Method for assessing the impact of large-scale fracturing of a deep thermal reservoir on vulnerable structures, impact assessment device, and electronic device and computer-readable storage medium for performing the impact assessment method

Abstract

Providing a method for assessing the impact of fragile structures on large-scale fracturing in deep thermal reservoirs "Solution: Based on a precise depiction of the fragile structure of the formation and a study of its mechanical properties, the spatial distribution of the structure is determined, well locations and networks are arranged, fracturing zones are selected, and the fracturing suitability of the formation is comprehensively evaluated. Furthermore, a thermal-fluid-solid coupled damage model and a thermal-fluid-solid-chemical coupled damage model are established to study the activation conditions of the original fragile structure surface, and the fluid filtration characteristics of the structure and the maximum discharge volume that can be safely fractured are evaluated. Based on this, triaxial fracturing physical simulations and numerical simulations are carried out to clarify the influence laws of the fragile structure surface on the expansion and seepage flow of fracture cracks, and to clarify the influence mechanism of the fragile structure on large-scale fracturing of the formation under high temperature and pressure conditions."

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, apparatus, device and medium for evaluating the influence of vulnerable structures on large-scale fracturing construction of deep thermal reservoirs. [Background technology]

[0002] The impact of fracturing on deep thermal reservoirs is more complex than that on oil, gas, or coal reservoirs, primarily due to the following four factors: (1) Deep thermal reservoirs generally have a blocky structure, and the internal fracturing structures are generally not well developed, making reservoir formation through fracturing difficult. To address this shortcoming, it is crucial to detect and identify the internal fracturing structures, evaluate the fracturing suitability of the thermal reservoir, and then optimize well location and well network layout accordingly. (2) Oil and gas reservoirs are generally confined to a completely enclosed structure or a closed permeable rock body. Therefore, reservoir fracturing and modification generally do not require consideration of the risk of fracturing fluid flowing along the fracturing structures. However, in the fracturing modification of deep thermal reservoirs, the reservoir is typically under high temperature and pressure and is not completely enclosed laterally. Therefore, the reservoir generally contains little or no water. Temperature affects reactivation modification of weak structural surfaces, so the flow loss and flow impedance of the fracturing fluid must be considered. (3) Temperature is an important characteristic parameter of deep thermal reservoirs. Numerical simulation studies of fracturing modification of deep thermal reservoirs must consider the effect of the temperature field, i.e., the four-field thermal-fluid-solid-chemical (THMC) coupling, which is more complex than the three-field fluid-solid-chemical (THM) coupling for conventional oil and gas reservoirs and coal reservoirs. (4) The morphology of natural weak structural surfaces, especially faults, cracks, and caverns within deep thermal reservoirs, has a stress concentration effect, significantly hindering the expansion of artificial fractures and potentially inducing seismic risks.

[0003] Currently, the assessment of the impact of fragile structures on large-scale fracturing in deep thermal reservoirs typically relies on numerical simulation and emulation methods, using finite element analysis software to perform numerical simulations of deep thermal reservoirs. The simulations take into account the impact of fragile structures, analyze the reservoir stress distribution, fracture extension path, and fluid flow conditions during fracturing, and use the simulation results to predict the fracturing effects and evaluate the impact of fragile structures. However, these numerical simulation and emulation methods typically focus on analyzing the internal conditions of the reservoir during fracturing and ignore the impact of fragile structures on large-scale fracturing in deep thermal reservoirs under the multi-field coupling of reservoir structure, temperature, seepage flow, stress, and chemical fields. As a result, when assessing the impact of fragile structures on large-scale fracturing in deep thermal reservoirs, the results often deviate significantly from actual results, making it difficult to reflect the true interaction between fragile structures and deep thermal reservoirs. Summary of the Invention [Problem to be solved by the invention]

[0004] An embodiment of the present invention provides a method for evaluating the influence of brittle structures on large-scale fracturing of deep thermal reservoirs. This solves the problem that the prior art, i.e., current methods, usually focus on analyzing the internal conditions of the reservoir during the fracturing process, and ignore the influence of brittle structures under the multi-field coupled action of reservoir structure, temperature field, seepage flow field, stress field, and chemical field on large-scale fracturing of deep thermal reservoirs. Therefore, when evaluating the influence of brittle structures on large-scale fracturing of deep thermal reservoirs, the evaluation results deviate greatly from the actual evaluation results, making it difficult to reflect the true interaction situation between the brittle structures and deep thermal reservoirs. [Means for solving the problem]

[0005] An embodiment of the present invention provides a method for assessing the impact of large-scale fracturing of a deep thermal reservoir on a vulnerable structure, Obtaining fracturing characteristics of the deep thermal reservoir, the fracturing characteristics representing the rock brittleness, the development characteristics of the internal fragile structure, and the internal geostress distribution in the deep thermal reservoir during fracturing; Obtaining the deformation characteristics and fracturing crack expansion characteristics of the fragile structure inside the deep thermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and determining the fracturing parameters and operation parameters for large-scale fracturing operation in the deep thermal reservoir through the deformation characteristics and fracturing crack expansion characteristics under the premise of not inducing an earthquake, wherein the deformation characteristics and fracturing crack expansion characteristics represent the conditions under which the fracturing fluid enters the fragile structure, the fragile structure is pulled open, and the fracturing crack expands within the fragile structure, and evaluating the possibility of inducing an earthquake; A step of performing a large-scale fracturing construction simulation on the deep thermal reservoir based on the fracturing characteristics of the deep thermal reservoir and the fracturing parameters and construction parameters during the fracturing construction, and obtaining the interaction laws of fluid flow, heat transfer, and rock deformation between the deep thermal reservoir and the internal brittle structure during the dynamic expansion process of the fracturing crack network; and evaluating the influence of the fragile structure on the large-scale fracturing operation of the deep thermal reservoir according to the interaction law of fluid flow, heat transfer, and rock deformation in the dynamic expansion process of the fracturing crack network.

