Downscaled physical experimental system and simulation method for supercritical CO2 geothermal mining

Abstract

The present invention discloses a scaled-down physical experiment system for supercritical CO2 geothermal mining, comprising an S-CO2 generation system, an S-CO2 temperature and pressure control system, a small-scale geothermal simulation system, an S-CO2 recovery system, an S-CO2 pressure and temperature measurement system, a rock physical and mechanical property testing system, and a safety protection system; a hybrid numerical simulation method: utilizing the small-scale physical experiment system to conduct experiments under different surrounding rock pressures, reservoir temperatures, injected S-CO2 temperatures, and flow rates; conducting physical and mechanical property measurement tests on rock samples before and after the experiments to obtain small-scale physical experiment data, and analyzing changes in the physical and mechanical parameters of the rock samples before and after the experiments; inputting the physical and mechanical parameters of the rock samples after the experiments into a small-scale numerical model, analyzing and calibrating them through a parameter automatic calibration system, and obtaining the physical and mechanical parameters of the rock samples, which are then input into a large-scale numerical model to analyze mining efficiency, dynamic hazards, and feasibility under different thermal reservoir conditions, flow rates, and pressures at an engineering scale.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal energy development, and more specifically, relates to a supercritical CO2 geothermal mining scale-down physical experiment system and simulation method. Background Art

[0002] In recent decades, global warming and increasingly frequent extreme weather events are closely linked to the carbon dioxide released by the combustion of fossil fuels such as coal and oil. To simultaneously support economic development and reduce carbon dioxide emissions, the efficient development and utilization of green and clean renewable energy sources has become a pressing challenge. Geothermal energy, compared to other renewable energy sources (such as wind power, hydropower, and solar power), offers advantages such as continuous and stable operation, widespread distribution, large reserves, and low power generation costs. Therefore, accelerating its development and utilization is crucial.

[0003] Geothermal energy resources can be divided into three categories: hydrothermal geothermal (surface hot springs), shallow geothermal energy (groundwater within 200 meters), and hot dry rock (geothermal energy stored in hot, dry rock, generally without water). Hydrothermal and shallow geothermal energy are currently being gradually utilized in my country, while hot dry rock geothermal is still in the research stage. Hot dry rock refers to high-temperature, dense rock masses that do not contain water or water vapor. It is primarily found below 3,000 meters below the surface, with temperatures ranging from approximately 150°C to 600°C. Currently, the most common method for extracting high-temperature geothermal energy is the use of enhanced geothermal systems (EGS). EGS involves modifying the hot dry rock formations through fracturing or blasting, creating artificial heat reservoirs with high permeability. Low-temperature fluids are then injected into the formation to extract the abundant geothermal resources stored in the hot dry rock for practical production and daily life (such as power generation and heating).

[0004] Currently, most projects using EGS systems to extract geothermal energy use water as the low-temperature working fluid. However, practical applications have shown that water has the following disadvantages: 1. Water reacts with minerals in the rock, producing substances that clog rock fractures, reducing permeability and thus impacting geothermal extraction efficiency. 2. During the extraction process, large amounts of water can penetrate deep into the strata, resulting in a waste of water resources. 3. Water can physically and chemically affect the rock mass, reducing the lifespan of the geothermal extraction system. Using supercritical carbon dioxide as the low-temperature working fluid offers the following advantages: 1. Supercritical carbon dioxide (S-CO2) has better heat-carrying properties than water and, under the same conditions, a higher heat extraction rate than water. 2. It reduces water consumption and is relatively easy to obtain in large quantities. 3. S-CO2 does not scale wellbores, surface equipment, or various pipelines. 4. It can be used for geological storage of CO2, enabling the integration of geothermal extraction and CO2 geological storage, further mitigating the greenhouse effect.

[0005] Currently, the mechanisms of geothermal energy extraction using supercritical carbon dioxide are not fully understood, both domestically and internationally. Direct in-situ engineering research requires significant investment, while experimental studies are relatively small and fail to reflect actual conditions. With the rapid development of numerical simulation technology, numerical software can be used to simulate complex boundary conditions. Compared to physical experiments, this approach requires less investment and is faster, allowing for large-scale, engineering-scale numerical analysis. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and propose a reduced-scale physical experimental system and simulation method for supercritical CO2 geothermal extraction. By combining the small-scale physical experimental system with numerical simulation technology, it can be used to more scientifically study and analyze related issues of engineering-scale supercritical carbon dioxide geothermal extraction.

