calculated result of FNS=3 mm has the smallest error compared with the analytical solution, which meets the accuracy requirements.

[0083] Substituting FNS=3mm into the engineering-scale numerical model under the actual condition of multiple bedding planes in shale reservoirs, the entire process of longitudinal propagation of hydraulic fractures was simulated. Figure 3 The image shows the numerical simulation results of the cross-layer propagation morphology of hydraulic fractures in five sub-layers of the IV sub-section of an oilfield. Figure 3 As shown, after the fracturing was completed, the final fracture height was approximately 13m.

[0084] like Figure 4 As shown, this application also provides a device for calculating the height of hydraulic fracturing fractures in shale, comprising: a setup unit 201 for collecting geological and engineering data of each rock layer in the target well and establishing a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; a determination unit 202 for determining the fracture initiation size; and a calculation unit 203 for calculating the height of hydraulic fracturing fractures based on the fracture initiation size and the set of fluid-structure interaction control equations.

[0085] In this application, the embodiment of the device for calculating the fracture height in shale hydraulic fracturing is basically similar to the embodiment of the method for calculating the fracture height in shale hydraulic fracturing. For relevant details, please refer to the description of the embodiment of the method for calculating the fracture height in shale hydraulic fracturing.

[0086] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method steps for calculating the height of hydraulic fracturing fractures in shale.

[0087] This application also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps of the above-described method for calculating the height of hydraulic fracturing fractures in shale.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for calculating the fracture height in shale hydraulic fracturing, characterized in that, include: Collect geological and engineering data of each rock stratum in the target well, and establish a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; Determine the crack initiation size; The height of the hydraulic fracturing fracture was calculated based on the fracture initiation size and the fluid-structure interaction control equations.

2. The method for calculating the fracture height in shale hydraulic fracturing according to claim 1, characterized in that, Collect geological and engineering data of each rock stratum in the target well, and establish a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures, including: Collect geological and engineering data of each rock stratum for the target well. Based on the collected data, simplify and stratify the reservoir, determine the number of bedding planes, and establish an engineering-scale numerical model of the actual shale reservoir under the condition of multiple bedding planes. Establish a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures, including: establishing the rock mass elastic deformation equation and the fluid flow equation within the fracture; fluid flow includes: fluid flow along closed natural fractures and flow through open hydraulic fracture channels; use the Reynolds equation to describe the fluid motion in open hydraulic fractures, and use the pressure diffusion equation to describe the fluid flow in closed natural fractures.

3. The method for calculating the fracture height in shale hydraulic fracturing according to claim 1 or 2, characterized in that, The fluid-structure interaction governing equations for the longitudinal propagation of hydraulic fractures include: Based on the collected geological and engineering data, the geological and mechanical parameters of each rock layer were determined. Based on the on-site construction discharge rate and fracturing fluid viscosity, the injection rate driving the longitudinal propagation of the fracture was calculated. The boundary conditions of the fluid-structure interaction control equations at the fracture inlet were given. The formula for calculating the injection rate driving the longitudinal propagation of the fracture is as follows: In the formula: The two-dimensional injection rate is represented by A, and the cross-sectional area of ​​the crack is represented by A. h represents the average crack width; h represents the PKN crack height. ρ is the Poisson's ratio of the rock; G is the shear modulus of the rock; q is the flow velocity through a fracture wing; t represents the fracturing fluid viscosity; t represents the fracturing fluid injection time.

4. The method for calculating the fracture height in shale hydraulic fracturing according to claim 1 or 2, characterized in that, Determining the crack initiation size includes: determining the numerical implementation plan for the crack initiation size. Potential crack initiation points are determined based on stress-strength analysis, and a new crack of predetermined length d is placed at these points; Using the current stress state, the opening displacement of the precast crack is calculated, and the stress intensity factor is calculated using the displacement correlation method. The stress intensity factor is compared with the fracture toughness of the rock. If the fracture meets the nucleation criteria, the fracture is considered a newly generated fracture; otherwise, the pre-existing fracture is deleted.

5. The method for calculating the fracture height in shale hydraulic fracturing according to claim 4, characterized in that, Determining the crack initiation size also includes: The simulation process for determining the crack initiation size includes: A crack propagation model in a homogeneous elastic medium was constructed as a control group. Different d values ​​were used in the simulation to make the crack propagation rate and internal pressure level match the analytical solution of the control group; if the d value is greater than the threshold, the strength criterion cannot be met, and the simulation results do not match the control group results. If the numerical result remains consistent with the theoretical solution when the value of d is reduced, then the maximum value of d at this time is determined as the crack initiation size.

6. The method for calculating the fracture height in shale hydraulic fracturing according to claim 1 or 2, characterized in that, Based on the fracture initiation size and the fluid-structure interaction control equations, the hydraulic fracturing fracture height is calculated by: embedding the determined fracture initiation size into the fluid-structure interaction control equations, numerically simulating the longitudinal propagation process of hydraulic fractures in multi-layered foliated shale, and predicting the final fracture height that the fracture can reach.

7. The method for calculating the fracture height in shale hydraulic fracturing according to claim 6, characterized in that, Based on the fracture initiation size and the fluid-structure interaction control equations, the hydraulic fracturing fracture height is calculated as follows: The fracture height is used to determine whether the fracture is in contact with the bedding plane at the current moment. If it is not in contact with the bedding plane, the stress intensity factor at the fracture tip is compared with the fracture toughness of the reservoir. If the critical condition is met, the fracture will extend vertically. If the critical condition is not met, the fracture height will remain unchanged. If the crack comes into contact with the bedding plane, it is necessary to determine whether the crack initiation process can be completed on the other side of the bedding plane and continue to propagate. When the crack moves away from the bedding plane, the unit size is gradually increased to the centimeter level to complete the longitudinal propagation process of the crack in each layer. When the net pressure at the crack tip cannot overcome the resistance to vertical propagation, longitudinal crack propagation stops, resulting in the final crack height.

8. A device for calculating the height of hydraulic fracturing fractures in shale, characterized in that, include: Establish a unit to collect geological and engineering data of each rock stratum in the target well, and establish a set of fluid-structure interaction control equations for the longitudinal propagation of hydraulic fractures; A defined element is used to determine the crack initiation size. The calculation unit is used to calculate the height of the hydraulic fracturing fracture based on the fracture initiation size and the fluid-structure interaction control equations.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method described in any one of claims 1-7.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method according to any one of claims 1-7.

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