Method for evaluating influence of weak structure on deep heat storage large-scale fracturing construction

Abstract

The invention discloses a method for evaluating the influence of a weak structure on deep heat storage large-scale fracturing construction, and relates to the technical field of deep high-temperature geothermal reservoir exploration and development. Based on deep heat storage weak structure fine description and mechanical property research, spatial distribution, well position deployment and well pattern deployment of the deep heat storage weak structure are found out, and the deep heat storage large-scale fracturing construction influence is evaluated. The method comprises the following steps: selecting a fracturing layer section, comprehensively evaluating the fracturing property of heat storage, establishing a heat-fluid-solid coupling damage model THMD and a heat-fluid-solid-chemical coupling damage model THMCD on the basis, and researching the activation condition of a primary weak structure surface to evaluate the filtration characteristic of the weak structure and the maximum displacement capable of implementing safe fracturing; on the basis of the above researches, triaxial fracturing physical simulation and numerical simulation researches are developed, the law of the weak structure facing fracturing crack propagation and the influence of the weak structure on seepage flow is clarified, and the influence action mechanism of the weak structure on deep heat storage large-scale fracturing under the condition of deep heat storage high temperature pressure is disclosed.

Description

Technical Field

[0001] The present invention relates to the technical field of deep high-temperature geothermal reservoir exploration and development, and particularly relates to an evaluation method, device, equipment and medium for the influence of a weak structure on large-scale fracturing construction of a deep geothermal reservoir. Background Technique

[0002] Deep geothermal resources are resources that combine "heat, minerals, and water", and are also clean and environment-friendly energy sources, which can be widely applied in fields such as power generation, heating and heating supply, healthcare, hot spring bathing, planting and breeding, tourism, and real estate development; geothermal resources are renewable resources and can also be comprehensively recycled, with the characteristics of pollution-free, convenient development and utilization (direct utilization), and high development value, which have important significance for improving the urban grade, improving the urban environment, adjusting the energy structure, and improving people's living conditions, and can also achieve remarkable economic, social, and environmental benefits.

[0003] Although deep geothermal resources have advantages such as large reserves, renewability, and environmental friendliness, compared with production, they have higher development costs and technical investments than traditional fossil fuels such as oil and natural gas; therefore, how to improve the heat exchange efficiency and heat extraction capacity is a key scientific problem that urgently needs to be solved in the current development and utilization of deep geothermal reservoirs, and its core task is how to break through large-scale fracturing to create reservoirs and obtain an ideal fracture network structure with a larger volume as much as possible; from the current research, breaking through the technical bottleneck of efficient earthquake control and large-scale fracturing is the primary problem for realizing the commercial development of deep geothermal reservoirs, and has important academic value, engineering significance, and social benefits.

[0004] In large-scale fracturing of deep geothermal reservoirs, the influence of weak structures is more complex than that in oil and gas reservoirs and coal reservoirs, mainly reflected in four aspects: ① Deep geothermal reservoirs generally show a block-like structure, and weak structures are generally not developed inside the reservoir, making it difficult to create reservoirs through fracturing. To make up for this deficiency, it is extremely important to find and identify weak structures inside the reservoir, evaluate the fracturability of the geothermal reservoir, and then optimize well location design and well pattern deployment; ② Oil and gas reservoirs generally define a complete trap structure or are confined within a certain closed permeable rock mass. When fracturing and reforming oil and gas reservoirs, generally, the problem of fracturing fluid loss along weak structural planes does not need to be considered. However, in the fracturing and reforming of deep geothermal reservoirs, due to the high temperature and high pressure of the geothermal reservoir and the fact that it is not a complete stratigraphic trap body in the horizontal direction, and the geothermal reservoir generally contains little or no water, temperature has an impact on the reactivation and transformation of weak structural planes, and the flow loss and flow impedance of fracturing fluids need to be considered; ③ Temperature is an important characteristic parameter of deep geothermal reservoirs. Numerical simulation studies on the fracturing and reforming of deep geothermal reservoirs need to consider the effect of the temperature field, that is, the coupling of the four fields of heat-fluid-solid-chemistry (THMC), which is more complex than the coupling of the three fields of fluid-solid-chemistry (THM) in traditional oil and gas reservoirs and coal reservoirs; ④ The morphology of natural weak structural planes, especially structures such as faults, fractures, and pores developed inside deep geothermal reservoirs, has a stress concentration effect, seriously interfering with the propagation of artificial fractures and easily inducing seismic risks.

[0005] At present, when evaluating the influence of weak structures during large-scale fracturing of deep geothermal reservoirs, numerical simulation and simulation methods are usually adopted. Using finite element analysis software, numerical simulation of deep geothermal reservoirs is carried out. In the simulation, the influence of weak structures is considered, and the stress distribution, fracture propagation path, and fluid flow situation in the reservoir during the fracturing process are analyzed to predict the fracturing effect through the simulation results and evaluate the influence of weak structures; however, this numerical simulation and simulation method usually only focuses on analyzing the internal situation of the reservoir during the fracturing process, while ignoring the influence of weak structures on the large-scale fracturing construction of deep geothermal reservoirs under the multi-field coupling action of reservoir structure, temperature field, seepage field, stress field, and chemical field during fracturing. As a result, when evaluating the influence of weak structures on the large-scale fracturing of deep geothermal reservoirs, there is a large deviation from the true evaluation results, and it is difficult to reflect the true interaction between weak structures and deep geothermal reservoirs. Summary of the Invention

[0006] An embodiment of the present invention provides an evaluation method for the influence of weak structures on the large-scale fracturing construction of deep geothermal reservoirs, which can solve the problem in the prior art that the existing methods usually only focus on analyzing the internal situation of the reservoir during the fracturing process, while ignoring the influence of weak structures on the large-scale fracturing construction of deep geothermal reservoirs under the multi-field coupling action of reservoir structure, temperature field, seepage field, stress field, and chemical field during fracturing. As a result, when evaluating the influence of weak structures on the large-scale fracturing of deep geothermal reservoirs, there is a large deviation from the true evaluation results, and it is difficult to reflect the true interaction between weak structures and deep geothermal reservoirs.

