A method and system for evaluating thin interbedded shale oil through layer fracture height

Abstract

The present application belongs to the technical field of oil development fracturing, and relates to a method and system for evaluating fracture height through layer of thin interbed type shale oil, the method comprising: S1, constructing a longitudinal continuous multi-small layer geomechanical model of different sweet spot positions; S2, constructing different thin interbed characteristic fracturing physical simulation experiments based on the geomechanical model; S3, constructing different thin interbed characteristic fracture propagation numerical simulation experiments based on the geomechanical model; S4, combining the physical simulation experiment and the numerical simulation experiment, and constructing a thin interbed type shale oil fracture height through layer evaluation chart according to the stress difference and the interlayer thickness of different reservoirs. The system comprises a first construction module, a second construction module, a third construction module and a fourth construction module. The present application determines the artificial fracture propagation law under different lithological sequences, mechanical parameters and interlayer interface characteristics, establishes a fracture height evaluation chart in the region, and thus specifically guides the fracturing scheme optimization and improves the overall transformation effect of the sweet spot.

Description

Technical Field

[0001] This invention belongs to the field of fracturing technology in petroleum development, and specifically relates to a method and system for evaluating fracture height and cross-layer penetration in thin interbedded shale oil. Background Technology

[0002] The Jimsar Depression, a typical representative of saline lacustrine mixed-sedimentary shale oil, is characterized by deep burial, high frequency interlayering of source and reservoir layers, well-developed bedding, and complex stress distribution. Different reservoir layers exhibit varying lithological stacking patterns, geological stratification properties, and interlayer interface properties, significantly influencing the final morphology of hydraulic fractures. Previous practice has used multiple monitoring methods to test the vertical propagation of fractures at different sweet spots. Post-compression well temperature testing and array sonic interpretation results from vertical wells at the upper sweet spot indicate that in P2l2… 2-2 Hydraulic fractures in laminar fracturing can connect to P2l2. 2-1 The lower oil layer, but not into P2l2 2-3 Layer. The results of the low-temperature array acoustic interpretation of the dessert straight well show that: in P2l1 2-2 Layered perforation, discharge rate 5.5m 3 Under the condition of / min, the hydraulic fracture breaks through the upper interlayer constraint and enters P2l1. 2-1 Layer; Displacement increased to 10m 3 At a rate of / min, fractures can simultaneously break through the upper and lower interlayers and expand within three small layers; this demonstrates a significant difference in longitudinal fracture expansion under different discharge rates. Furthermore, single-well fracture height testing only represents fracture expansion in a localized area and is not applicable to the entire region. The main controlling factors influencing the propagation pattern of artificial fractures and the longitudinal stimulation volume remain unclear, and there are significant differences in production rates after horizontal well pressure testing. Summary of the Invention

[0003] To address the challenges of complex hydraulic fracture propagation patterns, unclear controlling factors, and a lack of quantitative evaluation methods in thin-interbedded shale oil, this invention aims to develop methods for characterizing the mechanical properties of thin-interbedded shale, the interaction mechanism between geological interfaces and hydraulic fractures, and the theoretical study of fracture propagation in vertically heterogeneous reservoirs. By constructing a set of fracturing physical simulation and fracture propagation numerical simulation methods suitable for thin-interbedded shale oil, the invention clarifies the propagation patterns of artificial fractures under different lithological sequences, mechanical parameters, and interlayer interface characteristics, and establishes a fracture height evaluation map for the region. This provides targeted guidance for optimizing fracturing schemes and improving the overall stimulation effect of sweet spots.

[0004] The technical solution adopted in this invention is as follows: a method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil, the method comprising the following steps:

[0005] S1. Construct a longitudinally continuous multi-layered geomechanical model for different dessert locations;

[0006] S2. Based on the geomechanical model, construct physical simulation experiments for fracturing with different thin interlayer characteristics;

[0007] S3. Based on the geomechanical model, construct numerical simulation experiments of fracture propagation with different thin interbedded characteristics;

[0008] S4. Combining physical simulation experiments and numerical simulation experiments, and based on the stress difference and interlayer thickness of different reservoirs, construct an evaluation chart for high-penetration fractures in thin interbedded shale oilfields.

[0009] Further, step S1 includes: based on core observation, computed tomography and well logging curve interpretation, conducting core description and micro-macro testing analysis to determine interlayer interface characteristics, rock mechanical properties and geostress profile characteristics; and establishing a longitudinally continuous multi-layer geomechanical model for different sweet spot locations based on interlayer interface characteristics, rock mechanical properties and geostress profile characteristics.

