High-temperature high-pressure true triaxial fracturing physical simulation experiment system

Abstract

The application discloses a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system, which comprises a heating and temperature control module, a loading module, a pump injection module, a sample loading module and a monitoring module, and can meet the test conditions of the high-temperature true triaxial fracturing physical simulation experiment through organic combination. The heating and temperature control module can heat the sample to reach the formation temperature condition, and the loading module can apply non-uniform stress to the sample. The pump injection module for multi-fracture expansion can perform fracturing physical simulation on the sample, that is, high-pressure fluid drives fracture expansion, and the pressure and flow in the fracture during the expansion of each fracture are monitored. The monitoring module for fracture expansion monitors the rupture, fracture and fracture expansion of the sample through acoustic and optical monitoring methods. Organic combination of the several main functional modules ensures that the test meets the formation high-temperature and high-pressure geological condition physical simulation, the fracture expansion physical simulation and the fracture expansion characteristic depiction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fracturing and thermal fluid curing, and particularly relates to a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system. BACKGROUND

[0002] Dry hot rock, deep unconventional oil and gas, oil shale, and "coal underground gasification hydrogen and methane" are important strategic replacement mineral resources, which have the outstanding characteristics of high rock layer temperature, large reserves, and green low carbon. The hydrogen and methane produced by underground gasification (600 to 1200 DEG C) of 1000 to 3000 meters deep coal which is difficult to exploit by traditional methods is about 4 times the conventional reserves. The efficient exploitation of strategic replacement mineral energy resources requires the construction of fractures and the modification of permeability of the reservoir, and then the efficient exploitation, in which the fracturing of the rock mass by high-pressure fluid and the driving of the crack expansion is the core technology. High temperature is a prominent geological feature, and the expansion law of the high-temperature rock layer fracturing crack is much more complex than that of the normal temperature rock layer. Since the related theory and technology are still in the initial stage, the high-temperature fracturing crack expansion mechanism is unknown and difficult to measure and control in the field. It is necessary to carry out a high-temperature rock true triaxial loading condition fracturing physical simulation experiment to support the deepening of the theory, the optimization of the process technology, and the optimization of the construction parameters. Therefore, it is urgent to develop a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system to provide strong support for the modification theory and technology of the high-temperature reservoir permeability. SUMMARY

[0003] The purpose of the present application is to provide a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system, which realizes the real-time high-temperature and high-pressure fracturing physical simulation experiment with monitoring such as acoustic emission.

[0004] To solve the above technical problems, the embodiment of the present application provides a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system, which comprises: an overall frame and a heating and temperature control module, a loading module, a pump injection module, a monitoring module, and a sample loading module arranged in the overall frame.

[0005] The heating and temperature control module comprises a multi-channel servo temperature control module, a multi-layer combined high-temperature pressurizing plate, and a circulating water cooling module,

[0006] The multi-layer combined high-temperature pressurizing plate is in direct contact with the sample entering the fixed position through the sample loading module. The multi-channel servo temperature control module is used for heating the multi-layer combined high-temperature pressurizing plate. The circulating water cooling module is arranged inside the multi-layer combined high-temperature pressurizing plate and is used for cooling the multi-layer combined high-temperature pressurizing plate.

[0007] The loading module includes a load plate and a loading and unloading cylinder, wherein the loading and unloading cylinder provides pressure to the load plate, and the load plate is in direct contact with the multi-layer combined high-temperature pressure plate and transmits the pressure provided by the loading and unloading cylinder to the multi-layer combined high-temperature pressure plate;

[0008] The pumping module includes a pumping injection module and a pressure and flow measurement and control module. The pumping injection module is arranged inside the sample and is used to provide fracturing fluid for the sample. The pressure and flow measurement and control module is used to detect the real-time pumping pressure and flow inside the sample.

[0009] The monitoring module includes an acoustic emission monitoring device, a stress and pore pressure monitoring device, and an optical monitoring device. The acoustic emission monitoring device is used to perform visual analysis of acoustic emission signals, the stress and pore pressure monitoring device is used to monitor the stress and pore pressure in the sample in real time, and the optical monitoring device is used to monitor the continuous strain changes inside the sample structure and locate the location and size of cracks.