[0006] Preferably, obtaining the fracturing characteristics of the deep thermal reservoir includes: conducting drilling studies and logging analysis on the deep thermal reservoir to obtain spatial distribution characteristics of the geometric, physical, and mechanical properties of the deep thermal reservoir; Using diamond wire cutting method to process the borehole core drilled from the deep thermal reservoir into standard rock samples, and conducting rock triaxial mechanical experiments on the standard rock samples under different temperature and confining pressure conditions to obtain the stress-strain curves of the rock under different conditions, and the evolution characteristics of the pressure strength, elastic modulus, Poisson's ratio, cohesion and internal friction angle of the deep thermal reservoir; According to the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep thermal reservoir, a nonlinear damage constitutive model of rock is established to simulate the damage evolution law of the rock in the deep thermal reservoir during stress; Utilizing fractal method to establish a mechanical brittleness index model that reflects the rock deformation failure process of the deep thermal reservoir, and simulating the brittle characteristics, activation conditions and expansion manner of the brittle structure in the deep thermal reservoir; and constructing a three-dimensional multi-attribute model of the deep thermal reservoir containing the brittle structure, the model including a geostress field and a temperature field, and using the model to perform feature reconstruction of the geostress field and the temperature field of the hot dry rock mass, and obtaining the fracturing characteristics of the deep thermal reservoir based on the damage evolution law of the deep thermal reservoir, the brittle characteristics of the brittle structure, the activation conditions and expansion methods, and the geostress field and the temperature field of the hot dry rock mass.

[0007] Preferably, the acquisition of the deformation characteristics and fracturing crack extension characteristics of the fragile structure includes: Matrix acid treatment, hydraulic fracturing, and acid treatment fracturing experiments were carried out on the deep thermal reservoir. During the experiment, the geostress difference, the inclination angle of the weak structure surface, the cohesion force of the weak structure surface, the internal friction angle of the weak structure surface, and the tensile strength of the weak structure surface were taken into consideration, and the stress mechanism of the weak structure surface during the actual fracturing process was simulated to obtain the activation conditions of the original weak structure surface in the deep thermal reservoir. Here, the activation conditions are the temperature and the activation effect of the artificial crack expansion method on the original brittle structure surface; The method includes establishing a thermal-fluid-solid coupled damage model THMD and a thermal-fluid-solid-chemical coupled damage model THMCD, and simulating the deformation and failure characteristics of the natural brittle structure surface under multi-field coupling, where the deformation and failure characteristics of the natural brittle structure surface are the deformation characteristics and fracturing crack extension characteristics of the brittle structure, and obtaining the conditions under which the brittle structure will undergo tensile and shear fracture damage under the interference of the artificial crack, and after the fracturing fluid enters the brittle structure surface, the brittle structure surface will be pulled and cleaved, and the fracturing crack will turn and extend toward the brittle structure surface.

[0008] Preferably, determining fracturing parameters and construction parameters during large-scale fracturing construction of a deep thermal reservoir on the premise of not inducing an earthquake includes: According to the conditions under which the fragile structure plane is tensile-ruptured and the fracturing cracks are turned and expanded toward the fragile structure plane, a reactivation criterion for the fragile structure plane is established, and the reactivation criterion for the fragile structure plane is determined by considering the mechanical characteristics of the fragile structure plane, the injection conditions of the fracturing fluid, and the multi-field coupling, and by evaluating the fluid permeation characteristics and earthquake triggering potential of the fragile structure zone; The method includes a step of predicting the maximum discharge amount, construction pump pressure, total injected liquid amount, and effective rework volume (SRV) that can be safely used for fracturing in the deep thermal reservoir according to the activation conditions of the original weak structural surface in the deep thermal reservoir, the fluid filtration characteristics of the weak structural zone, and the possibility of earthquake induction, and predicting the fracturing parameters and construction parameters for large-scale fracturing construction in the deep thermal reservoir.

[0009] Preferably, the acquisition of the interaction law of fluid flow, heat transfer, and rock deformation between the deep heat reservoir and the internal weak structure during the dynamic expansion process of the fracturing crack network includes: preparing a number of multi-fractured rock samples, and conducting triaxial fracturing physical simulations on the multi-fractured rock samples under different injection media, heat treatment temperatures, cycle heat treatment times, horizontal stress differences, and different discharge conditions, to obtain the crack initiation and expansion process and pressure response law of the fracture network in deep thermal reservoir rock; Using room temperature fracturing fluid to simulate low-temperature shock, fracturing experiments are carried out on multi-cracked rock samples, and an acoustic emission device is used to monitor the evolution of the crack network during the low-temperature shock process. Micro-CT scans are performed on the crack network structure of the rock samples before and after the low-temperature shock, and the complex crack morphology is precisely described to obtain the dynamic expansion process of the fracturing crack network in the deep thermal reservoir rock; preparing a full-diameter test rock sample, creating a fracture in the test rock sample, and conducting a seepage flow parameter test on the test rock sample under different fracture width, confining pressure, and flow velocity conditions to obtain a multi-scale seepage flow law for a deep thermal reservoir; Based on the dynamic expansion process of the fracture network of deep thermal reservoir rock and the multi-scale seepage flow law, establish the mathematical physical governing equations of the stress field, temperature field and seepage flow field of the hot rock mass at the in-situ scale, obtain the influence relationship between the damage coefficients of different injection media and the thermal-fluid-solid-chemical equations, and form a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock; constructing an in-situ scale complex fracture network THMD fully coupled fracturing model according to a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock, wherein the in-situ scale complex fracture network THMD fully coupled fracturing model is a thermal-fluid-solid-damage fully coupled fracturing model; and simulating the interaction laws of fluid flow, heat transfer, and rock deformation during the dynamic expansion process of the fracturing fracture network based on an in-situ scale complex fracture network THMD fully coupled fracturing model.

