A method for optimizing and parameter selection of a compact reservoir fracture high control process technology

Abstract

The application discloses a kind of compact reservoir fracture high control process technical optimization and parameter optimization method, obtains the geological data of fracturing area;According to the true triaxial fracturing physical simulation experiment of geological data, the fracture height expansion law of preliminary determination fracturing dynamic;Through the proppant migration experiment of fracturing fracture, the fracture height evolution law of proppant in different pump injection conditions is preliminarily determined;Fracture physical model is constructed, according to the fracture physical model, the fracture height expansion law and the fracture evolution law of proppant are constructed fracture height evolution numerical simulation model;The sensitivity of each parameter to fracturing fracture height is analyzed in combination with physical model and numerical simulation model;According to the sensitivity of each parameter to fracturing fracture height, under the condition of different parameters and parameter combination, the optimization method and process technology corresponding to each parameter and parameter combination are obtained.The application considers the mutual influence of dynamic fracture height, support fracture height and dynamic-support fracture height, and more accurate fracture height control can be realized.

Description

Technical Field

[0001] This invention relates to the field of engineering control related to the efficient exploitation of unconventional oil and gas and geothermal energy, and particularly to a method for optimizing and selecting parameters of a high-control process for fracture in tight reservoirs. Background Technology

[0002] Unconventional oil and gas, such as tight sandstone oil and gas, shale oil and gas, coalbed methane, and carbonate rock oil and gas, as well as geothermal energy, such as hot dry rocks, are important energy sources.

[0003] In existing technologies, fracturing techniques are typically used to fracture rock masses using high-pressure fluids and drive fracture propagation. The aim is to create complex fractures in the rock formation, improve reservoir permeability, enhance oil and gas production, and form artificial fracture networks to improve the heat exchange efficiency of the heat transfer fluid between geothermal injection and production wells. In this technology, fracturing fractures often exhibit a geometric morphology where a main fracture coexists with multi-scale branch fractures around it. Therefore, controlling the overall morphology of the fracturing fractures largely depends on controlling the main fracture.

[0004] In practical applications, for formations containing oil and gas reservoirs and those with thick, non-oil and gas-bearing interlayers above and below, the fracture height needs to be limited to propagate within the reservoir to prevent ineffective propagation through the interlayers. For formations with multiple vertically distributed oil and gas layers, such as layered shale and thin interbedded sandstone, the fracture height needs to be increased to enhance its ability to penetrate the layers. For formations where the target reservoir has oil and gas layers only on one side of the upper or lower layer, the fracture height needs to be controlled to extend unilaterally, ensuring the fractures enter the oil and gas layer and preventing propagation in non-oil and gas-bearing layers. For hot dry rock formations, if the primary goal is to increase fracture propagation along the fracture length, then the fracture height also needs to be limited. However, current technologies lack methods for controlling fracture morphology, especially fracture height. Summary of the Invention

[0005] To overcome some of the problems mentioned in the background above, the present invention provides a method for optimizing and selecting parameters of high-controllability fracturing technology in tight reservoirs, so as to at least partially solve the above problems.

[0006] The present invention provides a method for optimizing and selecting parameters of high-controllability fracturing technology in tight reservoirs, including: acquiring geological data of the fracturing area.

[0007] Based on the geological data, a true triaxial fracturing physical simulation experiment was conducted to preliminarily determine the expansion law of dynamic fracture height under different geological conditions and pumping conditions.

[0008] Through proppant migration experiments in hydraulic fracturing fractures, the intra-fracture migration and accumulation height evolution of proppant under different pumping conditions were preliminarily determined.

[0009] A physical model of the hydraulic fracturing fracture is constructed, and a numerical simulation model of the fracture height evolution is constructed based on the physical model of the hydraulic fracturing fracture, the expansion law of the dynamic fracture height, and the evolution law of the proppant in the fracture.

[0010] The sensitivity of various parameters to hydraulic fracturing is analyzed by combining physical models and numerical simulation models.

[0011] Based on the sensitivity of each parameter to the crack height, optimization methods for each parameter under different parameter conditions are obtained.

[0012] Furthermore, when conducting true triaxial fracturing physical simulation experiments, it is ensured that the fracture propagation characteristics of the experiment and the fracturing engineering site are similar. Among these characteristics, the fracture propagation characteristics include the resistance of rock fracture, the resistance of fracturing fluid friction along the path, and the resistance of fracturing fluid filtration into the formation.

[0013] Furthermore, the constructed fracturing fracture physical model satisfies the fracture propagation mechanics criterion, the intra-fracture fluid flow criterion, the fluid-structure interaction criterion, and the proppant migration criterion, among which the fracture propagation mechanics criterion includes...

[0014] A fracture model was constructed based on the mechanical properties of the fracture process zone. Rock fracture tests were conducted based on the fracture model to determine the cohesive tensile strength of rock fractures, fracture opening displacement, fracture process zone length, fracture energy, and critical dissipation energy, thereby obtaining a clear fracture constitutive relationship.

[0015] The relationship between nonlinear fracture parameters and linear elastic fracture parameters is obtained based on the assumption of eliminating singularity at the tip of nonlinear cohesive cracks. The fluid flow criterion within the crack is expressed by a Newtonian flow model in the tangential direction and a filtration model in the normal direction.

[0016] The Newtonian flow model is as follows.

[0017] ,

[0018] In the formula: For displacement; For fluid pressure; The flow coefficient; For fluid viscosity; This refers to the crack opening.

[0019] The filtering model in the normal direction is as follows.

[0020] ,

[0021] In the formula, the subscripts o, b and i represent the upper surface, lower surface and crack of the crack, respectively, q is the filtration rate and c is the filtration coefficient.

[0022] The fluid-structure interaction criterion is represented by the following coupling model: the effective stress model.

[0023] ,

[0024] In the formula, Indicates effective stress. Indicates the total stress. Indicates the pore pressure of the wetting fluid. Represents the identity matrix.