[0007] The purpose of the present invention can be achieved through the following technical solutions.

[0008] The supercritical CO2 geothermal mining scale-down physical experimental system of the present invention includes an S-CO2 generation system, an S-CO2 temperature and pressure control system, a small-scale geothermal simulation system, an S-CO2 recovery system, an S-CO2 pressure and temperature measurement system, a rock physical and mechanical property testing system, and a safety protection system;

[0009] The S-CO2 generation system is composed of a supercritical reaction device, which is used to provide the supercritical carbon dioxide required for the experiment;

[0010] The S-CO2 temperature and pressure control system consists of a low-temperature constant-pressure tank and a back-pressure valve, which is used to convert the generated S-CO2 into a specific temperature and pressure state; the input port of the low-temperature constant-pressure tank is connected to the output port of the supercritical reaction device through a transportation pipeline, and the back-pressure valve is arranged on the transportation pipeline connected to the output port of the low-temperature constant-pressure tank;

[0011] The small-scale geothermal simulation system includes a high-temperature furnace, a K-series temperature controller, and a K-type double thermocouple, which are used to heat rock samples to a specific temperature and pressure and transmit temperature information to the NI analysis software in the computer. A rock sample with internal cracks is set in the furnace of the high-temperature furnace, and an S-CO2 injection pipe and an S-CO2 collection pipe are respectively set at both ends of the crack. The S-CO2 injection pipe is connected to the output port of the low-temperature constant pressure tank through a transportation pipeline, and the S-CO2 collection pipe is connected to the S-CO2 recovery system through a transportation pipeline. The K-series temperature controller is used to control the temperature and pressure in the high-temperature furnace; the K-type double thermocouple is used to monitor the temperature of the rock sample.

[0012] The S-CO2 recovery system consists of a CO2 storage tank, which is used to store and recover carbon dioxide after the experiment for reuse; the CO2 storage tank inlet is connected to the S-CO2 collection pipe through a transportation pipeline, and the CO2 storage tank outlet is connected to the low-temperature constant pressure tank input port through a transportation pipeline;

[0013] The S-CO2 pressure and temperature measurement system consists of an electric pressure valve, a flow sensor and a temperature sensor, and is used to measure the S-CO2 pressure, flow rate and temperature; the electric pressure valve is arranged on the transport pipeline connected between the low-temperature constant pressure tank input port and the supercritical reaction device output port; two flow sensors are provided, which are respectively provided on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe; two temperature sensors are provided, which are respectively provided on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe;

[0014] The rock physical and mechanical property testing system consists of an acoustic emission system, an ultrasonic measurement system, and a TJW-1000 electro-hydraulic servo compression testing machine, and is used to measure the modulus, strain, crack development, and bearing capacity changes of rock samples. The acoustic emission system consists of a waveguide rod, an acoustic emission sensor, a preamplifier, and an NI acquisition and analysis system, and is used to monitor and collect and analyze the acoustic emission phenomena of rock samples in real time during the test. One end of the waveguide rod is attached to the surface of the rock sample, and the other end extends to the outside of the high-temperature furnace. It is connected to the acoustic emission sensor, preamplifier, and NI acquisition and analysis system in sequence via a data cable to transmit the acoustic emission signal to the NI acquisition and analysis system. The ultrasonic measurement system consists of a PXI system, a power divider, and an ultrasonic receiving system, and is used to study the changes in the wave velocity and wave frequency of the acoustic wave signal propagating in the rock sample before and after the test, thereby indirectly reflecting the physical and mechanical parameters of the rock. The TJW-1000 electro-hydraulic servo compression testing machine is used to measure the changes in the uniaxial compressive strength mechanical properties of the rock sample before and after the experiment, and then analyze the changes in the modulus and cohesion of the rock sample.

[0015] The safety protection system consists of a safety valve and an electric pressure valve; two safety valves are provided, respectively on the transport pipeline connecting the output port of the supercritical reaction device and the input port of the low-temperature constant pressure tank, and on the transport pipeline connecting the output port of the low-temperature constant pressure tank and the S-CO2 injection pipe. When the pressure in the experimental system reaches the specified value, CO2 is automatically discharged to protect personal safety and the normal operation of the experimental equipment; the electric pressure valve is used to set the upper limit protection pressure of the CO2 pump. When the pressure of the pump reaches the upper limit value, the pump is automatically stopped for protection.