[0010] An embodiment of the present invention also provides an apparatus for assessing the influence of a vulnerable structure on a large-scale fracturing operation in a deep thermal reservoir, a fracturing characteristics module used to obtain the fracturing characteristics of the deep thermal reservoir, the fracturing characteristics representing the rock brittleness, the development characteristics of the internal fragile structure, and the internal geostress distribution in the deep thermal reservoir during fracturing; a simulation module for obtaining deformation characteristics and fracturing crack expansion characteristics of the fragile structure inside the deep thermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and using the deformation characteristics and fracturing crack expansion characteristics to determine fracturing parameters and operation parameters during large-scale fracturing operation in the deep thermal reservoir under the premise of not inducing an earthquake, where the deformation characteristics and fracturing crack expansion characteristics represent the conditions under which the fracturing fluid enters the fragile structure, the fragile structure is pulled open, and the fracturing crack expands within the fragile structure, and for evaluating the possibility of inducing an earthquake; Based on the fracturing characteristics of the deep thermal reservoir and the fracturing and construction parameters during fracturing construction, a large-scale fracturing construction simulation is carried out for the deep thermal reservoir, and the interaction laws of fluid flow, heat transfer, and rock deformation between the deep thermal reservoir and the internal brittle structure during the dynamic expansion process of the fracturing crack network are obtained. and an evaluation module used to evaluate the influence of brittle structures on large-scale fracturing construction in deep thermal reservoirs according to the interaction laws of fluid flow, heat transfer, and rock deformation in the dynamic expansion process of the fracturing crack network.

[0011] An embodiment of the present invention also provides an electronic device, comprising: a memory; and a processor; the memory is used to store a computer program; The processor, when executing the computer program stored in the memory, is used to implement the steps of the method for assessing the impact of vulnerable structures on large-scale fracturing construction in deep thermal reservoirs described above.

[0012] An embodiment of the present invention also provides a computer-readable storage medium, used to store a computer program, which, when executed by a processor, implements the steps of the method for assessing the impact of a fragile structure on a large-scale fracturing operation in a deep thermal reservoir described above. [Effects of the Invention]

[0013] The method for assessing the impact of fragile structures on large-scale fracturing construction in deep thermal reservoirs provided by the embodiments of the present invention has the following beneficial effects compared with the prior art:

[0014] This invention first obtains the fracturing characteristics of deep thermal reservoirs and establishes a thermal-fluid-solid coupled damage model (THMD) and a thermal-fluid-solid-chemical coupled damage model (THMCD) to predict the fracturing and construction parameters for large-scale fracturing in deep thermal reservoirs without inducing earthquakes. Based on the fracturing characteristics of deep thermal reservoirs and the fracturing and construction parameters for large-scale fracturing in deep thermal reservoirs, the interaction laws of fluid flow, heat transfer, and rock deformation in deep thermal reservoir rocks during the dynamic expansion process of the fracturing fracture network are evaluated from the perspective of simulating large-scale fracturing in deep thermal reservoirs. In this process, the reservoir structure represented by the fracturing characteristics during the fracturing of deep thermal reservoirs, as well as the temperature field, seepage field, stress field, and chemical field during the fracturing process represented by the interaction laws of fluid flow, heat transfer, and rock deformation, are taken into consideration. In other words, the influence of the brittle structure on large-scale fracturing of deep thermal reservoirs under the multi-field coupled action of the reservoir structure, temperature field, seepage field, stress field, and chemical field during fracturing is comprehensively considered, and the influence of the brittle structure on large-scale fracturing of deep thermal reservoirs can be truly and accurately evaluated. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of the overall flow of a method for assessing the impact of large-scale fracturing construction on fragile structures in deep thermal reservoirs provided by an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0016] In order to make the above-mentioned objects, features, and advantages of the present invention clearer and easier to understand, specific embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, many specific details are set forth 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 improvements without departing from the spirit of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0017] Referring to FIG. 1, an embodiment of the present invention provides a method for assessing the impact of large-scale fracturing operations on a fragile structure in a deep thermal reservoir, which includes the following steps:

[0018] Step 1: Study the three-dimensional spatial distribution characteristics of the weak structure of the deep thermal reservoir.

[0019] Geological, drilling, logging, and testing information are integrated, and data fusion and modeling techniques are used to clarify the spatial distribution of the geometric, physical, and mechanical properties of deep thermal reservoirs. After systematically analyzing the geological characteristics of deep thermal reservoirs, diamond wire cutting is used to process standard rock samples from outcrops or downhole cores of the deep thermal reservoirs. Real-time triaxial rock mechanics experiments are then conducted under different temperature and confining pressure conditions, achieving dual coupling of temperature and pressure. Based on the stress-strain curves obtained from the experiments, the evolution characteristics of compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle under different confining pressure coupling parameters are analyzed, a nonlinear damage constitutive model for rock is established, and the damage evolution laws of rock mechanics parameters are analyzed. Using fractal methods, a mechanical fragility index model is established to reflect the characteristics of the entire process of rock deformation and failure, and the fragility, activation conditions, and expansion methods of the fragile structure are analyzed. A three-dimensional multi-attribute model (geostress field, temperature field) of the deep thermal reservoir, including the fragile structure of the thermal reservoir, is established to realize the reconstruction of the geostress field and temperature field characteristics of the hot dry rock. The fracturing suitability of the thermal reservoir is comprehensively evaluated based on the fragility of the rock, the development characteristics of the fragile structure, and the geostress distribution.

[0020] Fractal theory combines fractal geometry, physics, and solid mechanics to describe the irregularity, nonlinearity, and randomness of rock deformation and failure processes. By studying the distribution of debris and calculating its fractal dimension, a correlation model between debris fractal dimension and rock brittleness index is established. Based on this correlation model, elastic analysis, plastic internal force redistribution analysis, elasto-plastic analysis, plastic limit analysis, and test analysis methods are used to study the mechanical behavior of brittle structures. Geostress analysis takes into account factors such as depth, crustal thickness, lithology, seismic activity, and geological structure, and studies the effects of brittle structures on the physical and mechanical properties of rocks, including changes in rock permeability, porosity, elastic modulus, and Poisson's ratio. At the same time, three-dimensional simulation is carried out using Petrel software to establish a geological model framework, and the sequential Gaussian interpolation method is adopted to establish a porosity and permeability model, which is combined with temperature data to establish a temperature field model. Taking into account the high ground stress problem, the thermal stress field and geostress field of the supporting structure and surrounding rocks are studied.

[0021] Step 2: Study on the influence of the fragile structure of the deep thermal reservoir on fracturing operation.

