Fracture height crossing evaluation method and system for thin interbed shale oil

Abstract

The invention belongs to the technical field of petroleum development fracturing, and relates to a thin interbed shale oil seam height crossing evaluation method and system, and the method comprises the steps: S1, constructing a longitudinal continuous multi-small-layer geomechanical model at different dessert positions; s2, on the basis of a geomechanical model, different thin interbed characteristic fracturing physical simulation experiments are constructed; s3, based on a geomechanical model, constructing different thin interbed characteristic crack propagation numerical simulation experiments; and S4, combining a physical simulation experiment with a numerical simulation experiment, and constructing a thin interbed shale oil seam high crossing evaluation chart according to the stress difference of different reservoir interlayers and the thickness of the interlayers. The system comprises a first construction module, a second construction module, a third construction module and a fourth construction module. According to the method, the artificial fracture propagation rule under different lithologic sequence, mechanical parameters and interlayer interface characteristics is determined, and the local fracture height evaluation chart is established, so that the optimization of the fracturing scheme is guided in a targeted manner, and the integral reconstruction effect of the dessert is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development and fracturing, and in particular relates to a method and system for evaluating the fracture height penetration of thin interbedded shale oil. Background Art

[0002] As a typical representative of mixed shale oil in saline lake basins, the Jimusar Sag is characterized by deep burial, high-frequency interlayering of source and reservoir, developed bedding, and complex stress distribution. Different reservoirs show different lithology superposition rules, geological stratification properties, and interlayer interface properties, which have an important influence on the final form of hydraulic fractures. In the early practice, a variety of monitoring methods were used to test the longitudinal expansion of fractures at different sweet spots. The well temperature test and array acoustic interpretation results of the upper sweet spot vertical well after pressure pressure showed that: in P 2 l 2 2-2 Hydraulic fractures can communicate 2 l 2 2-1 The oil layer below the layer, but not into the P 2 l 2 2-3 The results of the temperature and array acoustic interpretation of the vertical well in the lower sweet spot show that: 2 l 1 2-2 Layer perforation, displacement 5.5m 3 / min, the hydraulic fracture breaks through the upper interlayer and enters P 2 l 1 2-1 Layer; displacement increased to 10m 3 / min, the fractures can simultaneously break through the upper and lower interlayers and expand in three sets of small layers; showing that there are obvious differences in the longitudinal expansion of fractures under different displacement rates. In addition, the single well fracture height test only represents the fracture expansion in a local area and is not applicable to the whole area. The main controlling factors affecting the expansion law of artificial fractures and the vertical transformation volume are still unclear, and the production of horizontal wells after pressure treatment is very different. Summary of the invention

[0003] In view of the problems of complex expansion law of hydraulic fractures in thin interbedded shale oil, unclear main controlling factors, and lack of quantitative evaluation methods, the present invention aims to carry out research on thin interbedded mechanical property characterization methods, geological interface and hydraulic fracture mechanism, and vertical heterogeneous reservoir fracture expansion theory. By constructing a set of fracturing physical simulation and fracture expansion numerical simulation methods suitable for thin interbedded shale oil, the expansion law of artificial fractures under different lithological sequences, mechanical parameters, and interlayer interface characteristics are clarified, and a fracture height evaluation plate for this area is established. This can provide targeted guidance for the optimization of fracturing schemes and improve the overall transformation effect of sweet spots.

[0004] The technical solution adopted by the present invention is as follows: a method for evaluating the high penetration of thin interbedded shale oil, the method comprising the following steps:

[0005] S1. Construct a longitudinal continuous multi-layer geomechanical model at different sweet spots;

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

[0007] S3. Based on the geomechanical model, numerical simulation experiments on crack propagation with different thin interlayer characteristics were constructed;

[0008] S4. Combine physical simulation experiments with numerical simulation experiments, and construct a high penetration evaluation chart for thin interlayered shale oil fractures based on the stress difference and thickness of different reservoir barriers.

[0009] Furthermore, step S1 includes: based on core observation, electronic computer tomography and logging curve interpretation, conducting core description and micro-macro test analysis to determine the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics; according to the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics, establishing a longitudinal continuous multi-layer geomechanical model at different sweet spot positions.