[0016] One end of the S-CO2 injection pipe is set at one end of the crack, and the other end is connected to the output port of the low-temperature constant pressure tank through a transportation pipeline; one end of the S-CO2 collection pipe is set at the other end of the crack, and the other end is connected to the inlet of the CO2 storage tank through a transportation pipeline.

[0017] Steel plates are provided on the upper and lower surfaces of the rock sample, a calcium silicate pad is provided at the bottom of the steel plate on the lower surface, and a calcium silicate pad ball is provided between the steel plate on the lower surface and the calcium silicate pad.

[0018] The transport pipeline is composed of a high-pressure seamless steel pipe with a diameter of 1 cm and a pipeline insulation material, which is used to transport CO2 while isolating it from the outside temperature to prevent interference with the outside temperature experiment.

[0019] The purpose of the present invention can also be achieved through the following technical solutions.

[0020] The present invention is based on a hybrid numerical simulation method of a scaled-down physical experimental system for supercritical CO2 geothermal mining, and includes the following steps:

[0021] Step 1: Using the supercritical CO2 geothermal mining scale-down physical experimental system, experiments were conducted under different surrounding rock pressures, reservoir temperatures, injected S-CO2 temperatures, and flow rates.

[0022] Step 2: Before and after the experiment, physical and mechanical property measurement tests were conducted on the rock samples. The changes in the physical and mechanical parameters of the rock samples before and after the experiment were analyzed based on the small-scale physical experimental data obtained from the experiments.

[0023] The third step: input the physical and mechanical parameters of the rock sample after the test into the small-scale numerical model in the small-scale numerical model system that is a mirror image of the small-scale physical experiment system to obtain small-scale numerical simulation data. The small-scale numerical simulation data and the small-scale physical experiment data of the second step are analyzed and calibrated by the parameter automatic calibration system to obtain the physical and mechanical parameters of the rock sample, which are input into the large-scale numerical model to analyze the mining efficiency, dynamic hazards and feasibility under different thermal reservoir conditions, flow rates and pressures at the engineering scale.

[0024] The small-scale numerical model system includes a small-scale numerical model and a parameter automatic calibration system that are mirror images of the small-scale physical experiment system;

[0025] The parameter automatic calibration system adopts Newton iteration algorithm, firstly, the small-scale physical experimental data y in the second step is test The physical and mechanical parameters x of the rock sample after the test are obtained k Input into the small-scale numerical model to obtain the small-scale numerical simulation data y num , and then calculate the small-scale physical experimental data y test With small-scale numerical simulation data y num If the error between them is less than the set error value, the rock sample parameters are output; if it is greater than the error value, the physical and mechanical parameters x are calculated according to the Newton iteration method. k Assign a new value to x k+1 , re-input it into the small-scale numerical model and perform calculations again until the error is less than the set error value.

[0026] The large-scale numerical model adopts the discrete lattice spring model and finite volume method coupling model of thermal coupling proposed by Professor Zhao Gaofeng's research group at Tianjin University. First, a heat conduction model is established based on the finite volume method, and then the heat conduction model is coupled to the discrete lattice spring model. The thermal expansion / contraction, thermal damage, and creep behavior of the rock are used to simulate the physical and mechanical changes of the reservoir rock under high temperature and high pressure geological conditions over a certain period of time, thereby providing analysis and prediction of the mining efficiency, feasibility and possible dynamic disasters of the geothermal mining process.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] (1) The present invention combines small-scale physical experiments with numerical simulations to more accurately derive rock physical and mechanical parameters.

[0029] (2) The present invention utilizes the more accurate parameters obtained to provide data support for the calculation of large-scale numerical models.

[0030] (3) The present invention can simulate the physical and mechanical changes of reservoir rocks more accurately based on the TM-DLSM large-scale numerical model, thereby providing certain assistance for geothermal mining projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the scaled-down physical experimental system for supercritical CO2 geothermal mining according to the present invention;

[0032] Figure 2 A side sectional view of the small- and medium-scale geothermal simulation system of the present invention;

[0033] Figure 3 This is a front cross-sectional view of the small- and medium-scale geothermal simulation system of the present invention;

[0034] Figure 4 is a flow chart of the hybrid numerical simulation method of the present invention;

[0035] Figure 5 This is a schematic diagram of the automatic calibration parameters of the Newton iteration method in the present invention;

[0036] Figure 6 It is the large-scale numerical model and related dimensions in this invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings.

