Ultra-large physical simulation system for earthquake induction and safety regulation in hot dry rock development

Abstract

The invention belongs to the technical field of induced earthquakes in hot dry rock exploitation, and provides a hot dry rock development induced earthquake and safety regulation ultra-large physical simulation system which comprises an experimental model, the experimental model comprises a top surface, a bottom surface and side surfaces, and distributed stress loading systems are arranged on the top surface, the bottom surface and the side surfaces of the experimental model; a heating feedback system is arranged between the distributed stress loading system and the bottom surface and the side surface of the experimental model, and an injection well and a production well are formed in the experimental model along opposite angles; the first temperature sensor, the high-temperature-resistant deformation sensor and the high-temperature-resistant fluid pressure sensor are arranged on the prefabricated fault, and the high-temperature-resistant acoustic emission and microseismic sensor is arranged on the boundary of the experimental model, so that the prefabricated fault is comprehensively monitored in the experimental process; the whole-process monitoring of the inoculation process of the induced earthquake caused by injection and production of the hot dry rock, the sliding of the prefabricated fault and the fracture of the bedrock is realized, and the mechanism of the induced earthquake is revealed.

Description

Technical Field

[0001] This application belongs to the technical field of induced earthquakes in enhanced geothermal system (EGS) exploitation, and particularly relates to an ultra-large physical simulation system for induced earthquakes and safety control in EGS development. Background Art

[0003] Field tests are one of the important means to study induced earthquakes and safety control in EGS exploitation. This method truly restores the EGS exploitation process, but its disadvantages are also obvious. It requires a large amount of manpower and material resources, and once an earthquake is actually induced, the consequences are serious. In addition, it is difficult to accurately and reliably monitor faults in the engineering field environment, and it is difficult to conduct single-variable research. Therefore, the influence of many factors on induced earthquakes in EGS injection and production is not clear. The research on the mechanism of induced earthquakes in EGS exploitation based on laboratory experiments has always been a hot topic, but most of them focus on induced earthquakes during hydraulic fracturing, and the problem of induced earthquakes during injection and production has been ignored. In addition, the existing simulation systems still have limitations in simulating the occurrence environment of EGS. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related technologies.

[0005] To solve the above problems, this application provides an ultra-large physical simulation system for induced earthquakes and safety control in EGS development, including: An experimental model, the experimental model includes a top surface, a bottom surface and side surfaces. A distributed stress loading system is arranged on the top surface, the bottom surface and the side surfaces of the experimental model. A heating feedback system is arranged between the distributed stress loading system and the bottom surface and the side surfaces of the experimental model. An injection well and a production well are arranged diagonally on the experimental model; A prefabricated fault, the prefabricated fault is arranged in the experimental model and is located between the injection well and the production well; A fluid injection system, the fluid injection system performs hydraulic fracturing on the experimental model through the injection well to form a connected fracture network between the injection well and the prefabricated fault; A fluid production system, the fluid production system performs hydraulic fracturing on the experimental model through the production well to form a connected fracture network between the production well and the prefabricated fault; The fluid injection system injects fluid into the injection well, and the fluid is discharged into the fluid production system through the fracture network. The fluid injection system and the fluid production system collect the temperature of the fluid before injection and the temperature of the fluid after discharge; Detection system, which is arranged on the experimental model and the prefabricated fault, and is used to detect the stress state, deformation degree and temperature distribution of the prefabricated fault, and can also detect the rupture conditions of the prefabricated fault and its surrounding areas.

[0006] Optionally, the detection system includes a first sensor assembly and a second sensor assembly. The first sensor assembly is arranged on the prefabricated fault, and the second sensor assembly is arranged on the bottom surface, top surface and side surfaces of the experimental model.

[0007] Optionally, the first sensor assembly includes: a first temperature sensor, a high-temperature resistant deformation sensor and a high-temperature resistant fluid pressure sensor. The first temperature sensor, the high-temperature resistant deformation sensor and the high-temperature resistant fluid pressure sensor are arranged on the prefabricated fault; The second sensor assembly includes: a high-temperature resistant acoustic emission and microseismic sensor. The high-temperature resistant acoustic emission and the microseismic sensor are arranged on the top surface, bottom surface and side surfaces of the experimental model.

[0008] Optionally, the detection system further includes: an analog-to-digital converter, an amplifier and a detection controller. The detection controller is electrically connected to the first sensor assembly and the second sensor assembly through the analog-to-digital converter and the amplifier.

[0009] Optionally, the fluid injection system includes: a reservoir, an injection pressure pump, an injection flow pump, a pre-charged accumulator, a pre-filter, a tracer and a second temperature sensor; An injection pipeline is arranged between the reservoir and the injection well. The injection pressure pump, the injection flow pump, the pre-charged accumulator, the pre-filter, the tracer and the second temperature sensor are sequentially arranged on the injection pipeline.

[0010] Optionally, the fluid production system includes: a third temperature sensor, a post-filter, a post-charged accumulator, a production flow pump, a production pressure pump and a waste water tank; A production pipeline is arranged between the waste water tank and the production well. The third temperature sensor, the post-filter, the post-charged accumulator, the production flow pump and the production pressure pump are sequentially arranged on the production pipeline.

[0011] Optionally, the distributed stress loading system is used to apply true triaxial stress to the experimental model. A heat preservation and cooling system is arranged between the distributed stress loading system and the top surface of the experimental model and the heating feedback system.