[0010] In addition, the multi-layer combined high-temperature pressurized plate includes: a heating and pressurizing layer, a high-temperature resistant middle layer, and a loading layer;

[0011] The heating and pressurizing layer is in direct contact with the sample and is provided with a socket, in which a plurality of heating rods and a temperature sensor are arranged. The heating rods and the temperature sensor are connected to the multi-channel servo temperature control module; the heating and pressurizing layer is also provided with an acoustic emission sensor waveguide rod;

[0012] The material of the high-temperature resistant intermediate layer is a high-temperature resistant heat-insulating material, and the high-temperature resistant intermediate layer has a cooling chamber for placing an acoustic emission sensor, and the cooling chamber is used to place and protect the acoustic emission sensor, wherein the acoustic emission sensor and the acoustic emission sensor waveguide rod are correspondingly arranged, and the cooling chamber is connected to the circulating water circuit;

[0013] The loading layer is in direct contact with the carrying plate.

[0014] In addition, the outermost side of the cooling chamber is a double-layered, approximately annular structure with a water inlet and outlet, and a hole for placing the acoustic sensor. The cooling chamber is used to cool the acoustic sensor placed inside it and to withstand the pressure of the sample loaded by the supporting plate.

[0015] The depth of the middle hole of the cooling chamber where the acoustic emission sensor is placed is greater than the height of the acoustic emission sensor;

[0016] The water inlet and outlet of the cooling chamber are connected to the circulating water circuit. The hollow space of the acoustic emission sensor is placed in the cooling chamber. From the inner side close to the sample to the outer side, there are the acoustic emission sensor waveguide rod, the acoustic emission sensor, a spring and a reaction force cover. The acoustic emission sensor waveguide rod has a small cross-sectional area at the end contacting the sample and a large cross-sectional area at the end contacting the acoustic emission sensor.

[0017] A coupling agent is also applied to the joint portion between the acoustic emission sensor and the acoustic emission sensor waveguide rod;

[0018] The spring is fixed to the cooling chamber via the reaction force cover. The spring is compressed to apply compressive stress to the acoustic emission sensor and the acoustic emission sensor waveguide rod, so that the acoustic emission sensor and the acoustic emission sensor waveguide rod are tightly pressed against the sample. At the same time, a coupling agent is applied between the end of the acoustic emission sensor of the waveguide rod and the sample.

[0019] In addition, the circulating water circuit is connected to each cooling chamber through a water pipeline. The circulating water circuit circulates water from bottom to top, and a diverter is used for diversion and merging of each cooling chamber.

[0020] In addition, the pump injection module includes a high-precision injection pump, an oil-water separator, and a multiphase fluid pump injection system;

[0021] The high-precision injection pump is the power source of the pump injection module; the oil-water isolator is a piston container, and the two spaces separated by the piston are respectively connected to the injection pump and the sample injection pipe, among which the space connected to the sample injection pipe stores liquid fracturing medium.

[0022] In addition, the pressure and flow measurement and control module includes a pressure sensor arranged at the liquid outlet end of the oil-water isolator, and the pressure sensor is used to monitor the fluid pressure pumped into the sample; a flow sensor is used to monitor the pumping flow; and a displacement sensor is used to monitor the displacement stroke of the oil-water isolator piston and further calculate the pumping flow.

[0023] In addition, the fracturing medium includes at least one of a proppant, a temporary plugging agent, a water-based fracturing fluid, and an oil-based fracturing fluid. The water-based fracturing fluid and the oil-based fracturing fluid are used to control at least one physical and chemical property of the pumping fluid, including viscosity, pH, and filtration loss characteristics.

[0024] In addition, the pumping module is also equipped with storage tanks and pumping devices for CO2, N2, steam gaseous and supercritical multiphase fluids, which are used for fracturing multiphase fluids as fracturing media; it is also equipped with a fracturing medium heating and steam exciter heating system, which is used for high-temperature fluids as fracturing media for fracturing physical simulation.