[0038] The principle of the present invention is to calibrate the basic mechanical parameters of the multi-physics field numerical model through small-scale experiments, and then establish an engineering-scale geothermal mining simulation model on a computer by scaling up the scale, and then study the mining efficiency, dynamic hazards and feasibility under different working conditions such as thermal reservoir conditions, flow rates and pressures.

[0039] like Figures 1 to 3 As shown, the supercritical CO2 geothermal mining scaled-down physical experimental system of the present invention mainly includes an S-CO2 generation system, an S-CO2 temperature and pressure control system, a small-scale geothermal simulation system, an S-CO2 recovery system, an S-CO2 pressure and temperature measurement system, a rock physical and mechanical properties testing system, and a safety protection system.

[0040] The S-CO2 generation system is mainly composed of a supercritical reaction device, which is used to provide the supercritical carbon dioxide required for the experiment.

[0041] The S-CO2 temperature and pressure control system consists of a low-temperature constant-pressure tank and a back-pressure valve, which are used to convert the generated S-CO2 into a specific temperature and pressure state. The input port of the low-temperature constant-pressure tank is connected to the output port of the supercritical reactor via a transport pipeline, and the back-pressure valve is installed on the transport pipeline connected to the output port of the low-temperature constant-pressure tank.

[0042] The small-scale geothermal simulation system primarily includes a high-temperature furnace, a K-series temperature controller, and a K-type dual thermocouple, which are used to heat rock samples to a specific temperature and pressure and transmit temperature information to the NI analysis software within a computer. A rock sample with internal fractures is placed within the furnace of the high-temperature furnace. An S-CO2 injection pipe and an S-CO2 collection pipe are located at either end of the fracture. The S-CO2 injection pipe is connected to the output port of a low-temperature constant pressure tank via a transport pipeline, and the S-CO2 collection pipe is connected to the S-CO2 recovery system via a transport pipeline. Steel plates are placed on both the upper and lower surfaces of the rock sample. A calcium silicate pad is placed at the bottom of the lower steel plate, and a calcium silicate ball is placed between the lower steel plate and the calcium silicate pad. The K-series temperature controller is used to control the temperature and pressure within the high-temperature furnace, and the K-type dual thermocouple is used to monitor the temperature of the rock sample.

[0043] Specifically, one end of the S-CO2 injection pipe is set at one end of the fissure, and the other end is connected to the output port of the low-temperature constant pressure tank through a transportation pipeline; one end of the S-CO2 collection pipe is set at the other end of the fissure, and the other end is connected to the inlet of the CO2 storage tank through a transportation pipeline.

[0044] The S-CO2 recovery system primarily consists of a CO2 storage tank, which is used to store and recover carbon dioxide after experiments for reuse, effectively preventing high CO2 concentrations in the laboratory from harming experimenters. The CO2 tank inlet is connected to the S-CO2 collection pipe via a transport pipeline, and the CO2 tank outlet is also connected to the low-temperature constant pressure tank inlet via a transport pipeline.

[0045] The S-CO2 pressure and temperature measurement system is composed of an electric pressure valve, a flow sensor and a temperature sensor, and is used to measure the S-CO2 pressure, flow rate and temperature. The electric pressure valve is arranged on the transport pipeline connected between the low-temperature constant pressure tank input port and the supercritical reaction device output port. Two flow sensors are provided, which are respectively arranged on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and on the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe. Two temperature sensors are provided, which are respectively arranged on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and on the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe.

[0046] The rock physical and mechanical property testing system consists of an acoustic emission system, an ultrasonic measurement system, and a TJW-1000 electro-hydraulic servo compression testing machine. It is used to measure the modulus, strain, crack development, and bearing capacity changes of rock samples. The acoustic emission system consists of a waveguide rod, an acoustic emission sensor, a preamplifier, and an NI acquisition and analysis system. It is used to monitor, collect, and analyze acoustic emission phenomena in rock samples in real time during the test. The waveguide rod can be made of steel, with one end attached to the surface of the rock sample and the other end extending to the outside of the high-temperature furnace. It is connected to the acoustic emission sensor, preamplifier, and NI acquisition and analysis system in sequence via data cables, transmitting the acoustic emission signals to the NI acquisition and analysis system. The acoustic emission sensor can be a FUJI-1045S acoustic emission sensor, and the preamplifier can be a PXPA2 preamplifier.