[0012] Optionally, the heating feedback system includes: A bottom heating element, which is arranged on the bottom surface of the experimental model; Side heating elements, which are arranged on the sides of the experimental model; A heating controller, which is electrically connected to the bottom heating element and the side heating elements.

[0013] Optionally, the heat preservation and cooling system includes: A heat preservation and insulation layer, which is arranged on the top surfaces of the bottom heating element, the side heating elements and the experimental model; A cooling layer, which is arranged between the heat preservation and insulation layer and the distributed stress loading system; A cooling unit, the water outlet of which is connected to the water inlet of the cooling layer, the water inlet of which is connected to the water outlet of the cooling layer. An inlet temperature monitoring device is arranged between the water outlet of the cooling unit and the water inlet of the cooling layer, and an outlet temperature monitoring device is arranged between the water inlet of the cooling unit and the water outlet of the cooling layer.

[0014] Optionally, the prefabricated fault is one of a normal fault, a reverse fault and a strike-slip fault.

[0015] The large-scale physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development provided in the embodiments of the present invention has the following beneficial effects: 1. Compared with the traditional simulation experimental system for induced earthquake in enhanced geothermal system development, the present application constructs a five-meter-level large-scale deep three-dimensional physical model through 3D printing and integrated molding technology, and depicts the geometric characteristics of the prefabricated fault structure more precisely. While significantly increasing the indoor experimental scale of enhanced geothermal system development, the simulation of the prefabricated fault is closer to the real geological conditions, effectively improving the reliability of the experimental results.

[0016] 2. By adding the distributed stress loading system in the present application, the stress environment of the experimental model is closer to the real occurrence environment; through the settings of the thermal feedback system and the heat preservation and cooling system, a super-high enhanced geothermal system simulation environment of 400 °C is realized, and at the same time, the loading of the temperature gradient can be realized, highly reproducing the deep geothermal environment.

[0017] 3. By directly installing the first temperature sensor, the high-temperature resistant deformation sensor and the high-temperature resistant fluid pressure sensor on the prefabricated fault, and arranging the high-temperature resistant acoustic emission and microseismic sensors at the boundary of the experimental model, the whole process of the gestation process of induced earthquake caused by enhanced geothermal system injection and production, the slip of the prefabricated fault and the fracture of the bedrock is comprehensively monitored during the experiment, revealing the mechanism of induced earthquake.

[0018] 4. The present application adopts different injection and production methods through a fluid injection system and a fluid production system, and through the monitoring of a monitoring system, compares and analyzes the influence of different injection and production methods on induced earthquakes, explains the mechanism of induced earthquakes by different injection and production methods, and forms a safe injection and production method for hot dry rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the front view structure diagram of the simulation system of the present invention; Figure 2 is the structure diagram of the experimental model of the present invention; Figure 3 is the internal structure diagram of the experimental model of the present invention; Figure 4 is the three-dimensional structure diagram of the connection between the distributed stress loading system and the experimental model of the present invention; Figure 5 is the front view sectional structure diagram of the connection between the distributed stress loading system and the experimental model of the present invention; Figure 6 is the three-dimensional structure diagram of the distribution of monitoring points on the preset fault of the present invention; Figure 7 is the front view structure diagram of the distribution of monitoring points on the preset fault of the present invention; Figure 8 is the side view structure diagram of the distribution of monitoring points on the preset fault of the present invention; Figure 9 is the top view structure diagram of the distribution of monitoring points on the preset fault of the present invention; Figure 10 is the normal fault structure diagram of the prefabricated fault of the present invention; Figure 11 is the reverse fault structure diagram of the prefabricated fault of the present invention; Figure 12 is the strike-slip fault structure diagram of the prefabricated fault of the present invention.

[0020] The reference numerals are shown as: 1. Experimental model; 11. Injection well; 12. Production well; 2. Distributed stress loading system; 3. Heating feedback system; 31. Bottom heating element; 32. Side heating element; 33. Heating controller; 4. Prefabricated fault; 41. Normal fault; 42. Reverse fault; 43. Strike-slip fault; 5. Fluid injection system; 51. Reservoir; 52. Injection pressure pump; 53. Injection flow pump; 54. Prefilter accumulator; 55. Prefilter; 56. Tracer; 57. Second temperature sensor; 6. Fluid production system; 61. Third temperature sensor; 62. Postfilter; 63. Postfilter accumulator; 64. Production flow pump; 65. Production pressure pump; 66. Wastewater tank; 7. Detection system; 71. First temperature sensor; 72. High-temperature deformation sensor; 73. High-temperature fluid pressure sensor; 74. High-temperature acoustic emission and microseismic sensor; 75. Analog-to-digital converter; 76. Amplifier; 77. Detection controller; 8. Thermal insulation and cooling system; 81. Thermal insulation layer; 82. Cooling layer; 83. Cooling unit; 84. Inlet temperature monitoring device; 85. Outlet temperature monitoring device. Detailed implementation manners