[0007] An evaluation method for the influence of weak structures on large-scale fracturing construction of deep geothermal reservoirs provided by an embodiment of the present invention includes the following steps: Obtain the fracturing characteristics of the deep geothermal reservoir; the fracturing characteristics characterize the internal rock brittleness, the development characteristics of internal weak structures, and the in-situ stress distribution within the deep geothermal reservoir during fracturing; Obtain the deformation characteristics of internal weak structures and the fracture propagation characteristics of fracturing in the deep geothermal reservoir under the coupled action of heat, fluid flow, solid, and chemical fields, and determine the fracturing parameters and construction parameters of the deep geothermal reservoir during large-scale fracturing construction on the premise of not inducing earthquakes through the deformation characteristics and the fracture propagation characteristics of fracturing; wherein, the deformation characteristics and the fracture propagation characteristics of fracturing characterize the conditions for the fracturing fluid to enter the weak structure, causing the weak structure to be tensioned and opened, and for the fracturing fractures to propagate in the weak structure, so as to evaluate the possibility of inducing earthquakes; Based on the fracturing characteristics of the deep geothermal reservoir, as well as the fracturing parameters and construction parameters during fracturing construction, conduct a simulation of large-scale fracturing construction of the deep geothermal reservoir to obtain the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fracture network in the deep geothermal reservoir and its internal weak structures; Evaluate the construction influence of weak structures on large-scale fracturing of deep geothermal reservoirs according to the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fracture network.

[0008] Preferably, the obtaining of the fracturing characteristics of the deep geothermal reservoir includes: Conduct drilling research and logging analysis on the deep geothermal reservoir to obtain the spatial distribution characteristics of the geometry, physical, and mechanical properties of the deep geothermal reservoir; Use the diamond wire cutting method to make standard rock samples from the downhole cores drilled from the deep geothermal reservoir, conduct rock triaxial mechanical experiments on the standard rock samples under different temperature and confining pressure conditions, obtain the stress-strain curves of the rock under different conditions, and the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep geothermal reservoir; According to the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep geothermal reservoir, establish a constitutive model of rock nonlinear damage to simulate the damage evolution law of the rock in the deep geothermal reservoir during the stress-bearing process; Use the fractal method to establish a mechanical brittleness index model reflecting the rock deformation and failure process of the deep geothermal reservoir, and simulate the brittle characteristics, activation conditions, and propagation modes of the internal weak structures in the deep geothermal reservoir; According to the spatial distribution characteristics of the geometric, physical and mechanical properties of the deep geothermal reservoir with an embedded structure, a three-dimensional geological model of the deep geothermal reservoir with an embedded weak structure is constructed. The in-situ stress field and temperature field attribute information of the deep geothermal reservoir with an embedded weak structure are integrated into the three-dimensional geological model to construct a three-dimensional multi-attribute model of the deep geothermal reservoir with an embedded weak structure. The model is used to reconstruct the characteristics of the in-situ stress field and temperature field of the high-temperature rock mass, and based on the damage evolution law of the deep geothermal reservoir, the brittle characteristics, activation conditions and propagation modes of the weak structure, as well as the in-situ stress field and temperature field of the high-temperature rock mass, the fracturing characteristics of the deep geothermal reservoir are obtained.

[0009] Preferably, the acquisition of the deformation characteristics and fracturing crack propagation characteristics of the weak structure includes: Conduct matrix acidification, hydraulic fracturing and acid fracturing experiments on the deep geothermal reservoir, and consider the in-situ stress difference, dip angle of the weak structural plane, cohesion of the weak structural plane, internal friction angle of the weak structural plane and tensile strength of the weak structural plane during the experiment to simulate the stress mechanism of the weak structural plane during the actual fracturing process and obtain the activation conditions of the primary weak structural plane in the deep geothermal reservoir; Among them, the activation condition is the activation effect of temperature and the propagation mode of the artificial fracture on the primary weak structural plane; Establish a thermo-hydro-mechanical-damage model THMD and a thermo-hydro-mechanical-chemical-damage model THMCD; simulate and obtain the deformation and failure characteristics of the natural weak structural plane under the coupling action of multiple fields; the deformation and failure characteristics of the natural weak structural plane are the deformation characteristics and fracturing crack propagation characteristics of the weak structure, including: under the interference of the artificial fracture, the weak structure undergoes tensile and shear failure damage, and obtain the conditions for the weak structural plane to be tensionally opened and the fracturing crack to turn and propagate into the weak structural plane after the fracturing fluid enters the weak structural plane.

[0010] Preferably, the determination of the fracturing parameters and construction parameters of the deep geothermal reservoir during large-scale fracturing construction on the premise of not inducing earthquakes includes: According to the conditions for the weak structural plane to be tensionally opened and the fracturing crack to turn and propagate into the weak structural plane, a reactivation criterion for the weak structural plane is constructed. The reactivation criterion for the weak structural plane considers the mechanical properties of the weak structural plane, the injection conditions of the fracturing fluid and the coupling action of multiple fields to evaluate the filtration characteristics of the weak structural zone and the possibility of inducing earthquakes; According to the activation conditions of the primary weak structural plane in the deep geothermal reservoir, the filtration characteristics of the weak structural zone and the possibility of inducing earthquakes, predict the maximum displacement, construction pump pressure, total injection fluid volume and effective stimulated reservoir volume SRV that the deep geothermal reservoir can safely fracture, and predict the fracturing parameters and construction parameters of the large-scale fracturing construction of the deep geothermal reservoir.