[0047] The ultrasonic measurement system, consisting of a PXI system, a power splitter, and an ultrasonic receiving system, is used to study changes in acoustic wave velocity, frequency, and other parameters propagating through rock samples before and after testing, indirectly reflecting the rock's physical and mechanical properties. The TJW-1000 electro-hydraulic servo compression testing machine is used to measure changes in the uniaxial compressive strength and mechanical properties of rock samples before and after testing, thereby analyzing changes in parameters such as modulus and cohesion.

[0048] The safety protection system consists of a safety valve and an electric pressure valve. Two safety valves are installed, one on the transport pipeline connecting the supercritical reactor output and the low-temperature constant pressure tank input, and the other on the transport pipeline connecting the low-temperature constant pressure tank output and the S-CO2 injection pipe. These valves automatically discharge CO2 when the pressure within the experimental system reaches a specified value, protecting personnel and ensuring the normal operation of the experimental equipment. The electric pressure valve can be used to set the upper limit protection pressure of the CO2 pump. When the pump pressure reaches the upper limit, it automatically stops the pump for protection.

[0049] In the above, the transport pipeline is composed of a high-pressure seamless steel pipe with a diameter of 1 cm (GB5310-2008 high-pressure boiler tube) and a pipeline insulation material (rock wool), which is used to transport CO2 while isolating the external temperature to prevent interference with the external temperature experiment.

[0050] The present invention is based on the hybrid numerical simulation method of the above-mentioned supercritical CO2 geothermal mining scale-down physical experimental system. Figure 4 As shown, the specific implementation process is as follows:

[0051] Step 1: Using the supercritical CO2 geothermal mining scale-down physical experimental system, experiments were conducted under different surrounding rock pressures, reservoir temperatures, injected S-CO2 temperatures, and flow rates.

[0052] ① The output port of the HLJCF-2 supercritical reactor can be connected to the input port of the low-temperature constant pressure tank through a delivery pipeline. A safety valve and an electric pressure valve are installed on this section of the delivery pipeline, and the delivery pipeline is connected to the outlet of the CO2 storage tank through a three-way joint, so that the CO2 after the test can be recycled.

[0053] ② Connect the low-temperature constant pressure tank to the small-scale geothermal simulation system through a transmission pipeline. Install a flow sensor, temperature sensor, back pressure valve, and safety valve on the transmission pipeline, and connect the flow sensor and temperature sensor to the NI acquisition and analysis system through a data cable.

[0054] To ensure uniform heating of the rock sample within the high-temperature furnace, a calcium silicate block and four calcium silicate balls were placed underneath the sample. A steel plate was placed on each of the top and bottom surfaces of the rock sample, with a circle of bolts placed between the two plates. The confining pressure of the rock sample was adjusted by tightening the bolts. The waveguide rod was connected to the acoustic emission sensor, its preamplifier, and the NI acquisition and analysis system via a data cable.

[0055] For example: the steel plate dimensions are 28 × 18 × 0.5 cm, the calcium silicate spacer blocks are 10 × 5 × 3 cm, and the four calcium silicate spacer balls have a diameter of 1 cm. The high-temperature furnace can be an electric heating furnace with internal dimensions of 30 × 20 × 12 cm. The diameters of the S-CO2 injection and collection tubes are both 3 cm.

[0056] For example, a rock sample measuring 25×15×5cm (granite or sandstone) with internal fractures measuring 15×10×0.5cm is used. The two S-CO2 injection and production ports for the S-CO2 injection and collection tubes, as well as the reservoir fractures within the rock sample, are carved using a precision engraving machine. After carving, a high-temperature, high-pressure adhesive is used to bond the gap between the sample surface and the reservoir when the rock fractures are cut. The two S-CO2 injection tubes for CO2 injection and the S-CO2 collection tube for CO2 production within the sample are wrapped with thermally insulating rock wool.

[0057] ③ Connect the small-scale geothermal simulation system to the CO2 storage tank through a transmission pipeline. The transmission pipeline is equipped with a flow sensor and a temperature sensor to measure the CO2 flow and temperature after the test.

[0058] ④ Conduct multiple tests under different surrounding rock pressures, reservoir temperatures, injected S-CO2 temperatures, and flow rates.

[0059] Step 2: Before and after the experiment, physical measurement tests and mechanical property measurement tests (such as ultrasonic testing and uniaxial compression testing) are carried out on the rock samples. The changes in the physical and mechanical parameters of the rock samples before and after the experiment are analyzed through the small-scale physical experimental data obtained from the experiments.