[0021] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0022] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0023] In the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0025] Referring to Figures 1 - 12 As shown, according to an embodiment of the present application, a super-large physical simulation system for induced earthquakes and safety regulation in enhanced geothermal system (EGS) development is provided, including: An experimental model 1, the experimental model 1 includes a top surface, a bottom surface and side surfaces. A distributed stress loading system 2 is provided on the top surface, the bottom surface and the side surfaces of the experimental model 1. A heating feedback system 3 is provided between the distributed stress loading system 2 and the bottom surface and the side surfaces of the experimental model 1. An injection well 11 and a production well 12 are arranged diagonally on the experimental model 1; A prefabricated fault 4, the prefabricated fault 4 is arranged in the experimental model 1 and is located between the injection well 11 and the production well 12; A fluid injection system 5, the fluid injection system 5 performs hydraulic fracturing on the experimental model 1 through the injection well 11 so as to form a connected fracture network between the injection well 11 and the prefabricated fault 4; A fluid production system 6, the fluid production system 6 performs hydraulic fracturing on the experimental model 1 through the production well 12 so as to form a connected fracture network between the production well 12 and the prefabricated fault 4; The fluid injection system 5 injects fluid into the injection well 11, the fluid is discharged into the fluid production system 6 through the fracture network, and the fluid injection system 5 and the fluid production system 6 collect the temperature of the fluid before injection and the temperature of the fluid after discharge; A detection system 7, the detection system 7 is arranged on the experimental model 1 and the prefabricated fault 4, and is used for detecting the stress state, deformation degree and temperature distribution of the prefabricated fault 4, and at the same time, the fracture condition of the prefabricated fault 4 and its surrounding area can be detected.

[0026] Specifically, the experimental model 1 is printed by a 3D printing device, and its size is 5m×5m×5m. Compared with the traditional model, it can more realistically reflect the actual scale of the enhanced geothermal system (EGS) reservoir. The distributed stress loading system 2 arranged on its top surface, bottom surface and side surfaces can realize true triaxial stress loading on the experimental model 1, and is used to simulate the stress environment of the enhanced geothermal system (EGS) in the formation. The heating feedback system 3 arranged between the distributed stress loading system 2 and the bottom surface and side surfaces of the experimental model 1 is used to heat the experimental model 1 to simulate the thermal environment of the enhanced geothermal system (EGS), improve the accuracy of the experimental results. The injection well 11 and the production well 12 are arranged diagonally on the experimental model 1, providing a reliable channel for the subsequent injection and production of fluid.

[0027] The prefabricated fault 4 is arranged between the injection well 11 and the production well 12 in the experimental model 1. The size of the prefabricated fault 4 is 2m×1.5m×0.3m, and its strike and dip in the experimental model 1 are determined according to the requirements of the simulation experiment. After the distributed stress loading system 2 applies the boundary stress to the experimental model 1 to reach the target value, the stress loading is kept constant. The heating feedback system 3 heats the experimental model 1. After heating to the target value, the temperature is kept constant. The fluid injection system 5 injects fluid into the experimental model 1 through the injection well 11 to fracture the experimental model 1, so as to form a connected fracture network between the injection well 11 and the prefabricated fault 4. At the same time, the fluid production system 6 injects fluid into the experimental model 1 through the production well 12 to fracture the experimental model 1, forming a fracture network between the production well 12 and the prefabricated fault 4. During this process, the detection system 7 monitors the fracturing process, accurately locates the fracture position, and is used to explore the crack propagation law during the hydraulic fracturing process and reveal the seismogenic mechanism induced by the hydraulic fracturing of hot dry rock.

[0028] After a connected fracture network is formed between the injection well 11 and the production well 12 and the prefabricated fault 4, the fluid injection system 5 injects fluid in a flow injection manner. The fluid injection system 5 can record the temperature of the injected fluid. The fluid is pumped out by the fluid production system 6 through the fracture network in a flow control manner, and the fluid production system 6 records the temperature of the produced fluid. During the fluid injection, the detection system 7 monitors the fracture, temperature, fluid pressure and slip conditions of the prefabricated fault 4. When it is detected that the prefabricated fault 4 undergoes a sudden and rapid slip, accompanied by a large number of fracture events, it is considered that an earthquake event is induced. At this time, the injection is stopped, the experimental data is saved, and then by changing the flow control injection-production to pressure control injection-production or cyclic control injection-production, the experimental data is re-collected, and the slip characteristics and fracture conditions of the prefabricated fault 4 are monitored until an earthquake event is induced again. After the experiment, the total heat extraction is calculated by the formula Q = CM(T out -T in ). Q - total heat extraction, C - specific heat capacity of the fluid, M - mass of the fluid, T out - temperature of the produced fluid, T in - temperature of the injected fluid. The heat extraction efficiency of the hot dry rock during the fluid injection-production process can be calculated. According to the injection pump and the production pump, the flow rate and pressure of the fluid can be monitored. The volume of the fluid can be obtained through the flow rate and time, and then the mass of the fluid can be obtained. The data monitored by the detection system 7 is used to calculate the slip law, temperature evolution, spatial distribution of fluid pressure and magnitude of the prefabricated fault 4, compare and analyze the influence of different injection-production methods on induced earthquakes, explain the mechanism of induced earthquakes by different injection-production methods, and form a safe injection-production method for hot dry rock.

[0029] Among them, the materials of the experimental model 1 and the prefabricated fault 4 are composed of a variety of materials such as quartz sand, barite powder, high-strength gypsum, cement, paraffin, and portland cement. Their mechanical properties and thermal physical properties are highly similar to those of hot dry rock and natural faults.

[0030] Among them, when 3D printing the experimental model 1, an injection well 11 and a production well 12 are arranged diagonally on the experimental model 1 by means of prefabricated printing. The distance between the injection well 11 and the production well 12 is 3.0 m, the depth is 2.5 m, the diameter is 75 mm, the open hole section is 200 mm, the casing is made of 29CrMo44 steel, and the cementing method is epoxy resin bonding.

[0031] Among them, the distributed stress loading system 2 can apply true triaxial stress to the six faces of the experimental model 1, and each face of the experimental model has 25 loading cylinders.