[0025] Stress balance equation:

[0026] ,

[0027] In the formula, Indicates the total stress. Indicates the virtual strain rate of the reservoir matrix. Represents the volume of the calculation unit. This represents the surface force per unit area. Represents the imaginary velocity field of the reservoir matrix. Indicates the area where the load is applied. This refers to the volume force per unit volume.

[0028] Continuity equation:

[0029] ,

[0030] In the formula, Indicates fluid density, Indicates a unit of time. Indicates porosity. Represents the unit outward normal vector. It indicates Darcy's speed.

[0031] Darcy's Law:

[0032] ,

[0033] In the formula, Represents gravitational acceleration. Indicates penetration rate. Indicates fluid pressure. This represents the position vector.

[0034] The proppant transport criterion is expressed by a proppant transport model; the mass conservation equation in the proppant transport model is as follows:

[0035] ,

[0036] in, Represents the velocity vector. The time is indicated, and the subscripts w and s indicate the liquid phase and sand phase, respectively. This indicates the volume percentage of each phase, and a phase relationship exists: + =1.

[0037] The momentum conservation equation in the proppant transport model is as follows:

[0038] ,

[0039] ,

[0040] In the formula, Indicates density, Represents the stress tensor. This indicates shared pressure between the two parties. represents the sand phase pressure, and F represents the interphase force.

[0041] The phase conservation equation in the proppant transport model is as follows:

[0042] ,

[0043] The interphase forces are as follows:

[0044] ,

[0045] The interphase momentum exchange coefficient The definition is as follows:

[0046] ,

[0047] in It refers to the viscosity of the liquid. This is the drag coefficient of the proppant, which can be defined using existing empirical formulas:

[0048] ,

[0049] In the formula Represents the Reynolds number.

[0050] Furthermore, when insufficient fluid pressure, net pressure loss, and reduced strength factor occur within the crack due to proppant accumulation, the crack propagation resistance reduction function caused by proppant accumulation is obtained through a proppant transport model, as shown in the following formula:

[0051] ,

[0052] in, It is the stress intensity factor. It is the initial net pressure within the seam. It is the pressure drop in the proppant accumulation zone. It is the loss factor. It is the characteristic length of the crack. This is the current crack length. It is the characteristic length of the crack tip;

[0053] A model for reducing the resistance to crack propagation is constructed based on the crack propagation resistance reduction function.

[0054] Furthermore, the construction of the numerical simulation model for fracture height evolution includes: constructing a numerical simulation model for hydraulic fracture propagation.

[0055] By introducing cohesive fracture elements into the fracture model characterizing the fracture process zone using the finite element method, and embedding the cohesive fracture elements between the finite element meshes of the cohesive fracture model, a numerical simulation model of fracture propagation is obtained by simulating the propagation of the fracturing fracture through the sequential failure of the cohesive fracture under fluid injection conditions.

[0056] Constructing a numerical simulation model for proppant migration: The proppant migration carried by the sand slurry was characterized by multiphase flow simulation method to obtain a numerical simulation model for proppant migration.

[0057] For multiphase flow simulation methods, the governing equations are discretized and solved before numerical simulation. This transforms the mass and momentum conservation equations of the proppant transport model from partial differential equations that are difficult to solve directly into a set of algebraic equations that are easy to solve in numerical simulation.

[0058] A numerical simulation model of fracture height evolution was obtained by combining the numerical simulation model of hydraulic fracturing fracture propagation and the numerical simulation model of proppant migration.

[0059] Furthermore, the analysis of the sensitivity of various parameters to the fracture height by combining physical models and numerical simulation models includes: firstly, conducting physical simulation through a physical model of the fracture to analyze the influence of various parameters included in geological and engineering factors on the dynamic fracture height and the support fracture height, and obtaining the overall parameter influence law.

[0060] Then, numerical simulation is performed using a numerical simulation model to conduct in-depth analysis of the parameters included in the geological and engineering factors, and to quantitatively determine the influence of each parameter on the dynamic elevation and support joint height.

[0061] Finally, sensitivity analysis was conducted, using the ratios of the changes in dynamic elevation and support joint height to the changes in each parameter as sensitivity factors to determine and rank the sensitivity of dynamic elevation and support joint height to different geological and engineering parameters.

[0062] Furthermore, when the parameters are pump injection rate, pump stop time, sand content ratio in the proppant, and particle size in the proppant, the optimization method includes: reducing the pump injection rate and controlling the pump injection rate within a first preset range; advancing the pump stop time and controlling the pump stop time within a second preset range; reducing the sand content ratio in the proppant and increasing the particle size in the proppant.

[0063] Furthermore, when the parameter is the proppant type, the optimization method includes selecting two proppant types: floating and sinking.

[0064] By combining the numerical simulation model of crack height evolution and the content ratio of floating proppant and sinking proppant as influencing factors, simulation analysis was conducted to determine the critical ratio of floating proppant to sinking proppant that helps to make the critical support crack height at the upper and lower ends of the crack approximately equal and is conducive to the isotropic propagation of the crack on the upper and lower sides of the crack height.

[0065] By adjusting the different ratios of floating proppant and sinking proppant, the differential propagation of the upper and lower sides of the hydraulic fracture can be optimized.

[0066] Compared with the prior art, the present invention has the following beneficial effects.

[0067] This invention integrates fracture mechanics and plasticity mechanics by combining cohesive fracture tensile softening. It constructs a thermoplastic cohesive fracture model using a thermoplastic constitutive modeling method and determines the constitutive relationship between cohesion, opening displacement, and temperature. The resulting fracturing fracture discrimination criterion has high accuracy and applicability, providing a foundation for modeling "more complex high-temperature rock fractures". The simulation of proppant transport and accumulation adopts the Euler-Euler two-phase flow simulation method, which has the advantages of stability, efficiency, and high accuracy.