[0025] In addition, the optical monitoring device comprises a fiber grating; the fiber grating is embedded in the sample structure and on the surface, a high-strength transparent glass plate is arranged on the fiber grating, and a camera is arranged behind the high-strength transparent glass plate.

[0026] In addition, the sample loading module comprises two groups of vertical sample loading sliding rails, and the two groups of sample loading sliding rails correspond to one platform respectively to form a double-layer slidable combined platform for placing the sample.

[0027] Compared with the prior art, the main functional modules of the high-temperature and high-pressure true triaxial fracturing physical simulation experiment system provided by the present application, i.e., the heating and temperature control module, the loading module, the pump injection module, the sample loading module and the monitoring module, can be organically combined to meet the test conditions of the high-temperature true triaxial fracturing physical simulation test. The heating and temperature control module can heat the sample to reach the formation temperature condition, and the loading module can apply the ground stress to the sample. The pump injection module for multi-fracture expansion can perform fracturing physical simulation on the sample, i.e., high-pressure fluid drives fracture expansion, and the pressure and fracture flow in the process of each fracture expansion are monitored. The monitoring module for fracture expansion can monitor the acoustic emission information under high temperature through acoustic and optical monitoring methods, and obtain the monitoring sample rupture, fracture and fracture expansion. The organic combination of the several main functional modules ensures that the test meets the "formation high-temperature and high-pressure geological condition physical simulation, fracture expansion physical simulation and fracture expansion feature description". BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 FIG. 1 is a structural schematic diagram of a high-temperature and high-pressure true triaxial fracturing physical simulation experiment system according to an embodiment of the present application;

[0029] Figure 2 FIG. 2 is a schematic diagram of a multi-layer combined high-temperature pressurizing plate according to an embodiment of the present application;

[0030] Figure 3 FIG. 3 is a schematic diagram of an overall frame according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the embodiments of the present application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that in the embodiments of the present application, many technical details are proposed in order to make the readers better understand the present application. However, the technical scheme claimed by the present application can be realized even without these technical details and various changes and modifications based on the following embodiments. The division of the following embodiments is for the convenience of description, and should not constitute any limitation on the specific implementation of the present application, and the embodiments can be combined and referenced with each other under the premise of no contradiction.

[0032] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It is important to understand that conducting a high-temperature true triaxial fracturing physical simulation test requires the following conditions: First, high temperature and confining pressure conditions must be applied to the sample to simulate the high temperature and ground stress conditions of the actual formation; then, high-pressure fluid is pumped into the sample to drive the crack expansion, which is used to physically simulate the expansion of the fracturing crack; during the fracturing crack expansion process, acoustic, optical and other monitoring methods are used, and a variety of sensors are used to monitor the expansion characteristics of the crack.

[0033] One embodiment of the present invention relates to a high-temperature and high-pressure true triaxial fracturing physical simulation experimental system, which can be used to physically simulate the high-temperature and normal-temperature rock fracturing crack expansion in deep high-temperature oil and gas production, geothermal production, high-temperature modified production of oil shale and coal, and surrounding rock control in underground mines. It can also be used for true triaxial loading and multi-field coupling of thermal flow and solidification in other rock engineering fields. Its outstanding feature is that it can carry out fracturing physical simulation experiments with monitoring such as acoustic emission under real-time high temperature and high pressure. Figure 1 As shown, it includes: an overall frame and a heating and temperature control module, a loading module, a pumping module, a monitoring module, and a loading module arranged in the overall frame; the heating and temperature control module includes a multi-channel servo temperature control module, a multi-layer combined high-temperature pressure plate, and a circulating water cooling module. The multi-layer combined high-temperature pressure plate is in direct contact with the sample that enters the fixed position through the loading module; the multi-channel servo temperature control module is used to heat the multi-layer combined high-temperature pressure plate; the circulating water cooling module is arranged inside the multi-layer combined high-temperature pressure plate to cool the multi-layer combined high-temperature pressure plate; the loading module includes a load-bearing plate and a loading and unloading cylinder. The loading and unloading cylinder provides pressure for the load-bearing plate. The load-bearing plate and the multi-layer combined high-temperature pressure plate are in direct contact with each other. The pressure plate is in direct contact and transmits the pressure provided by the loading and unloading cylinder to the multi-layer combined high-temperature pressure plate; the pumping module includes a pumping injection module and a pressure and flow measurement and control module. The pumping injection module is arranged inside the sample and is used to provide fracturing fluid for the sample; the pressure and flow measurement and control module is used to detect the real-time pumping pressure and flow inside the sample; the monitoring module includes an acoustic emission monitoring device, a stress and pore pressure monitoring device, and an optical monitoring device. The acoustic emission monitoring device is used to perform visual analysis on the acoustic emission signal, the stress and pore pressure monitoring device is used to monitor the stress and pore pressure in the sample in real time, and the optical monitoring device is used to monitor the continuous strain changes inside the sample structure and locate the location and size of the cracks.

