A method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs

Abstract

The present invention discloses a method for evaluating the influence of weak structures on large-scale fracturing construction of deep heat reservoirs, which relates to the technical field of exploration and development of deep high-temperature geothermal reservoirs. Based on the detailed characterization and mechanical property research of weak structures of deep heat reservoirs, the present invention identifies the spatial distribution of weak structures of deep heat reservoirs, deploys well locations and well patterns, optimizes fracturing layers, and comprehensively evaluates the fracturing ability of the heat reservoirs. On this basis, a heat-fluid-solid coupling damage model THMD and a heat-fluid-solid-chemical coupling damage model THMCD are established to study the activation conditions of native weak structural surfaces, evaluate the filtration characteristics of weak structures, and the maximum displacement that can be safely fractured. Based on the above research, triaxial fracturing physical simulation and numerical simulation research are carried out to clarify the influence of weak structures on fracturing crack expansion and their influence on seepage, and reveal the influence mechanism of weak structures under high temperature and pressure conditions of deep heat reservoirs on large-scale fracturing of deep heat reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of deep high-temperature geothermal reservoir exploration and development, and in particular to a method, device, equipment and medium for evaluating the impact of weak structures on large-scale fracturing construction of deep geothermal reservoirs. Background Art

[0002] The influence of weak structure on large-scale fracturing of deep thermal reservoirs is more complicated than that of oil and gas reservoirs and coal reservoirs, which is mainly reflected in four aspects: ① Deep thermal reservoirs generally have block-like structures, and weak structures inside the reservoirs are generally not developed, making it difficult to create reservoirs through fracturing. To make up for this deficiency, it is extremely important to find and implement weak structures inside the reservoirs, evaluate the fracturing ability of thermal reservoirs, and then optimize well location design and well pattern deployment; ② Oil and gas reservoirs are generally limited to a complete closed structure or confined to a closed permeable rock body. Reservoir fracturing transformation generally does not need to consider the problem of fracturing fluid loss along the weak structure surface, while deep thermal reservoir fracturing transformation, due to the high temperature and high pressure of thermal reservoirs, and in the horizontal direction, ③ Temperature is an important characteristic parameter of deep thermal reservoirs. Numerical simulations of deep thermal reservoir fracturing reconstruction need to consider the effect of the temperature field, namely the four-field coupling of heat-fluid-solidification-chemical (THMC), which is more complex than the three-field coupling of fluid-solidification-chemical (THM) in traditional oil and gas reservoirs and coal reservoirs. ④ The morphology of natural weak structural surfaces, especially the faults, cracks, and pores developed in deep thermal reservoirs, has a stress concentration effect, which seriously interferes with the expansion of artificial fractures and easily induces earthquake risks.

[0003] At present, the impact of weak structures on deep thermal reservoirs during large-scale fracturing is usually evaluated by numerical simulation and emulation methods. Finite element analysis software is used to perform numerical simulations on deep thermal reservoirs. In the simulations, the influence of weak structures is taken into account, and the stress distribution, crack propagation path and fluid flow of the reservoir during fracturing are analyzed to predict the fracturing effect and evaluate the impact of weak structures through simulation results. However, these numerical simulation and emulation methods usually only focus on analyzing the internal conditions of the reservoir during fracturing, while ignoring the impact of weak structures on large-scale fracturing construction of deep thermal reservoirs under the multi-field coupling of reservoir structure, temperature field, seepage field, stress field and chemical field during fracturing. As a result, when evaluating the impact of weak structures on deep thermal reservoirs during large-scale fracturing, the results deviate greatly from the actual evaluation results, making it difficult to reflect the true interaction between weak structures and deep thermal reservoirs. Summary of the Invention

[0004] The embodiment of the present invention provides a method for evaluating the impact of weak structures on large-scale fracturing construction of deep heat reservoirs, which can solve the problem in the existing technology that the current means usually only focus on analyzing the internal conditions of the reservoir during the fracturing process, but ignore the impact of weak structures on large-scale fracturing construction of deep heat reservoirs under the multi-field coupling of reservoir structure, temperature field, seepage field, stress field and chemical field during fracturing. As a result, when evaluating the impact of weak structures on deep heat reservoirs in large-scale fracturing, the results deviate greatly from the actual evaluation results, making it difficult to reflect the actual interaction between weak structures and deep heat reservoirs.

[0005] An embodiment of the present invention provides a method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs, comprising the following steps:

[0006] Obtaining the fracturing characteristics of the deep thermal reservoir; the fracturing characteristics characterize the internal rock brittleness, internal weak structure development characteristics and internal ground stress distribution of the deep thermal reservoir during fracturing;

[0007] Obtain the deformation characteristics and fracture propagation characteristics of weak structures within deep thermal reservoirs under the coupled effects of heat, fluid, solid, and chemical fields. Determine the fracturing parameters and construction parameters for large-scale fracturing of deep thermal reservoirs without inducing earthquakes based on these characteristics. These characteristics characterize the conditions under which fracturing fluid enters weak structures, causing them to stretch and expand, and fracture propagation within them, thereby assessing the likelihood of inducing earthquakes.

[0008] Based on the fracturing characteristics of deep thermal reservoirs, as well as the fracturing and construction parameters during fracturing, a large-scale fracturing simulation of deep thermal reservoirs was conducted to obtain the interaction between the deep thermal reservoir and the internal weak structure during the dynamic expansion of the fracture network, including fluid flow, heat transfer, and rock deformation.

[0009] Based on the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network, the impact of weak structure on the large-scale fracturing of deep thermal reservoirs is evaluated.