[0032] As Figure 1 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 、 Figure 8 and Figure 9 shown, in some embodiments, optionally, the detection system 7 includes a first sensor assembly and a second sensor assembly. The first sensor assembly is arranged on the prefabricated fault 4, and the second sensor assembly is arranged on the bottom surface, top surface, and side surfaces of the experimental model 1.

[0033] The first sensor assembly includes: a first temperature sensor 71, a high-temperature resistant deformation sensor 72, and a high-temperature resistant fluid pressure sensor 73. The first temperature sensor 71, the high-temperature resistant deformation sensor 72, and the high-temperature resistant fluid pressure sensor 73 are arranged on the prefabricated fault 4; The second sensor assembly includes: a high-temperature resistant acoustic emission and microseismic sensor 74. The high-temperature resistant acoustic emission and microseismic sensor 74 is arranged on the top surface, bottom surface, and side surfaces of the experimental model 1.

[0034] Specifically, the first sensor assembly includes a first temperature sensor 71, a high-temperature resistant deformation sensor 72, and a high-temperature resistant fluid pressure sensor 73. The first temperature sensor 71, the high-temperature resistant deformation sensor 72, and the high-temperature resistant fluid pressure sensor 73 are all multiple and are installed at intervals on both sides of the prefabricated fault 4.

[0035] The first temperature sensor 71 is mainly used for collecting the temperature distribution of the prefabricated fault 4. The model is PT100, and its resistance value has an approximately linear relationship with the temperature change. It has high precision and good stability, and the temperature measurement range is -200~850 °C. During the injection and production process of hot dry rock, it can accurately monitor the local temperature changes caused by fluid migration and rock fracture friction.

[0036] The high-temperature deformation-resistant sensor 72 uses KH high-temperature welded strain gauges, which are welded on the surface of the prefabricated fault 4. It has a self-compensation function and can work stably in a high-temperature environment of 550 °C to accurately measure the slip behavior of the prefabricated fault 4.

[0037] The high-temperature fluid pressure sensor 73 can withstand a high temperature of 400 °C and a high pressure of 70 MPa, with an accuracy of ±1 kPa. It is mainly used to measure the fluid pressure on the prefabricated fault 4 during experiments.

[0038] The second sensor assembly includes a high-temperature acoustic emission and microseismic sensor 74. It uses a high-temperature acoustic emission sensor based on LGS crystals and has a broadband response ability of 28 kHz - 274 kHz. It is arranged in an array on the top, bottom, and side surfaces of the experimental model 1 to form a spatial cross-monitoring network, realizing the collection and accurate positioning of the rupture signals during the fluid fracturing process and the slip of the prefabricated fault 4 induced by injection, and the earthquake-induced process, so as to reveal the seismogenic mechanism of enhanced geothermal system injection-induced earthquakes.

[0039] As Figure 1 shown, in some embodiments, optionally, the detection system 7 further includes: an analog-to-digital converter 75, an amplifier 76, and a detection controller 77. The detection controller 77 is electrically connected to the first sensor assembly and the second sensor assembly through the analog-to-digital converter 75 and the amplifier 76.

[0040] Specifically, the analog-to-digital converter 75 can convert the sensor signals output in analog form, such as the first temperature sensor 71 and the high-temperature deformation-resistant sensor 72, into digital signals with extremely high resolution. In the high-temperature and complex electromagnetic environment of the enhanced geothermal system simulation experiment, the anti-interference filtering circuit built in the analog-to-digital converter 75 can effectively filter out the electromagnetic noise generated by the operation of equipment such as the heating feedback system 3 and the fluid injection system 5, ensuring the accuracy of data conversion. The amplifier 76 is used to enhance the weak sensor signals to ensure that the signals are not distorted during transmission. The acoustic emission signals generated by the rock mass rupture captured by the high-temperature acoustic emission and microseismic sensor 74 are extremely weak and are easily affected by the transmission distance and environmental factors. The amplifier 76 has the ability to amplify signals in a wide frequency range and can specifically amplify these weak signals in multiple stages. At the same time, advanced noise reduction technology is used to suppress the growth of noise while amplifying the signals. After being processed by the amplifier 76, the intensity of the acoustic emission signals is significantly improved, enabling subsequent data acquisition and analysis to more clearly identify the characteristic parameters of the rock mass rupture events, such as the signal arrival time, waveform shape, etc., so as to achieve the accurate positioning and analysis of the rock mass rupture behavior during the earthquake-induced process.

[0041] The detection controller 77 is connected to the analog-to-digital converter 75 and the amplifier 76 through a data bus, and receives the processed data in real time. The intelligent algorithm built into the detection controller 77 can perform real-time analysis on the monitoring data. Researchers can remotely monitor the experimental process, retrieve historical data, and perform data analysis and model optimization through the network, greatly improving the convenience of the experiment and the research efficiency.

[0042] As Figure 1 shown, in some embodiments, optionally, the fluid injection system 5 includes: a reservoir 51, an injection pressure pump 52, an injection flow pump 53, a pre-charged accumulator 54, a pre-filter 55, a tracer 56, and a second temperature sensor 57; An injection pipeline is provided between the reservoir 51 and the injection well 11, and the injection pressure pump 52, the injection flow pump 53, the pre-charged accumulator 54, the pre-filter 55, the tracer 56, and the second temperature sensor 57 are sequentially arranged on the injection pipeline.