[0034] In one example, a multi-channel servo temperature control module primarily includes a multi-channel thermostat, multi-channel temperature sensors, and heating rods embedded in a multi-layered, modular, high-temperature pressurized platen. For each heating channel, the thermostat sets the heating temperature, sends commands, and controls the heating rods' temperature rise. The temperature sensor senses the temperature in real time and provides feedback to the thermostat. If the temperature exceeds the set point, heating stops. If it falls below the set point, heating continues until the temperature stabilizes at the set point.

[0035] Multi-layer combined high temperature pressure plate Figure 2 As shown, it includes: a heating and pressurizing layer, a high-temperature resistant intermediate layer, and a loading layer; the heating and pressurizing layer is in direct contact with the sample and is provided with a socket, in which multiple heating rods and temperature sensors are arranged, and the heating rods and temperature sensors are connected to the multi-channel servo temperature control module; the heating and pressurizing layer is also provided with an acoustic emission sensor waveguide rod. The provision of the heating and pressurizing layer, on the one hand, prevents the individual sensors from directly contacting the high-temperature sample; on the other hand, it allows the individual sensors to be closer to a "point" due to the reduced contact surface, which is more consistent with the "coordinate point" in the source inversion equation. The rounded end of the acoustic emission sensor waveguide rod is in full contact with the sample, and the other end is in full contact with the acoustic emission sensor. The position of the waveguide rod depends on the placement of the acoustic emission sensor and is synchronized with the position of the acoustic emission sensor.

[0036] The high-temperature-resistant intermediate layer is made of high-temperature insulating material and features a cooling chamber for the acoustic emission sensor. The cooling chamber houses and protects the acoustic emission sensor, which is positioned corresponding to the sensor's waveguide probe. The cooling chamber is connected to the circulating water circuit. The high-temperature-resistant intermediate layer protects the acoustic emission sensor and true triaxial loading platform, preventing damage to the equipment from high temperatures.

[0037] The loading layer is in direct contact with the bearing plate and can withstand ground stresses of >60MPa. Field measurements have shown that when the sample is heated and temperature-controlled to 300°C, the acoustic emission sensor remains below 30°C.