[0060] The third step: input the physical and mechanical parameters of the rock sample after the test into the small-scale numerical model in the small-scale numerical model system that is a mirror image of the small-scale physical experiment system to obtain small-scale numerical simulation data. The small-scale numerical simulation data and the small-scale physical experiment data of the second step are analyzed and calibrated by the parameter automatic calibration system to obtain the physical and mechanical parameters of the rock sample, which are input into the large-scale numerical model to analyze the mining efficiency, dynamic hazards and feasibility under different thermal reservoir conditions, flow rates, pressures and other working conditions at the engineering scale.

[0061] The small-scale numerical model system of the present invention mainly includes: a small-scale numerical model mirrored with the small-scale physical experiment system and a parameter automatic calibration system.

[0062] The parameter automatic calibration system adopts Newton iteration algorithm, firstly, the small-scale physical experimental data y in the second step is test The physical and mechanical parameters x of the rock sample after the test are obtained k Input into the small-scale numerical model to obtain the small-scale numerical simulation data y num , and then calculate the small-scale physical experimental data y test With small-scale numerical simulation data y num If the error f(x) is less than the set error value, the rock sample parameters are output; if it is greater than the error value, the physical and mechanical parameters x are calculated according to the Newton iteration method. k Assign a new value to x k+1 , re-input it into the small-scale numerical model and then perform the calculation until the error is less than the set error value. Figure 5 shown.

[0063]

[0064] Among them, x k and x k+1 are the iteration values in the kth and (k+1)th iterations respectively, α is the correction factor, which can be set to 0.98 in the present invention, and △x is x k+1 increment.

[0065] Through the above steps, the large-scale physical experimental data can be compared and corrected with the small-scale numerical simulation data. After multiple iterations, the rock sample parameters are output to provide more reasonable and accurate parameters for the large-scale numerical model, thereby analyzing the mining efficiency, dynamic hazards and feasibility under different thermal reservoir conditions, flow rates, pressures and other working conditions at the engineering scale.

[0066] In order to more realistically simulate the changes in rock physical and mechanical parameters in actual geothermal projects, the large-scale numerical model of the present invention adopts the thermal-mechanical-distinct lattice spring model (TM-DLSM) and the finite volume method (FVM) coupling model proposed by the research group of Professor Zhao Gaofeng of Tianjin University. First, a heat conduction model is established based on the finite volume method (FVM), and then the heat conduction model is coupled to the discrete lattice spring model (DLSM). Through the thermal expansion / contraction, thermal damage, and creep behavior of the rock, the physical and mechanical changes of the reservoir rock under high temperature and high pressure geological conditions within a certain period of time are simulated, thereby providing analysis and prediction for the mining efficiency, feasibility and possible dynamic disasters of the geothermal mining process. Among them, the real-time thermal damage model of the rock can be established based on the characteristic parameters of the acoustic emission signal.

[0067] The large-scale numerical simulation is divided into three processes: ① S-CO2 flow and heat transfer process in the injection well; ② S-CO2 flow and heat transfer process in the reservoir; ③ S-CO2 flow and heat transfer process in the production well.

[0068] Model size: Figure 6 Where Lr represents the length of the rock formation, Wr represents the width of the rock formation, and Hr represents the thickness of the rock formation; Lc represents the length of the reservoir, Wc represents the width of the reservoir, and Hc represents the height of the reservoir. The fracture is located at the center of the rock formation. For example, the model parameters in this invention are Lr = 300 meters, Wr = 200 meters, Hr = 150 meters; Lc = 100 meters, Wc = 80 meters, and Hc = 30 meters. The diameter of the S-CO2 injection and production port is 0.2 meters. This model uses a "one injection, one production" method to simulate the flow of S-CO2 within the reservoir and the absorption of heat from the hot dry rock.

[0069] Assumptions: ① S-CO2 does not chemically react with rock; ② Rock is homogeneous and isotropic; 3. S-CO2 flows at a constant velocity within the model; ③ Thermal damage is caused by uneven deformation between different materials during heating, resulting in cracks, and cracks expand within the mineral particles during cooling.