[0011] Preferably, obtaining the interaction law of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion of the fracture network in the deep geothermal reservoir and the internal weak structure includes: Prepare multiple multi-fracture rock samples, and conduct triaxial fracturing physical simulations on the multi-fracture rock samples under different injection media, heat treatment temperatures, numbers of cyclic heating treatments, horizontal stress differences, and different discharge rates to obtain the fracture network initiation and expansion process of the deep geothermal reservoir rock and the pressure response law; Use a normal temperature fracturing fluid to simulate low-temperature impact and conduct a fracturing experiment on the multi-fracture rock sample. Use an acoustic emission device to monitor the fracture network evolution during the low-temperature impact, perform micro-CT scanning on the fracture network structure of the rock sample before and after the low-temperature impact, and finely describe the complex fracture morphology to obtain the dynamic expansion process of the fracture network in the deep geothermal reservoir rock; Prepare full-diameter test rock samples, open fractures on the test rock samples, and conduct seepage parameter tests on the test rock samples under different fracture widths, confining pressures, and flow rates to obtain the multi-scale seepage law of the deep geothermal reservoir; Based on the dynamic expansion process of the fracture network in the deep geothermal reservoir rock and the multi-scale seepage law, establish the mathematical and physical control equations of the in-situ scale high-temperature rock mass stress field, temperature field, and seepage field, and obtain the influence relationship between the damage coefficient of different injection media and the heat-fluid-solid-chemical equation to form the temperature-seepage-stress-chemistry-damage constitutive model of the deep geothermal reservoir rock; According to the temperature-seepage-stress-chemistry-damage constitutive model of the deep geothermal reservoir rock, construct an in-situ scale complex fracture network THMD fully coupled fracturing model, and 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, simulate the interaction law of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion of the fracture network.

[0012] The embodiment of the present invention also provides an evaluation device for the influence of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir, including: A fracturing characteristic module for obtaining the fracturing characteristics of the deep geothermal reservoir; the fracturing characteristics characterize the internal rock brittleness of the deep geothermal reservoir during fracturing, the development characteristics of the internal weak structure, and the in-situ stress distribution inside; A simulation module for obtaining the deformation characteristics of the internal weak structure and the fracturing fracture propagation characteristics of the deep geothermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and determining the fracturing parameters and construction parameters during the large-scale fracturing construction of the deep geothermal reservoir without inducing earthquakes through the deformation characteristics and the fracturing fracture propagation characteristics; wherein, the deformation characteristics and the fracturing fracture propagation characteristics characterize the conditions for the fracturing fluid to enter the weak structure and cause the weak structure to be pulled open and the fracturing fracture to propagate in the weak structure to evaluate the possibility of inducing earthquakes; An evaluation module is used to simulate the large-scale fracturing construction of a deep geothermal reservoir based on the fracturing characteristics of the deep geothermal reservoir, as well as the fracturing parameters and construction parameters during the fracturing operation, so as to obtain the interaction laws of fluid flow, heat transfer, and rock mass deformation between the deep geothermal reservoir and the internal weak structure during the dynamic expansion of the fracture network; According to the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion of the fracture network, evaluate the construction impact of the weak structure on the large-scale fracturing of the deep geothermal reservoir.

[0013] An embodiment of the present invention also provides an electronic device, including a memory and a processor; The memory is used to store a computer program; When the processor is used to execute the computer program stored in the memory, the steps of the above-mentioned evaluation method for the impact of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir are implemented.

[0014] An embodiment of the present invention also provides a computer-readable storage medium for storing a computer program, and when the computer program is executed by a processor, the steps of the above-mentioned evaluation method for the impact of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir are implemented.

[0015] An embodiment of the present invention provides an evaluation method for the impact of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir. Compared with the prior art, its beneficial effects are as follows: The present invention first obtains the fracturing characteristics of the deep geothermal reservoir, and predicts the fracturing parameters and construction parameters during the large-scale fracturing construction of the deep geothermal reservoir on the premise of not inducing earthquakes by establishing a thermo-hydro-mechanical-chemical coupling damage model THMD and a thermo-hydro-mechanical-chemical-damage coupling model THMCD; then, based on the fracturing characteristics of the deep geothermal reservoir, as well as the fracturing parameters and construction parameters during the fracturing operation, from the perspective of simulating the large-scale fracturing construction of the deep geothermal reservoir, evaluate the interaction laws of fluid flow, heat transfer, and rock mass deformation of the deep geothermal reservoir rock during the dynamic expansion of the fracture network; this process takes into account the reservoir structure characterized by the fracturing characteristics of the deep geothermal reservoir during fracturing, as well as the temperature field, seepage field, stress field, and chemical field during the fracturing process characterized by the interaction laws of fluid flow, heat transfer, and rock mass deformation, that is, comprehensively considers the impact of the weak structure on the large-scale fracturing construction of the deep geothermal reservoir under the multi-field coupling action of the reservoir structure, temperature field, seepage field, stress field, and chemical field during fracturing, and can truly and accurately evaluate the impact of the weak structure on the large-scale fracturing of the deep geothermal reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall process of an evaluation method for the impact of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0018] See Figure 1 , an embodiment of the present invention provides an evaluation method for the influence of soft structures on the large-scale fracturing construction of deep geothermal reservoirs, including the following steps: Step 1: Study on the three-dimensional spatial distribution characteristics of soft structures in deep geothermal reservoirs.