[0038] In one example, the outermost side of the cooling chamber is a double-layered, approximately annular structure with a water inlet and a water outlet, and a hole for placing an acoustic sensor. The cooling chamber is used to cool the acoustic sensor placed inside it, and is also used to withstand the pressure of the load-bearing plate loaded on the sample; the depth of the middle hole in the cooling chamber where the acoustic emission sensor is placed is greater than the height of the acoustic emission sensor; the water inlet and the water outlet of the cooling chamber are connected to the circulating water circuit, and the hollow space in the cooling chamber where the acoustic emission sensor is placed, from the inside close to the sample to the outside, is the acoustic emission sensor waveguide rod, the acoustic emission sensor, the spring, and the reaction cover; the acoustic emission sensor waveguide rod has a small cross-sectional area at the end contacting the sample and a large cross-sectional area at the end contacting the acoustic emission sensor, which avoids direct contact between the acoustic emission sensor and the sample. The high-temperature damage caused by contact reduces the contact area between the acoustic emission sensor and the sample, thereby increasing the demand for the sensor contact surface to be closer to one point in the source inversion, and the contact surface between the acoustic emission sensor waveguide rod and the cooling chamber is larger, so that the high temperature generated by the acoustic emission sensor waveguide rod contacting the sample can be quickly transmitted to avoid damaging the acoustic emission sensor. The acoustic emission sensor and the acoustic emission sensor waveguide rod are also coated with a coupling agent at the joint part to enhance the waveguiding effect; the spring is fixed to the cooling chamber through the reaction cover, and the spring is compressed to apply compressive stress to the acoustic emission sensor and the acoustic emission sensor waveguide rod, so that the whole formed by the acoustic emission sensor and the acoustic emission sensor waveguide rod is tightly pressed on the sample, and at the same time, a coupling agent is coated between the end of the waveguide rod acoustic emission sensor and the sample.

[0039] In one example, a circulating water circuit connects each cooling chamber via a water pipeline. The circulating water circuit circulates water from bottom to top, and a diverter is used for diversion and merging of each cooling chamber. Each acoustic emission cooling chamber is connected via a water pipeline, so that each acoustic emission sensor can be precisely cooled. All cooling chambers in the multi-layer combined high-temperature pressure plate located on the same plane of the rectangular specimen are connected in sequence, and the circulating water circuit circulates water from bottom to top, that is, there are a total of 6 water inlets and 6 water outlets under the test state. At the same time, water circulation cooling can also be performed on a single cooling chamber or any number of cooling chambers. The water injection pipelines and water outlet pipelines of all acoustic emission cooling chambers are respectively integrated into the main pipeline, and diverters can be used for diversion and merging. The main pipeline's inlet is filled with cold water, while the outlet is filled with hot water. A refrigeration unit is used between the inlet and outlet ends to ensure the circulating water is cold. Alternatively, the system can ensure only cold water is flowing through the inlet, while the water at the outlet can be discharged or recycled. The system also monitors the circulating water temperature in real time, controlling the flow rate to servo-control the water temperature. If the temperature exceeds the set point, the water flow is increased or the chiller's cooling temperature is lowered.

[0040] In one example, the overall framework is as follows Figure 3As shown, including the main frame, nine pairs of loading and unloading piston and large piston, the main frame is provided with sample loading cavity, wherein nine pairs of loading and unloading piston in the cavity, the large piston outside the main frame cavity. The main frame includes nut (1), gasket (2), bearing plate 1 (3), cushion block (10), cylinder (11), connecting screw (12), bearing plate 2 (13), pull rod (14), track wheel (15), platform (16), support plate (17), clamp (18), cylinder cushion block (19), bracket (20). Loading and unloading piston includes fan-shaped plate (21), piston (22), arc plate (23), return piston (24), fastening screw (25). Large piston includes oil cylinder cover (4), oil cylinder body (5), piston (6), snap ring (7), oil cylinder piston rod through cover (8), piston rod (9).

[0041] The platform is used for supporting the whole machine, and the upper end is connected with two support plates. The support plates are connected through the pull rod. The loading cavity is fixed above the platform through the cushion block. Nine loading and unloading oil cylinders are distributed on the inner surface of the cavity. Two loading and unloading oil cylinders are arranged in the X direction, two pairs of loading and unloading oil cylinders are arranged in the Y direction, and one loading and unloading oil cylinder and the large oil cylinder form a pair in the Z direction. The loading and unloading oil cylinder and the large oil cylinder are controlled through the adjusting liquid inlet valve to control the movement of the piston. The sample is loaded and unloaded by the confining pressure, and each pair of loading and unloading oil cylinder can be independently controlled. The design has two functions: on the one hand, it can load the large size sample with non-uniform stress, and on the other hand, it can realize the test of 300*300*300mm 3 cubic and 300*300*600mm 3 rectangular sample. Through the design concept, the size of the equipment is increased, the bearing capacity is increased, and more size samples can be tested.