[0010] Further step S2 includes: constructing fracturing physical simulation samples with different thin interbedded characteristics based on the lithological sequence, rock mechanical properties, and interlayer interface properties of the downhole core and outcrops; conducting fracturing physical simulation experiments of multiple clusters of fractures in horizontal well sections under different thin interbedded characteristics using a one-step segmented fracturing string and a true triaxial layered pressurization device; and then quantitatively characterizing the artificial fracture propagation morphology based on acoustic emission monitoring and CT scanning technology to determine the laws and controlling factors of artificial fracture competition initiation, cross-layering, and induced lamination opening under different thin interbedded characteristics.

[0011] Furthermore, step S3 includes: comprehensively applying outcrop profiles and core computed tomography images to establish an equivalent characterization method for bedding parameters; using the discrete element method to solve the problem of medium discontinuity caused by bedding, constructing a three-dimensional model of fracture propagation in a horizontal well of thin interbedded shale oil, conducting numerical simulation experiments on the propagation of multiple clusters of fractures in the horizontal well section under different thin interbedded characteristics, and quantitatively evaluating the fracture morphology.

[0012] Further, step S3 specifically includes: S31, characterizing the bedding of strata with bedding at different scales; S32, establishing a discrete element mechanical model considering bedding based on discrete element mechanics theory; S33, establishing the inlet pressure equation for each cluster of fractures based on the "wellbore-perforation-fracture" system; considering the fracturing fluid in the fracture as an incompressible Newtonian fluid in laminar flow within a flat plate, establishing the continuity equation and the global mass conservation equation;

[0013] S34. Establish a crack propagation fluid-structure interaction model using the multi-field coupling method.

[0014] Furthermore, the bedding characterization in step S31 specifically includes: the formula for calculating the equivalent bedding density is:

[0015] ρ' BP =ρ BP ×k BP / k'BP

[0016] Where, ρ' BP k' represents the equivalent bedding density in the model. BP ρ represents the equivalent stratification permeability in the model. BP k represents the actual bedding density of the stratigraphy. BP This represents the actual stratigraphic permeability.

[0017] The formula for calculating the equivalent bedding spacing is:

[0018] d BP =1 / ρ' BP ;

[0019] Where, ρ' BP The equivalent bedding density in the model; d BP The equivalent bedding spacing in the model;

[0020] The formula for calculating the equivalent layer width is:

[0021]

[0022] Among them, k' BP w' represents the equivalent stratification permeability in the model. BP The equivalent layer width in the model.

[0023] Further, step S32 specifically includes: based on discrete element mechanics theory, establishing a discrete element mechanics model that considers bedding, including the small displacement linear elastic dynamic equation characterizing rock deformation and the rock fracture criterion equation;

[0024] The linear elastic dynamic equation for small displacement is:

[0025] σ ij,j +b i -(ρ+α)u i,t =0

[0026] Where, σ ij,j b is the Cauchy stress tensor; i For body force; ρ is rock density; α is damping coefficient; u i,t Let be the displacement at time t;

[0027] The rock fracture criterion equation is:

[0028]

[0029] Among them, F n F s These are the normal force and the tangential force, respectively; k n k s These are the normal and tangential spring stiffnesses, respectively; Δu n , Δus These represent the normal and tangential relative displacements between adjacent nodes, respectively.

[0030] Further, step S33 includes: the pressure equation at the inlet of each cluster of fractures is:

[0031] p w =p p,k +p in,k k = 1, 2, ..., n f ;

[0032] Where, p p,k For k-crack perforation friction; p in,k p is the inlet pressure of the k-crack. w n is the inlet pressure of the crack; f The number of cracks;

[0033] The continuity equation is:

[0034]

[0035] The global mass conservation equation is:

[0036]

[0037] Where p is the fluid pressure; μ is the fluid viscosity; w is the dynamic crack width; t is time; Ω represents the global spatial region; s is the coordinate of any point within the crack; q l The fracturing fluid loss is q. The matrix has ultra-low permeability, and the effect of fracturing fluid loss is ignored in the model. l =0; Q0 is the construction displacement.

[0038] Furthermore, step S34 specifically includes: solving the fluid-structure interaction equation as follows:

[0039]

[0040] Where p is the fluid pressure; w is the slit width; μ is the displacement; w k p is the seam width of the current step. k p is the fluid pressure at the current step. k+1 p is the fluid pressure for the next iteration step. k+1 / 2 The dynamic seam width is subject to pressure from subsequent iterations; u k+1 w is the displacement for the next iteration step. k+1 Let F be the crack width for the next iteration; A be the global stiffness matrix; α be the empirical coefficient; F be the crack closure pressure; and t be the time. This represents the rate of change of seam width per unit time.