[0019] Integrate geological, drilling, logging, test and other information, and use technologies such as data fusion and model construction to reveal the spatial distribution of the geometric, physical and mechanical properties of deep geothermal reservoirs; on the basis of systematically analyzing the geological characteristics of deep geothermal reservoirs, use diamond wire cutting to make standard rock samples from the outcrops or downhole cores of deep geothermal reservoirs, and successively carry out rock triaxial mechanical experiments under different temperature and confining pressure conditions in real time to achieve double coupling of temperature and pressure; based on the stress-strain curves obtained from experimental tests, analyze the evolution characteristics of compressive strength, elastic modulus, Poisson's ratio, cohesion and internal friction angle under different constant-pressure coupling parameters, establish a constitutive model of rock nonlinear damage, and analyze the damage evolution law of rock mechanical parameters; use fractal methods, etc., to establish a mechanical brittleness index model reflecting the whole process characteristics of rock deformation and failure, analyze the brittleness, activation conditions and propagation modes of soft structures, establish a three-dimensional multi-attribute model (geostress field, temperature field) of deep geothermal reservoirs for soft structures in the geothermal reservoir, and realize the reconstruction of the characteristics of the geostress field and temperature field of high-temperature rock masses; according to the brittleness of rocks, the development characteristics of soft structures and the distribution of geostress, comprehensively evaluate the fracturability of geothermal reservoirs.

[0020] Among them, the fractal theory combines fractal geometry, physics, and solid mechanics to describe the irregularity, nonlinearity, and randomness in the process of rock deformation and failure. By studying the distribution law of cuttings and calculating their fractal dimensions, a correlation model between the fractal dimension of cuttings and the rock brittleness index is established. Based on the correlation model between the fractal dimension of cuttings and the rock brittleness index, 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. The in-situ stress considers factors such as formation 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 parameters such as rock permeability, porosity, elastic modulus, and Poisson's ratio. At the same time, Petrel software is used for 3D simulation to establish a geological model framework, and sequential Gaussian interpolation method is used to establish porosity and permeability models, and a temperature field model is established in combination with temperature data. Considering the problem of high in-situ stress, the thermal stress field and in-situ stress field of the support structure and surrounding rock are studied.

[0021] Step 2: Study on the influence of weak structures in deep thermal reservoirs on fracturing construction.

[0022] Adopt a technical method combining indoor experiments and numerical simulations to conduct matrix acidification, hydraulic fracturing, and acid fracturing experiments. Considering the in-situ stress difference, dip angle of the weak structural plane, cohesion of the weak structural plane, internal friction angle of the weak structural plane, and tensile strength of the weak structural plane, etc., study the activation conditions of the primary weak structural plane, that is, the activation effect of temperature and the propagation mode (turning, passing through) of artificial fractures on the primary weak structural plane. Establish thermo-hydro-mechanical-damage (THMD) and thermo-hydro-mechanical-chemical-damage (THMCD) models to study the deformation and failure characteristics of natural weak structural planes under the action of multi-field coupling, that is, under the interference of artificial fractures, tensile and shear failure damages occur, analyze the conditions for fracturing fluid to enter the weak structural plane and cause the weak structural plane to be tensioned and opened, and for fracturing cracks to turn and expand along the weak structural plane, construct a reactivation criterion for the weak structural plane, evaluate the filtration characteristics of the weak structural zone and the possibility of induced earthquakes. Predict and estimate the maximum displacement, construction pump pressure, total injected liquid volume, and effective stimulated reservoir volume (SRV) that can implement safe fracturing, etc., optimize fracturing parameters and construction parameters, guide the optimization of the fracturing construction plan, and clarify the influence of weak structures in deep thermal reservoirs on fracturing construction.

[0023] Specifically: Indoor experiments are carried out by precisely controlling the experimental conditions to simulate the deep geothermal reservoir environment, and matrix acidification, hydraulic fracturing, and acid fracturing experiments are conducted. During the experimental process, the mechanical responses of rock samples and the fracture propagation are monitored in real time to obtain experimental data. Numerical simulation uses advanced numerical calculation software to establish a deep geothermal reservoir geological model and simulate the fracturing construction process under different in-situ stress conditions and characteristics of weak structural planes. Through numerical simulation, the propagation path, shape, and fracturing effect of fractures 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.

[0024] Matrix acidification is achieved by squeezing acid fluid into the pores of the reservoir rock under a pressure lower than the fracture pressure of the reservoir rock, dissolving the particles and blockages in the pore space, expanding the pore space, and increasing the formation permeability. Hydraulic fracturing is carried out by injecting liquid with high pressure to form fractures in the formation and improve the formation permeability. During the hydraulic fracturing process, the propagation of fractures is affected by factors such as in-situ stress and rock mechanical properties. Acid fracturing combines the principles of acidification and hydraulic fracturing. First, fractures are formed by hydraulic fracturing, and then acid fluid is injected to dissolve the rock on the fracture wall surface, expanding the fracture conductivity. Acid fracturing can more effectively transform the reservoir and increase the production of oil and gas wells.