[0043] Specifically, the reservoir 51 is designed with a large capacity of 4m×3m×1.5m, which can meet the water demand for long-term and large-flow experiments and supply water for the entire injection system. The injection pressure pump 52 has a pressure output capacity of up to 70 MPa and an accuracy of 1% FS. By applying high-pressure fluid to the injection well 11, it fractures the experimental model 1 and forms a connected fracture network between the injection well 11 and the prefabricated fault 4, providing a basis for subsequent fluid flow. The injection flow pump 53 is used for large-flow fluid injection control, with a flow rate of up to 200 L / s. When the injection capacity of the injection pressure pump 52 is limited after fracturing and cannot meet the large-flow requirements for inducing earthquakes, the injection flow pump 53 intervenes to provide a greater flow control injection function. The pre-charged accumulator 54 can effectively absorb the pressure fluctuations during fluid injection. When the injection pressure pump 52 starts, stops, or adjusts the pressure, the accumulator can quickly release or store energy to prevent pressure mutations from impacting the pipeline and equipment, and avoid problems such as pipeline vibration, loosening of connectors, and even equipment damage caused by pressure fluctuations, ensuring a smooth transition of the system pressure. The pre-filter 55 adopts a high-precision filter screen and a multi-layer filtration structure, which can intercept impurities such as rock debris, sediment, and rust in the fluid. When the fluid injection system 5 switches to different working modes or there is a fluid backflow situation, the pre-filter 55 can effectively protect equipment such as the injection pressure pump 52 and the injection flow pump 53, prevent impurities from entering the pump body and causing wear, extend the service life of the equipment, and ensure the smooth progress of the experiment.

[0044] The tracer 56 is selected from radioactive substances such as barium or iodine. During the fluid injection process, by controlling the opening degree of the valve, the tracer 56 can be mixed into the fluid in a predetermined proportion. As the fluid flows in the fracture network, the tracer 56 will adhere to the surface of the fault and surrounding fractures. After the experiment is completed, cutting the experimental model 1 can visually present the expansion morphology, distribution range of the fractures, and the migration path of the fluid, providing a clear visual basis for researchers to analyze the rock mass rupture during the slip process of the prefabricated fault 4. The second temperature sensor 57 is installed on the injection pipeline to monitor the temperature change of the injected fluid in real time.

[0045] As Figure 1 shown, in some embodiments, optionally, the fluid production system 6 includes: a third temperature sensor 61, a post-filter 62, a post-accumulator 63, a production flow pump 64, a production pressure pump 65, and a waste water tank 66; A production pipeline is provided between the waste water tank 66 and the production well 12, and the third temperature sensor 61, the post-filter 62, the post-accumulator 63, the production flow pump 64, and the production pressure pump 65 are sequentially arranged on the production pipeline.

[0046] Specifically, the third temperature sensor 61 is used to monitor the temperature of the produced fluid. The post-filter 62 adopts a multi-layer composite filtering structure, which can effectively intercept the cuttings, broken rock particles, and other impurities carried in the produced fluid. During the experiment, hydraulic fracturing and fluid flow may cause the internal rock debris of the experimental model 1 to enter the production pipeline. The post-filter 62 can prevent these impurities from entering the production flow pump 64 and the production pressure pump 65, avoiding damage to the equipment due to wear, greatly extending the service life of the equipment, and ensuring the long-term stable operation of the production system. The post-accumulator 63 is mainly responsible for stabilizing the pressure fluctuation during the production process. When the production pressure pump 65 starts or stops or adjusts the pressure, and the production flow pump 64 adjusts the flow rate, the post-accumulator 63 can quickly absorb or release pressure, maintain the pressure stability in the pipeline, and prevent problems such as pipeline vibration and interface leakage caused by pressure mutation.

[0047] The maximum pressure of the production pressure pump 65 can reach 70 MPa, and the accuracy is 1% FS. In the initial stage of production and injection, it is mainly used for hydraulic fracturing between the production well 12 and the prefabricated fault 4 to form a connected fluid flow channel, providing a basis for subsequent production and injection operations. After the fracturing is completed, the production flow pump 64 has a flow output capacity of up to 200 L / s, and can quickly and stably extract the high-temperature fluid after heat exchange from the experimental model 1. When the extraction capacity of the production pressure pump 65 is limited after the fracturing and cannot meet the requirements of induced earthquake in the injection and production of hot dry rock, the production flow pump 64 intervenes to work and provides a greater flow control for the extraction function. The wastewater tank 66 has a large-capacity design with dimensions of 4m × 3m × 1.5m, which can meet the storage requirements of wastewater generated during long-term experiments. The maximum discharge flow rate is 2000 L / h to ensure that the wastewater can be discharged in time.

[0048] As Figure 1 shown, in some embodiments, optionally, the distributed stress loading system 2 is used to apply true triaxial stress to the experimental model 1, and a thermal insulation and cooling system 8 is provided between the distributed stress loading system 2 and the top surface of the experimental model 1 and the heating feedback system 3.

[0049] Specifically, the distributed stress loading system 2 can apply true triaxial stress to the six surfaces of the experimental model 1 to simulate the stress environment of hot dry rock in the formation. The heating feedback system 3 is used to heat the experimental model 1 to simulate the thermal environment of hot dry rock. Since the safe operating temperature of the distributed stress loading system 2 is not higher than 55°, the thermal insulation and cooling system 8 is installed inside the distributed stress loading system 2 to ensure the safety of the distributed stress loading system 2.