[0070] Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific functions and working processes. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. A supercritical CO2 geothermal mining scale-down physical experimental system, characterized by: Including S-CO2 generation system, S-CO2 temperature and pressure control system, small-scale geothermal simulation system, S-CO2 recovery system, S-CO2 pressure and temperature measurement system, rock physical and mechanical properties testing system, and safety protection system; The S-CO2 generation system is composed of a supercritical reaction device, which is used to provide the supercritical carbon dioxide required for the experiment; The S-CO2 temperature and pressure control system consists of a low-temperature constant pressure tank and a back pressure valve, which is used to convert the generated S-CO2 into a specific temperature and pressure state; The low-temperature constant-pressure tank input port is connected to the supercritical reaction device output port through a transport pipeline, and the back-pressure valve is arranged on the transport pipeline connected to the low-temperature constant-pressure tank output port; The small-scale geothermal simulation system includes a high-temperature furnace, a K-series temperature controller, and a K-type double thermocouple, which are used to heat rock samples to a specific temperature and pressure and transmit temperature information to the NI analysis software in the computer. A rock sample with internal cracks is set in the furnace of the high-temperature furnace, and an S-CO2 injection pipe and an S-CO2 collection pipe are respectively set at both ends of the crack. The S-CO2 injection pipe is connected to the output port of the low-temperature constant pressure tank through a transportation pipeline, and the S-CO2 collection pipe is connected to the S-CO2 recovery system through a transportation pipeline. The K-series temperature controller is used to control the temperature and pressure in the high-temperature furnace; the K-type double thermocouple is used to monitor the temperature of the rock sample. The S-CO2 recovery system consists of a CO2 storage tank, which is used to store and recover carbon dioxide after the experiment for reuse; the CO2 storage tank inlet is connected to the S-CO2 collection pipe through a transportation pipeline, and the CO2 storage tank outlet is connected to the low-temperature constant pressure tank input port through a transportation pipeline; The S-CO2 pressure and temperature measurement system consists of an electric pressure valve, a flow sensor and a temperature sensor, and is used to measure the S-CO2 pressure, flow rate and temperature; the electric pressure valve is arranged on the transport pipeline connected between the low-temperature constant pressure tank input port and the supercritical reaction device output port; two flow sensors are provided, which are respectively provided on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe; two temperature sensors are provided, which are respectively provided on the transport pipeline connected between the low-temperature constant pressure tank output port and the S-CO2 injection pipe, and the transport pipeline connected between the CO2 storage tank inlet and the S-CO2 collection pipe; The rock physical and mechanical property testing system consists of an acoustic emission system, an ultrasonic measurement system, and a TJW-1000 electro-hydraulic servo compression testing machine, and is used to measure the modulus, strain, crack development, and bearing capacity changes of rock samples. The acoustic emission system consists of a waveguide rod, an acoustic emission sensor, a preamplifier, and an NI acquisition and analysis system, and is used to monitor and collect and analyze the acoustic emission phenomena of rock samples in real time during the test. One end of the waveguide rod is attached to the surface of the rock sample, and the other end extends to the outside of the high-temperature furnace. It is connected to the acoustic emission sensor, preamplifier, and NI acquisition and analysis system in sequence via a data cable to transmit the acoustic emission signal to the NI acquisition and analysis system. The ultrasonic measurement system consists of a PXI system, a power divider, and an ultrasonic receiving system, and is used to study the changes in the wave velocity and wave frequency of the acoustic wave signal propagating in the rock sample before and after the test, thereby indirectly reflecting the physical and mechanical parameters of the rock. The TJW-1000 electro-hydraulic servo compression testing machine is used to measure the changes in the uniaxial compressive strength mechanical properties of the rock sample before and after the experiment, and then analyze the changes in the modulus and cohesion of the rock sample. The safety protection system consists of a safety valve and an electric pressure valve; two safety valves are provided, one on the transport pipeline connecting the output port of the supercritical reaction device and the input port of the low-temperature constant pressure tank, and the other on the transport pipeline connecting the output port of the low-temperature constant pressure tank and the S-CO2 injection pipe. When the pressure in the experimental system reaches the specified value, CO2 is automatically discharged to protect personal safety and the normal operation of the experimental equipment; the electric pressure valve is used to set the upper limit protection pressure of the CO2 pump. When the pressure of the pump reaches the upper limit value, the pump is automatically stopped for protection; Using the above experimental system, experiments were carried out under different surrounding rock pressures, reservoir temperatures, S-CO2 injection temperatures, and flow rates. Before and after the experiments, physical measurement tests and mechanical property measurement tests were carried out on the rock samples. The small-scale physical experimental data obtained from the experiments were used to analyze the changes in the physical and mechanical parameters of the rock samples before and after the experiments. The physical and mechanical parameters of the rock samples after the experiments were input into a small-scale numerical model in the small-scale numerical model system that mirrored the small-scale physical experimental system to obtain small-scale numerical simulation data. The small-scale numerical simulation data and the small-scale physical experimental data were analyzed and calibrated by the parameter automatic calibration system to obtain the physical and mechanical parameters of the rock samples, which were input into the large-scale numerical model to analyze the mining efficiency, dynamic hazards, and feasibility under different thermal reservoir conditions, flow rates, and pressures at the engineering scale.