[0041] Furthermore, this invention also proposes a fracture-high cross-layer evaluation system for thin interbedded shale oil, the system comprising a first construction module, a second construction module, a third construction module, and a fourth construction module; wherein,

[0042] The first construction module is used to construct a longitudinally continuous multi-layered geomechanical model of different dessert locations;

[0043] The second building module is used to construct physical simulation experiments of fracturing with different thin interlayer characteristics based on the geomechanical model;

[0044] The third module is used to construct numerical simulation experiments of fracture propagation with different thin interlayer characteristics based on geomechanical models;

[0045] The fourth module combines physical and numerical simulation experiments to construct an evaluation chart of high-penetration fractures in thin interbedded shale oil reservoirs based on the stress difference and interlayer thickness of different reservoirs.

[0046] Furthermore, the first construction module includes a determination unit and an establishment unit: the determination unit is used to conduct core description and micro-macro testing analysis based on core observation, computer tomography, and well logging curve interpretation to determine the interlayer interface characteristics, rock mechanical properties, and geostress profile characteristics; the establishment unit is used to establish a longitudinally continuous multi-layer geomechanical model for different sweet spot locations based on the interlayer interface characteristics, rock mechanical properties, and geostress profile characteristics.

[0047] The advantages of this invention compared to the prior art are as follows:

[0048] In thin-layered interbedded shale oil, the development of reservoir compartments varies significantly at different sweet spots, and the distribution of microseismic events differs markedly across different well trajectories or perforation locations, directly impacting the morphology of artificial fracture propagation and the effectiveness of stimulation. This invention, based on the actual lithological superposition patterns of the reservoir and the rock mechanical characteristics of thin-layered interbedded formations, clarifies the propagation patterns and controlling factors of artificial fractures. Targeted fracturing schemes and differentiated stimulation scale designs can be developed; on the one hand, this ensures the overall effectiveness of sweet spots and enhances post-fracturing productivity of horizontal wells; on the other hand, it controls and reduces investment per well, improving the scale and efficiency of thin-layered interbedded shale oil development.

[0049] Furthermore, in the early stages of development, this invention can be used to quickly establish a fracture height evaluation chart suitable for thin interbedded shale oil in the region. During field practice, by continuously improving the understanding of the block's lithological sequence, mechanical characteristics, and interface properties, the fracture height discrimination chart is constantly updated and iterated, thereby guiding the rapid establishment of differentiated fracturing schemes and targeted optimization of fracturing processes and key parameters in the production areas to be developed.

[0050] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention will be realized and obtained from the description and the drawings. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 A flowchart illustrating a method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil.

[0053] Figure 2 This is a schematic diagram of the rock mechanics parameters and geostress calculation profile corrected based on experimental test results.

[0054] Figure 3a For the minimum principal stress model of the lower dessert, Figure 3b For the maximum principal stress model of the lower dessert, Figure 3c For the tensile strength model of the lower sweet spot, Figure 3d For the Poisson's ratio size model of the dessert, Figure 3e For the Young's modulus model of the dessert, Figure 3f A pressure model for the overlying strata of the lower sweet spot;

[0055] Figure 4 A schematic diagram of the results of a physical simulation experiment;

[0056] Figure 5 A schematic diagram of a discrete element mechanical model considering bedding;

[0057] Figure 6 A schematic diagram of a thin interbedded shale oil fracture height discrimination chart;

[0058] Figure 7a , Figure 7b These are schematic diagrams comparing fracture parameters in typical sections (JHW01711 well and Ji187_H well);

[0059] Figure 8 This is a schematic diagram of a fracture height cross-layer evaluation system for thin interbedded shale oil. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] This invention provides a method for evaluating fracture height across thin interbedded shale oil layers. By constructing physical simulation and numerical simulation methods for fracturing in thin interbedded shale oil layers, the method clarifies the propagation law of artificial fractures under different lithological sequences, mechanical parameters, and interlayer interface characteristics, establishes a fracture height evaluation chart, guides the optimization of fracturing parameters, and improves the overall stimulation effect.

[0062] In this embodiment of the invention, the reservoir is located in the lower sweet spot of the Jimsar block. This reservoir is a thin interbedded shale oil reservoir, and the parameters of the Jimsar shale oil reservoir are shown in Table 1.