[0010] Preferably, obtaining the fracturing characteristics of the deep heat reservoir includes:

[0011] Conduct drilling research and logging analysis on deep heat reservoirs to obtain the spatial distribution characteristics of the geometric, physical and mechanical properties of deep heat reservoirs;

[0012] Using diamond wire cutting, downhole cores drilled from deep thermal reservoirs were made into standard rock samples. Triaxial mechanical tests were then conducted on these standard rock samples under different temperatures and confining pressures to obtain the stress-strain curves of the rocks under different conditions, as well as the evolution characteristics of the deep thermal reservoir's compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle.

[0013] Based on the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of deep thermal reservoirs, a constitutive model of nonlinear rock damage is established to simulate the damage evolution law of rocks in deep thermal reservoirs during stress.

[0014] Using fractal methods, a mechanical brittleness index model reflecting the deformation and failure process of rocks in deep thermal reservoirs was established to simulate the brittle characteristics, activation conditions, and expansion mode of weak structures in deep thermal reservoirs.

[0015] A three-dimensional multi-attribute model of deep heat reservoirs with embedded weak structures is constructed. The model includes the ground stress field and temperature field. The model is used to reconstruct the characteristics of the ground stress field and temperature field of the high-temperature rock mass. Based on the damage evolution law of the deep heat reservoir, the brittle characteristics, activation conditions and expansion mode of the weak structure, and the ground stress field and temperature field of the high-temperature rock mass, the fracturing characteristics of the deep heat reservoir are obtained.

[0016] Preferably, the acquisition of the deformation characteristics and the fracturing crack expansion characteristics of the weak structure includes:

[0017] Conduct matrix acidification, hydraulic fracturing, and acid fracturing experiments on deep thermal reservoirs. During the experiments, the ground stress difference, the inclination angle of the weak structural surface, the cohesion of the weak structural surface, the internal friction angle of the weak structural surface, and the tensile strength of the weak structural surface were taken into account to simulate the force mechanism of the weak structural surface during the actual fracturing process and obtain the activation conditions of the original weak structural surface in the deep thermal reservoir.

[0018] Among them, the activation conditions are the activation effect of temperature and the propagation mode of artificial cracks on the original weak structural surface;

[0019] A thermal-fluid-solid coupled damage model THMD and a thermal-fluid-solid-chemical coupled damage model THMCD are established; the deformation and failure characteristics of natural weak structural surfaces under multi-field coupling are simulated; the deformation and failure characteristics of natural weak structural surfaces are the deformation characteristics of the weak structure and the fracturing crack expansion characteristics, including: under the interference of artificial cracks, the weak structure undergoes tensile and shear damage, and the conditions under which the weak structural surface is tensilely stretched and the fracturing crack turns to expand toward the weak structural surface after the fracturing fluid enters the weak structural surface are obtained.

[0020] Preferably, the determination of the fracturing parameters and construction parameters during large-scale fracturing construction of deep thermal storage without inducing earthquakes includes:

[0021] Based on the conditions of tensile expansion of weak structural surfaces and the diversion of hydraulic fractures to weak structural surfaces, a weak structural surface reactivation criterion was constructed. This criterion takes into account the mechanical properties of the weak structural surface, the injection conditions of the fracturing fluid, and the multi-field coupling effect to evaluate the filtration characteristics of the weak structural zone and the possibility of induced earthquakes.

[0022] Based on the activation conditions of the original weak structural surfaces in deep thermal reservoirs, the filtration characteristics of the weak structural zones and the possibility of induced earthquakes, the maximum displacement, construction pump pressure, total injected fluid volume and effective stimulation volume (SRV) that can be safely implemented in deep thermal reservoirs are predicted. The fracturing parameters and construction parameters for large-scale fracturing construction in deep thermal reservoirs are also predicted.

[0023] Preferably, obtaining the interaction between the deep heat reservoir and the internal weak structure in the process of dynamic expansion of the fracture network, including fluid flow, heat transfer and rock deformation, comprises:

[0024] Prepare multiple multi-fracture rock samples and perform triaxial fracturing physical simulations on them under different injection media, heat treatment temperatures, number of cyclic heating treatments, horizontal stress differences, and different displacement conditions to obtain the initiation and expansion process of the fracture network in deep thermal reservoir rocks, as well as the pressure response law;

[0025] Fracturing experiments were conducted on multi-fracture rock samples using room-temperature fracturing fluid to simulate low-temperature shock. Acoustic emission equipment was used to monitor the evolution of the fracture network during the low-temperature shock process. Micro-CT scanning of the fracture network structure of the rock samples before and after the low-temperature shock was performed, and a detailed description of the complex fracture morphology was obtained to understand the dynamic expansion process of the fracture network in deep thermal reservoir rocks.

[0026] Prepare full-diameter test rock samples, create cracks in them, and test the seepage parameters of the test rock samples under different crack widths, confining pressures, and flow rates to obtain the multi-scale seepage laws of deep heat reservoirs.

[0027] Based on the dynamic expansion process of the fracture network in deep thermal reservoir rocks and the multi-scale seepage law, the mathematical and physical control equations of the stress field, temperature field, and seepage field of high-temperature rock mass at in-situ scale are established. The influence relationship between the damage coefficient of different injection media and the heat-fluid-solidification-chemical equation is obtained to form a temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks.

[0028] Based on the temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks, an in-situ scale complex fracture network THMD fully coupled fracturing model is constructed. The in-situ scale complex fracture network THMD fully coupled fracturing model is a heat-fluid-solid-damage fully coupled fracturing model.

[0029] Based on the in-situ scale complex fracture network THMD fully coupled fracturing model, the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network is simulated.

[0030] The embodiment of the present invention further provides a device for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs, comprising:

[0031] A fracturing characteristic module is used to obtain the fracturing characteristics of the deep thermal reservoir; the fracturing characteristics characterize the internal rock brittleness, internal weak structure development characteristics and internal ground stress distribution of the deep thermal reservoir during fracturing;

[0032] A simulation module is used to obtain the deformation characteristics and fracture propagation characteristics of weak structures within deep thermal reservoirs under the coupled effects of heat, fluid, solid, and chemical fields. These characteristics are used to determine the fracturing parameters and construction parameters for large-scale fracturing of deep thermal reservoirs without inducing earthquakes. These characteristics characterize the conditions under which fracturing fluid enters weak structures, causing them to stretch and expand, and fracture propagation within them, thereby assessing the likelihood of inducing earthquakes.