[0068] Based on the physical model of rock fracture and proppant migration and accumulation, this invention describes the relationship between dynamic fracture height and proppant fracture height by constructing a fracture propagation resistance reduction model caused by proppant accumulation. Proppant accumulation leads to insufficient fluid pressure within the fracture, resulting in a reduction of the intra-fracture pressure driving fracture propagation. By constructing the fracture propagation resistance reduction model caused by proppant accumulation, the controlling equation relationship between dynamic fracture height and proppant fracture height (proppant accumulation height) is established.

[0069] This invention uses the regulation of the "driving force" and "resistance" of fracture propagation and the optimal timing as the overall control principle for fracture height. Increasing the driving force of fracture propagation and reducing the propagation resistance helps to increase fracture height; conversely, increasing the propagation resistance and reducing the driving force helps to suppress fracture height. The timing of regulation determines the efficiency of the two methods. Numerical simulations show the influence of various pumping parameters and proppant parameters on the driving force of fracture propagation, and fracture height can be controlled through multi-parameter optimization.

[0070] This invention employs a self-suspended proppant with an absolute density less than water to seal the upper seam tip; and a proppant with an absolute density greater than water to seal the lower seam tip; thereby increasing the bilateral expansion resistance and controlling the dynamic seam height. By obtaining the correlation between proppant density, equilibrium time, and the maximum propped seam height, the invention achieves the goal of controlling the propped seam height using proppant density.

[0071] This invention, based on the dual-sided proppant height suppression technology involving sinking and floating, enhances the sinking and floating of proppant during fracturing fluid injection, further increasing the propagation resistance of fracturing fractures and thus suppressing fracture height increases. By simulating and determining the effects of pump stop time, pump stop timing, pumping parameters before and after stop time, and proppant type on fracture height, this invention utilizes parameter control to achieve the goal of controlling fracture height.

[0072] This invention uses a multivariate linear fitting method to orthogonally analyze the influence of different geological and engineering factors on joint height, thereby obtaining a joint height prediction model; and employs a deep learning-based intelligent method to predict dynamic joint height and support joint height. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of a method for optimizing and selecting parameters for high-controllability technology of tight reservoir fracture in one embodiment of the present invention.

[0074] Figure 2 This is a schematic diagram of the dynamic seam height and support seam height according to an embodiment of the present invention.

[0075] Figure 3 This is a schematic diagram of the fracture process of a hydraulic fracturing crack according to an embodiment of the present invention.

[0076] Figure 4 This is a simplified model diagram of fluid flow-filtration loss within the slit according to an embodiment of the present invention.

[0077] Figure 5 This is a simplified mechanical model diagram of how proppant deposition increases crack propagation resistance in the numerical simulation method of this invention.

[0078] Figure 6 This is a schematic diagram of the double-sided controlled seam technology for injecting sinking and floating particles according to an embodiment of the present invention. Detailed Implementation

[0079] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of the present invention to facilitate a better understanding of this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction. The technical solutions of the application will be further described in detail below with reference to the accompanying drawings.

[0080] This invention provides an optimization method for high-controllability technology and parameter selection in tight reservoir fracture treatment; such as... Figure 1 Step 1 shows the acquisition of geological data for the fracturing area: the geological data obtained through the survey includes the comprehensive columnar section and vertical profile with faults of the target development area; the reservoir data surveyed includes the permeability and porosity of reservoir rocks in typical target blocks, the relative permeability of oil and gas, the relative permeability of water, and reservoir PVT data.

[0081] The survey focused on drilling and completion design and construction, including geological design, logging data from typical wells, comprehensive logging records, wellbore stability analysis, ground failure pressure testing, and casing damage in fractured wells. Reservoir core samples were also obtained to determine composition, microstructure, and rock mechanical parameters.

[0082] The key focus is on the fracturing operations in the target development area, including fracturing procedures, construction parameters, perforation parameters, fracturing fluid properties, single-well fracturing fluid injection time and total injection volume, pumping procedure table, fracturing construction curves, and data such as tracers and microseismic interpretation of fracturing fracture size; and the development and drainage processes of typical wells in the target block are investigated.

[0083] Step 2: Conduct a true triaxial fracturing physical simulation experiment based on the geological data to preliminarily determine the dynamic fracture height propagation law: by taking rock cores in situ, determine the mineral composition, microstructure and rock mechanical parameters of the target reservoir rocks, including the elastic-plastic-viscosity mechanical parameters of the target reservoir's tensile-tensile-shear-compression-shear, strength parameters and a complete set of linear elastic-nonlinear fracture parameters.

[0084] Rock outcrops or artificially similar samples were selected for physical simulation experiments of true triaxial fracturing. By adjusting the displacement, viscosity, pumping procedure and proppant injection, the propagation law of dynamic fracture height was preliminarily determined.

[0085] like Figure 2As shown, during fracturing, a proppant containing various particle sizes (coarse sand, medium-fine sand, medium-coarse sand, and fine sand) is injected from the proppant inlet, accumulating to form multiple sand dikes of different heights. The total height of the proppant accumulation is the propping fracture height, and the liquid fracture height is the dynamic fracture height.

[0086] In a further embodiment of this example, the fracturing physical simulation test needs to focus on the similarity between the experimental and engineering field fracture propagation characteristics. It is necessary to evaluate the three resistances of the fracturing fracture and their relative strengths: the resistance of rock fracture, the resistance of frictional friction of the fracturing fluid, and the resistance of the fracturing fluid filtration into the formation. By adjusting the test conditions, the consistency of the fracturing fracture propagation resistance characteristics under engineering and experimental conditions can be achieved, thereby satisfying the similarity between fracturing engineering and testing.

[0087] Step 3 uses proppant migration experiments in hydraulic fracturing fractures to preliminarily determine the intra-fracture migration and accumulation height evolution of proppant under different pumping conditions.