[0022] Using a combined laboratory test and numerical simulation technique, we conducted matrix acidizing, hydraulic fracturing, and acid fracturing experiments. We considered geostress differentials, the dip angle of the weak tectonic surface, the cohesion of the weak tectonic surface, the internal friction angle of the weak tectonic surface, and the tensile strength of the weak tectonic surface to study the activation conditions of the natural weak tectonic surface, namely, the activation effects of temperature and the expansion mode (redirection and penetration) of the artificial crack on the natural weak tectonic surface. We established a thermal-fluid-solid coupled damage (THMD) model and a thermal-fluid-solid-chemical coupled damage (THMCD) model to study the deformation and failure characteristics of the natural weak tectonic surface under multi-field coupling, namely, the tensile and shear failure damage caused by the interference of the artificial crack. We analyzed the conditions under which the fracturing fluid penetrates the weak tectonic surface, causing tensional rupture of the weak tectonic surface and the fracturing crack redirecting and expanding toward the weak tectonic surface. We established a reactivation criterion for the weak tectonic surface and evaluated the fluid permeability of the weak tectonic zone and its potential for earthquake triggering. This method predicts and estimates the maximum discharge rate, pump pressure, total injection volume, and effective rework volume (SRV) that can be safely used for fracturing, selects fracturing and construction parameters, guides the optimization of fracturing construction methods, and clarifies the influence of the fragile structure of deep thermal reservoirs on fracturing construction.

[0023] in particular: Laboratory tests precisely controlled experimental conditions to simulate a deep thermal reservoir environment, conducting matrix acidizing, hydraulic fracturing, and acid fracturing experiments. During the experiments, the mechanical response of rock samples and fracture expansion were monitored in real time to obtain experimental data. Numerical simulations utilized advanced computational software to establish a geological model of the deep thermal reservoir and simulate the fracturing process under different geostress conditions and fragile structural characteristics. Numerical simulations predicted the fracture expansion path, shape, and fracturing effects, providing theoretical support for laboratory tests. Laboratory experimental data and numerical simulation results were compared and analyzed to verify the accuracy of the model, and the numerical simulation parameters were adjusted based on the experimental results to improve the accuracy and reliability of the simulation.

[0024] Matrix acidizing involves forcing acid into reservoir pore spaces under pressure lower than the reservoir rock's fracturing pressure, dissolving particles and blockages in the pore space, expanding the pore space, and improving the formation's permeability. Hydraulic fracturing involves injecting fluid using a high-pressure pump to form fractures in the formation, improving the formation's permeability. During the hydraulic fracturing process, fracture expansion is influenced by factors such as geostress and rock mechanics. Acid fracturing combines the principles of acidizing and hydraulic fracturing. First, fractures are formed using hydraulic fracturing, and then acid is injected to dissolve the fracture wall rock and expand the fracture's flow capacity. Acid fracturing can more effectively modify reservoirs and improve oil and gas well production.

[0025] Geostress differences have a significant impact on the strength and stability of rock masses. During fracturing, geostress differences affect the direction and shape of fracture extension, which in turn affects the fracturing effect. The inclination angle of the weak structure plane significantly affects the strength of rock masses. Different inclination angles can lead to different failure modes, such as normal slip and shear failure, affecting the safety and stability of the process. Mechanical parameters such as the cohesion, internal friction angle, and tensile strength of the weak structure plane determine the shear and tensile strength of the weak structure plane. During fracturing, these mechanical parameters of the weak structure plane affect the fracture extension path and shape, which in turn affects the fracturing effect. Temperature changes affect the physical and chemical properties of rock masses, such as the thermal expansion coefficient and elastic modulus of rock. High temperatures in deep thermal reservoir environments significantly change the mechanical properties of rock, further affecting the stability and activation conditions of the weak structure plane. The artificial fracture extension method affects the activation conditions of the weak structure plane. If the crack changes direction, it may bypass the weak plane and mitigate the damage to it, but if the crack penetrates the weak plane, it may directly damage the weak plane and affect its stability.

[0026] The thermal-fluid-solid coupled damage (THMD) model considers thermal-fluid-solid coupling effects and simulates the hydraulic crack expansion process to clarify the effects of temperature, seepage flow, and stress fields on crack expansion, providing a theoretical basis for optimizing fracturing construction plans. The thermal-fluid-solid-chemical coupled damage (THMCD) model, established based on the gas heat flow equation, turbulence equation, solid heat conduction equation, and thermoelasticity equation, analyzes the compressible thermal flow characteristics of gas in the cavern chamber and the thermomechanical response of the lining and surrounding rock during the hydrogen storage injection and extraction process in lined rock caverns. The thermal-fluid-solid coupled damage (THMD) model and thermal-fluid-solid-chemical coupled damage (THMCD) model comprehensively consider factors such as geostress, temperature, seepage flow, and chemical action to study their effects on rock deformation and failure. At the same time, they study the physical and mechanical properties of rock, such as stress, strength, deformation, failure, and fluid-heat-chemical transport, thereby solving the deformation and stability issues of engineered rock.

[0027] Under the interference of artificial fractures, the fractures can damage the fragile structure, affecting its internal force distribution, shear capacity, and deformation probability. After fracturing fluid enters the fragile structure, the high-pressure fracturing fluid generates internal pressure in the fractures and fragile surfaces at each level, causing them to expand and stretch within the space. If the pumping pressure of the high-pressure fracturing fluid is sufficiently high, the fracturing fluid will enter the fragile structure and tensilely open the fragile structure. Based on the energy release rate minimization principle, we obtain the strain energy release rate conditions for hydraulic crack expansion in any direction, taking into account factors such as geostress and friction. We then establish reactivation criteria based on the mechanical properties and geological conditions of the fragile structure, and predict and control the activation behavior of the fragile structure. Because fragile structures have high permeability, are prone to compressive deformation, have low self-stabilizing capacity, and contain a large amount of clay minerals, a method combining laboratory tests and numerical simulations can be used to evaluate the fluid filtration characteristics of fragile structure zones. When predicting the possibility of earthquake induction, we study the influence of vulnerable structural surfaces on the dynamic response of slopes during earthquakes, i.e., their influence on the slope dynamic response evaluation index and their influence on the spatial distribution of slope seismic energy and slope plastic failure mode, to provide a scientific basis for earthquake prediction and slope stability assessment, and to evaluate the possibility of earthquake induction.