[0025] The in-situ stress difference has an important impact on the strength and stability of rock masses. During the fracturing construction process, the in-situ stress difference will affect the propagation direction and shape of fractures, and thus affect the fracturing effect. The dip angle of the weak structural plane has a significant impact on the strength of rock masses. Different dip angles will lead to different failure forms, such as bedding plane landslides and shear failures, affecting the safety and stability of the project. The mechanical parameters such as the cohesion, internal friction angle, and tensile strength of the weak structural plane determine the shear strength and tensile strength of the weak structural plane. During the fracturing construction process, these mechanical parameters of the weak structural plane will affect the propagation path and shape of fractures, and thus affect the fracturing effect. Temperature changes will affect the physical and chemical properties of rock masses, such as the thermal expansion coefficient and elastic modulus of rocks. In the deep geothermal reservoir environment, the temperature is relatively high, and the mechanical properties of rocks will change significantly, thus affecting the stability and activation conditions of the weak structural plane. The propagation mode of artificial fractures will affect the activation conditions of the weak structural plane. When the fracture turns, it may bypass the weak structural plane, reducing the damage to it. When the fracture crosses the weak structural plane, it may directly damage the weak structural plane, affecting its stability.

[0026] The thermo-hydro-mechanical-damage (THMD) model takes into account the thermo-hydro-mechanical coupling effect. By simulating the process of hydraulic fracture propagation, it reveals the influence of temperature, seepage, and stress fields on fracture propagation, providing a theoretical basis for optimizing the fracturing construction plan. The thermo-hydro-mechanical-chemical-damage (THMCD) model is established based on the gas thermal flow equation, turbulent flow equation, solid heat conduction equation, and thermo-elasticity equation. It analyzes the compressible thermal flow characteristics of the gas in the cavern during the injection and production process of the lined rock cavern for hydrogen storage and the thermodynamic responses of the lining layer and surrounding rock. The thermo-hydro-mechanical-damage (THMD) model and the thermo-hydro-mechanical-chemical-damage (THMCD) model comprehensively consider factors such as in-situ stress, temperature, seepage, and chemical action, study their effects on rock mass deformation and failure, and simultaneously study the physical and mechanical properties of rock mass such as stress, strength, deformation, failure, and fluid-thermal-chemical transport to solve the problems of engineering rock mass deformation and stability.

[0027] Under the interference of artificial fractures, the fractures pose hazards to the weak structures, affecting the internal force distribution, shear resistance performance, and deformation probability of the structures. After the fracturing fluid enters the weak structural plane, the high-pressure fracturing fluid generates internal pressure on various levels of fractures and weak surfaces, causing the fractures 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 plane, causing the weak structural plane to be tensioned and opened. Based on the principle of minimizing the energy release rate, the conditions for the strain energy release rate of the hydraulic crack propagating in any direction considering factors such as in-situ stress and friction are obtained. And based on the mechanical properties and geological conditions of the weak structural plane, a reactivation criterion is constructed to predict and control the activation behavior of the weak structural plane. The weak structural plane has strong water permeability, is prone to compressive deformation, has poor self-stabilizing ability, and contains a lot of clay minerals. The filtration characteristics of the weak structural zone can be evaluated by combining laboratory tests and numerical simulations. When predicting the possibility of induced earthquakes, study the influence of the weak structural plane on the dynamic response of the seismic slope, including the influence on the evaluation index of the slope dynamic response and the influence on the spatial distribution of the slope seismic energy and the slope plastic failure mode, providing a scientific basis for earthquake prediction and slope stability evaluation and assessing the possibility of induced earthquakes.

[0028] Determine the maximum displacement that can implement safe fracturing based on fracturing equipment capacity, wellhead device pressure-bearing capacity, formation fracture pressure, etc.; the prediction of the maximum wellhead pump pressure needs to consider the maximum pump pressure allowed by the fracturing equipment and wellhead device, and the construction pump pressure can be predicted by methods such as predicting the formation fracture pressure and reducing the frictional resistance along the way; the calculation of the total injected liquid volume needs to consider factors such as the geological conditions of the formation and the thickness of the fractured layer, so as to calculate the total injected liquid volume of the fracturing fluid that can implement safe fracturing. The total liquid volume of the fracturing fluid is the sum of the liquid volumes of the preflush fluid, proppant-carrying fluid, and displacement fluid; screen and optimize events according to the hydraulic fracturing fracture mechanism, the chronological order of fracture times at the event points, the spatial combination characteristics, and the credibility of the events, and quantitatively interpret the geometric characteristics (fracture length, fracture width, fracture height) of the fracturing fractures, so as to calculate the effective stimulated reservoir volume (SRV); establish a reservoir hydraulic fracturing model based on the maximum displacement, construction pump pressure, total injected liquid volume, and effective stimulated reservoir volume (SRV) that can implement safe fracturing. Taking the extension of the hydraulic fracture in the reservoir as the criterion, optimize the fracturing parameters of the first layer, and then use the fracturing parameters of the first layer to calculate the fracture morphology of the upper layer section. Taking the non-connection of the upper and lower layer fractures as the judgment standard, calculate the fracture morphology of the upper layer section under different interlayer thicknesses, determine the interlayer thickness that can prevent the connection of the upper and lower layer fractures, and finally determine the final fracturing interval, and optimize the construction parameters and fracturing parameters of the upper layer section; in guiding the optimization of the fracturing construction plan, the existence of weak structural planes will affect the initiation pressure of hydraulic fracturing. At the same time, the deep geothermal reservoir weak structures (such as natural weak planes, cleats, etc.) will affect the initiation mode of hydraulic fracturing fractures, and the weak structural planes will affect the propagation direction of hydraulic fractures.

[0029] Step 3: Study on the influence of deep geothermal reservoir weak structures on the fracturing construction effect.