[0088] Step 4: Constructing the physical model of hydraulic fracturing fractures: Based on the physical model of hydraulic fracturing fractures, the fracture height propagation law, and the proppant evolution law within the fracture, construct a numerical simulation model of fracture height evolution; for processes such as rock fracture, fluid flow within the fracture, and proppant migration in hydraulic fracturing, conduct physical simulation experiments in combination with geological and engineering conditions, select specific physical models and determine the key parameters of the mathematical formulas in the physical models, use mathematical formulas to quantitatively characterize the physical logic between various physical quantities and the logical progression relationship between various criteria, and complete the construction of the physical model.

[0089] Numerical computation essentially involves solving various equations in a constitutive model for a complex geometric model. Physical modeling combined with numerical computation simulates the hydraulic fracturing process, forming a numerical simulation model of fracture height evolution.

[0090] When conducting numerical simulations, the parameter selection references the range of each parameter in the physical model, and takes into account the influence trends and laws obtained from the physical simulation method (i.e., constraining the range of each parameter in the numerical simulation model based on the expansion law of the dynamic fracture height under different geological conditions and pumping conditions, and the evolution law of proppant migration and accumulation height under different pumping conditions), to ensure that the results obtained from the numerical simulation are consistent with the physical laws.

[0091] In a further embodiment of this example, constructing a physical model of hydraulic fracturing includes: constructing a mechanical discrimination model for fracture propagation; and considering the prominent characteristics of fracture in rock-like materials.

[0092] like Figure 3As shown, a hydraulic microcrack zone composed of a large number of microcracks is formed at the tip of the initial pressure crack. During the fracture process, microcracks initiate and merge to form new crack surfaces. First, a fracture model is constructed based on the mechanical properties of the fracture process zone, and a thermoplastic constitutive model is constructed using the thermoplastic constitutive modeling method.

[0093] In a further embodiment of this example, rock fracture tests are conducted to determine the cohesive tensile strength of rock fractures, fracture opening displacement, fracture process zone length, fracture energy, and critical dissipation energy, thereby obtaining a clear fracture constitutive relationship.

[0094] In a further embodiment of this example, the relationship between nonlinear fracture parameters and linear elastic fracture parameters is obtained based on the assumption of eliminating singularity at the tip of nonlinear cohesive cracks.

[0095] Construct a fluid flow model within the slit, such as Figure 4 As shown, the fluid at the fracture tip exhibits tangential and normal flows relative to the fracture propagation direction, with the fluid being lost into the seepage layer via normal flow. The tangential flow is modeled using Newton's flow model, while the normal flow uses a filtration model. For tangential flow along the fracture propagation direction, Newton's flow model is used.

[0096] ,

[0097] ,

[0098] In the formula, For displacement; For fluid pressure; The flow coefficient; The crack opening; This represents the fluid viscosity.

[0099] Normal filtration occurs perpendicular to the slit surface, using a fluid filtration model:

[0100] ,

[0101] In the formula, the subscripts t, b and i represent the upper surface, lower surface and fissure of the crack, respectively, q is the filtration rate, p is the fluid pressure and c is the filtration coefficient.

[0102] Construct a multi-field coupling model; effective stress model:

[0103] ,

[0104] In the formula, Indicates effective stress. Indicates the total stress. Indicates the pore pressure of the wetting fluid. Represents the identity matrix.

[0105] Stress equilibrium equation:

[0106] ,

[0107] In the formula, Indicates the total stress. Indicates the virtual strain rate of the reservoir matrix. Represents the volume of the calculation unit. This represents the surface force per unit area. Represents the imaginary velocity field of the reservoir matrix. Indicates the area where the load is applied. This refers to the volume force per unit volume.

[0108] Continuity equation:

[0109] ,

[0110] In the formula, Indicates fluid density, Indicates a unit of time. Indicates porosity. Represents the unit outward normal vector. It indicates Darcy's speed.

[0111] Darcy's Law:

[0112] ,

[0113] In the formula, Represents gravitational acceleration. Indicates penetration rate. Indicates fluid pressure. This represents the position vector.

[0114] A proppant transport model is constructed; the mass conservation equation in the proppant transport model is as follows:

[0115] ,

[0116] In the formula, Represents the velocity vector. The time is indicated, and the subscripts w and s indicate the liquid phase and sand phase, respectively. This indicates the volume percentage of each phase, and a phase relationship exists: + =1.

[0117] The momentum conservation equation in the proppant transport model is as follows:

[0118] ,

[0119] ,

[0120] in, Indicates density, Represents the stress tensor. This indicates shared pressure between the two parties. Indicates sand phase pressure, It represents the interaction force between phases.

[0121] The phase conservation equation in the proppant transport model is as follows:

[0122] ,

[0123] Interphase forces can be calculated using the following empirical formula:

[0124] ,

[0125] Among them, the interphase momentum exchange coefficient The definition is as follows:

[0126] ,

[0127] In the formula, It refers to the viscosity of the liquid. This is the drag coefficient of the proppant, which can be defined using existing empirical formulas:

[0128] ,

[0129] In the formula, Represents the Reynolds number.

[0130] In a further embodiment of this example, constructing a numerical simulation model of fracture height evolution includes: constructing a numerical simulation model of hydraulic fracturing fracture propagation, and using various numerical calculation methods such as finite element method, discrete element method, boundary element method, finite difference method, finite volume method, material point method, and phase field method to construct the numerical model.

[0131] In a further embodiment of this example, the cohesive crack model characterizing the fracture process zone is introduced into the cohesive crack element using the finite element method, and the cohesive crack element is embedded between the finite element mesh. Under fluid injection conditions, the propagation of the fracturing crack is simulated by the sequential failure of the cohesive crack, which is used to calculate the dynamic crack height, i.e., the crack height driven by the fracturing fluid.

[0132] The numerical simulation model for crack propagation described above includes rock elastoplastic mechanical parameters, physical parameters such as rock porosity and permeability, geological conditions such as geostress, temperature, formation pore pressure and clay content, engineering parameters such as pumping fluid discharge rate, viscosity and filtration characteristics, and the dynamic changes of the above parameters during crack propagation. The influence of clay content on crack propagation can be quantified using a thermoplastic fracture model.