[0033] An evaluation module is used to simulate large-scale fracturing operations for deep thermal reservoirs based on the fracturing characteristics of the deep thermal reservoirs and the fracturing and operation parameters during fracturing operations. This module aims to understand the interaction between the deep thermal reservoirs and internal weak structures during the dynamic expansion of the fracture network, including fluid flow, heat transfer, and rock deformation.

[0034] Based on the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network, the impact of weak structure on the large-scale fracturing of deep thermal reservoirs is evaluated.

[0035] An embodiment of the present invention further provides an electronic device, including a memory and a processor;

[0036] The memory is used to store computer programs;

[0037] The processor is configured to implement the steps of the above-mentioned method for evaluating the impact of weak structures on large-scale fracturing construction of deep thermal reservoirs when executing the computer program stored in the memory.

[0038] An embodiment of the present invention further provides a computer-readable storage medium for storing a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for evaluating the impact of weak structures on large-scale fracturing construction of deep thermal reservoirs.

[0039] The embodiment of the present invention provides a method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs. Compared with the prior art, the method has the following beneficial effects:

[0040] The present invention first obtains the fracturing characteristics of deep thermal reservoirs, and predicts the fracturing parameters and construction parameters of deep thermal reservoirs during large-scale fracturing construction without inducing earthquakes by establishing a heat-fluid-solid coupling damage model THMD and a heat-fluid-solid-chemical coupling damage model THMCD; then, based on the fracturing characteristics of deep thermal reservoirs and the fracturing parameters and construction parameters during fracturing construction, the fluid flow, heat transfer and rock mass of deep thermal reservoir rocks during the dynamic expansion of the fracture network are evaluated from the perspective of large-scale fracturing construction simulation of deep thermal reservoirs. The interaction law of deformation; this process takes into account the reservoir structure represented by the fracturing characteristics of deep heat reservoirs during fracturing, as well as the temperature field, seepage field, stress field and chemical field in the fracturing process represented by the interaction law of fluid flow, heat transfer and rock deformation. That is, it comprehensively considers the influence of weak structure on large-scale fracturing construction of deep heat reservoirs under the multi-field coupling of reservoir structure, temperature field, seepage field, stress field and chemical field during fracturing, and can truly and accurately evaluate the influence of weak structure on large-scale fracturing of deep heat reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of the overall process of a method for evaluating the impact of weak structures on large-scale fracturing construction in deep thermal reservoirs provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] See also Figure 1 The embodiment of the present invention provides a method for evaluating the impact of weak structures on large-scale fracturing construction of deep thermal reservoirs, comprising the following steps:

[0044] Step 1: Study on the three-dimensional spatial distribution characteristics of weak structures in deep heat reservoirs.

[0045] By integrating geological, drilling, logging, and testing information and utilizing data fusion and model building techniques, the spatial distribution of the geometric, physical, and mechanical properties of deep heat reservoirs is revealed. Based on a systematic analysis of the geological characteristics of deep heat reservoirs, standard rock samples are prepared from outcrops or downhole cores using diamond wire cutting. Real-time triaxial mechanical experiments are then conducted on the rocks under varying temperatures and confining pressures, achieving dual coupling of temperature and pressure. Based on the stress-strain curves obtained from these experiments, the evolution of compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle under different pressure-stabilizing coupling parameters is analyzed. A constitutive model for nonlinear damage in rock is established, and the damage evolution patterns of rock mechanical parameters are analyzed. Using fractal methods and other methods, a mechanical brittleness index model is developed to reflect the entire process of rock deformation and failure. The brittleness, activation conditions, and expansion patterns of weak structures are analyzed, and a three-dimensional multi-attribute model (in-situ stress and temperature fields) of deep heat reservoirs with weak structures is constructed, enabling reconstruction of the in-situ stress and temperature fields of high-temperature rock masses. The fracturing potential of the reservoir is comprehensively evaluated based on rock brittleness, the development of weak structures, and the distribution of in-situ stress.

[0046] Fractal theory combines fractal geometry, physics, and solid mechanics to describe the irregularity, nonlinearity, and randomness of rock deformation and failure. By studying the distribution pattern of rock debris and calculating its fractal dimension, a correlation model between the fractal dimension of rock debris and the rock brittleness index is established. Based on this correlation model, elastic analysis, plastic internal force redistribution analysis, elastoplastic analysis, plastic limit analysis, and experimental analysis methods are used to study the mechanical behavior of weak structures. In-situ stress considers factors such as stratum depth, crustal thickness, lithology, seismic activity, and geological structure to study the influence of weak structures on the physical and mechanical properties of rocks, including changes in rock permeability, porosity, elastic modulus, and Poisson's ratio. Petrel software is used for three-dimensional simulation to establish a geological model framework. The porosity and permeability models are established using the sequential Gaussian interpolation method, and a temperature field model is established in combination with temperature data. Considering high in-situ stress, the thermal and in-situ stress fields of the support structure and surrounding rock are studied.

[0047] Step 2: Study the impact of the weak structure of deep heat reservoir on fracturing construction.