[0042] The overall frame has the structural design of considering "convenient sample loading" and "saving space". The sample loading overall structure includes two groups of vertical sample loading slide rails, which are "guide slide rail for moving sample to chamber port" and "slide rail for guiding sample into loading chamber in loading chamber". The sample is moved to the loading chamber port and into the loading chamber. The movable loading and unloading oil cylinder parallel to the loading chamber can also move in the "guide slide rail for moving sample to chamber port", and move to the loading chamber port without blocking the loading chamber during sample loading, which is convenient for sample loading. Based on the above overall structure, the design matched with the guide rail is a double-layer slidable combined platform for placing sample and loading plate. The platform is composed of upper and lower layers:

[0043] The bottom of the lower platform is designed with a pulley that matches the "guide rail for transporting the sample to the chamber port", which is used to move the platform-sample-loading plate assembly to the loading chamber port; at the same time, the upper surface of the lower platform is provided with a slide rail of the same size as the "slide rail for guiding the sample into the loading chamber", which is used to place the upper platform. At the same time, the slide rail on the upper surface of the lower platform is aligned with the slide rail in the loading chamber, which serves as the judgment standard for the platform-sample-loading plate assembly to move to a reasonable position.

[0044] The upper platform is equipped with a sample and a loading plate. The bottom of the upper platform is provided with a pulley that matches the "slide rail for guiding the sample into the loading chamber". This design enables the upper platform, the sample and the loading plate to be pushed into the loading chamber together. The part of the upper platform that contacts the loading piston is not an integrated structure with the entire upper platform and is detachable. When the piston is loaded, it is lifted with the piston to load the surrounding rock for the sample.

[0045] In one example, the loading module consists of 9 sets of loading and unloading cylinders, pressure plates and large cylinders, wherein the loading and unloading cylinders are arranged in pairs. Two pairs of loading and unloading cylinders are arranged in the X direction, two pairs of loading and unloading cylinders are arranged in the Y direction, and one loading and unloading cylinder forms a pair with the large cylinder in the Z direction. The above cylinder settings can realize true triaxial loading. Each loading and unloading cylinder is composed of a loading cylinder, an unloading cylinder and a piston rod. During the loading process, the liquid inlet valve of each loading cylinder is opened, and the liquid inlet valve of each unloading cylinder is closed, so that the hydraulic oil is injected into the lower part of the return piston, pushing the piston rod to move and push the high-temperature pressure plate close to the sample, completing the confining pressure loading of the sample. When unloading the confining pressure, the liquid inlet valve of each loading cylinder is closed, and the liquid inlet valve of each unloading cylinder is opened, so that the hydraulic oil is injected into the upper part of the return piston, thereby pushing the piston rod to move upward, so that the bearing plate is away from the high-temperature pressure plate, completing the unloading confining pressure process. Each loading and unloading cylinder is independently provided with a liquid inlet valve and a liquid return valve, so that the loading and unloading of each loading and unloading cylinder can be independently controlled, thereby realizing the loading of non-uniform stress.

[0046] The loading system can be used for 300×300×600mm 3 The rectangular specimen is tested by placing a 300×300×300mm 3 The cube reaction block can also be used for 300×300×300mm 3 The test can be carried out on a cube specimen. Pads can be added to test smaller specimens. Through this design concept, the equipment size is increased and the load-bearing capacity is increased, so that more specimens can be tested.

[0047] In one example, the pumping and injection module includes a high-precision injection pump, an oil-water isolator, and a multiphase fluid pumping and injection system. The high-precision injection pump serves as the module's power source. The oil-water isolator is a piston container with two compartments separated by a piston, connected to the injection pump and a sample injection pipe, respectively. The compartment connected to the sample injection pipe contains the liquid fracturing medium. The pressure and flow measurement and control module includes a pressure sensor at the outlet of the oil-water isolator to monitor the pressure of the fluid pumped into the sample; a flow sensor to monitor the pumping flow rate; and a displacement sensor to monitor the displacement of the oil-water isolator piston and further calculate the pumping flow rate.