[0133] Construct a numerical simulation model for proppant transport: Characterize the transport of proppant carried by sand slurry through multiphase flow simulation methods, such as the Euler-Euler multiphase flow simulation method and the Euler-Lagrange multiphase flow simulation method; the Euler-Euler two-phase flow simulation method has the advantages of stability, efficiency and high accuracy, and can be given priority.

[0134] For the multiphase flow simulation equations, the governing equations are discretized and solved before numerical simulation. This transforms the mass conservation equations and momentum conservation equations of the proppant transport model from partial differential equations that are difficult to solve directly into a set of algebraic equations that are easy to solve in numerical simulation, thereby enabling stable, efficient, and high-precision simulation of the proppant transport process.

[0135] Finite volume method, finite difference method and finite element method can be used; the preferred method is the finite volume method, which has the advantages of stable calculation and high format accuracy (second-order accuracy), and can be used to solve the governing equations in a discrete manner.

[0136] This method is mainly used to determine the proppant's migration distance along the crack length and its accumulation height along the crack height, with a focus on analyzing the accumulation height along the crack height. The proppant's accumulation height along the crack height is defined as the proppant's proppant height. To address the challenge of difficult mesh generation and a large number of meshes due to the high aspect ratio of the crack height-width cross-section, this method can be used to determine the proppant's height using geometric similarity models and similarity analysis methods.

[0137] Numerical model for proppant transport includes parameters such as proppant particle size, multi-particle size combination, proppant density, and proppant carrying solution concentration.

[0138] It should be noted that when constructing a numerical simulation model of crack height evolution, the large aspect ratio of the crack height often makes mesh generation difficult. In the embodiments of this invention, the following method can be used to solve this problem: the hydraulic fracturing crack of the crack height-crack aperture section has the prominent feature of a very large aspect ratio, which makes the model mesh generation face the problems of "low number of elements but element height and width distortion" and "comparable element polygonal size but huge number of elements".

[0139] The present invention proposes a modeling method for constructing similar geometric models: (1) The dynamic crack height of the actual size of the project is reduced by different proportions to construct numerical crack models with different geometric sizes. For different numerical models, the same fluid velocity, sand ratio, viscosity, proppant parameters, etc. are selected to carry out numerical simulation of proppant migration. The critical time when the proportion of proppant crack height to dynamic crack height is the same for different models is obtained, thereby determining the correlation function of "dynamic crack height - critical proppant accumulation time".

[0140] (2) Using the scaled-down model, based on the multiple pumping discharge rates of the actual project, the flow velocities within the multiple gaps of the small-size model are determined and simulations are carried out, thereby obtaining the critical time for the proppant to reach the equilibrium critical value under the multiple flow velocities within the gaps.

[0141] (3) By using the "dynamic crack height - critical proppant accumulation time" function relationship, based on the critical equilibrium accumulation height and time of proppant obtained from the small-size model, the critical equilibrium accumulation height of proppant for engineering-sized cracks can be inferred.

[0142] (4) Based on the above method, by adding calculation examples, a model function is constructed to characterize the correlation between the normalized prop joint height and fracturing fluid flow rate, viscosity, proppant particle size-density-concentration, etc., so as to quickly infer the prop joint height under different pumping conditions.

[0143] In addition, considering that the changes in pumping rate and fracture length and width during the simulation of fracturing fracture propagation will change the flow velocity of the fluid inside the fracture, the flow velocity is used as a key parameter to calculate the proppant migration, and thus obtain the proppant accumulation height in the fracture height direction.

[0144] Furthermore, by utilizing the proppant stacking height, the reduction of intracranial pressure driving crack propagation due to proppant stacking and the decrease in crack driving force at the crack tip caused by proppant stacking are calculated, resulting in an increase in crack propagation resistance and a difference in the upper and lower propagation resistance of the crack height-crack width cross section.

[0145] like Figure 5 As shown, the half-seam length at the seam tip is The length of the support material buildup at the lower end of the seam tip is The initial net pressure within the seam is The breakage pressure in the proppant accumulation area is The reduction function of crack propagation resistance caused by proppant accumulation can be obtained through a numerical simulation model of proppant migration, as shown in the following formula:

[0146] ,

[0147] In the formula, It is the stress intensity factor. It is the initial net pressure within the seam. It is the pressure drop in the proppant accumulation zone. It is the loss factor. It is the characteristic length of the crack. This is the current crack length. It is the characteristic length of the crack tip.

[0148] The resistance reduction function is substituted as an influencing parameter into the numerical simulation model of hydraulic fracturing crack propagation to achieve a combination of the two.

[0149] After obtaining the numerical simulation model, the process also includes using the expansion law of the dynamic fracture height under certain geological and pumping conditions, and preliminarily determining the intra-fracture migration and accumulation height evolution law of proppant under different pumping conditions to calibrate the parameters of the numerical simulation model and verify the numerical simulation model.

[0150] Parameter calibration: Representative fracturing engineering cases were selected as calibration cases. Geological, geostress and mechanical parameters of the rock strata to be fractured in the field were selected. Numerical simulations were carried out for the pumping procedure, displacement, viscosity, proppant pumping procedure and proppant type of the fracturing project. The goal was to make the dynamics of the numerical simulation and the proppant fracture height of the in-situ fracturing project consistent, and to determine the correspondence between the numerical simulation and the fracturing project parameters.

[0151] Model Validation: Based on this, three or more fracturing engineering cases were selected. Numerical simulations were performed using the calibrated numerical simulation model, taking into account engineering geological, mechanical, and engineering parameters. The consistency between the dynamic-support fracture height obtained from the numerical simulation and the measured dynamic-support fracture height in the engineering was analyzed to determine the model's effectiveness. Preferably, if the consistency rate between the calculated fracture height and the measured fracture height in each case is ≥85%, the numerical model is considered effective.