[0028] The maximum discharge volume for safe fracturing is determined based on factors such as the fracturing equipment capacity, wellhead pressure capacity, and formation fracturing pressure. The maximum pumping pressure at the wellhead must be estimated based on the maximum pumping pressure allowed by the fracturing equipment and wellhead. The pumping pressure can be predicted by predicting formation fracturing pressure and reducing frictional resistance along the way. The total injection volume must take into account factors such as the geological conditions of the formation and the thickness of the fractured layer, and is used to calculate the total injection volume for safe fracturing. The total volume of fracturing fluid is the sum of the volumes of pre-fluid, sand-carrying fluid, and replacement fluid. Events are selected and optimized based on the hydraulic fracturing mechanism, the fracture time sequence of the event points, spatial combination characteristics, and event reliability. The geometric characteristics of the fractured fracture (fracture length, width, and height) are quantitatively interpreted, and the effective rework volume (SRV) is calculated. Based on the maximum discharge rate, pumping pressure, total injection volume, and effective rework volume (SRV) for safe fracturing, a reservoir hydraulic fracturing model is established. The first-layer fracturing parameters are selected based on the hydraulic fracture propagation within the reservoir. The first-layer fracturing parameters are then used to calculate the fracture morphology of the upper layer. Based on the non-communication of the upper and lower layers, the fracture morphology of the upper and lower layers is calculated for different isolation layer thicknesses. The thickness of the isolation layer that can prevent the fracture propagation between the upper and lower layers is determined. Finally, the final fracturing layer is determined, and the construction parameters and fracturing parameters for the upper layer are optimized. In guiding the optimization of the fracturing construction plan, the presence of weak structural planes affects the hydraulic fracturing fracture pressure. At the same time, the weak structural structure of the deep thermal reservoir (natural weak planes, fractures, etc.) affects the hydraulic fracturing fracture propagation pattern, and the weak structural planes affect the hydraulic fracture propagation direction.

[0029] Step 3: Study on the influence of the fragile structure of the deep thermal reservoir on the fracturing operation effect.

[0030] Random multi-fractured rock samples were prepared to study the crack initiation, expansion, and pressure response laws of fracture networks in deep thermal reservoir rocks under different injection media (water, acid, CO2), heat treatment temperatures, cycle heating cycles, horizontal stress differences, and discharge rates. Cold shock was simulated using room-temperature fracturing fluid, and the evolution characteristics of the fracture network were monitored using acoustic emission and tracers. Micro-CT was used to scan the fracture networks in the rock samples before and after the experiment to describe the complex fracture morphology. Full-diameter test rock samples were prepared, artificial fractures were introduced, and seepage flow parameter tests were conducted under different fracture widths, confining pressures, and flow velocities. Real-time analysis of seepage flow characteristics clarified the main controlling factors affecting fluid seepage flow laws, accurately depicted the dynamic expansion process of complex fracture networks, and revealed multi-scale seepage flow laws for different injection media. Based on the microscopic damage evolution of rocks and their fracture mechanisms, combined with previous experimental tests and theoretical analysis, we established mathematical physical governing equations for the stress, temperature, and seepage fields of hot rocks at the in-situ scale. We proposed the influence relationships between the damage coefficients of different injection media and the thermal-fluid-solid-chemical equations, and formed a rock temperature-seepage-stress-chemical-damage constitutive model for deep thermal reservoirs. Based on this, we constructed a fully coupled THMD fracturing model for complex fracture networks at the in-situ scale to analyze the interaction laws of fluid flow, heat transfer, and rock deformation during the fracture initiation and expansion process in the fracture network. We investigated the influence laws of complex geological factors such as different geothermal temperatures, thermal conductivity, geostresses, pore pressures, and natural fragile structure morphologies, as well as different fracturing discharges, fracturing fluid types, and temporary blockage diversions, on the fracture initiation, expansion, and stress field changes in complex fracture networks, thereby clarifying the influence of the fragile structure of deep thermal reservoirs on the fracturing effect.

[0031] in particular: Tin strips were prepared to simulate cracks, and mortar material was prepared to simulate rock material. The tin strips and mortar material were mixed and stirred to randomly distribute the tin strips throughout the mortar material. The mixture was then placed in a mold and vibrated to produce multi-fractured rock samples. The effects of different injection media (water, acid, and CO2) on crack extension were investigated, and it was found that supercritical CO2 induces complex crack morphologies and can interact with low-temperature-induced thermal stresses during thermal reservoir fracturing. The evolution of the mechanical elastic-plastic characteristics of mid- and deep-level geothermal reservoir rocks under high temperatures was studied, and it was found that high temperatures have a significant effect on the redirection and extension of artificial cracks, enhancing the plasticity of rock and changing the crack extension pattern. The effects of thermal cycling on the macroscopic mechanical properties and crack extension of rocks were investigated, and it was found that increasing the number of thermal cycles reduces the crack initiation stress of rock, affecting its crack extension capacity. We investigated the effect of horizontal principal stress ratio on the expansion and evolution of fracturing fracture networks and found that as the horizontal principal stress ratio increased, the area occupied by the hydraulic fracture network in the x-axis direction gradually decreased, increasing the resistance to fracture expansion. We also investigated the effect of different discharge rates on hydraulic fracture expansion and found that injecting low-viscosity fracturing fluid at large discharge rates or high-viscosity fracturing fluid at medium to small discharge rates can connect hydraulic fractures with cavities that are close to and at a small angle to the initial extension direction. We simulated low-temperature impact tests using room-temperature fracturing fluid by switching products between high-temperature and low-temperature chambers to evaluate the performance of materials in low-temperature environments. We also used acoustic emission and tracers to monitor the evolution of the fracture network. We used acoustic emission to monitor the rock fracture process and clarify the mechanism of hydraulic fracture network formation, and tracers to monitor the flow path of the fracturing fluid and study the evolution of the fracture network. At the same time, micro-CT is used to scan the fracture network of the rock samples before and after the experiment, and by processing the CT scan data before and after fracturing, parameters such as fracture extension, dip angle, and fracture rate can be quantitatively described.