[0030] Prepare random multi-fractured rock samples, and conduct research on the fracture network initiation, propagation, and pressure response laws of deep geothermal reservoir rocks under different injection media (water, acid, CO2), heat treatment temperatures, cyclic heating treatment times, horizontal stress differences, and different displacement rates. Use normal temperature fracturing fluid to simulate low-temperature impact, and use means such as acoustic emission and tracers to monitor the fracture network evolution characteristics. Use micro-CT to scan the fracture network of rock samples before and after experiments to describe complex fracture morphologies; prepare full-diameter test rock samples, prepare artificial fractures, conduct seepage parameter tests under different fracture widths, confining pressures, and flow rates, and analyze seepage characteristics in real time to clarify the main controlling factors affecting fluid seepage laws, accurately depict the dynamic expansion process of complex fracture networks, and reveal the multi-scale seepage laws of different injection media; based on the mesoscopic damage evolution and failure mechanism of rocks, combined with previous experimental tests and theoretical analyses, establish the mathematical and physical control equations of the stress field, temperature field, and seepage field of high-temperature rock masses at in-situ scale, propose the influence relationship between the damage coefficients of different injection media and the heat-flow-solidification equation, and form the temperature-seepage-stress-chemistry-damage constitutive model of deep geothermal reservoir rocks; on this basis, construct the THMD fully coupled fracturing model of complex fracture networks at in-situ scale, and analyze the interaction laws of fluid flow, heat transfer, and rock mass deformation during the fracture network initiation and propagation processes; study the influence laws of complex geological factors such as different geothermal temperatures, heat conduction capabilities, in-situ stresses, pore pressures, and natural weak structural plane morphologies, as well as different fracturing displacement rates, fracturing fluid types, and temporary plugging and diversion on the fracture network initiation, propagation, and stress field changes, and clarify the influence of weak structures in deep geothermal reservoirs on fracturing effects.

[0031] Specifically: Tin bars were prepared to simulate cracks, 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 loaded into a molding mold and vibrated to form, so that the tin bars were randomly distributed, and multi-crack rock samples were obtained; the effects of different injection media (water, acid, CO2) on crack propagation were studied, and it was found that supercritical CO2 would lead to more complex crack morphology, which could play a synergistic role with low-temperature induced thermal stress during thermal reservoir fracturing; the evolution law of the mechanical elastic-plastic characteristics of medium-deep geothermal reservoirs under high temperature was studied, and it was found that high temperature has an important influence on the turning and expansion of artificial cracks, and high temperature can enhance the plasticity of rocks and change the expansion mode of cracks; the effects of thermal cycles 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 would reduce the crack initiation stress of rocks and affect the expansion capacity of cracks; the effect of the horizontal principal stress ratio on the expansion 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 the x-axis direction gradually decreased, and the resistance of fracture extension increased; the influence of different displacements on the extension of hydraulic fractures was studied, and it was found that large displacement of low-viscosity fracturing fluid or small and medium displacement of high-viscosity fracturing fluid can communicate with caves that are smaller and closer to the initial extension direction of hydraulic fractures; normal temperature fracturing fluid was used to simulate low-temperature impact, that is, the low-temperature impact test was carried out by switching products between high-temperature box and low-temperature box to evaluate the performance of materials in low-temperature environment; acoustic emission and tracer methods 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 the evolution characteristics of fracture network were studied; 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, which can quantitatively describe the parameters such as fracture opening, inclination, and fracture rate.

[0032] 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 smeared on the joint surface of the damaged horizontal section rock sample to bond the three-layer blocks and fill the depressions on the side of the core column and other cracked parts. After filling, compaction and bonding are carried out 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, generate cracks on the concrete surface, and form artificial cracks; based on the multifunctional 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 finite element method or finite difference method, are used to solve the seepage field, generate high-precision seepage data graphs, and analyze the seepage characteristics.

[0033] In the determination of the main controlling factors affecting fluid seepage laws, due to the strong polar molecular interaction at the solid-liquid interface, a boundary layer is adsorbed on the pore wall surface, making it unable to participate in the flow, thus resulting in non-linearity. In the same low-permeability porous medium, if the solid-liquid surface has a greater molecular force, the starting pressure gradient will be higher. 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 force between the solid-liquid surfaces on seepage. When the molecular force of the solid surface in the porous medium reaches a certain value, its influence on fluid seepage can be basically ignored, and the seepage then turns into the Darcy type. As the pressure gradient gradually increases, the influence of the molecular force on the solid-liquid surface on seepage will gradually weaken. Then, the high-performance reservoir simulator tNavigator software FS1.1 is used to simulate fracture propagation, establish the maximum principal stress direction field, and simulate the propagation directions of different segment clusters to accurately depict the dynamic propagation process of complex fracture networks and reveal the multi-scale seepage laws of different injection media.

[0034] Starting from the mesoscopic structural level of rock materials, based on mesoscopic damage mechanics, elastic thermodynamics, and Biot's classical seepage mechanics theory, a numerical model describing the thermal-seepage-stress-damage coupling effect of rock mesoscopic structures is established. Through the injection pressure-time curves obtained by simulating with the TOUGH-RFPA elastic model and damage model, the influence relationships of different injection media on the damage coefficient and the heat-flow-solidification equation are analyzed. Using mechanism analysis methods, system identification methods, and hybrid analysis methods, the above content is analyzed to establish a coupling model of the seepage field and stress field of rock masses.

[0035] On the basis of the above research, Comsol software is used to simulate the THMD coupling model of rock hydraulic fracturing damage. Based on the assumptions of linear elastic fracture mechanics (LEFM), the stability and propagation trajectory of cracks are controlled by calculating the stress intensity factor. Cracks are automatically set at any point and any angle on the boundary to form the function of crack propagation, and the network can be adjusted arbitrarily along the propagated cracks to analyze the interaction laws of fluid flow, heat transfer, and rock mass deformation during the initiation and propagation of fracture networks.