[0152] Furthermore, using the numerical model that has been calibrated above, the fracture height expansion under different geological and engineering parameter conditions is simulated, and its sensitivity is analyzed.

[0153] The measured fracture heights mentioned above are mostly achieved by adding tracers to the fracturing fluid and marking the proppant to identify the dynamic fracture height and proppant fracture height of the wellbore rock. Microseismic monitoring can also be used to monitor the fracture height. For vertical well fracturing, both tracer and microseismic measurement can be used simultaneously, while for horizontal well fracturing, microseismic measurement is more commonly used.

[0154] In step 5, the sensitivity of various parameters to fracture height is analyzed by combining physical and numerical simulation models. First, the parameters are determined. In this embodiment, the geological parameters mainly include reservoir-interstitial layer thickness, in-situ stress difference, rock mechanics, and physical property parameters. The reservoir-interstitial layer thickness needs to be based on the field geological conditions, setting typical reservoir-interstitial layer thicknesses. The in-situ stress difference includes two types of factors: reservoir in-situ stress difference and inter-layer in-situ stress difference between the reservoir and interstitial layers. Rock mechanics parameters include, but are not limited to, the elastic modulus, Poisson's ratio, and fracture toughness of the reservoir and interstitial layers, as well as other elastic-plastic-strength-fracture parameters. Physical property parameters mainly include, but are not limited to, the permeability, porosity, and clay content of the reservoir and interstitial layers.

[0155] The engineering parameters include five categories: pumping parameters, fracturing fluid properties, proppant characteristics, pumping procedures, and perforation parameters. Pumping parameters include pumping rate and fluid volume, fracturing fluid properties mainly include viscosity, type, and filtration characteristics, proppant characteristics mainly include proppant particle size, density, particle size combination, and concentration, pumping procedures include the pumping rate, viscosity, and proppant-particle-concentration combination at different stages of fracturing fluid pumping, and perforation parameters mainly include helical and directional arrangement, number of perforations, and perforation diameter.

[0156] The sensitivity of various parameters to fracture height was analyzed by combining physical and numerical simulation models. This included: first, physical simulation using a physical model to analyze the influence of typical parameters from geological and engineering factors on dynamic and support fracture height, obtaining the overall parameter influence patterns; second, numerical simulation using a numerical simulation model to refine the analysis of each parameter included in geological and engineering factors, quantitatively determining the influence of each factor on dynamic and support fracture height; and finally, sensitivity analysis, using the ratio of fracture height change to the change of influencing factors as the sensitivity factor, to determine and rank the sensitivity of dynamic and support fracture height to different geological and engineering parameters.

[0157] Finally, in step 6, based on the sensitivity of each parameter to the crack height, the control methods corresponding to each parameter under different parameter control conditions are obtained.

[0158] In this embodiment, the principle and preferred method for single-parameter fracture control height in tight sandstone reservoirs are as follows:

[0159] Regarding geological factors: When the reservoir stress remains constant, the increase in the minimum horizontal stress difference between the reservoir and the interlayer significantly inhibits the expansion of the maximum dynamic fracture height and the maximum supported fracture height. Under the same stress difference, the greater the minimum horizontal stress, the smaller the maximum dynamic fracture height and the maximum supported fracture height. With the continuous increase of the elastic modulus of the reservoir and interlayer, both the maximum dynamic fracture height and the maximum supported fracture height increase, while the maximum dynamic fracture width decreases. Moreover, the change in the elastic modulus of the interlayer is more sensitive to the impact of fracture height on the interlayer than on the reservoir. The improvement of the fracture toughness of the interlayer inhibits the increase of dynamic fracture height and supported fracture height, and the change in the fracture toughness of the interlayer is more sensitive to the impact of fracture height on the reservoir than on the reservoir. The influence of Poisson's ratio and reservoir-interlayer physical properties is weak. With the increase of the clay content of the reservoir and interlayer, the dynamic fracture height and the supported fracture height decrease, and the inhibition effect of the interlayer is greater than that of the reservoir.

[0160] In terms of engineering factors: increasing the viscosity of fracturing fluid contributes to increasing dynamic fracture height and dynamic fracture width, significantly affects propped fracture height, but reduces propped fracture height; increasing fluid volume and displacement increases maximum dynamic fracture height and width, with maximum propped fracture height initially increasing with displacement and then stabilizing, and increasing exponentially with fluid volume; propped fracture height increases quadratically with particle size, and linearly with density but not significantly; sand ratio has little effect on dynamic fracture height, and propped fracture height generally decreases linearly with sand ratio; when various types of submerged proppant are mixed in different proportions and pumped into fractures, the resulting maximum propped fracture height is basically the same, and all depend on the maximum particle size, with smaller particle size added first and accumulating first at the far end of the wellbore, and larger particle size added first and accumulating first at the near end of the wellbore.

[0161] The method for synergistic optimization of pumping parameters and proppant parameters is as follows: The overall principle for controlling the fracture height is to regulate the "driving force" and "resistance" of fracture propagation and optimize the timing: increasing the driving force of fracture propagation and reducing the propagation resistance helps to increase the fracture height; while increasing the propagation resistance of fracture propagation and reducing the driving force helps to suppress the fracture height, and the timing of regulation determines the regulation efficiency of the above two methods.

[0162] The driving force for fracture propagation is mainly controlled by displacement and fluid volume: increasing or decreasing displacement can increase or decrease the driving force for dynamic fracturing fracture propagation, while increasing or decreasing fluid volume helps to enhance or inhibit the time for the driving force to promote fracture propagation.

[0163] Crack propagation resistance control is mainly implemented by adjusting the proppant height: the propagation resistance is high on the proppant accumulation side, and the position of the proppant height and its ratio to the dynamic crack height affect the dynamic crack height. Therefore, the higher the critical proppant height reached by proppant accumulation, the more significant the increase in resistance; the faster the critical proppant height is reached, the more conducive it is to proppant accumulation to the critical value under lower dynamic crack height conditions, resulting in a larger ratio of proppant height to dynamic crack height and a more obvious increase in resistance.