[0048] The pumping module is connected to a high-precision injection pump, multiple oil-water isolators, and multiple high-pressure injection pipelines buried in the specimen, which can physically simulate the expansion of multiple fracturing cracks and independently monitor the pressure and liquid inflow of each crack; the high-precision injection pump, an oil-water isolator, and multiple high-pressure injection pipelines buried in the specimen can also be used to simulate the expansion of multiple fracturing cracks, but the pressure and liquid inflow of each fracturing crack cannot be independently monitored.

[0049] Fracturing medium, the pumping medium placed in the oil-water isolator in the pumping module, is most commonly used as water-based fracturing fluid and oil-based fracturing fluid. Common fracturing fluids are based on water or oil. Different chemicals can be added to the pumped water and oil to regulate the physical and chemical properties of the pumped fluid, such as viscosity, pH, and filtration characteristics.

[0050] The pumping module also features temporary fracturing and proppant delivery. This includes physical simulation of temporary fracturing, achieved by adding different types of temporary plugging agents to the fracturing fluid and pumping them along with the fluid. Temporary fracturing is used when only some of the initiating clusters within a segment are expanding. This method blocks the initiation point (perforation cluster) of the dominant fracture propagation, thereby promoting fracture formation in other clusters. It also blocks the tip of the dominant fracture propagation, preventing the increase in length and branching of the dominant fracture, thereby increasing fracture complexity. Proppant pumping simulation involves adding proppant particles to the fracturing fluid and injecting them into the fracture. When pumping is stopped, the fracture pressure decreases, and the fracture closes, they propel the fracture open, thereby improving fracture conductivity. Since both temporary plugging agents and proppant are solid additives, they are designed to prevent them from sinking to the bottom of the oil-water separator and becoming difficult to carry over with the fracturing fluid. The system's oil-water separators are designed to be swinging, mechanically stirred, or magnetically stirred to prevent the sedimentation of additives such as temporary plugging agents and proppants, while ensuring uniform mixing of the additives with the fracturing fluid. The swinging oil-water separator uses a motor and a swing frame to oscillate the separator, preventing proppant particles from settling. The magnetic stirring design utilizes the repulsion of like charges in magnetic materials to achieve mixing of the fracturing fluid and additives. The mechanical type uses a motorized stirring rod installed inside the oil-water separator to suspend the additives in the fracturing fluid.

[0051] The pumping module is equipped with storage tanks and pumping devices for gaseous and supercritical multiphase fluids such as CO2, N2, and steam, allowing for fracturing using these fluids as the fracturing medium. It is also equipped with heating systems such as a fracturing medium heater and steam activator to simulate the physical fracturing of high-temperature fluids. High-temperature fluid fracturing is primarily used for high-temperature modified fracturing in oil shale and oil-rich coal.

[0052] In one example, the monitoring module includes an acoustic emission monitoring device, a stress and pore pressure monitoring device, an optical monitoring device, etc. The acoustic emission monitoring device includes a multi-channel acoustic emission acquisition instrument, a data acquisition display, a signal line, multiple acoustic emission sensors, and multiple signal amplifiers. The acoustic emission sensor is placed in a chamber in the high-temperature pressurized plate. The signal line is led out from a special groove in the high-temperature pressurized plate, connected to the acoustic emission amplifier, and then to the acoustic emission acquisition instrument. The waveform and frequency and other parameters are observed through the data acquisition display. Software such as RockAE can be preferably used to analyze these parameters, thereby visualizing the acoustic emission signal. The stress and pore pressure monitoring device consists of a high-precision injection pump, a stress data acquisition instrument, and a pore pressure sensor. The software can monitor the stress and pore pressure in the sample in real time.

[0053] Optical monitoring devices include digital image correlation (DIC) and fiber Bragg grating (FBG). FBG technology can be used to monitor and locate cracks. In fracture monitoring during fracturing simulation experiments, FBGs are embedded within and on the surface of the specimen structure, passed through a high-strength transparent glass plate, and then placed behind the glass to a camera. This not only monitors continuous strain changes within the specimen structure, but also accurately locates the crack's location and size.