[0032] To prepare full-diameter test rock specimens, natural rock sample powders were selected based on the pore-characteristic test results and mixed with organic adhesives at different weight ratios. The resulting viscous mixture was applied to the mating surfaces of the fractured horizontal section rock specimens, bonding the three blocks together and filling the recesses and other cracks on the sides of the core column. After filling, the test rock specimens were compressed and bonded together. The Brazilian splitting tension crack induction method was used, and a pressure tester was used to apply pressure to the sides of cylindrical concrete specimens, creating tensile stress under load, which then cracked the concrete surface and formed artificial cracks. Seepage flow parameter tests were conducted under different crack widths, confining pressures, and flow velocities using the MTS815 triaxial seepage flow test system, a multifunctional mechanical experimental device. Numerical simulation methods such as the finite element method and finite difference method were used to solve the seepage flow field, generate high-precision seepage flow data maps, and analyze the seepage flow characteristics.

[0033] In determining the main controlling factors affecting fluid seepage flow law, the strong polar molecular interaction at the solid-liquid interface causes one-sided boundary layers to adsorb to the pore wall, preventing them from participating in flow and resulting in nonlinearity. In the same low-permeability porous medium, the stronger the solid-liquid interface with intermolecular forces, the higher the initial pressure gradient. Under the same pressure gradient, the lower the flow rate, the lower the permeability of the porous medium, and the greater the influence of intermolecular forces between solid and liquid surfaces on the seepage flow. Once the permeability of the porous medium reaches a certain value, the influence of solid surface molecules on the fluid seepage flow becomes essentially negligible, and the seepage flow transforms into a Darcy-type flow. As the pressure gradient gradually increases, the influence of solid-liquid surface intermolecular forces on the seepage flow gradually weakens. We then performed a fracture expansion simulation using the high-performance oil reservoir simulator tNavigator software FS1.1. We established the maximum principal stress direction field and simulated the expansion directions of different zones and clusters. This accurately depicted the dynamic expansion process of complex fracture networks and revealed the multi-scale seepage flow law for different injection media.

[0034] Starting from the microscopic structure level of rock materials, we establish a numerical model to describe the thermal-seepage-stress-damage coupling of rock microstructures based on microscopic damage mechanics, elastic thermodynamics, and Biot's classical seepage flow dynamics theory. Through simulations using the TOUGH-RFPA elastic model and damage model, we analyze the influence of different injection media on the damage coefficient and the thermal-fluid-solid-chemical equations through injection pressure-time change curves. Using mechanism analysis, system identification, and hybrid analysis methods, we analyze the above content and establish a coupled model of the rock seepage flow field and stress field.

[0035] Based on the above research, Comsol software was used to simulate a rock hydraulic fracture damage THMD coupled model, and based on the assumed conditions of linear elastic fracture mechanics (LEFM), the stress intensity coefficient was calculated to control the stability and expansion trajectory of the crack, automatically setting cracks at any point and any angle on the boundary, forming crack expansion functions, and freely adjusting the network along the expanding crack. The crack initiation in the crack network and the interaction laws of fluid flow, heat transfer, and rock deformation during the expansion process were analyzed.

[0036] This project investigates changes in the physical and mechanical properties of rock under different geothermal conditions and their effects on the initiation and expansion of fracture networks. It also investigates the principles of heat transfer through rock under different thermal conductivity conditions and their effects on the initiation and expansion of fracture networks. It also investigates the principles of stress distribution in rock under different geostress conditions and their effects on the initiation and expansion of fracture networks. It also investigates the principles of fluid flow through rock under different pore pressure conditions and their effects on the initiation and expansion of fracture networks. It also investigates rock failure patterns under different natural fragile structural surface morphologies and their effects on the initiation and expansion of fracture networks. It also uses a large-scale true triaxial fracturing facility to establish a temporary blockage deflection fracturing physical simulation device and conduct experiments to investigate the principles of fracture initiation and expansion of fracture networks under different fracturing discharge conditions and their effects on stress field changes. It also investigates the principles of fracture initiation and expansion of fracture networks under different fracturing fluid types and their effects on stress field changes. The effects of temporary closure diversion technology on the initiation and expansion of fracture networks and its effect on improving fracturing effectiveness are studied. Based on the above research results, the effects of the fragile structure of deep thermal reservoirs on the physical and mechanical properties of rocks during the fracturing process are studied, and the effects of the fragile structure on fracturing effectiveness are investigated, and the effects of the fragile structure of deep thermal reservoirs on fracturing effectiveness are clarified.

[0037] This study aims to solve the difficult problem of pre-assessing the impact of fragile structures on large-scale fracturing in deep thermal reservoirs. Based on a precise description of the fragile structures and a study of their mechanical properties, the study identifies the spatial distribution of the fragile structures in deep thermal reservoirs, arranges well locations and well networks, selects fracturing zones, and comprehensively evaluates the fracturing suitability of the thermal reservoir. Thermal-fluid-solid and thermal-fluid-solid-chemical coupled damage models (THMD and THMCD) are established to study the activation conditions of the original fragile structures, evaluate the fluid filtration characteristics of the fragile structures, and assess the maximum discharge rate for safe fracturing (without triggering an earthquake). Physical and numerical simulations of true triaxial fracturing are conducted to clarify the influence of fragile structures on the expansion and seepage flow of fractured cracks, and to clarify the mechanism of the influence of fragile structures on large-scale fracturing in deep thermal reservoirs.

[0038] The above-described examples merely represent some embodiments of the present invention, and although the descriptions are specific and detailed, they should not be understood as limiting the scope of the patented invention. It should be noted that those skilled in the art may make some modifications and improvements without departing from the concept of the present invention, and all of these fall within the scope of protection of the present invention. Therefore, the scope of protection of the patented invention should be determined by the appended claims.