[0164] Based on the above control principles, for tight sandstone reservoirs with thick interlayers above and below, a multi-parameter optimization method for suppressing fracture height is proposed to "rapidly and significantly" increase the resistance to fracture propagation on both sides: adopting a low displacement rate is beneficial to suppressing dynamic fracture height growth; the higher the critical fracture height, the more beneficial it is to control dynamic fracture height growth, and the favorable measures are low sand ratio, large particle size, low displacement, and low liquid volume; by stopping the pump to enhance proppant settling, the earlier the pump is stopped, the more effective the fracture height control is, but the premise is to avoid excessive fracture height on one side.

[0165] The following are the process technology and parameter optimization methods for double-sided crack suppression using injection of sinking and floating proppant: Process technology methods: such as Figure 6As shown, both upper and lower proppants are added to the fracturing fluid simultaneously. The upper proppant, with an absolute density lower than that of the fracturing fluid, is used to seal the upper fracture tip, while the lower proppant, with an absolute density greater than that of the fracturing fluid, is used to seal the lower fracture tip. This ultimately increases the propagation resistance on both sides, achieving simultaneous suppression of the upper and lower fracture heights of the fracturing fracture.

[0166] Parameter optimization method: Based on the established control law of single factors on the crack height of the pressure fracture, the types of floating and sinking proppant are selected. Combining physical simulation test and numerical simulation method, the content ratio of floating proppant to sinking proppant is taken as the influencing factor. The simulation analysis is carried out to determine the critical ratio of floating-sinking proppant that helps the critical support crack height at the upper and lower ends of the crack to be approximately equal and is conducive to the equidirectional expansion of the crack on the upper and lower sides of the crack height.

[0167] Preferably, for tight sandstone reservoirs with thick interlayers above and below, the maximum proppant fracture height increases as the proppant density decreases; when the proppant dosage: sand content ≈ 2:1, the critical proppant fracture heights at the upper and lower ends of the fracture are approximately equal, which is conducive to isotropic propagation.

[0168] In addition, by adjusting the different ratios of floating and sinking proppant, the proppant is made to accumulate at different heights on the upper and lower sides of the fracture, thereby promoting the expansion of the difference between the upper and lower sides of the pressure fracture.

[0169] The slug variable displacement proppant sinking and floating technology for controlling fracture height and its parameter optimization method are as follows: The slug variable displacement proppant sinking and floating technology for controlling fracture height is based on a dual-sided fracture height suppression technology involving the injection of sinking and floating proppant. The main method involves stopping the pump during the fracture propagation process driven by the fracturing fluid, enhancing the sinking and floating of the proppant, and further increasing the propagation resistance of the fracturing fracture to suppress fracture height increase. Specifically, it is necessary to determine the impact of pump stop time, pump stop timing, pumping parameters before and after pump stop, and proppant type on fracture height through simulation, and to optimize the most effective pumping parameters.

[0170] Preferably, for tight sandstone reservoirs with thick interlayers above and below, pumping should be stopped as early as possible when the dynamic fracture height is low, so that the proppant accumulates and seals the upper and lower sides of the fracture, thereby increasing the resistance to fracture propagation; then, pumping should continue at a low flow rate to increase the resistance to fracture propagation and weaken the driving force of fracture propagation, thereby suppressing the fracture height.

[0171] In addition, in the embodiments of the present invention, software can also be designed to implement the above control: the software design includes method one: multivariate linear fitting method, which combines the influence law of each determined parameter on the crack propagation driving force and resistance to obtain the weight factor of each geological and engineering influencing factor on the crack height, and constructs a multivariate fitting model of each influencing factor and dynamic-support crack height to quickly obtain the crack height under different geological-engineering factors and process conditions.

[0172] A multiple linear fitting algorithm was used to orthogonally analyze the influence of different geological and engineering factors on the dynamic fracture height and the prop fracture height, thereby obtaining a fracture height prediction model. For the dynamic fracture height, the linear expression for calculating the dynamic fracture height was first determined as follows.

[0173] Dynamic seam height = weight coefficient 1 × factor 1 + weight coefficient 2 × factor 2 + weight coefficient 3 × factor 3 + ...; Support seam height = weight coefficient 1 × factor 1 + weight coefficient 2 × factor 2 + weight coefficient 3 × factor 3 + ...; By determining the weight coefficients of different influencing factors, the dynamic seam height prediction model under the influence of different factors can be quantitatively determined.

[0174] Method 2: Intelligent Approach: Intelligent approaches using deep learning are employed to predict dynamic and support joint heights, including but not limited to the following methods: Constructing a high-dimensional feature space based on geological and engineering parameters, filtering key features through principal component analysis (PCA) or recursive feature elimination (RFE), and using algorithms such as gradient boosting trees (XGBoost / LightGBM) or random forests, combined with Bayesian hyperparameter optimization and SHAP value interpretability analysis, to establish a prediction model for dynamic joint heights and support joint heights.

[0175] To address complex nonlinear relationships, a hybrid deep learning model of 1D-CNN-LSTM is designed. The model's generalization ability for small samples is improved through a transfer learning pre-training-fine-tuning strategy, and Monte Carlo Dropout or Bayesian neural network is used to quantify the uncertainty in prediction.

[0176] Further integrate multi-source data, use graph neural networks (GNN) to model the spatial topology of cracks, or integrate multimodal information based on the Transformer architecture to achieve prediction of dynamics and support crack height.

[0177] Finally, the models constructed by methods one and two can be used to determine the dynamic and support seam height under different combinations of influencing factors. The influencing factors are set as input parameters, and the dynamic and support seam height are set as solution parameters. A seam height prediction software under the orthogonal influence of multiple factors can be developed and obtained.