[0050] As Figure 1 、 2 、3 shown, in some embodiments, optionally, the heating feedback system 3 includes: A bottom heating element 31, which is arranged on the bottom surface of the experimental model 1; A side heating element 32, which is arranged on the side surface of the experimental model 1; A heating controller 33, which is electrically connected to the bottom heating element 31 and the side heating element 32.

[0051] Specifically, the heating feedback system 3 includes a bottom heating element 31, side heating elements 32, and a heating controller 33. The bottom heating element 31 is installed at the bottom of the experimental model 1, and its size matches the bottom surface of the experimental model 1. There are four groups of side heating elements 32, which are installed on the four side surfaces of the experimental model 1. Both the bottom heating element 31 and the side heating elements 32 are composed of 5 small heating plates spliced together. Each small heating plate consists of multiple heating rods and can be independently controlled. When some heating rods fail, the adjacent heating rods can automatically increase the power for compensation to maintain the stability of the overall heating effect, which not only improves the reliability of the heating system but also facilitates later maintenance and replacement. The coordinated operation of the bottom heating element 31 and the side heating elements 32 can form a wrapped heating environment around the experimental model 1, achieving a high-temperature simulation of up to 400 °C, and the heating rate is stably controlled at 5 °C / h to simulate the real geothermal environment of dry hot rocks. The heating controller 33 is used to control the power of the bottom heating element 31 and the side heating elements 32. It consists of a computer, a power control cabinet, and a temperature sensor, and dynamically adjusts the heating power according to the temperature conditions in different regions to achieve precise control of the target temperature.

[0052] Among them, the sizes of both the bottom heating element 31 and the side heating elements 32 are 4.9 m × 4.9 m.

[0053] Such as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 As shown in a heat insulation layer 81, which is arranged on the top surfaces of the bottom heating element 31, the side heating elements 32, and the experimental model 1; a cooling layer 82, which is arranged between the heat insulation layer 81 and the distributed stress loading system 2; a cooling unit 83, the water outlet of the cooling unit 83 is connected to the water inlet of the cooling layer 82, the water inlet of the cooling unit 83 is connected to the water outlet of the cooling layer 82, an inlet temperature monitoring device 84 is arranged between the water outlet of the cooling unit 83 and the water inlet of the cooling layer 82, and an outlet temperature monitoring device 85 is arranged between the water inlet of the cooling unit 83 and the water outlet of the cooling layer 82.

[0054] Specifically, the heat insulation layer 81 is installed on the top surfaces of the bottom heating element 31, the side heating elements 32, and the experimental model 1, and is used to prevent the experimental model 1 from exchanging heat with other equipment and the air, resulting in rapid heat loss and the experimental model 1 being unable to reach the target temperature required for the experiment.

[0055] The thermal insulation layer 81 is made of high-strength high-temperature-resistant mica fiber board, with a uniaxial compressive strength of not less than 30 MPa, a maximum heat resistance of up to 1000 °C, a voltage breakdown resistance index as high as 20 KV / MM, and a thermal conductivity of only about 0.9 W / (m·K). Its excellent heat insulation performance effectively prevents the high temperature inside the experimental model 1 from conducting to the outside world.

[0056] The cooling layer 82 is processed from stainless steel, with dimensions of 4.9 m × 4.9 m × 0.1 m. One side is closely attached to the thermal insulation layer 81, and the other side is directly in contact with the distributed stress loading system 2, ensuring structural strength while effectively transferring heat. Precision holes are reserved inside the cooling layer 82 and copper tubes are inserted to construct an efficient cooling liquid circulation channel. When the residual heat that cannot be completely isolated by the thermal insulation layer 81 is transferred to the cooling layer 82, the flowing cooling liquid quickly absorbs heat through the copper tubes, maintaining the temperature within a safe range, preventing the distributed stress loading system 2 from failing due to high temperature, and ensuring its stable operation at a safe working temperature not exceeding 55 °C, guaranteeing the accuracy and reliability of stress loading.

[0057] The cooling unit 83 realizes the continuous cooling and recycling of the cooling liquid through an efficient refrigeration cycle. The water outlet of the cooling unit 83 is connected to the water inlet of the cooling layer 82, and the water inlet is connected to the water outlet of the cooling layer 82 to form a closed cooling circulation loop. During the circulation process, the inlet temperature monitoring device 84 and the outlet temperature monitoring device 85 continuously monitor the temperature change of the cooling liquid and transmit the data to the control system of the cooling unit 83 in real time. When the outlet temperature monitoring device 85 detects that the temperature of the cooling liquid is higher than the safety threshold, the cooling unit 83 automatically increases the refrigeration power to quickly reduce the temperature of the cooling liquid.

[0058] Among them, the dimensions of the thermal insulation layer 81 are all 4.9 m × 4.9 m.

[0059] Such as Figure 10 、 Figure 11 And Figure 12 As shown, in some embodiments, optionally, the prefabricated fault 4 is one of the normal fault 41, reverse fault 42, and strike-slip fault 43.

[0060] Specifically, the normal fault 41, reverse fault 42, and strike-slip fault 43 are mainly distinguished according to the stress conditions. The stress state of the normal fault 41 is SV > SH > Sh, the stress state of the reverse fault 42 is SH > Sh > SV, and the stress state of the strike-slip fault 43 is SH > SV > Sh. Different prefabricated faults 4 are used to analyze the influence of different fault types on the induced earthquake and safety control of enhanced geothermal system injection and production, where SV is the vertical principal stress; SH is the maximum horizontal principal stress, and Sh is the minimum horizontal principal stress.