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

[0011] Furthermore, step S3 includes: comprehensively applying outcrop profiles and core computer tomography images to establish an equivalent characterization method for bedding parameters; using discrete element method to solve the medium discontinuity problem caused by bedding, constructing a three-dimensional model of fracturing crack extension in thin interlayered shale oil horizontal wells, carrying out numerical simulation experiments on the extension of multiple clusters of cracks in horizontal well sections under different thin interlayer characteristics, and quantitatively evaluating the fracture morphology.

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

[0013] S34. Use the multi-field coupling method to establish a fluid-solid coupling model for crack extension.

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

[0015] ρ' BP =ρ BP ×k BP / k' BP

[0016] Among them, ρ' BP is the equivalent bedding density in the model; k' BP is the equivalent bedding permeability in the model; ρ BP is the actual stratum bedding density; k BP is the actual formation permeability;

[0017] The calculation formula of equivalent bedding spacing is:

[0018] d BP =1 / ρ' BP ;

[0019] Among them, ρ' BP is the equivalent bedding density in the model; d BP is the equivalent bedding spacing in the model;

[0020] The calculation formula of equivalent bedding width is:

[0021]

[0022] Among them, k' BP is the equivalent bedding permeability in the model; w' BP is the equivalent bedding width in the model.

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

[0024] The dynamic equation of small displacement linear elasticity is:

[0025] σ ij,j +b i -(ρ+α)u i,t =0

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

[0027] The rock fracture criterion equation is:

[0028]

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

[0030] Further, step S33 includes: the pressure equation of each cluster fracture entrance is:

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

[0032] Among them, p p,k is the perforation friction of crack k; p in,k is the entrance pressure of crack k; p w is the crack entrance pressure; n f is 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 the time; Ω represents the global spatial region; s is the coordinate of any point in the crack; q l is the fracturing fluid loss. The matrix has ultra-low permeability and the fracturing fluid loss effect is ignored in the model, that is, q l =0;Q 0 For construction displacement.

[0038] Further, step S34 specifically includes: solving the fluid-solid coupling equation:

[0039]

[0040] Where p is the fluid pressure; w is the slit width; μ is the displacement; w k is the gap width of the current step; p k is the fluid pressure of the current step; p k+1 is the fluid pressure of the next iteration step; p k+1 / 2 is the dynamic crack width subjected to the pressure of the subsequent iteration step; uk+1 is the displacement of the next iteration step; w k+1 is the crack width of the next iteration step; A is the overall stiffness matrix; α is the empirical coefficient; F is the crack closure pressure; t is the time; is the rate of change of the slit width per unit time.

[0041] In addition, the present invention also proposes a thin interbedded shale oil fracture high penetration evaluation system, the system comprises a first building block, a second building block, a third building block and a fourth building block; wherein,

[0042] The first construction module is used to construct a longitudinally continuous multi-layer geomechanical model at different sweet spots;

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

[0044] The third building module is used to construct numerical simulation experiments on fracture extension with different thin interlayer characteristics based on the geomechanical model;

[0045] The fourth construction module is used to combine physical simulation experiments with numerical simulation experiments, and to construct a high penetration evaluation chart for thin interlayered shale oil fractures based on the stress difference and thickness of different reservoir barriers.

[0046] Furthermore, 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 test analysis based on core observation, electronic computer tomography and logging curve interpretation, and determine the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics; the establishment unit is used to establish a longitudinally continuous multi-layer geomechanical model at different sweet spot positions based on the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The development of reservoirs and barriers at different sweet spots in thin interbedded shale oil varies greatly, and the distribution of microseismic event points at different wellbore trajectories or perforation positions varies significantly, which directly affects the expansion morphology of artificial fractures and the transformation effect. The present invention can be used to clarify the expansion law and main control factors of artificial fractures according to the actual lithology of the reservoir and the mechanical characteristics of thin interbedded rocks. Targeted fracturing plans can be formulated, and the scale of transformation can be designed in a differentiated manner; on the one hand, the overall utilization effect of the sweet spots can be guaranteed, and the post-fracturing production capacity of horizontal wells can be improved; on the other hand, the investment in a single well can be reduced, and the scale-benefit development level of thin interbedded shale oil can be improved.