[0178] When the software performs fracture height prediction calculations for multiple fracturing processes, the process for determining dynamic fracture height and support fracture height for constant displacement pump fracturing is as follows: (a) Based on geological factors, the preliminary dynamic fracture height is obtained through simulation calculation; (b) Based on the obtained dynamic fracture height, considering engineering factors (such as displacement, particle size, density, viscosity, etc.), the preliminary support fracture height is calculated through simulation calculation; (c) After obtaining the support fracture height, considering the influence of engineering factors and support fracture height on fracture propagation, the maximum dynamic fracture height is finally calculated.

[0179] For the variable displacement pump fracturing process, the process for determining the dynamic fracture height and the support fracture height is as follows: (a) First, select the total fluid volume, assume constant displacement pump fracturing, and determine the dynamic fracture height and the support fracture height corresponding to different displacement conditions. This step is the same as the three steps in process one; (b) After obtaining the dynamic fracture height and the support fracture height under different fluid volume conditions, the dynamic fracture height and the support fracture height under the variable displacement are finally obtained by weighted averaging of the fracture height of each sub-stage mentioned above.

[0180] For the pump shutdown settling and proppant sealing process, the procedure for determining the dynamic crack height and proppant height is as follows: (a) Before pump shutdown, calculate the dynamic crack height and proppant height, following the same calculation procedure as in Process 2; (b) After pump shutdown, based on the existing proppant height parameters and the selected engineering parameters, determine the increase in crack propagation resistance, and then correct the dynamic crack height based on the new crack propagation resistance. The corresponding software development can be implemented based on the above design approach.

[0181] The above-described embodiments are merely descriptions of the implementation methods of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for optimizing and selecting parameters of high-controllability fracturing technology in tight reservoirs, characterized in that, include: Obtain geological data of the fracturing area; Based on the geological data, a true triaxial fracturing physical simulation experiment was conducted to preliminarily determine the expansion law of dynamic fracture height under different geological conditions and pumping conditions. Through proppant migration experiments in hydraulic fracturing fractures, the intra-fracture migration and accumulation height evolution of proppant under different pumping conditions were preliminarily determined. A physical model of the hydraulic fracturing fracture is constructed, and a numerical simulation model of the fracture height evolution is constructed based on the physical model of the hydraulic fracturing fracture, the proppant evolution law in the fracture, and the proppant evolution law in the fracture. The sensitivity of various parameters to hydraulic fracturing height was analyzed by combining physical models and numerical simulation models. Based on the sensitivity of each parameter to the height of the hydraulic crack, optimization methods for each parameter are obtained under different parameter conditions. The numerical simulation model for the evolution of seam height includes: Constructing a numerical simulation model for hydraulic fracturing fracture propagation: By introducing cohesive fracture elements into the fracture model characterizing the fracture process zone using the finite element method, and embedding the cohesive fracture elements between the finite element meshes of the cohesive fracture model, the propagation of the fracturing fracture is simulated by the sequential failure of the cohesive fracture under fluid injection conditions, thus obtaining a numerical simulation model of fracturing fracture propagation. Constructing a numerical simulation model for proppant transport: A numerical simulation model of proppant migration was obtained by characterizing the proppant transport carried by the sand-fluid using a multiphase flow simulation method. For multiphase flow simulation methods, the governing equations are discretized and solved before numerical simulation, so that the mass conservation equations and momentum conservation equations of the proppant transport model are transformed from partial differential equations that are difficult to solve directly into a set of algebraic equations that are easy to solve in numerical simulation. A numerical simulation model of fracture height evolution was obtained by combining the numerical simulation model of hydraulic fracturing fracture propagation and the numerical simulation model of proppant migration.

2. The method for optimizing and selecting parameters of high-controllability technology for pressure fracture in tight reservoirs according to claim 1, characterized in that, When conducting true triaxial fracturing physical simulation experiments, ensure that the fracture propagation characteristics of the experiment and the fracturing engineering site are similar; Among them, fracture propagation characteristics include the resistance of rock fracturing, the resistance of fracturing fluid friction along the path, and the resistance of fracturing fluid filtration into the formation.

3. The method for optimizing and selecting parameters of high-controllability technology for pressure fracture in tight reservoirs according to claim 1, characterized in that, The analysis of the sensitivity of various parameters to hydraulic fracture height by combining physical models and numerical simulation models includes: First, physical simulation is performed using a hydraulic fracturing fracture physical model to analyze the influence of various parameters included in geological and engineering factors on dynamic fracture height and support fracture height, thereby obtaining the overall parameter influence law. Then, numerical simulation is carried out through numerical simulation model to conduct in-depth analysis of the parameters included in the geological and engineering factors, and to quantitatively determine the influence of each parameter on the dynamic elevation and support joint height. Finally, sensitivity analysis was conducted, using the ratios of the changes in dynamic elevation and support joint height to the changes in each parameter as sensitivity factors to determine and rank the sensitivity of dynamic elevation and support joint height to different geological and engineering parameters.

4. The method for optimizing and selecting parameters of high-controllability technology for pressure fracture in tight reservoirs according to claim 1, characterized in that, When the parameters are pump injection rate, pump shutdown time, sand content ratio in the proppant, and particle size in the proppant, the optimization methods include: Reduce the pump flow rate and control it within the first preset range; advance the pump stop time and control it within the second preset range. Reduce the proportion of sand in the proppant and increase the particle size of the proppant particles.

5. The method for optimizing and selecting parameters of high-controllability technology for pressure fracture in tight reservoirs according to claim 1, characterized in that, When the parameter is a proppant type, the optimization methods include: Two types of proppant were selected: floating and sinking. By combining the numerical simulation model of crack height evolution and the content ratio of floating proppant and sinking proppant as influencing factors, simulation analysis was conducted to determine the critical ratio of floating proppant to sinking proppant that is conducive to equal critical proppant height at the upper and lower ends of the crack and to equidirectional expansion of the crack at the upper and lower sides of the crack height. By adjusting the different ratios of floating proppant and sinking proppant, the differential propagation of the upper and lower sides of the hydraulic fracture can be optimized.

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