[0061] The experiments of the ultra-large physical simulation system for induced earthquakes and safety control in enhanced geothermal system (EGS) development include the following steps: Step 1: Install the thermal insulation layer 81 and the cooling layer 82 on the bottom of the bottom heating element 31 from top to bottom. After installation, place the bottom heating element 31 on the printing platform to print the 5m×5m×5m experimental model 1. During this process, the printing of the prefabricated fault 4 can be automatically completed within the experimental model 1. During the printing process, the calibrated first temperature sensor 71, high-temperature acoustic emission and microseismic sensor 74, high-temperature deformation sensor 72, and high-temperature fluid pressure sensor 73 are sequentially embedded at the specified positions according to the coordinates. Similarly, the injection well 11 and the production well 12 are reserved during the printing process. After printing, it is transported to the constant temperature and humidity chamber for 28 days of model curing; Step 2: After curing, install casings in the injection well 11 and the production well 12. Lower 29CrMo44 steel casings into the injection well 11 and the production well 12, and leave a 200mm open hole section to facilitate fluid injection. After the casings are lowered, epoxy resin is poured between the casings and the wellbore for cementing. After cementing, the detection system 7 tests the first temperature sensor 71, high-temperature acoustic emission and microseismic sensor 74, high-temperature deformation sensor 72, and high-temperature fluid pressure sensor 73, and the heating feedback system 3 tests the bottom heating element 31. After normal testing, install the side heating element 32, the thermal insulation layer 81, and the cooling layer 82. Transport the assembled experimental model 1 to the distributed stress loading system 2. Connect the fluid injection system 5 to the injection well 11 and the fluid production system 6 to the production well 12, and check and tidy up the tightness of the connections; Step 3: Start the distributed stress loading system 2 to apply boundary stress to the experimental model 1. After the boundary stress reaches the target value, keep the stress loading constant. At the same time, start the heating feedback system 3, the thermal insulation and cooling system 8, and the detection system 7. The heating feedback system 3 heats the experimental model 1 at a heating rate of 5℃ / h, and the temperature control accuracy is accurate to ±1℃. The opening of the thermal insulation and cooling system 8 mainly plays a protective role. When the return water temperature of the cooling layer 82 is higher than 55℃, the cooling unit 83 will automatically start to actively cool down to ensure that the distributed stress loading system 2 is not damaged by temperature. The operation of the cooling unit 83 will run through the entire experimental process. The start of the detection system 7 is used to monitor the thermal cracking behavior of the experimental model 1 and the prefabricated fault 4 under the action of thermal stress during the heating process.

[0062] When the detection system 7 monitors that the temperature on the prefabricated fault 4 reaches the target, the heating feedback system 3 is adjusted from the heating state to the heat preservation state, which can better maintain the temperature of the experimental model 1 while reducing energy consumption. Fluids are injected into the experimental model 1 from the injection well 11 through the fluid injection system 5 for hydraulic fracturing, so as to form a connected fracture network between the injection well 11 and the prefabricated fault 4. At the same time, the fluid production system 6 is connected to the production well 12, and fluids are injected into the experimental model 1 from the production well 12 through the fluid production system 6, so as to form connected fractures between the production well 12 and the prefabricated fault 4. During this process, the high-temperature acoustic emission and microseismic sensor 74 accurately locates the fracture events during the fracturing process, which is used to explore the crack propagation law during the hydraulic fracturing process and reveal the seismogenic mechanism induced by the hydraulic fracturing of hot dry rock.

[0063] After the injection well 11 and the production well 12 form connected fractures with the prefabricated fault 4, injection-production experiments are carried out. The injection flow pump 53 injects a large amount of fluids into the experimental model 1 in a flow control injection manner through the injection well 11, and the temperature of the injected water is recorded by the second temperature sensor 57. At the same time, the production flow pump 64 also extracts fluids in a flow control manner, and the temperature of the extracted fluids is recorded by the third temperature sensor 61. Finally, the fluids are discharged into the waste water tank 66. During the injection period, the detection system 7 is used to monitor the fracture, temperature, fluid pressure and slip conditions of the prefabricated fault 4. When it is monitored that the fault suddenly slips rapidly and is accompanied by a large number of fracture events, it is considered that an earthquake event is induced. At this time, the injection is stopped and the experimental data are saved.

[0064] By changing the flow control injection-production method to a pressure control injection-production method or a cyclic control injection-production method. Among them, the pressure control injection-production method is to keep the pressures of the injection flow pump 53 and the production flow pump 64 unchanged for injection-production; the cyclic control injection-production method is that the injection flow pump 53 and the production flow pump 64 stop injecting and producing for a period of time and then start the same injection method after a period of time. For example: with a constant injection pressure of 10 MPa, the injection flow pump and the production flow pump stop injecting after injecting and producing for 10 days, and then start injecting and producing again after 10 days of stopping. The experimental data are re-collected, and the slip characteristics and fracture conditions of the fault are observed until an earthquake event is induced again. After the injection-production test is completed, a tracer 56 is added, and a small amount of water is injected again using the injection flow pump 53, so that the tracer 56 remains in the fractures of the experimental model 1 and the prefabricated fault 4. After the experiment is over, the hot dry rock similarity experimental model 1 is cut to observe the fracture propagation.