[0063] Table 1. Parameters of Jimsar Shale Oil Reservoirs

[0064]

[0065]

[0066] A method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil, such as... Figure 1 As shown, the process includes the following steps: S1, constructing a longitudinally continuous multi-layered geomechanical model for different sweet spot locations; S2, based on the geomechanical model, constructing physical simulation experiments for fracturing with different thin interbedded characteristics; S3, based on the geomechanical model, constructing numerical simulation experiments for fracture propagation with different thin interbedded characteristics; S4, combining physical simulation experiments and numerical simulation experiments, and constructing an evaluation chart for high-penetration fractures in thin interbedded shale oil reservoirs based on the stress difference and interlayer thickness of different reservoirs.

[0067] Step S1 includes: based on core observation, computed tomography, and well logging interpretation, conducting refined core description and micro-macroscopic testing analysis of the Jimsar shale oil, clarifying the characteristics of the laminar / bedding-lithological interface, rock mechanical properties, and in-situ stress characteristics. Based on experimental test results, corrected rock mechanical parameters and in-situ stress calculation profiles are obtained, such as... Figure 2 As shown, the next dessert is P2l1. 2-1 Layer and P2l1 2-2 The interlayer tensile strength difference and the minimum horizontal principal stress difference are 0.5 MPa and 2 MPa, respectively. (Lower sweet spot P2l1) 2-2 Layer and P2l1 2-3The interlayer tensile strength difference and the minimum horizontal principal stress difference are 1 MPa and 4.5 MPa, respectively. Based on rock mechanics parameters (Young's modulus, Poisson's ratio, in-situ stress, etc.), a relevant fracturing geomechanical model is established, such as... Figures 3a-3f As shown, the maximum horizontal principal stress in the lower sweet spot ranges from 50.21 MPa to 106.18 MPa, with the block containing the maximum horizontal principal stress of 50.21 to 84 MPa accounting for 52.3% of the lower sweet spot. The stress in this block decreases from northwest to southeast across the entire plane. The minimum horizontal principal stress in the lower sweet spot ranges from 37.25 MPa to 81.11 MPa, with the block containing the minimum horizontal principal stress of 37.25 to 70 MPa accounting for 86.1% of the lower sweet spot. The stress in this block decreases from northwest to southeast across the entire plane. The Young's modulus in the lower sweet spot ranges from 22.50 GPa to 72.82 GPa, with the block containing the Young's modulus of 22.50 to 56 GPa accounting for 78.2% of the lower sweet spot. The density of the blocks decreases from northwest to southeast. The Poisson's ratio of the lower sweet spot is 0.1–0.34, with blocks having a Poisson's ratio of 0.1–0.31 accounting for 84.9% of the lower sweet spot. The overall density of the blocks decreases from northwest to southeast in plan view. The overlying strata pressure of the lower sweet spot is 59.03 MPa–88.26 MPa, with blocks having an overlying strata pressure of 59.03–80 MPa accounting for 98.3% of the lower sweet spot. The overall density of the blocks decreases from northwest to southeast in plan view. The tensile strength of the lower sweet spot is 5.79 MPa–17.12 MPa, with blocks having a tensile strength of 5.79–14 MPa accounting for 37.2% of the lower sweet spot. The overall density of the blocks decreases from northwest to southeast in plan view.

[0068] In step S2, based on the systematic testing and benchmarking of lithological sequence, rock mechanical properties, and interlayer interface properties of downhole cores and outcrops, physical simulation samples with different thin interbedded characteristics are constructed for fracturing. Multi-cluster fracture propagation model experiments are conducted in horizontal well sections using a one-step segmented fracturing string and a true triaxial layered pressurization device. The propagation morphology of artificial fractures is quantitatively characterized using acoustic emission monitoring and high-precision CT scanning technology, clarifying the laws and main controlling factors of artificial fracture competition initiation, trans-layering, and induced laminar flow opening under different thin interbedded characteristics. The physical simulation experimental results are as follows: Figure 4 As shown, this indicates that under different thin interlayer characteristics at different levels of the lower sweet spot, hydraulic fractures exhibit different trans-layer morphologies, particularly at P2l1. 2-1 Hydraulic fractures propagate across layers, in P2l1 2-2 The lithological interface inhibits fracture propagation in P2l1 2-3 Hydraulic fractures in the layer achieve cross-layer propagation.

[0069] In step S3, the discrete element method is used to solve the problem of medium discontinuity caused by bedding, and a three-dimensional model of fracture propagation in a thin, interlayered shale oil horizontal well is constructed, such as... Figure 5As shown, the basic governing equations of the three-dimensional model of multi-cluster fracturing fracture propagation in a horizontal well include the fracturing fluid wellbore flow equation, the fracturing fluid flow equation (i.e., the continuity equation), the rock mass governing equation, and the propagation criterion. The solution is obtained using a hybrid method of finite element method (FEM) and discrete element method (DEM). This model can take into account complex geological features such as reservoir bedding, natural fractures, and anisotropy.