[0048] Using a technical method that combines indoor experiments and numerical simulations, matrix acidizing, hydraulic fracturing, and acid fracturing experiments were carried out. Taking into account the ground stress difference, the inclination angle of the weak structural surface, the cohesion of the weak structural surface, the internal friction angle of the weak structural surface, and the tensile strength of the weak structural surface, the activation conditions of the original weak structural surface were studied, that is, the activation effect of temperature and the expansion mode of artificial cracks (diversion, penetration) on the original weak structural surface; thermal-fluid-solid coupled damage (THMD) and thermal-fluid-solid-chemical coupled damage (THMCD) models were established to study the deformation of natural weak structural surfaces under multi-field coupling. Destruction characteristics, that is, tensile and shear damage occurs under the interference of artificial fractures, and the conditions for fracturing fluid to enter the weak structural surface, causing the weak structural surface to be tensilely opened and the fracturing cracks to turn to and expand into the weak structural surface, are analyzed. The reactivation criteria of the weak structural surface are constructed, and the filtration characteristics of the weak structural zone and the possibility of inducing earthquakes are evaluated; the maximum displacement, construction pump pressure, total injection fluid volume and effective stimulation volume (SRV) that can be safely implemented are predicted and estimated, and the fracturing parameters and construction parameters are optimized to guide the optimization of the fracturing construction plan and clarify the influence of the weak structure of deep heat reservoirs on fracturing construction.

[0049] Specifically:

[0050] Indoor experiments simulate deep thermal reservoir environments by precisely controlling experimental conditions, conducting matrix acidification, hydraulic fracturing, and acid fracturing experiments. During the experiments, the mechanical response of rock samples and crack expansion are monitored in real time to obtain experimental data. Numerical simulation uses advanced numerical calculation software to establish a deep thermal reservoir geological model and simulate the fracturing construction process under different ground stress conditions and weak structural surface characteristics. Through numerical simulation, the expansion path, morphology, and fracturing effect of cracks can be predicted, providing theoretical support for indoor experiments. The experimental data obtained from indoor experiments are compared and analyzed with the numerical simulation results to verify the accuracy of the model, and the numerical simulation parameters are corrected according to the experimental results to improve the accuracy and reliability of the simulation.

[0051] Matrix acidizing is achieved by squeezing acid into the pores of the reservoir at a pressure lower than the fracture pressure of the reservoir rock, dissolving particles and blockages in the pore space, expanding the pore space, and increasing the permeability of the formation. Hydraulic fracturing is achieved by pumping liquid at high pressure to form cracks in the formation and improve the permeability of the formation. During the hydraulic fracturing process, the expansion of the cracks is affected by factors such as ground stress and rock mechanical properties. Acid fracturing combines the principles of acidizing and hydraulic fracturing. Cracks are first formed through hydraulic fracturing, and then acid is injected to dissolve the rock on the crack wall and expand the fracture conductivity. Acid fracturing can more effectively transform the reservoir and increase oil and gas well production.

[0052] Different in-situ stress differences significantly influence the strength and stability of rock masses. During fracturing, these differences can affect the direction and morphology of crack propagation, thereby affecting the fracturing effect. The inclination angle of weak structural surfaces significantly affects the strength of rock masses. Different inclination angles can lead to different failure modes, such as bedding landslides and shear failures, which can affect the safety and stability of the project. Mechanical parameters such as cohesion, internal friction angle, and tensile strength of weak structural surfaces determine their shear and tensile strengths. During fracturing, these mechanical parameters of weak structural surfaces affect the propagation path and morphology of cracks, thereby affecting the fracturing effect. Temperature changes can affect the physical and chemical properties of rock masses, such as the thermal expansion coefficient and elastic modulus. In deep thermal reservoir environments, high temperatures can significantly alter the mechanical properties of rock, affecting the stability and activation conditions of weak structural surfaces. The propagation mode of artificial fractures can also affect the activation conditions of weak structural surfaces. When cracks deflect, they may bypass the weak structural surface, minimizing damage to it. However, when cracks pass through the weak structural surface, they may directly damage it, affecting its stability.

[0053] The thermal-fluid-solid coupling damage (THMD) model takes into account the thermal-fluid-solid coupling effect. By simulating the hydraulic fracture propagation process, it reveals the influence of temperature, seepage, and stress fields on fracture propagation, providing a theoretical basis for optimizing fracturing construction schemes. The thermal-fluid-solid-chemical coupling damage (THMCD) model is established based on the gas heat flow equation, turbulence equation, solid heat conduction equation, and thermoelasticity equation. It analyzes the compressible thermal flow characteristics of the gas in the cavern during the injection and production of hydrogen storage in lined caverns and the thermodynamic response of the lining layer and surrounding rock. The thermal-fluid-solid coupling damage (THMD) model and the thermal-fluid-solid-chemical coupling damage (THMCD) model comprehensively consider factors such as ground stress, temperature, seepage, and chemical reactions to study their influence on rock deformation and failure. At the same time, they study the physical and mechanical properties of the rock mass, such as stress, strength, deformation, failure, and fluid-heat-chemical transmission, to solve the deformation and stability problems of engineering rock masses.

[0054] Under the interference of artificial cracks, cracks cause harm to weak structures, affecting the internal force distribution, shear resistance and deformation probability of the structure; after the fracturing fluid enters the weak structural surface, the high-pressure fracturing fluid generates internal pressure on the cracks and weak surfaces at all levels, causing the cracks and weak surfaces to expand and extend inside the space. When the pumping pressure of the high-pressure fracturing fluid is large enough, the fracturing fluid will enter the interior of the weak structural surface, causing the weak structural surface to be stretched and opened. Based on the principle of minimizing the energy release rate, the conditions for the strain energy release rate of hydraulic cracks extending in any direction when considering factors such as ground stress and friction are obtained, and based on the mechanical properties and geological characteristics of the weak structural surface, the strain energy release rate of hydraulic cracks extending in any direction is obtained. Conditions are established and reactivation criteria are constructed to predict and control the activation behavior of weak structural surfaces; weak structural surfaces are highly permeable, prone to compression deformation, have poor self-stabilization ability, and contain many clay minerals. The filtration loss characteristics of weak structural zones can be evaluated by combining laboratory tests and numerical simulations; when predicting the possibility of induced earthquakes, the influence of weak structural surfaces on the dynamic response of seismic slopes is studied, including the influence on the evaluation indicators of slope dynamic response and the influence on the spatial distribution of slope seismic energy and the plastic failure mode of slopes, to provide a scientific basis for earthquake prediction and slope stability evaluation and to assess its possibility of inducing earthquakes.