[0065] The temperature difference of the fluid is detected by the second temperature sensor 57 and the third temperature sensor 61, the total amount of heat extraction from the hot dry rock is calculated, and the slip law of the fault, the temperature evolution, the spatial distribution of the fluid pressure and the magnitude are calculated based on the data of the detection system 7. The influence of different injection-production methods on induced earthquakes is compared and analyzed, the mechanism of induced earthquakes by different injection-production methods is explained, and a safe injection-production method for hot dry rock is formed.

[0066] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present application, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development, characterized in that, Comprising: An experimental model (1), the experimental model (1) includes a top surface, a bottom surface and side surfaces, a distributed stress loading system (2) is provided on the top surface, the bottom surface and the side surfaces of the experimental model (1), and a heating feedback system (3) is provided between the distributed stress loading system (2) and the bottom surface and the side surfaces of the experimental model (1), and an injection well (11) and a production well (12) are provided on the experimental model (1) diagonally; A prefabricated fault (4), the prefabricated fault (4) is arranged inside the experimental model (1) and is located between the injection well (11) and the production well (12); A fluid injection system (5), the fluid injection system (5) performs hydraulic fracturing on the experimental model (1) through the injection well (11) so as to form a connected fracture network between the injection well (11) and the prefabricated fault (4); A fluid production system (6), the fluid production system (6) performs hydraulic fracturing on the experimental model (1) through the production well (12) so as to form a connected fracture network between the production well (12) and the prefabricated fault (4); The fluid injection system (5) injects fluid into the injection well (11), the fluid passes through the fracture network and is discharged into the fluid production system (6), and the fluid injection system (5) and the fluid production system (6) collect the temperature of the fluid before injection and the temperature of the fluid after discharge; A detection system (7), the detection system (7) is arranged on the experimental model (1) and the prefabricated fault (4) for detecting the stress state, deformation degree and temperature distribution of the prefabricated fault (4), and simultaneously can detect the fracture condition of the prefabricated fault (4) and its surrounding area.

2. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 1, characterized in that, The detection system (7) includes a first sensor assembly and a second sensor assembly, the first sensor assembly is arranged on the prefabricated fault (4), and the second sensor assembly is arranged on the bottom surface, the top surface and the side surfaces of the experimental model (1).

3. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 2, characterized in that, The first sensor assembly includes: a first temperature sensor (71), a high-temperature resistant deformation sensor (72) and a high-temperature resistant fluid pressure sensor (73), and the first temperature sensor (71), the high-temperature resistant deformation sensor (72) and the high-temperature resistant fluid pressure sensor (73) are arranged on the prefabricated fault (4); The second sensor assembly includes: a high-temperature resistant acoustic emission and microseismic sensor (74), and the high-temperature resistant acoustic emission and the microseismic sensor (74) are arranged on the top surface, the bottom surface and the side surfaces of the experimental model (1).

4. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 3, wherein The detection system (7) further includes: an analog-to-digital converter (75), an amplifier (76) and a detection controller (77), and the detection controller (77) is electrically connected to the first sensor assembly and the second sensor assembly through the analog-to-digital converter (75) and the amplifier (76).

5. The super-large physical simulation system for induced earthquake and safety control in enhanced geothermal system development according to claim 1, characterized in that, The fluid injection system (5) includes: a reservoir (51), an injection pressure pump (52), an injection flow pump (53), a pre - accumulator (54), a pre - filter (55), a tracer (56), and a second temperature sensor (57); An injection pipeline is provided between the reservoir (51) and the injection well (11), and the injection pressure pump (52), the injection flow pump (53), the pre - accumulator (54), the pre - filter (55), the tracer (56), and the second temperature sensor (57) are sequentially arranged on the injection pipeline.

6. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 1, characterized in that, The fluid production system (6) includes: a third temperature sensor (61), a post - filter (62), a post - accumulator (63), a production flow pump (64), a production pressure pump (65), and a waste water tank (66); A production pipeline is provided between the waste water tank (66) and the production well (12), and the third temperature sensor (61), the post - filter (62), the post - accumulator (63), the production flow pump (64), and the production pressure pump (65) are sequentially arranged on the production pipeline.

7. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 1, characterized in that The distributed stress loading system (2) is used to apply true triaxial stress to the experimental model (1), and a heat preservation and cooling system (8) is provided between the distributed stress loading system (2) and the top surface of the experimental model (1) and the heating feedback system (3).

8. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 7, characterized in that, The heating feedback system (3) includes: A bottom heating element (31) which is arranged on the bottom surface of the experimental model (1); A side heating element (32) which is arranged on the side surface of the experimental model (1); A heating controller (33) which is electrically connected to the bottom heating element (31) and the side heating element (32).

9. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 8, characterized in that, The heat preservation and cooling system (8) includes: A heat preservation and insulation layer (81) which is arranged on the bottom heating element (31), the side heating element (32), and the top surface of the experimental model (1); A cooling layer (82) which is arranged between the heat preservation and insulation layer (81) and the distributed stress loading system (2); A cooling unit (83), the water outlet of the cooling unit (83) is connected to the water inlet of the cooling layer (82), the water inlet of the cooling unit (83) is connected to the water outlet of the cooling layer (82), an inlet temperature monitoring device (84) is arranged between the water outlet of the cooling unit (83) and the water inlet of the cooling layer (82), and an outlet temperature monitoring device (85) is arranged between the water inlet of the cooling unit (83) and the water outlet of the cooling layer (82).

10. The super-large physical simulation system for induced earthquake and safety regulation in enhanced geothermal system development according to claim 1, characterized in that The pre - formed fault (4) is one of a normal fault (41), a reverse fault (42), and a strike - slip fault (43).

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