[0049] In addition, in the early stage of development, the present invention can be used to quickly establish a set of fracture height evaluation charts suitable for thin interbedded shale oil in the region. In the field practice process, by continuously improving the understanding of the block's lithology sequence, mechanical characteristics, and interface properties, the fracture height discrimination chart is continuously updated and iterated, thereby guiding the production area to be built to quickly establish a differentiated fracturing plan and optimize the fracturing process and key parameters in a targeted manner.

[0050] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 It is a schematic flow chart of a method for evaluating the high penetration of thin interbedded shale oil;

[0053] Figure 2 It is a schematic diagram of the rock mechanical parameters and ground stress calculation profile corrected based on the experimental test results;

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

[0055] Figure 4 It is a schematic diagram of the results of physical simulation experiments;

[0056] Figure 5 Schematic diagram of the discrete element mechanics model considering bedding;

[0057] Figure 6 This is a schematic diagram of the thin interbedded shale oil fracture height identification chart;

[0058] Figure 7a , Figure 7b They are the schematic diagrams of fracture parameter comparison of typical sections (Well JHW01711 and Well Ji 187_H);

[0059] Figure 8 This is a schematic diagram of a fracture high penetration evaluation system for thin interbedded shale oil. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] The present invention provides a method for evaluating the fracture height and penetration of thin interbedded shale oil. By constructing a physical simulation method for fracturing thin interbedded shale oil and a numerical simulation method for fracture extension, the expansion law of artificial fractures under different lithological sequences, mechanical parameters, and interlayer interface characteristics is clarified, a fracture height evaluation chart is established, the optimization of fracturing parameters is guided, and the overall transformation effect is improved.

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

[0063] Table 1 Jimusar shale oil reservoir parameters

[0064]

[0065]

[0066] A method for evaluating the fracture height penetration of thin interbedded shale oil, such as Figure 1 As shown, the method comprises the following steps: S1, constructing a longitudinal continuous multi-layer geomechanical model at different sweet spots; S2, constructing a physical simulation experiment of fracturing with different thin interlayer characteristics based on the geomechanical model; S3, constructing a numerical simulation experiment of fracture extension with different thin interlayer characteristics based on the geomechanical model; S4, combining the physical simulation experiment with the numerical simulation experiment, and constructing a high penetration evaluation chart of thin interlayer shale oil fractures according to the stress difference of different reservoir interlayers and the thickness of the interlayer.

[0067] Step S1 includes: Based on core observation, electronic computer tomography and logging curve interpretation, carry out detailed core description and micro-macro test analysis of Jimusar shale oil to clarify the characteristics of lamination / bedding-lithology interface, rock mechanical properties, and geostress characteristics. The rock mechanical parameters and geostress calculation profiles corrected based on experimental test results, such as Figure 2 As shown, the next dessert P 2 l 1 2-1 Layer and P 2 l 12-2 The inter-layer tensile strength difference and the minimum horizontal principal stress difference are 0.5MPa and 2MPa respectively. 2 l 1 2-2 Layer and P 2 l 1 2-3 The inter-layer tensile strength difference and the minimum horizontal principal stress difference are 1MPa and 4.5MPa respectively. Combined with rock mechanics parameters (Young's modulus, Poisson's ratio, ground stress, etc.), a relevant fracturing geomechanics model is established, such as Figure 3a-3f As shown, the maximum horizontal principal stress of the lower sweet spot is 50.21MPa~106.18MPa, and the blocks with the maximum horizontal principal stress of 50.21~84MPa account for 52.3% of the lower sweet spot. On the plane, the entire block decreases from northwest to southeast; the minimum horizontal principal stress of the lower sweet spot is 37.25MPa~81.11MPa, and the blocks with the minimum horizontal principal stress of 37.25~70MPa account for 86.1% of the lower sweet spot. On the plane, the entire block decreases from northwest to southeast; the Young's modulus of the lower sweet spot is 22.50GPa~72.82GPa, and the blocks with the Young's modulus of 22.50~56GPa account for 78.2% of the lower sweet spot. The block shows a decreasing trend from northwest to southeast; the Poisson's ratio of the lower sweet spot is 0.1-0.34, and the blocks with Poisson's ratio of 0.1-0.31 account for 84.9% of the lower sweet spot, and the entire block shows a decreasing trend from northwest to southeast on the plane; the overlying rock pressure of the lower sweet spot is 59.03MPa-88.26MPa, and the blocks with overlying rock pressure of 59.03-80MPa account for 98.3% of the lower sweet spot, and the entire block shows a decreasing trend from northwest to southeast on the plane; the tensile strength of the lower sweet spot is 5.79MPa-17.12MPa, and the blocks with tensile strength of 5.79-14MPa account for 37.2% of the lower sweet spot, and the entire block shows a decreasing trend from northwest to southeast on the plane.