Claims

1. A method for assessing the impact of large-scale fracturing work on a deep thermal reservoir on a vulnerable structure, comprising: Obtaining fracturing characteristics of the deep thermal reservoir, the fracturing characteristics representing the rock brittleness, the development characteristics of the internal fragile structure, and the internal geostress distribution in the deep thermal reservoir during fracturing; Obtaining the deformation characteristics and fracturing crack expansion characteristics of the fragile structure inside the deep thermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and determining the fracturing parameters and operation parameters for large-scale fracturing operation in the deep thermal reservoir through the deformation characteristics and fracturing crack expansion characteristics under the premise of not inducing an earthquake, wherein the deformation characteristics and fracturing crack expansion characteristics represent the conditions under which the fracturing fluid enters the fragile structure, the fragile structure is pulled open, and the fracturing crack expands within the fragile structure, and evaluating the possibility of inducing an earthquake; A step of performing a large-scale fracturing construction simulation on the deep thermal reservoir based on the fracturing characteristics of the deep thermal reservoir and the fracturing parameters and construction parameters during the fracturing construction, and obtaining the interaction laws of fluid flow, heat transfer, and rock deformation between the deep thermal reservoir and the internal brittle structure during the dynamic expansion process of the fracturing crack network; Evaluating the influence of fragile structures on large-scale fracturing construction in deep thermal reservoirs according to the interaction laws of fluid flow, heat transfer, and rock deformation in the dynamic expansion process of the fracturing crack network; The acquisition of the deformation characteristics and fracturing crack extension characteristics of the fragile structure includes: Matrix acid treatment, hydraulic fracturing, and acid treatment fracturing experiments were carried out on the deep thermal reservoir. During the experiment, the geostress difference, the inclination angle of the weak structure surface, the cohesion force of the weak structure surface, the internal friction angle of the weak structure surface, and the tensile strength of the weak structure surface were taken into consideration, and the stress mechanism of the weak structure surface during the actual fracturing process was simulated to obtain the activation conditions of the original weak structure surface in the deep thermal reservoir. Here, the activation conditions are the temperature and the activation effect of the artificial crack expansion method on the original brittle structure surface; Establishing a thermal-fluid-solid coupled damage model THMD and a thermal-fluid-solid-chemical coupled damage model THMCD, and obtaining the deformation and fracture characteristics of the natural fragile structure surface under multi-field coupling action through simulation, the deformation and fracture characteristics of the natural fragile structure surface are the deformation characteristics and fracturing crack extension characteristics of the fragile structure, and obtaining the conditions under which the fragile structure will undergo tensile and shear fracture damage under the interference of the artificial crack, the fracturing liquid will enter the fragile structure surface, the fracturing structure surface will be pulled open, and the fracturing crack will turn and extend towards the fragile structure surface; The interaction law of fluid flow, heat transfer, and rock deformation between the deep heat reservoir and the internal weak structure during the dynamic expansion process of the fracturing crack network is obtained. preparing a number of multi-fractured rock samples, and conducting triaxial fracturing physical simulations on the multi-fractured rock samples under different injection media, heat treatment temperatures, cycle heat treatment times, horizontal stress differences, and different discharge conditions, to obtain the crack initiation and expansion process and pressure response law of the fracture network in deep thermal reservoir rock; Using room temperature fracturing fluid to simulate low-temperature shock, fracturing experiments are carried out on multi-cracked rock samples, and an acoustic emission device is used to monitor the evolution of the crack network during the low-temperature shock process. Micro-CT scans are performed on the crack network structure of the rock samples before and after the low-temperature shock, and the complex crack morphology is precisely described to obtain the dynamic expansion process of the fracturing crack network in the deep thermal reservoir rock; preparing a full-diameter test rock sample, creating a fracture in the test rock sample, and conducting a seepage flow parameter test on the test rock sample under different fracture width, confining pressure, and flow velocity conditions to obtain a multi-scale seepage flow law for a deep thermal reservoir; Based on the dynamic expansion process of the fracture network of deep thermal reservoir rock and the multi-scale seepage law, establish the mathematical physical governing equations of the stress field, temperature field and seepage field of the hot rock mass at the in-situ scale, obtain the influence relationship between the damage coefficients of different injection media and the heat-fluid-solid-chemical equation, and form a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock; Constructing an in-situ scale complex fracture network THMD fully coupled fracturing model according to a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock, wherein the in-situ scale complex fracture network THMD fully coupled fracturing model is a thermal-fluid-solid-damage fully coupled fracturing model; A method for evaluating the impact of brittle structures on large-scale fracturing construction in deep thermal reservoirs, characterized by including a step of simulating the interaction laws of fluid flow, heat transfer, and rock deformation during the dynamic expansion process of a fracturing fracture network based on an in-situ scale complex fracture network THMD fully coupled fracturing model.

2. The acquisition of the fracturing characteristics of the deep thermal reservoir includes: conducting drilling studies and logging analysis on the deep thermal reservoir to obtain spatial distribution characteristics of the geometric, physical, and mechanical properties of the deep thermal reservoir; Using diamond wire cutting method to process the borehole core drilled from the deep thermal reservoir into standard rock samples, and conducting rock triaxial mechanical experiments on the standard rock samples under different temperature and confining pressure conditions to obtain the stress-strain curves of the rock under different conditions, and the evolution characteristics of the pressure strength, elastic modulus, Poisson's ratio, cohesion and internal friction angle of the deep thermal reservoir; According to the evolution characteristics of the compressive strength, elastic modulus, Poisson's ratio, cohesion, and internal friction angle of the deep thermal reservoir, a nonlinear damage constitutive model of rock is established to simulate the damage evolution law of the rock in the deep thermal reservoir during stress; Utilizing fractal method to establish a mechanical brittleness index model that reflects the rock deformation failure process of the deep thermal reservoir, and simulating the brittle characteristics, activation conditions and expansion manner of the brittle structure in the deep thermal reservoir; 2. The method for assessing the impact of brittle structures on large-scale fracturing construction of deep thermal reservoirs as described in claim 1, further comprising the steps of: constructing a three-dimensional multi-attribute model of a deep thermal reservoir containing brittle structures, the model including geostress fields and temperature fields; using the model to reconstruct the characteristics of the geostress fields and temperature fields of the hot dry rock mass; and obtaining the fracturing characteristics of the deep thermal reservoir based on the damage evolution law of the deep thermal reservoir, the brittle characteristics of the brittle structures, the activation conditions and expansion methods, and the geostress fields and temperature fields of the hot dry rock mass.