[0070] The process includes the following steps: S31, bedding characterization of strata with bedding development at different scales, with bedding characterization parameters including density, distribution, mechanical properties, and permeability; bedding calculation is part of the rock matrix parameters used to construct the fracture propagation model, and is ultimately transformed into part of the horizontal bedding parameters in the discrete element-based bedding reservoir fracture propagation model, thus distinguishing it from bedding and matrix;

[0071] Since the model cannot be configured with the actual number of bedding planes, multiple bedding planes in the actual strata are equivalent to a single bedding plane in the model. The equivalent bedding plane permeability is the permeability of a single bedding plane in the model, which is the total permeability of several bedding planes in the strata.

[0072] The equivalent bedding density or equivalent permeability satisfies the following relationship:

[0073] ρ' BP =ρ BP ×k BP / k' BP ;

[0074] Where, ρ' BP k' represents the equivalent bedding density in the model. BP ρ represents the equivalent stratification permeability in the model. BP k represents the actual bedding density of the stratigraphy. BP This represents the actual stratigraphic permeability.

[0075] The equivalent bedding spacing satisfies the following relationship:

[0076] d BP =1 / ρ' BP ;

[0077] Where, ρ′ BP The equivalent bedding density in the model; d BP The equivalent bedding spacing in the model.

[0078] The equivalent layer width satisfies the following relationship:

[0079]

[0080] Among them, k' BP w' represents the equivalent stratification permeability in the model. BP The equivalent layer width in the model.

[0081] S32. Based on the discrete element method (DEM) theory, a DEM model considering bedding is established. According to the DEM theory, the formation in the horizontal well section is discretized into several matrix block elements. Adjacent matrix block elements are connected by virtual springs, which transmit interaction forces. The fracture of the spring represents the fracturing of the rock. There is a joint element between two contacting matrix block elements, which is used to calculate the flow of fracturing fluid and the distribution of fluid pressure within the fracture. The fluid pressure acts as an external load on the fracture surface (i.e., the contact surface of the blocks). Then, the finite element method is applied to solve the deformation of the continuous blocks, and the discrete element method is applied to calculate the fracture of the spring.

[0082] The following governing equations are used to characterize rock deformation and rock fracture criteria;

[0083] The motion of the rock matrix mass conforms to Newton's second law. Considering the deformability of the mass, the linear elastic dynamic equation for small displacements is:

[0084] σ ij,j +b i -(ρ+α)u i,t =0;

[0085] Where, σ ij,j b is the Cauchy stress tensor; i For body force; ρ is rock density; α is damping coefficient; u i,t Let be the displacement at time t;

[0086] The rock fracture criterion equation is:

[0087]

[0088] In the formula: F n F s These are the normal force and tangential force, respectively, in N; k n k s These are the normal and tangential spring stiffnesses, respectively; Δu n ,Δu s These are the normal and tangential relative displacements between adjacent nodes, in mm.

[0089] S33. For multi-cluster fracturing problems, the injected fracturing fluid enters each cluster of fractures through the wellbore and perforations. The fluid injection rate for each cluster is controlled by the "wellbore-perforation-fracture" system. Since the flow friction in the horizontal section of the wellbore is relatively low, the frictional resistance along the wellbore is temporarily ignored. Therefore, the inlet pressure of each cluster of fractures satisfies:

[0090] p w =p p,k +p in,k k = 1, 2, ..., n f ;

[0091] Where, p p,kp represents the perforation friction of the k-crack, in MPa. in,k p is the inlet pressure of the k-crack, in MPa. w n is the inlet pressure of the crack, in MPa. f This represents the number of cracks.

[0092] The fracturing fluid inside the fracture is considered as an incompressible Newtonian fluid in a flat plate, satisfying the continuity equation and the global mass conservation equation.

[0093] The continuity equation is:

[0094]

[0095] The global mass conservation equation is:

[0096]

[0097] Where p is the fluid pressure in MPa; w is the dynamic crack width in meters; t is time in seconds; Ω represents the global spatial region; s is the coordinate of any point within the crack; q l This refers to the fracturing fluid filtrate loss, expressed in m³. 3 / s, the matrix has ultra-low permeability, and the effect of fracturing fluid loss is ignored in the model, i.e., q l =0; Q0 is the construction displacement, in m³ 3 / s; μ is the fluid viscosity, in Pa·s.