[0068] In step S2, based on the systematic testing and benchmarking of the lithological sequences, rock mechanical properties and interlayer interface properties of the downhole cores and outcrops, physical simulation specimens of fracturing with different thin interlayer characteristics are constructed; a physical simulation experiment of multiple clusters of fracture extension in the horizontal well section is carried out using a one-step segmented fracturing string and a true triaxial layered pressurization device. The morphology of artificial fracture extension is quantitatively characterized based on acoustic emission monitoring and high-precision CT scanning technology, and the laws and main controlling factors of artificial fracture competition initiation, penetration, and induced lamination opening under different thin interlayer characteristics are clarified. The results of the physical simulation experiment are as follows: Figure 4 As shown in the figure, it shows that under the different thin interlayer characteristics of different layers in the lower sweet spot, the hydraulic fractures present different interlayer forms. 2 l 1 2-1 The hydraulic fractures of the layers are extended through the layers. 2 l 12-2 The lithology interface of the layer inhibits the expansion of cracks. 2 l 1 2-3 The hydraulic fractures of the layers can be extended through the layers.

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

[0070] The method comprises the following steps: S31, characterizing the bedding of strata with bedding development at different scales, wherein the bedding characterization parameters include density, distribution, mechanical properties, and permeability; bedding calculation is a part of the rock matrix parameters for constructing a fracture propagation model, and is ultimately converted into a part of the horizontal bedding parameters in a bedding reservoir fracture propagation model based on discrete elements, thereby distinguishing between bedding and matrix;

[0071] Since the model cannot set the bedding according to the number of beddings in the actual stratum, multiple beddings in the actual stratum are equivalent to one bedding in the model. The equivalent bedding permeability is the total permeability of several beddings in the stratum equivalent to the permeability of one bedding in the model.

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

[0073] ρ' BP =ρ BP ×k BP / k' BP ;

[0074] Among them, ρ' BP is the equivalent bedding density in the model; k' BP is the equivalent bedding permeability in the model; ρ BP is the actual stratum bedding density; k BP is the actual stratum permeability.

[0075] The equivalent bedding spacing satisfies the relationship:

[0076] d BP =1 / ρ' BP ;

[0077] Among them, ρ′ BP is the equivalent bedding density in the model; d BP is the equivalent bedding spacing in the model.

[0078] The equivalent bedding width satisfies the relationship:

[0079]

[0080] Among them, k' BP is the equivalent bedding permeability in the model; w' BP is the equivalent bedding width in the model.

[0081] S32. Based on the discrete element mechanics theory, a discrete element mechanics model considering bedding is established; according to the discrete element theory, the horizontal well section formation is discretized into several matrix block units, and the adjacent matrix block units are linked by virtual springs, and the interaction force is transmitted. The fracture of the spring represents the fracture of the rock. There is a joint unit between two contacting matrix block units, which is used to calculate the flow of fracturing fluid in the fracture and the distribution of fluid pressure. The fluid pressure acts as an external load on the fracture surface (i.e., the contact surface of the block), and then the finite element method is used to solve the deformation of the continuous block, and the discrete element method is used to calculate the fracture of the spring;

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

[0083] The movement of rock matrix blocks conforms to Newton's second law. Considering that the blocks are deformable, the small displacement linear elastic dynamic equation is:

[0084] σ ij,j +b i -(ρ+α)u i,t =0;

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

[0086] The rock fracture criterion equation is:

[0087]

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

[0089] S33. For multi-cluster fracturing, the fracturing fluid is injected into each cluster of fractures through the wellbore and perforation. The fluid flow rate of each cluster is controlled by the "wellbore-perforation-fracture" system. Since the friction resistance of the horizontal wellbore flow is small, the friction resistance along the wellbore is temporarily ignored, so the inlet pressure of each cluster of fractures satisfies:

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

[0091] Among them, p p,k is the perforation friction of the k fracture, in MPa; p in,k is the entrance pressure of crack k, in MPa; p w is the crack entrance pressure, in MPa; n f is the number of cracks.