[0055] The maximum displacement that can be used for safe fracturing is determined based on the capacity of the fracturing equipment, the pressure bearing capacity of the wellhead device, the formation breakdown pressure, etc. The prediction of the maximum pump pressure at the wellhead needs to consider the maximum pump pressure that the fracturing equipment and wellhead device can withstand. The construction pump pressure can be predicted by predicting the formation breakdown pressure and reducing the friction along the way. The calculation of the total injection volume needs to consider factors such as the geological conditions of the formation and the thickness of the fracture layer to calculate the total injection volume of the fracturing fluid that can be used for safe fracturing. The total volume of the fracturing fluid is the sum of the volumes of the pre-fluid, the sand-carrying fluid, and the displacement fluid. Event screening and optimization are carried out based on the hydraulic fracturing mechanism, the rupture time sequence of the event points, the spatial combination characteristics, and the credibility of the event. The geometric characteristics of the fracture (fracture length, fracture width, fracture height) are quantitatively interpreted to calculate the effective stimulation volume (SRV). A reservoir hydraulic fracturing model was established based on the maximum displacement, construction pump pressure, total injected fluid volume, and effective stimulation volume (SRV) for safe fracturing. The first-layer fracturing parameters were optimized based on the expansion of hydraulic fractures within the reservoir. The first-layer fracturing parameters were then used to calculate the fracture morphology of the upper layer. The non-connection of the upper and lower layer fractures was used as the criterion for judging the fracture morphology of the upper layer under different interlayer thicknesses. The interlayer thickness that could prevent the connection between the upper and lower layer fractures was determined. Finally, the final fracturing layer was determined, and the construction parameters and fracturing parameters of the upper layer were optimized. In guiding the optimization of the fracturing construction plan, the presence of weak structural surfaces will affect the initiation pressure of hydraulic fracturing. At the same time, weak structures in deep thermal reservoirs (such as natural weak surfaces and cleats) will affect the initiation mode of hydraulic fracturing fractures, and weak structural surfaces will affect the expansion direction of hydraulic fractures.

[0056] Step 3: Study on the impact of the weak structure of deep heat reservoir on the effect of fracturing construction.

[0057] Prepare random multi-fracture rock samples, carry out research on the cracking and expansion of deep thermal reservoir rock fracture network and pressure response law under different injection media (water, acid, CO2), heat treatment temperature, number of cyclic heating treatments, horizontal stress difference, different displacement and other conditions, use room temperature fracturing fluid to simulate low temperature shock, use acoustic emission and tracer methods to monitor the evolution characteristics of fracture network, use micro CT to scan the fracture network of rock samples before and after the experiment, and describe the complex fracture morphology; prepare full diameter test rock samples, prepare artificial fractures, carry out seepage parameter tests under different fracture widths, confining pressures and flow rates, and analyze the seepage characteristics in real time, clarify the main controlling factors affecting the fluid seepage law, accurately characterize the dynamic expansion process of complex fracture network, and reveal the multi-scale seepage law of different injection media; based on the evolution of rock microscopic damage and its destruction mechanism, combined with Through preliminary experimental tests and theoretical analysis, mathematical and physical control equations for the stress field, temperature field, and seepage field of high-temperature rock masses at an in-situ scale were established, and the influence relationship between the damage coefficient of different injection media and the heat-fluid-solidification-chemical equation was proposed, forming a temperature-seepage-stress-chemistry-damage constitutive model of deep heat storage rocks. On this basis, an in-situ scale THMD fully coupled fracturing model of complex fracture networks was constructed to analyze the interaction between fluid flow, heat transfer, and rock deformation during the initiation and expansion of the fracture network. The influence of complex geological factors such as different ground temperatures, thermal conductivity, ground stress, pore pressure, and natural weak structural surface morphology, as well as different fracturing displacements, fracturing fluid types, and temporary plugging and diversion on the initiation, expansion, and stress field changes of complex fracture networks were studied to clarify the influence of the weak structure of deep heat storage on the fracturing effect.

[0058] Specifically:

[0059] Tin bars were prepared to simulate cracks, and mortar materials were prepared to simulate rock materials. The tin bars and mortar materials were mixed and stirred so that the tin bars were randomly distributed in the mortar materials. The mixture was placed into a molding mold and vibrated to form it so that the tin bars were randomly distributed, and multi-crack rock samples were prepared. The effects of different injection media (water, acid, CO2) on crack propagation were studied, and it was found that supercritical CO2 will lead to more complex crack morphology, which can play a synergistic role with low-temperature induced thermal stress during the thermal reservoir fracturing process. The evolution law of the mechanical elastic-plastic characteristics of medium- and deep-layer geothermal reservoirs under high temperature was studied, and it was found that high temperature has an important influence on the direction and propagation of artificial cracks. High temperature can enhance the plasticity of rocks and change the propagation mode of cracks. The effects of thermal cycling on the macroscopic mechanical properties of rocks and crack propagation were studied, and it was found that an increase in the number of thermal cycles will reduce the crack initiation stress of rocks and affect the propagation capacity of cracks. The effect of the horizontal principal stress ratio on the propagation evolution of the fracture network was studied. The influence of horizontal principal stress ratio was studied, and it was found that with the increase of horizontal principal stress ratio, the range of hydraulic fracture network in x-axis direction gradually decreased, and the resistance of fracture extension increased; the influence of different displacement on the extension of hydraulic fracture was studied, and it was found that the injection of low viscosity fracturing fluid with large displacement or high viscosity fracturing fluid with small or medium displacement could connect the caves with smaller angle and closer distance to the initial extension direction of hydraulic fracture; normal temperature fracturing fluid was used to simulate low temperature shock, that is, the low temperature shock test was carried out by switching the product between high temperature box and low temperature box to evaluate the performance of the material in low temperature environment; acoustic emission and tracer were used to monitor the evolution characteristics of fracture network, that is, acoustic emission was used to monitor the rock fracture process, revealing the formation mechanism of hydraulic fracture network, and tracer was used to monitor the flow path of fracturing fluid, and studying the evolution characteristics of fracture network; at the same time, micro-CT was used to scan the fracture network of rock samples before and after the experiment, and the CT scanning data before and after fracturing were processed to quantitatively describe the parameters such as fracture opening, inclination, fracture rate, etc.