[0036] Study the changes in the physical and mechanical properties of rocks under different geothermal conditions, and their effects on the initiation and expansion of fracture networks; study the laws of heat transfer in rocks under different thermal conductivity conditions, and their effects on the initiation and expansion of fracture networks; study the laws of stress distribution in rocks under different geostress conditions, and their effects on the initiation and expansion of fracture networks; study the laws of fluid flow in rocks under different pore pressure conditions, and their effects on the initiation and expansion of fracture networks; study the fracture patterns of rocks under different natural weak structural surface morphologies, and their effects on the initiation and expansion of fracture networks. At the same time, a temporary plugging and diverting fracturing physical simulation device was established using large-scale true triaxial fracturing equipment and experiments were conducted to study the laws of fracture initiation and expansion under different fracturing displacement conditions, as well as their effects on stress field changes; to study the laws of fracture initiation and expansion under different fracturing fluid types, as well as their effects on stress field changes; to study the effects of temporary plugging and diverting technology on fracture initiation and expansion, as well as its role in improving fracturing effects; 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.

[0037] 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 fine characterization of weak structures of deep heat reservoirs and the study of mechanical properties, 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. Heat-fluid-solid and heat-fluid-solid-chemical coupling 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 fracturing crack expansion and their influence on seepage, and reveal the influence mechanism of weak structures in large-scale fracturing of deep heat reservoirs.

[0038] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An evaluation method for the influence of a weak structure on large-scale fracturing construction of deep geothermal reservoirs, characterized in that, The method includes the following steps: Obtaining the fracturing characteristics of the deep geothermal reservoir; the fracturing characteristics characterize the internal rock brittleness, the development characteristics of internal weak structures, and the in-situ stress distribution during fracturing of the deep geothermal reservoir; Obtaining the deformation characteristics of the internal weak structures and the fracturing crack propagation characteristics in the deep geothermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and determining the fracturing parameters and construction parameters for large-scale fracturing construction of the deep geothermal reservoir without inducing earthquakes based on the deformation characteristics and the fracturing crack propagation characteristics; wherein, the deformation characteristics and the fracturing crack propagation characteristics characterize the conditions under which the fracturing fluid enters the weak structure to cause the weak structure to be tensioned and opened, and the fracturing cracks propagate in the weak structure, so as to evaluate the possibility of inducing earthquakes; Based on the fracturing characteristics of the deep geothermal reservoir, as well as the fracturing parameters and construction parameters during fracturing construction, simulating the large-scale fracturing construction of the deep geothermal reservoir to obtain the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fracturing fracture network in the deep geothermal reservoir and its internal weak structures; Evaluating the construction impact of the weak structure on the large-scale fracturing of the deep geothermal reservoir according to the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fracturing fracture network.

2. The evaluation method for the influence of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir according to claim 1, characterized in that The obtaining of the fracturing characteristics of the deep geothermal reservoir includes: Conducting drilling research and logging analysis on the deep geothermal reservoir to obtain the spatial distribution characteristics of the geometry, physical properties, and mechanical properties of the deep geothermal reservoir; Using the diamond wire cutting method to make the downhole core drilled from the deep geothermal reservoir into a standard rock sample, and conducting rock triaxial mechanical experiments on the standard rock sample under different temperature and confining pressure conditions to obtain the stress-strain curves of the rock under different conditions, as well as the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep geothermal reservoir; Based on the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep geothermal reservoir, establishing a constitutive model for nonlinear damage of the rock to simulate the damage evolution law of the rock in the deep geothermal reservoir during the stress application process; Using the fractal method to establish a mechanical brittleness index model reflecting the rock deformation and failure process of the deep geothermal reservoir, and simulating the brittleness characteristics, activation conditions, and propagation modes of the internal weak structures in the deep geothermal reservoir; According to the spatial distribution characteristics of the geometry, physical properties, and mechanical properties of the deep geothermal reservoir with embedded structures, constructing a three-dimensional geological model of the deep geothermal reservoir with embedded weak structures, integrating the in-situ stress field and temperature field attribute information of the deep geothermal reservoir with embedded weak structures into the three-dimensional geological model, constructing a three-dimensional multi-attribute model of the deep geothermal reservoir with embedded weak structures, using the model to reconstruct the characteristics of the high-temperature rock mass in-situ stress field and temperature field, and obtaining the fracturing characteristics of the deep geothermal reservoir based on the damage evolution law of the deep geothermal reservoir, the brittleness characteristics, activation conditions, and propagation modes of the weak structures, as well as the high-temperature rock mass in-situ stress field and temperature field.

3. An evaluation method for the influence of a weak structure on large-scale fracturing construction of deep geothermal reservoirs according to claim 1, characterized in that, The obtaining of the deformation characteristics of the weak structure and the fracturing crack propagation characteristics includes: Matrix acidification, hydraulic fracturing, and acid fracturing experiments were conducted on deep geothermal reservoirs, and during the experiments, the in-situ stress difference, dip angle of weak structural planes, cohesion of weak structural planes, internal friction angle of weak structural planes, and tensile strength of weak structural planes were considered to simulate the stress mechanism of weak structural planes during the actual fracturing process and obtain the activation conditions of primary weak structural planes in deep geothermal reservoirs; Among them, the activation conditions are the activation effects of temperature and the propagation mode of artificial fractures on primary weak structural planes; A thermo-hydro-mechanical-damage model THMD and a thermo-hydro-mechanical-chemical-damage model THMCD were established; the deformation and failure characteristics of natural weak structural planes under the coupling action of multiple fields were simulated and obtained; the deformation and failure characteristics of the natural weak structural planes are the deformation characteristics of weak structures and the propagation characteristics of fracturing cracks, including: under the interference of artificial fractures, weak structures are damaged by tension and shear, and after fracturing fluid enters the weak structural planes, the conditions for the weak structural planes to open under tension and for fracturing cracks to turn and propagate along the weak structural planes are obtained.