[0098] Step S33 establishes the flow equations for the fluid in the horizontal wellbore and fractures to calculate the flow of fracturing fluid and the distribution of fluid pressure within the fracture. The fluid pressure acts as an external load on the fracture surface (i.e., the contact surface of the blocks). Then, the finite element method is applied to solve for the deformation of the continuous blocks. That is, the pressure distribution in the fracture is solved using the equations and converted into an external load on the surface nodes of the matrix block fracture. Then, the dynamic relaxation method is used to calculate the stress, strain, and displacement of the block system under the action of fluid pressure and the initial stress field. The normal relative displacement Δu between adjacent blocks is also considered. n Tangential relative displacement Δu s The dynamic crack width w and shear displacement of the hydraulic crack are used as known conditions for the next fluid calculation time step, and then the coupled iteration of the fluid pressure field and matrix block deformation is calculated.

[0099] S34. Establish a crack propagation fluid-structure interaction model using the multi-field coupling method;

[0100] Since rock deformation and fluid flow within the fracture interact, it is necessary to couple rock deformation with fluid flow within complex fractures to establish a tight gas volumetric fracturing complex fracture propagation model considering fluid-structure interaction. The relationship between fracturing fluid flow within the fracture and matrix block deformation is as follows: (1) Changes in fluid pressure at the matrix block boundary will affect the deformation of the matrix block, thus causing changes in fracture width; (2) Changes in fracture width cause changes in flow rate, ultimately affecting the distribution of fluid pressure within the fracture. A weak coupling method is used to implement the above iterative process. Before rock fracturing, the permeability (k) of the initial fracture (bedding, natural fracture) unit is... f ) should be related to the matrix permeability (k m Since the permeability and width of the fracture are equal, the relationship between the fracture permeability and width, k, can be used. f =w 2 / 12 gives the initial width of the crack. This provides an initial flow path for the fracturing fluid. The fracture width is constant within a single time step of calling the fluid flow solver. The pressure distribution in the fracture is solved using equations and converted into external loads on the surface nodes of the matrix block fracture. Then, the stress, strain, and displacement of the block system under fluid pressure and the initial stress field are calculated using the dynamic relaxation method. The normal relative displacement Δu between adjacent blocks is also calculated. n Tangential relative displacement Δu s The dynamic fracture width *w* and shear displacement degree of the hydraulic fracture serve as known conditions for the next fluid calculation time step, thereby calculating the coupled iteration of the fluid pressure field and the matrix block deformation. Pressure convergence at all nodes is used as the criterion for judgment.

[0101] The formula for solving the fluid-structure interaction problem using the Picard iteration is shown below:

[0102]

[0103] Where p is the fluid pressure; w is the slit width; μ is the displacement; w k p is the seam width of the current step. k p is the fluid pressure at the current step. k+1 p is the fluid pressure for the next iteration step. k+1 / 2 The dynamic seam width is subject to pressure from subsequent iterations; u k+1 w is the displacement for the next iteration step. k+1 Let F be the crack width for the next iteration; A be the global stiffness matrix; α be the empirical coefficient; F be the crack closure pressure; and t be the time. This represents the rate of change of seam width per unit time.

[0104] The solid stress field (the governing equation of the bulk) was calculated using the dynamic relaxation method, while the flow pressure field within the crack (the continuity equation) was calculated using the finite element method. Both were solved using Picard iteration. The coupled iteration of calculating the fluid pressure field (step S33) and the matrix bulk deformation (step S32) was performed using Picard iteration, and the final crack propagation was obtained by using the pressure convergence of all nodes as the criterion.

[0105] In step S4, a curve is plotted with the reservoir-interstitial stress difference as the abscissa and the interstitial thickness as the ordinate to obtain a shale oil fracture height discrimination chart under different lithological sequences, mechanical characteristics, and interlayer interface properties. The chart is shown below. Figure 6 As shown, based on different interlayer stress differences and shielding layer thicknesses, the diagram is divided into the seam height penetration zone, transition zone, and seam height suppression zone.

[0106] Based on the fracture height and cross-layer evaluation chart, combined with the well network and well spacing deployment and the distribution of interlayers, the lower sweet spot P2l1 in this area was determined. 2-2 Artificial fractures in reservoirs are mainly characterized by localized cross-layer fractures (see...) Figure 6 With the goal of utilizing multiple dessert layers vertically as a whole, the effectiveness of artificial crack propagation through layers and longitudinal support should be ensured. Therefore, the lower dessert layer P2l1 2-2 For horizontal wells, the fracturing flow rate and the proportion of pre-fracturing fluid should be appropriately increased, and the fracturing parameters should be optimized based on this principle.