[0060] When preparing full-diameter test rock samples, the natural rock sample powder particle size range is sorted according to the pore characteristic test results, and mixed with organic adhesives in different weight percentages. The prepared viscous mixture is applied to the joint surface of the damaged horizontal section rock sample to bond the three-layer blocks and fill the depressions and other cracked parts on the side of the core column. After filling, it is compacted and bonded to obtain the test rock sample; the Brazilian splitting tensile crack induction method is adopted, and pressure is applied to the side of the cylindrical concrete specimen using a pressure testing machine to load and form tensile stress, thereby generating cracks on the concrete surface and forming artificial cracks; based on the multi-functional mechanical experimental instrument MTS815 triaxial seepage test system, seepage parameter tests are carried out under different crack widths, confining pressures, and flow rates. Numerical simulation methods, such as the finite element method or the finite difference method, are used to solve the seepage field, generate high-precision seepage data graphs, and analyze the seepage characteristics.

[0061] In determining the main controlling factors affecting fluid seepage patterns, the strong polar molecular interaction at the solid-liquid interface causes a boundary layer to be adsorbed on the pore wall, preventing it from participating in the flow, thus generating nonlinearity. In the same low-permeability porous medium, the greater the molecular force on the solid-liquid surface, the higher the starting pressure gradient. Under the same pressure gradient, the smaller the flow rate, the lower the permeability of the porous medium, and the greater the influence of the molecular forces between the solid and liquid surfaces on the seepage. After the permeability of the porous medium reaches a certain value, the influence of the solid surface molecules on the fluid seepage can be basically ignored, and the seepage transforms into a Darcy-type flow. As the pressure gradient gradually increases, the influence of the molecular forces on the solid-liquid surface on the seepage will gradually weaken. Then, the high-performance reservoir simulator tNavigator software FS1.1 was used to simulate fracture propagation, establish the maximum principal stress direction field, and simulate the expansion direction of different segment clusters to accurately characterize the dynamic expansion process of the complex fracture network and reveal the multi-scale seepage patterns of different injection media.

[0062] Starting from the mesostructure of rock materials, a numerical model describing the coupled effects of heat, seepage, stress and damage on the rock mesostructure is established based on mesoscopic damage mechanics, elastic thermodynamics and Biot's classical seepage mechanics theory. The injection pressure-time curves obtained by simulating the TOUGH-RFPA elastic model and damage model are used to analyze the influence of different injection media on the damage coefficient and the heat-fluid-solidification equation. The mechanism analysis method, system identification method and hybrid analysis method are used to analyze the above content and establish a coupled model of rock seepage field and stress field.

[0063] Based on the above research, Comsol software was used to simulate the THMD coupled model of rock hydraulic fracturing damage. Based on the assumptions of linear elastic fracture mechanics (LEFM), the stability and propagation trajectory of the cracks were controlled by calculating the stress intensity factor. Cracks were automatically set at any point and angle on the boundary to form a crack expansion function. The network can be arbitrarily adjusted along the propagating cracks to analyze the interaction between fluid flow, heat transfer, and rock deformation during the initiation and propagation of the fracture network.

[0064] Study the changes in the physical and mechanical properties of rocks under different geothermal conditions, and their impact on the initiation and expansion of fracture networks; study the heat transfer laws in rocks under different thermal conductivity conditions, and their impact on the initiation and expansion of fracture networks; study the stress distribution laws of rocks under different geostress conditions, and their impact on the initiation and expansion of fracture networks; study the flow laws of fluids in rocks under different pore pressure conditions, and their impact on the initiation and expansion of fracture networks; study the fracture patterns of rocks under different natural weak structural surface morphologies, and their impact on the initiation and expansion of fracture networks. At the same time, a large-scale true triaxial fracturing equipment was used to establish a temporary plugging and diverting fracturing physical simulation device and conduct experiments to study the laws of fracture initiation and expansion under different fracturing displacement conditions, as well as their influence on stress field changes; the laws of fracture initiation and expansion under different fracturing fluid types, as well as their influence on stress field changes, were studied; the influence of temporary plugging and diverting technology on fracture initiation and expansion, as well as its role in improving fracturing effects, were studied; based on the above research results, the influence of the weak structure of deep heat reservoirs on the physical and mechanical properties of rocks during fracturing was studied, the influence of the weak structure on the fracturing effect was studied, and the influence of the weak structure of deep heat reservoirs on the fracturing effect was clarified.

[0065] The present invention aims to solve the problem of pre-evaluation of the impact of weak structures on large-scale fracturing construction of deep heat reservoirs. Based on the detailed characterization and mechanical property research of weak structures of deep heat reservoirs, the spatial distribution of weak structures of deep heat reservoirs is identified, well locations and well patterns are deployed, fracturing layers are optimized, and the fracturing ability of heat reservoirs is comprehensively evaluated. Thermal-fluid-solid and thermal-fluid-solid-chemical coupled damage models THMD and THMCD are established to study the activation conditions of native weak structural surfaces, evaluate the filtration characteristics of weak structures and the maximum displacement that can be safely fractured (without inducing earthquakes). True triaxial fracturing physical simulation and numerical simulation research are carried out to clarify the influence of weak structures on the expansion of fracturing cracks and their influence on seepage, and reveal the influence mechanism of weak structures in large-scale fracturing of deep heat reservoirs.