[0092] The fracturing fluid in the fracture is considered as the laminar flow of 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 m; t is the time in s; Ω represents the global spatial region; s is the coordinate of any point in the crack; q l is the fracturing fluid loss, in m 3 / s, the matrix has ultra-low permeability, and the effect of fracturing fluid loss is ignored in the model, that is, q l =0;Q 0 is the construction displacement, in m 3 / s; μ is the fluid viscosity, the unit is Pa·s.

[0098] Step S33 establishes the flow equations of the fluid in the horizontal wellbore and the cracks, which are used to calculate the flow of the fracturing fluid in the cracks and the distribution of the fluid pressure. The fluid pressure acts on the crack surface (i.e., the contact surface of the block) as an external load, and then the finite element method is applied to solve the continuous block deformation. That is, the pressure distribution in the cracks is solved by the equations, and it is converted into an external load on the surface nodes of the matrix block cracks, and then the dynamic relaxation method is used to calculate the stress, strain and displacement of the block system under the action of the fluid pressure and the initial stress field. The normal relative displacement Δu between adjacent blocks is n , tangential relative displacement Δus , which is the dynamic width w of the hydraulic fracture and the degree of shear misalignment, is used as the known condition 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 fluid-solid coupling model for crack propagation using a multi-field coupling method;

[0100] Since rock deformation and fluid flow in fractures affect each other, it is necessary to couple rock deformation with fluid flow in complex fractures and establish a complex fracture expansion model for tight gas volume fracturing that takes into account fluid-solid coupling. The relationship between fracturing fluid flow in fractures and matrix block deformation: (1) Changes in fluid pressure on the boundary surface of the matrix block will affect the deformation of the matrix block, thereby causing changes in the fracture width; (2) Changes in fracture width cause changes in flow rate, which ultimately affects the distribution of fluid pressure in the fracture. A weak coupling method is used here to implement the above iterative process. Before the rock breaks, the permeability (k f ) should be related to the matrix permeability (k m ) are equal, so the relationship between crack permeability and width k is used f =w 2 / 12, the initial width of the crack can be obtained To provide an initial flow channel for the fracturing fluid. The crack width is constant within a single time step of calling the fluid flow solver. The pressure distribution in the crack is solved by the equation and converted into external loads on the crack surface nodes of the matrix block. The dynamic relaxation method is then used to calculate the stress, strain and displacement of the block system under the action of fluid pressure and initial stress field. The normal relative displacement Δu between adjacent blocks is n , tangential relative displacement Δu s , which is the dynamic width w of the hydraulic fracture and the degree of shear dislocation, is used as the known condition for the next fluid calculation time step, and then the coupled iteration of the fluid pressure field and matrix block deformation is calculated. The pressure convergence of all nodes is used as the judgment condition.

[0101] The formula for solving the fluid-solid coupling problem using Picard iteration is as follows:

[0102]

[0103] Where p is the fluid pressure; w is the slit width; μ is the displacement; w k is the gap width of the current step; p k is the fluid pressure of the current step; p k+1 is the fluid pressure of the next iteration step; p k+1 / 2 is the dynamic crack width subjected to the pressure of the subsequent iteration step; u k+1 is the displacement of the next iteration step; w k+1is the crack width of the next iteration step; A is the overall stiffness matrix; α is the empirical coefficient; F is the crack closure pressure; t is the time; is the rate of change of the slit width per unit time.

[0104] The solid stress field (block control equation) is solved and calculated by the dynamic relaxation method, and the flow pressure field in the fracture (continuity equation) is calculated by the finite element method, and both are solved by Picard iteration. The Picard iteration is used to solve the coupled iteration of the fluid pressure field (step S33) and the matrix block deformation (step S32), and the final crack extension is obtained by using the pressure convergence of all nodes as the judgment condition.