3. Determining the fracturing parameters and construction parameters for large-scale fracturing of deep thermal reservoirs on the premise of not inducing the earthquake is According to the conditions under which the fragile structure plane is tensile-ruptured and the fracturing cracks are turned and expanded toward the fragile structure plane, a reactivation criterion for the fragile structure plane is established, and the reactivation criterion for the fragile structure plane is determined by considering the mechanical characteristics of the fragile structure plane, the injection conditions of the fracturing fluid, and the multi-field coupling, and evaluating the fluid permeation characteristics and earthquake triggering potential of the fragile structure zone; A method for assessing the impact of fragile structures on large-scale fracturing construction in deep thermal reservoirs as described in claim 1, characterized in that it includes a step of predicting the maximum discharge volume, construction pump pressure, total injected liquid volume, and effective rework volume (SRV) that can be safely performed in fracturing in deep thermal reservoirs according to the activation conditions of the original fragile structural surface in the deep thermal reservoir, the fluid filtration characteristics of the fragile structural zone, and the possibility of earthquake induction, and predicting the fracturing parameters and construction parameters for large-scale fracturing construction in deep thermal reservoirs.

4. A device for assessing the impact of a vulnerable structure on large-scale fracturing work in a deep thermal reservoir, a fracturing characteristics module used to obtain the fracturing characteristics of the deep thermal reservoir, the fracturing characteristics representing the rock brittleness, the development characteristics of the internal fragile structure, and the internal geostress distribution in the deep thermal reservoir during fracturing; a simulation module for obtaining deformation characteristics and fracturing crack expansion characteristics of the fragile structure inside the deep thermal reservoir under the coupled action of heat, fluid, solid, and chemical fields, and using the deformation characteristics and fracturing crack expansion characteristics to determine fracturing parameters and operation parameters during large-scale fracturing operation in the deep thermal reservoir under the premise of not inducing an earthquake, where the deformation characteristics and fracturing crack expansion characteristics represent the conditions under which the fracturing fluid enters the fragile structure, the fragile structure is pulled open, and the fracturing crack expands within the fragile structure, and for evaluating the possibility of inducing an earthquake; Based on the fracturing characteristics of the deep thermal reservoir and the fracturing and construction parameters during fracturing construction, a large-scale fracturing construction simulation is carried out for the deep thermal reservoir, and the interaction laws of fluid flow, heat transfer, and rock deformation between the deep thermal reservoir and the internal brittle structure during the dynamic expansion process of the fracturing crack network are obtained. an evaluation module used to evaluate the influence of fragile structures on large-scale fracturing construction of deep thermal reservoirs according to the interaction laws of fluid flow, heat transfer, and rock deformation in the dynamic expansion process of the fracturing crack network; The acquisition of the deformation characteristics and fracturing crack extension characteristics of the fragile structure includes: Matrix acid treatment, hydraulic fracturing, and acid treatment fracturing experiments were carried out on the deep thermal reservoir. During the experiment, the geostress difference, the inclination angle of the weak structure surface, the cohesion force of the weak structure surface, the internal friction angle of the weak structure surface, and the tensile strength of the weak structure surface were taken into consideration, and the stress mechanism of the weak structure surface during the actual fracturing process was simulated to obtain the activation conditions of the original weak structure surface in the deep thermal reservoir. Here, the activation conditions are the temperature and the activation effect of the artificial crack expansion method on the original brittle structure surface; Establishing a thermal-fluid-solid coupled damage model THMD and a thermal-fluid-solid-chemical coupled damage model THMCD, and obtaining the deformation and fracture characteristics of the natural fragile structure surface under multi-field coupling action through simulation, the deformation and fracture characteristics of the natural fragile structure surface are the deformation characteristics and fracturing crack extension characteristics of the fragile structure, and obtaining the conditions under which the fragile structure will undergo tensile and shear fracture damage under the interference of the artificial crack, the fracturing liquid will enter the fragile structure surface, the fracturing structure surface will be pulled open, and the fracturing crack will turn and extend towards the fragile structure surface; The interaction law of fluid flow, heat transfer, and rock deformation between the deep heat reservoir and the internal weak structure during the dynamic expansion process of the fracturing crack network is obtained. preparing a number of multi-fractured rock samples, and conducting triaxial fracturing physical simulations on the multi-fractured rock samples under different injection media, heat treatment temperatures, cycle heat treatment times, horizontal stress differences, and different discharge conditions, to obtain the crack initiation and expansion process and pressure response law of the fracture network in deep thermal reservoir rock; Using room temperature fracturing fluid to simulate low-temperature shock, fracturing experiments are carried out on multi-cracked rock samples, and an acoustic emission device is used to monitor the evolution of the crack network during the low-temperature shock process. Micro-CT scans are performed on the crack network structure of the rock samples before and after the low-temperature shock, and the complex crack morphology is precisely described to obtain the dynamic expansion process of the fracturing crack network in the deep thermal reservoir rock; preparing a full-diameter test rock sample, creating a fracture in the test rock sample, and conducting a seepage flow parameter test on the test rock sample under different fracture width, confining pressure, and flow velocity conditions to obtain a multi-scale seepage flow law for a deep thermal reservoir; Based on the dynamic expansion process of the fracture network of deep thermal reservoir rock and the multi-scale seepage law, establish the mathematical physical governing equations of the stress field, temperature field and seepage field of the hot rock mass at the in-situ scale, obtain the influence relationship between the damage coefficients of different injection media and the heat-fluid-solid-chemical equation, and form a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock; Constructing an in-situ scale complex fracture network THMD fully coupled fracturing model according to a temperature-seepage flow-stress-chemistry-damage constitutive model of deep thermal reservoir rock, wherein the in-situ scale complex fracture network THMD fully coupled fracturing model is a thermal-fluid-solid-damage fully coupled fracturing model; A device for evaluating the impact of brittle structures on large-scale fracturing construction in deep thermal reservoirs, characterized by including a step of simulating the interaction laws of fluid flow, heat transfer, and rock deformation during the dynamic expansion process of a fracturing fracture network based on an in-situ scale complex fracture network THMD fully coupled fracturing model.

5. An electronic device comprising a memory and a processor, the memory is used to store a computer program; An electronic device characterized in that the processor, when executing a computer program stored in the memory, is used to realize the steps of a method for assessing the impact of fragile structures on large-scale fracturing construction in deep thermal reservoirs, as described in any one of claims 1 to 3.

6. A computer-readable storage medium used to store a computer program, which, when executed by a processor, realizes the steps of a method for assessing the impact of a fragile structure on large-scale fracturing work in a deep thermal reservoir as described in any one of claims 1 to 3.

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