[0066] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs, characterized in that: The following steps are involved: Obtaining the fracturing characteristics of the deep thermal reservoir; the fracturing characteristics characterize the internal rock brittleness, internal weak structure development characteristics and internal ground stress distribution of the deep thermal reservoir during fracturing; Obtain the deformation characteristics and fracture propagation characteristics of weak structures within deep thermal reservoirs under the coupled effects of heat, fluid, solid, and chemical fields. Determine the fracturing parameters and construction parameters for large-scale fracturing of deep thermal reservoirs without inducing earthquakes based on these characteristics. These characteristics characterize the conditions under which fracturing fluid enters weak structures, causing them to stretch and expand, and fracture propagation within them, thereby assessing the likelihood of inducing earthquakes. Based on the fracturing characteristics of deep thermal reservoirs, as well as the fracturing and construction parameters during fracturing, a large-scale fracturing simulation of deep thermal reservoirs was conducted to obtain the interaction between the deep thermal reservoir and the internal weak structure during the dynamic expansion of the fracture network, including fluid flow, heat transfer, and rock deformation. Based on the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network, the impact of weak structure on large-scale fracturing in deep thermal reservoirs is evaluated. Obtaining the deformation characteristics of the weak structure and the expansion characteristics of the fracturing cracks includes: Conduct matrix acidification, hydraulic fracturing, and acid fracturing experiments on deep thermal reservoirs. During the experiments, the ground stress difference, the inclination angle of the weak structural surface, the cohesion of the weak structural surface, the internal friction angle of the weak structural surface, and the tensile strength of the weak structural surface were taken into account to simulate the force mechanism of the weak structural surface during the actual fracturing process and obtain the activation conditions of the original weak structural surface in the deep thermal reservoir. Among them, the activation conditions are the activation effect of temperature and the propagation mode of artificial cracks on the original weak structural surface; Establish a thermal-fluid-solid coupled damage model (THMD) and a thermal-fluid-solid-chemical coupled damage model (THMCD); simulate and obtain the deformation and failure characteristics of natural weak structural surfaces under multi-field coupling; the deformation and failure characteristics of natural weak structural surfaces are the deformation characteristics of the weak structure and the fracturing crack propagation characteristics, including: under the interference of artificial cracks, the weak structure undergoes tensile and shear damage, and obtains the conditions under which the weak structural surface is stretched in tension and the fracturing crack turns to propagate toward the weak structural surface after the fracturing fluid enters the weak structural surface; The method of obtaining the interaction between deep heat storage and internal weak structure in fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network includes: Prepare multiple multi-fracture rock samples and perform triaxial fracturing physical simulations on them under different injection media, heat treatment temperatures, number of cyclic heating treatments, horizontal stress differences, and different displacement conditions to obtain the initiation and expansion process of the fracture network in deep thermal reservoir rocks, as well as the pressure response law; Fracturing experiments were conducted on multi-fracture rock samples using room-temperature fracturing fluid to simulate low-temperature shock. Acoustic emission equipment was used to monitor the evolution of the fracture network during the low-temperature shock process. Micro-CT scanning of the fracture network structure of the rock samples before and after the low-temperature shock was performed, and a detailed description of the complex fracture morphology was obtained to understand the dynamic expansion process of the fracture network in deep thermal reservoir rocks. Prepare full-diameter test rock samples, create cracks in them, and test the seepage parameters of the test rock samples under different crack widths, confining pressures, and flow rates to obtain the multi-scale seepage laws of deep heat reservoirs. Based on the dynamic expansion process of the fracture network in deep thermal reservoir rocks and the multi-scale seepage law, the mathematical and physical control equations of the stress field, temperature field, and seepage field of high-temperature rock mass at in-situ scale are established. The influence relationship between the damage coefficient of different injection media and the heat-fluid-solidification-chemical equation is obtained to form a temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks. Based on the temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks, an in-situ scale complex fracture network THMD fully coupled fracturing model is constructed. The in-situ scale complex fracture network THMD fully coupled fracturing model is a heat-fluid-solid-damage fully coupled fracturing model. Based on the in-situ scale complex fracture network THMD fully coupled fracturing model, the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network is simulated.

2. The method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs according to claim 1, characterized in that: The method of obtaining the fracturing characteristics of the deep heat reservoir includes: Conduct drilling research and logging analysis on deep heat reservoirs to obtain the spatial distribution characteristics of the geometric, physical and mechanical properties of deep heat reservoirs; Using diamond wire cutting, downhole cores drilled from deep thermal reservoirs were made into standard rock samples. Triaxial mechanical tests were then conducted on these standard rock samples under different temperatures and confining pressures to obtain the stress-strain curves of the rocks under different conditions, as well as the evolution characteristics of the deep thermal reservoir's compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle. Based on the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of deep thermal reservoirs, a constitutive model of nonlinear rock damage is established to simulate the damage evolution law of rocks in deep thermal reservoirs during stress. Using fractal methods, a mechanical brittleness index model reflecting the deformation and failure process of rocks in deep thermal reservoirs was established to simulate the brittle characteristics, activation conditions, and expansion mode of weak structures in deep thermal reservoirs. A three-dimensional multi-attribute model of deep heat reservoirs with embedded weak structures is constructed. The model includes the ground stress field and temperature field. The model is used to reconstruct the characteristics of the ground stress field and temperature field of the high-temperature rock mass. Based on the damage evolution law of the deep heat reservoir, the brittle characteristics, activation conditions and expansion mode of the weak structure, and the ground stress field and temperature field of the high-temperature rock mass, the fracturing characteristics of the deep heat reservoir are obtained.