[0105] In step S4, a curve is drawn with the reservoir-interlayer stress difference as the abscissa and the interlayer thickness as the ordinate to obtain a shale oil fracture height discrimination chart under different lithology sequences, mechanical characteristics, and interlayer interface properties. Figure 6 As shown, according to different interlayer stress differences and barrier layer thicknesses, the plate is divided into fracture height penetration zone, transition zone, and fracture height suppression zone.

[0106] According to the fracture height penetration evaluation chart, combined with the well pattern and well spacing deployment and interlayer distribution, the lower sweet spot P in this area is determined. 2 l 1 2-2 Artificial fractures in the reservoir are mainly local penetration (see Figure 6 ), with the goal of mobilizing multiple vertical sweet spots as a whole, the artificial cracks should be extended through the layers and the effectiveness of the vertical support should be ensured. 2 l 1 2-2 The construction displacement of horizontal wells should be appropriately increased, and the proportion of pre-fluid should be increased, and the fracturing parameters should be optimized based on this principle.

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

[0108] Table 2 Comparison of construction parameters and production data of two wells (JHW01711 well and Ji 187_H well)

[0109]

[0110] In addition, the present invention also proposes a thin interbedded shale oil fracture high penetration evaluation system, such as Figure 8 As shown, the system includes a first building module, a second building module, a third building module and a fourth building module; wherein the first building module is used to construct a longitudinally continuous multi-layer geomechanical model at different sweet spot positions; the second building module is used to construct a physical simulation experiment of fracturing with different thin interlayer characteristics based on the geomechanical model; the third building module is used to construct a numerical simulation experiment of crack extension with different thin interlayer characteristics based on the geomechanical model; the fourth building module is used to combine the physical simulation experiment with the numerical simulation experiment, and construct a thin interlayer shale oil fracture high penetration evaluation plate according to the stress difference of different reservoir interlayers and the thickness of the interlayer.

[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 test analysis based on core observation, electronic computer tomography and logging curve interpretation, and determine the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics; the establishment unit is used to establish a longitudinally continuous multi-layer geomechanical model at different sweet spot positions based on the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics.

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

Claims

1. A method for evaluating the fracture height penetration of thin interbedded shale oil, characterized in that: The method comprises the following steps: S1. Construct a longitudinal continuous multi-layer geomechanical model at different sweet spots; S2. Based on the geomechanical model, construct a physical simulation experiment of fracturing with different thin interlayer characteristics; S3. Based on the geomechanical model, numerical simulation experiments on crack propagation with different thin interlayer characteristics were constructed; S4. Combine physical simulation experiments with numerical simulation experiments, and construct a high penetration evaluation chart for thin interlayered shale oil fractures based on the stress difference and thickness of different reservoir barriers.

2. A method for evaluating fracture height penetration of thin interbedded shale oil according to claim 1, characterized in that: Step S1 includes: Based on core observation, computer tomography and logging curve interpretation, core description and micro-macro testing analysis are carried out to determine the characteristics of interlayer interfaces, rock mechanical properties and geostress profile characteristics; According to the interlayer interface characteristics, rock mechanical properties and geostress profile characteristics, a longitudinal continuous multi-layer geomechanical model at different sweet spots is established.

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

4. The method for evaluating fracture height penetration of thin interbedded shale oil according to claim 1, characterized in that: Step S3 includes: An equivalent characterization method for bedding parameters is established by comprehensively applying outcrop profiles and core computer tomography images. The discrete element method is used to solve the medium discontinuity problem caused by bedding, and a three-dimensional model of fracturing crack propagation in thin interlayered shale oil horizontal wells is constructed. Numerical simulation experiments on the propagation of multiple clusters of fractures in horizontal well sections under different thin interlayer characteristics are carried out to quantitatively evaluate the fracture morphology.

5. A method for evaluating fracture height penetration of thin interbedded shale oil according to claim 4, characterized in that: Step S3 specifically includes: S31. Characterize the bedding of strata with different bedding scales; S32. Based on the discrete element mechanics theory, a discrete element mechanics model considering the layering is established; S33. Based on the "wellbore-perforation-fracture" system, establish the entrance pressure equation of each cluster of fractures; consider the fracturing fluid in the fracture as the laminar flow of incompressible Newtonian fluid in a flat plate, and establish the continuity equation and the global mass conservation equation; S34. Use the multi-field coupling method to establish a fluid-solid coupling model for crack extension.