2. The supercritical CO2 geothermal mining scale-down physical experimental system according to claim 1 is characterized in that: One end of the S-CO2 injection pipe is set at one end of the crack, and the other end is connected to the output port of the low-temperature constant pressure tank through a transportation pipeline; one end of the S-CO2 collection pipe is set at the other end of the crack, and the other end is connected to the inlet of the CO2 storage tank through a transportation pipeline.

3. The supercritical CO2 geothermal mining scale-down physical experimental system according to claim 1 is characterized in that: Steel plates are provided on the upper and lower surfaces of the rock sample, a calcium silicate pad is provided at the bottom of the steel plate on the lower surface, and a calcium silicate pad ball is provided between the steel plate on the lower surface and the calcium silicate pad.

4. The supercritical CO2 geothermal mining scale-down physical experimental system according to claim 1 is characterized in that: The transport pipeline is composed of a high-pressure seamless steel pipe with a diameter of 1 cm and a pipeline insulation material, which is used to transport CO2 while isolating it from the outside temperature to prevent interference with the outside temperature experiment.

5. A hybrid numerical simulation method based on the supercritical CO2 geothermal mining scale-down physical experimental system according to any one of claims 1 to 4, characterized in that: The following processes are included: Step 1: Using a scaled-down physical experimental system for supercritical CO2 geothermal mining, experiments were conducted under different surrounding rock pressures, reservoir temperatures, injected S-CO2 temperatures, and flow rates. Step 2: Before and after the experiment, physical and mechanical property measurement tests were conducted on the rock samples. The changes in the physical and mechanical parameters of the rock samples before and after the experiment were analyzed based on the small-scale physical experimental data obtained from the experiments. The third step: input the physical and mechanical parameters of the rock sample after the test into the small-scale numerical model in the small-scale numerical model system that is a mirror image of the small-scale physical experiment system to obtain small-scale numerical simulation data. The small-scale numerical simulation data and the small-scale physical experiment data of the second step are analyzed and calibrated by the parameter automatic calibration system to obtain the physical and mechanical parameters of the rock sample, which are input into the large-scale numerical model to analyze the mining efficiency, dynamic hazards and feasibility under different thermal reservoir conditions, flow rates and pressures at the engineering scale.

6. The hybrid numerical simulation method based on the supercritical CO2 geothermal mining scale-down physical experimental system according to claim 5 is characterized in that: The small-scale numerical model system includes a small-scale numerical model and a parameter automatic calibration system that are mirror images of the small-scale physical experiment system; The parameter automatic calibration system adopts Newton iteration algorithm, firstly, the small-scale physical experimental data y in the second step is test The physical and mechanical parameters x of the rock sample after the test are obtained k Input into the small-scale numerical model to obtain the small-scale numerical simulation data y num , and then calculate the small-scale physical experimental data y test With small-scale numerical simulation data y num If the error between them is less than the set error value, the rock sample parameters are output; if it is greater than the error value, the physical and mechanical parameters x are calculated according to the Newton iteration method. k Assign a new value to x k+1 , re-input it into the small-scale numerical model and perform calculations again until the error is less than the set error value.

7. The hybrid numerical simulation method based on the supercritical CO2 geothermal mining scale-down physical experimental system according to claim 5 is characterized in that: The large-scale numerical model adopts the discrete lattice spring model and finite volume method coupling model of thermal coupling proposed by Professor Zhao Gaofeng's research group at Tianjin University. First, a heat conduction model is established based on the finite volume method, and then the heat conduction model is coupled to the discrete lattice spring model. The thermal expansion / contraction, thermal damage, and creep behavior of the rock are used to simulate the physical and mechanical changes of the reservoir rock under high temperature and high pressure geological conditions over a certain period of time, thereby providing analysis and prediction of the mining efficiency, feasibility and possible dynamic disasters of the geothermal mining process.

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