[0107] Taking well JHW01711 (sweet spot) as an example, the comparison table of optimized fracturing parameters and production effects is shown in Table 2. From the fracture monitoring results, as... Figures 7a-7b As shown, the fracture height in a typical section of well JHW01711 (41.1m) after optimizing the fracturing parameters increased by 16.1% compared to the fracture height in a typical section of well Ji187_H (35.4m) without optimizing the fracturing parameters. Compared to well Ji187_H (lower sweet spot), with the same cumulative production days, well JHW01711 (lower sweet spot) saw a 31.1% increase in average daily oil production, indicating that the optimized fracturing parameters of this invention significantly improved the fracturing production effect.

[0108] Table 2 Comparison of construction parameters and production data of two wells (JHW01711 well and Ji187_H well)

[0109]

[0110] In addition, this invention also proposes a fracture height cross-layer evaluation system for thin interbedded shale oil, such as... Figure 8As shown, the system includes a first construction module, a second construction module, a third construction module, and a fourth construction module. The first construction module is used to construct a longitudinally continuous multi-layered geomechanical model for different sweet spot locations. The second construction module is used to construct physical simulation experiments of fracturing with different thin interbedded characteristics based on the geomechanical model. The third construction module is used to construct numerical simulation experiments of fracture propagation with different thin interbedded characteristics based on the geomechanical model. The fourth construction module is used to combine physical simulation experiments and numerical simulation experiments to construct an evaluation chart of high-penetration fractures in thin interbedded shale oil formations based on the stress difference and interlayer thickness of different reservoirs.

[0111] Specifically, the first construction module includes a determination unit and an establishment unit: the determination unit is used to carry out core description and micro-macro testing analysis based on core observation, electronic computed tomography and well logging curve interpretation, and to determine the interlayer interface characteristics, rock mechanical properties and geostress profile characteristics; the establishment unit is used to establish a longitudinally continuous multi-layer geomechanical model of different sweet spot locations based on the interlayer interface characteristics, rock mechanical properties and geostress profile characteristics.

[0112] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil, characterized in that, The method includes the following steps: S1. Construct a longitudinally continuous multi-layered geomechanical model for different dessert locations; S2. Based on the geomechanical model, construct physical simulation experiments for fracturing with different thin interlayer characteristics; S3. Based on the geomechanical model, construct numerical simulation experiments of fracture propagation with different thin interbedded characteristics; Step S3 includes: A three-dimensional model of fracture propagation in a horizontal well of thin interlayered shale oil was constructed. Numerical simulation experiments of multi-cluster fracture propagation in the horizontal well section under different thin interlayered characteristics were carried out to quantitatively evaluate the fracture morphology. Step S3 specifically includes: S31. Bedding characterization of strata with bedding development at different scales; S32. Based on the discrete element mechanics theory, establish a discrete element mechanics model that considers stratification; S33. Based on the "wellbore-perforation-fracture" system, establish the inlet pressure equation for each cluster of fractures; consider the fracturing fluid in the fracture as an incompressible Newtonian fluid in a flat plate, and establish the continuity equation and the global mass conservation equation. S34. Establish a crack propagation fluid-structure interaction model using the multi-field coupling method; S4. Combining physical simulation experiments and numerical simulation experiments, and based on the stress difference and interlayer thickness of different reservoirs, construct an evaluation chart for high-penetration fractures in thin interbedded shale oilfields.

2. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S1 includes: Based on core observation, computed tomography and well logging interpretation, core description and micro-macro testing analysis were carried out to determine the interlayer interface characteristics, rock mechanical properties and geostress profile characteristics. Based on the interlayer interface characteristics, rock mechanical properties, and geostress profile characteristics, a longitudinally continuous multi-layer geomechanical model was established for different sweet spot locations.

3. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S2 includes: Based on the lithological sequence, rock mechanical properties, and interlayer interface properties of downhole cores and outcrops, physical simulation samples with different thin interbedded characteristics were constructed. Through a one-step segmented fracturing string and a true triaxial layered pressurization device, physical simulation experiments of fracturing multiple clusters of fractures in horizontal well sections under different thin interbedded characteristics were carried out. Subsequently, based on acoustic emission monitoring and CT scanning technology, the propagation morphology of artificial fractures was quantitatively characterized, and the laws and controlling factors of artificial fracture competition initiation, cross-layering, and induced lamination opening under different thin interbedded characteristics were determined.

4. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S3 includes: By comprehensively applying outcrop profiles and core computed tomography images, an equivalent characterization method for bedding parameters is established; the discrete element method is used to solve the problem of medium discontinuity caused by bedding.

5. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S31, the characterization of bedding planes, specifically includes: The formula for calculating equivalent bedding density is: ； in, The equivalent bedding density in the model; The equivalent stratification permeability in the model; This represents the actual bedding density of the stratigraphy; The actual stratigraphic permeability; The formula for calculating the equivalent bedding spacing is: ； in, The equivalent bedding density in the model; The equivalent bedding spacing in the model; The formula for calculating the equivalent layer width is: ； in, The equivalent stratification permeability in the model; The equivalent layer width in the model.

6. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S32 specifically includes: Based on the discrete element mechanics theory, a discrete element mechanics model considering bedding is established, including the small displacement linear elastic dynamic equation characterizing rock deformation and the rock fracture criterion equation. The linear elastic dynamic equation for small displacement is: ； in, For Cauchy stress tensor; For physical strength; Density of the rock; The damping coefficient; Let be the displacement at time t; The rock fracture criterion equation is: ， ； in, F n , F s These are the normal force and the tangential force, respectively. k n , k s These are the normal and tangential spring stiffnesses, respectively. , These represent the normal and tangential relative displacements between adjacent nodes, respectively.

7. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S33 includes: The pressure equations at the inlet of each cluster of fractures are as follows: ； in, p p,k for k Perforation friction in cracks; p in,k for k The inlet pressure of the crack; p w This refers to the pressure at the crack inlet. n f The number of cracks; The continuity equation is: ； The global mass conservation equation is: ； in, p For fluid pressure; For fluid viscosity; w The dynamic crack width; t For time; The region represents the global spatial region; s is the coordinate of any point within the crack. q l The model represents the fracturing fluid loss. The matrix has extremely low permeability, and the effect of fracturing fluid loss is ignored. q l =0; For construction displacement.

8. The method for evaluating fracture height and cross-layer penetration in thin interbedded shale oil as described in claim 1, characterized in that, Step S34 specifically includes: The solution equation for fluid-structure interaction is: ； in, p For fluid pressure; w For seam width; μ For displacement; The seam width for the current step; The fluid pressure in the current step; The fluid pressure for the next iteration; The dynamic seam width is subject to pressure from subsequent iterations; This is the displacement for the next iteration step; The slit width for the next iteration; A The overall stiffness matrix; α This is an empirical coefficient; t represents the crack closure pressure; t represents time. This represents the rate of change of seam width per unit time.

9. A fracture height cross-layer evaluation system for thin interbedded shale oil, characterized in that, The system includes a first building module, a second building module, a third building module, and a fourth building module; wherein, The first construction module is used to construct a longitudinally continuous multi-layered geomechanical model of different dessert locations; The second building module is used to construct physical simulation experiments of fracturing with different thin interlayer characteristics based on the geomechanical model; The third module is used to construct numerical simulation experiments of fracture propagation with different thin interlayer characteristics based on geomechanical models; The third building module is used for: A three-dimensional model of fracture propagation in a horizontal well of thin interlayered shale oil was constructed. Numerical simulation experiments of multi-cluster fracture propagation in the horizontal well section under different thin interlayered characteristics were carried out to quantitatively evaluate the fracture morphology. The third building module is specifically used for: S31. Bedding characterization of strata with bedding development at different scales; S32. Based on the discrete element mechanics theory, establish a discrete element mechanics model that considers stratification; S33. Based on the "wellbore-perforation-fracture" system, establish the inlet pressure equation for each cluster of fractures; consider the fracturing fluid in the fracture as an incompressible Newtonian fluid in a flat plate, and establish the continuity equation and the global mass conservation equation. S34. Establish a crack propagation fluid-structure interaction model using the multi-field coupling method; The fourth module combines physical and numerical simulation experiments to construct an evaluation chart of high-penetration fractures in thin interbedded shale oil reservoirs based on the stress difference and interlayer thickness of different reservoirs.

10. The fracture height and cross-layer evaluation system for thin interbedded shale oil as described in claim 9, characterized in that, The first construction module includes a determining unit and a building unit: The defined unit is used to conduct core description and micro-macro testing analysis based on core observation, computer tomography, and well logging curve interpretation, and to determine the interlayer interface characteristics, rock mechanical properties, and geostress profile characteristics. The established unit is used to establish a longitudinally continuous multi-layer geomechanical model for different sweet spot locations based on interlayer interface characteristics, rock mechanical properties, and geostress profile characteristics.

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