3. The method for evaluating the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs according to claim 1, characterized in that: The determination of the fracturing parameters and construction parameters during large-scale fracturing construction of deep thermal storage without inducing earthquakes includes: Based on the conditions of tensile expansion of weak structural surfaces and the diversion of hydraulic fractures to weak structural surfaces, a weak structural surface reactivation criterion was constructed. This criterion takes into account the mechanical properties of the weak structural surface, the injection conditions of the fracturing fluid, and the multi-field coupling effect to evaluate the filtration characteristics of the weak structural zone and the possibility of induced earthquakes. Based on the activation conditions of the original weak structural surfaces in deep thermal reservoirs, the filtration characteristics of the weak structural zones and the possibility of induced earthquakes, the maximum displacement, construction pump pressure, total injected fluid volume and effective stimulation volume (SRV) that can be safely implemented in deep thermal reservoirs are predicted. The fracturing parameters and construction parameters for large-scale fracturing construction in deep thermal reservoirs are also predicted.

4. An evaluation device for the impact of weak structures on large-scale fracturing operations in deep thermal reservoirs, characterized in that: include: A fracturing characteristic module is used to obtain the fracturing characteristics of the deep thermal reservoir; the fracturing characteristics characterize the internal rock brittleness, internal weak structure development characteristics and internal ground stress distribution of the deep thermal reservoir during fracturing; A simulation module is used to obtain the deformation characteristics and fracture propagation characteristics of weak structures within deep thermal reservoirs under the coupled effects of heat, fluid, solid, and chemical fields. These characteristics are used to determine the fracturing parameters and construction parameters for large-scale fracturing of deep thermal reservoirs without inducing earthquakes. These characteristics characterize the conditions under which fracturing fluid enters weak structures, causing them to stretch and expand, and fracture propagation within them, thereby assessing the likelihood of inducing earthquakes. An evaluation module is used to simulate large-scale fracturing operations for deep thermal reservoirs based on the fracturing characteristics of the deep thermal reservoirs and the fracturing and operation parameters during fracturing operations. This module aims to understand the interaction between the deep thermal reservoirs and internal weak structures during the dynamic expansion of the fracture network, including fluid flow, heat transfer, and rock deformation. Based on the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network, the impact of weak structure on large-scale fracturing in deep thermal reservoirs is evaluated. Obtaining the deformation characteristics of the weak structure and the expansion characteristics of the fracturing cracks includes: Conduct matrix acidification, hydraulic fracturing, and acid fracturing experiments on deep thermal reservoirs. During the experiments, the ground stress difference, the inclination angle of the weak structural surface, the cohesion of the weak structural surface, the internal friction angle of the weak structural surface, and the tensile strength of the weak structural surface were taken into account to simulate the force mechanism of the weak structural surface during the actual fracturing process and obtain the activation conditions of the original weak structural surface in the deep thermal reservoir. Among them, the activation conditions are the activation effect of temperature and the propagation mode of artificial cracks on the original weak structural surface; Establish a thermal-fluid-solid coupled damage model (THMD) and a thermal-fluid-solid-chemical coupled damage model (THMCD); simulate and obtain the deformation and failure characteristics of natural weak structural surfaces under multi-field coupling; the deformation and failure characteristics of natural weak structural surfaces are the deformation characteristics of the weak structure and the fracturing crack propagation characteristics, including: under the interference of artificial cracks, the weak structure undergoes tensile and shear damage, and obtains the conditions under which the weak structural surface is stretched in tension and the fracturing crack turns to propagate toward the weak structural surface after the fracturing fluid enters the weak structural surface; The method of obtaining the interaction between deep heat storage and internal weak structure in fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network includes: Prepare multiple multi-fracture rock samples and perform triaxial fracturing physical simulations on them under different injection media, heat treatment temperatures, number of cyclic heating treatments, horizontal stress differences, and different displacement conditions to obtain the initiation and expansion process of the fracture network in deep thermal reservoir rocks, as well as the pressure response law; Fracturing experiments were conducted on multi-fracture rock samples using room-temperature fracturing fluid to simulate low-temperature shock. Acoustic emission equipment was used to monitor the evolution of the fracture network during the low-temperature shock process. Micro-CT scanning of the fracture network structure of the rock samples before and after the low-temperature shock was performed, and a detailed description of the complex fracture morphology was obtained to understand the dynamic expansion process of the fracture network in deep thermal reservoir rocks. Prepare full-diameter test rock samples, create cracks in them, and test the seepage parameters of the test rock samples under different crack widths, confining pressures, and flow rates to obtain the multi-scale seepage laws of deep heat reservoirs. Based on the dynamic expansion process of the fracture network in deep thermal reservoir rocks and the multi-scale seepage law, the mathematical and physical control equations of the stress field, temperature field, and seepage field of high-temperature rock mass at in-situ scale are established. The influence relationship between the damage coefficient of different injection media and the heat-fluid-solidification-chemical equation is obtained to form a temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks. Based on the temperature-seepage-stress-chemistry-damage constitutive model of deep thermal reservoir rocks, an in-situ scale complex fracture network THMD fully coupled fracturing model is constructed. The in-situ scale complex fracture network THMD fully coupled fracturing model is a heat-fluid-solid-damage fully coupled fracturing model. Based on the in-situ scale complex fracture network THMD fully coupled fracturing model, the interaction between fluid flow, heat transfer and rock deformation during the dynamic expansion of the fracture network is simulated.

5. An electronic device, characterized in that: include: memory and processor; The memory is used to store computer programs; The processor is configured to implement the steps of a method for evaluating the impact of weak structures on large-scale fracturing construction of deep thermal reservoirs as described in any one of claims 1 to 3 when executing the computer program stored in the memory.

6. A computer-readable storage medium, characterized in that Used to store a computer program, which, when executed by a processor, implements the steps of a method for evaluating the impact of a weak structure on large-scale fracturing construction of deep thermal storage as described in any one of claims 1 to 3.

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