6. A method for evaluating fracture height penetration of thin interbedded shale oil according to claim 5, characterized in that: The bedding characterization in step S31 specifically includes: The calculation formula of equivalent bedding density is: r' BP =ρ BP ×k BP / k' BP ; Among them, ρ′ BP is the equivalent bedding density in the model; k' BP is the equivalent bedding permeability in the model; ρ BP is the actual stratum bedding density; k BP is the actual formation permeability; The calculation formula of equivalent bedding spacing is: d BP =1 / ρ' BP ; Among them, ρ' BP is the equivalent bedding density in the model; d BP is the equivalent bedding spacing in the model; The calculation formula of equivalent bedding width is: Among them, k′ BP is the equivalent bedding permeability in the model; w' BP is the equivalent bedding width in the model.

7. A method for evaluating fracture height penetration of thin interbedded shale oil according to claim 5, 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 equations characterizing rock deformation and the rock fracture criterion equations; The dynamic equation of small displacement linear elasticity is: s ij,j +b i -(p+a)u i,t =0; Among them, σ ij,j is the Cauchy stress tensor; b i is the body force; ρ is the rock density; α is the damping coefficient; u i,t is the displacement at time t; The rock fracture criterion equation is: Among them, F n 、F s are normal force and tangential force respectively; k n , k s are the normal and tangential spring stiffnesses respectively; Δu n , Δu s are the normal and tangential relative displacements between adjacent nodes, respectively.

8. The method for evaluating the fracture height penetration of thin interbedded shale oil according to claim 5, characterized in that: Step S33 includes: The pressure equation at the entrance of each cluster of fractures is: p w =p p,k +p in,k ,k=1,2,...,n f ; Among them, p p,k is the perforation friction of crack k; p in,k is the entrance pressure of crack k; p w is the crack entrance pressure; n f is the number of cracks; The continuity equation is: The global mass conservation equation is: Where p is the fluid pressure; μ is the fluid viscosity; w is the dynamic crack width; t is the time; Ω represents the global spatial region; s is the coordinate of any point in the crack; q l is the fracturing fluid loss. The matrix has ultra-low permeability and the fracturing fluid loss effect is ignored in the model, that is, q l =0; Q0 is the construction displacement.

9. A method for evaluating fracture height penetration of thin interbedded shale oil according to claim 5, characterized in that: Step S34 specifically includes: The fluid-solid coupling solution equation is: Where p is the fluid pressure; w is the slit width; μ is the displacement; w k is the gap width of the current step; p k is the fluid pressure of the current step; p k+1 is the fluid pressure of the next iteration step; p k+1 / 2 is the dynamic crack width subjected to the pressure of the subsequent iteration step; u k+1 is the displacement of the next iteration step; w k+1 is the crack width of the next iteration step; A is the overall stiffness matrix; α is the empirical coefficient; F is the crack closure pressure; t is the time; is the rate of change of the slit width per unit time.

10. A thin interbedded shale oil fracture height penetration evaluation system, characterized in that: The system comprises a first building block, a second building block, a third building block and a fourth building block; wherein, The first construction module is used to construct a longitudinally continuous multi-layer geomechanical model at different sweet spots; The second construction module is used to construct a physical simulation experiment of fracturing with different thin interlayer characteristics based on the geomechanical model; The third building module is used to construct numerical simulation experiments on fracture extension with different thin interlayer characteristics based on the geomechanical model; The fourth construction module is used to combine physical simulation experiments with numerical simulation experiments, and to construct a high penetration evaluation chart for thin interlayered shale oil fractures based on the stress difference and thickness of different reservoir barriers.

11. A thin interbedded shale oil fracture height penetration evaluation system according to claim 10, characterized in that: The first building block includes a determining unit and a establishing unit: The determination unit is used to carry out core description and micro-macro testing analysis based on core observation, electronic computer tomography and logging curve interpretation, and to determine the characteristics of interlayer interfaces, rock mechanical properties and geostress profile characteristics; The unit is used to establish a longitudinal continuous multi-layer geomechanical model at different sweet spots according to the interlayer interface characteristics, rock mechanical properties and ground stress profile characteristics.

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