4. An evaluation method for the influence of a weak structure on large-scale fracturing construction in deep geothermal reservoirs according to claim 3, characterized in that Determining the fracturing parameters and construction parameters for large-scale fracturing construction of deep geothermal reservoirs without inducing earthquakes, including: According to the conditions for the weak structural planes to open under tension and for fracturing cracks to turn and propagate along the weak structural planes, a reactivation criterion for weak structural planes was constructed. The reactivation criterion for weak structural planes takes into account the mechanical properties of weak structural planes, the injection conditions of fracturing fluid, and the coupling action of multiple fields to evaluate the filtration characteristics of weak structural zones and the possibility of inducing earthquakes; Based on the activation conditions of primary weak structural planes in deep geothermal reservoirs, the filtration characteristics of weak structural zones, and the possibility of inducing earthquakes, the maximum displacement, construction pump pressure, total injected fluid volume, and effective stimulated reservoir volume SRV for safe fracturing in deep geothermal reservoirs were predicted, and the fracturing parameters and construction parameters for large-scale fracturing construction of deep geothermal reservoirs were predicted.

5. The evaluation method for the influence of a weak structure on large-scale fracturing construction in deep geothermal reservoirs according to claim 1, wherein Obtaining the interaction laws of fluid flow, heat transfer, and rock mass deformation during the dynamic propagation of fracture networks in deep geothermal reservoirs and internal weak structures, including: Multiple multi-fracture rock samples were prepared, and triaxial fracturing physical simulations were carried out on the multi-fracture rock samples under different injection media, heat treatment temperatures, numbers of cyclic heating treatments, horizontal stress differences, and different displacement conditions to obtain the initiation and propagation processes of fracture networks in deep geothermal reservoir rocks and the pressure response laws; A fracturing experiment was carried out on the multi-fracture rock samples by simulating low-temperature impacts with normal-temperature fracturing fluid. The evolution of the fracture network during the low-temperature impact was monitored using an acoustic emission device, and the fracture network structure of the rock samples before and after the low-temperature impact was scanned by micro-CT to finely describe the complex fracture morphology to obtain the dynamic propagation process of the fracture network in deep geothermal reservoir rocks; Full-diameter test rock samples were prepared, and fractures were opened on the test rock samples. The seepage parameters of the test rock samples were measured under different fracture widths, confining pressures, and flow rates to obtain the multi-scale seepage laws of deep geothermal reservoirs; Based on the dynamic expansion process of the fractured network in deep geothermal reservoirs and the multi-scale seepage law, establish the mathematical and physical control equations of the in-situ stress field, temperature field, and seepage field of high-temperature rock masses, and obtain the influence relationship between the damage coefficients of different injection media and the thermo-hydro-mechanical-chemical equations, so as to form a temperature-seepage-stress-chemistry-damage constitutive model for deep geothermal reservoir rocks. According to the temperature-seepage-stress-chemistry-damage constitutive model of deep geothermal reservoir rocks, construct a fully coupled THMD fracturing model of complex fracture networks at the in-situ scale, and the fully coupled THMD fracturing model of complex fracture networks at the in-situ scale is a fully coupled thermo-hydro-mechanical-damage fracturing model. Based on the fully coupled THMD fracturing model of complex fracture networks at the in-situ scale, simulate the interaction law of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fractured network.

6. An evaluation device for the influence of a weak structure on the large-scale fracturing construction of a deep geothermal reservoir, characterized in that, It includes: A fracturing characteristic module for obtaining the fracturing characteristics of deep geothermal reservoirs; the fracturing characteristics characterize the internal rock brittleness, the development characteristics of internal weak structures, and the in-situ stress distribution during fracturing of deep geothermal reservoirs. A simulation module for obtaining the deformation characteristics of internal weak structures and the fracture propagation characteristics of fracturing in deep geothermal reservoirs under the coupled action of heat, flow, solid, and chemical fields, and determining the fracturing parameters and construction parameters during large-scale fracturing construction of deep geothermal reservoirs without inducing earthquakes based on the deformation characteristics and fracture propagation characteristics of fracturing; among them, the deformation characteristics and fracture propagation characteristics of fracturing characterize the conditions for fracturing fluid to enter the weak structure and cause the weak structure to be pulled open and for the fracturing fracture to propagate in the weak structure, so as to evaluate the possibility of inducing earthquakes. An evaluation module for simulating the large-scale fracturing construction of deep geothermal reservoirs based on the fracturing characteristics of deep geothermal reservoirs and the fracturing parameters and construction parameters during fracturing construction, and obtaining the interaction law of fluid flow, heat transfer, and rock mass deformation between deep geothermal reservoirs and internal weak structures during the dynamic expansion process of the fractured network. According to the interaction law of fluid flow, heat transfer, and rock mass deformation during the dynamic expansion process of the fractured network, evaluate the construction influence of weak structures on the large-scale fracturing of deep geothermal reservoirs.

7. An electronic device, characterized in that, It includes: A memory and a processor; The memory is used to store computer programs; When the processor executes the computer programs stored in the memory, it realizes the steps of an evaluation method for the influence of weak structures on the large-scale fracturing construction of deep geothermal reservoirs as described in any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that, For storing computer programs, when the computer programs are executed by a processor, the steps of an evaluation method for the influence of weak structures on the large-scale fracturing construction of deep geothermal reservoirs as described in any one of claims 1 to 5 are realized.

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