[0054] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present invention, and that in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A high-temperature and high-pressure true triaxial fracturing physical simulation experimental system, characterized in that: include: An overall frame and a heating and temperature control module, a loading module, a pumping module, a monitoring module and a sample loading module arranged in the overall frame; The heating and temperature control module includes a multi-channel servo temperature control module, a multi-layer combined high-temperature pressure plate and a circulating water cooling module; The multi-layer combined high-temperature pressure plate is in direct contact with the sample that enters the fixed position through the sample loading module; the multi-channel servo temperature control module is used to heat the multi-layer combined high-temperature pressure plate; the circulating water cooling module is arranged inside the multi-layer combined high-temperature pressure plate, and is used to cool the multi-layer combined high-temperature pressure plate; The loading module includes a load plate and a loading and unloading cylinder, wherein the loading and unloading cylinder provides pressure to the load plate, and the load plate is in direct contact with the multi-layer combined high-temperature pressure plate and transmits the pressure provided by the loading and unloading cylinder to the multi-layer combined high-temperature pressure plate; The pumping module includes a pumping injection module and a pressure and flow measurement and control module. The pumping injection module is arranged inside the sample and is used to provide fracturing fluid for the sample; the pressure and flow measurement and control module is used to detect the real-time pumping pressure and flow inside the sample; The monitoring module includes an acoustic emission monitoring device, a stress and pore pressure monitoring device, and an optical monitoring device. The acoustic emission monitoring device is used to perform visual analysis on acoustic emission signals. The stress and pore pressure monitoring device is used to monitor the stress and pore pressure in the sample in real time. The optical monitoring device is used to monitor the continuous strain changes inside the sample structure and locate the location and size of cracks. The multi-layer combined high-temperature pressurized plate comprises: a heating and pressurizing layer, a high-temperature resistant intermediate layer and a loading layer; The heating and pressurizing layer is in direct contact with the sample and is provided with a socket, in which a plurality of heating rods and a temperature sensor are arranged. The heating rods and the temperature sensor are connected to the multi-channel servo temperature control module; the heating and pressurizing layer is also provided with an acoustic emission sensor waveguide rod; The material of the high-temperature resistant intermediate layer is a high-temperature resistant heat-insulating material, and the high-temperature resistant intermediate layer has a cooling chamber for placing an acoustic emission sensor, and the cooling chamber is used to place and protect the acoustic emission sensor, wherein the acoustic emission sensor and the acoustic emission sensor waveguide rod are correspondingly arranged, and the cooling chamber is connected to the circulating water circuit; The loading layer is in direct contact with the carrying plate; The outermost side of the cooling chamber is a double-layered, approximately annular structure with a water inlet and outlet, and a hole for placing the acoustic sensor. The cooling chamber is used to cool the acoustic sensor placed inside it and to withstand the pressure of the sample loaded by the supporting plate. The depth of the middle hole of the cooling chamber where the acoustic emission sensor is placed is greater than the height of the acoustic emission sensor; The water inlet and outlet of the cooling chamber are connected to the circulating water circuit. The hollow space of the acoustic emission sensor is placed in the cooling chamber. From the inner side close to the sample to the outer side, there are the acoustic emission sensor waveguide rod, the acoustic emission sensor, a spring, and a reaction force cover. The acoustic emission sensor waveguide rod has a small cross-sectional area at the end contacting the sample and a large cross-sectional area at the end contacting the acoustic emission sensor. A coupling agent is also applied to the joint portion between the acoustic emission sensor and the acoustic emission sensor waveguide rod; The spring is fixed to the cooling chamber via the reaction force cover. The spring is compressed to apply compressive stress to the acoustic emission sensor and the acoustic emission sensor waveguide rod, so that the acoustic emission sensor and the acoustic emission sensor waveguide rod are tightly pressed against the sample. At the same time, a coupling agent is applied between the end of the acoustic emission sensor of the waveguide rod and the sample.

2. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 1 is characterized in that: The circulating water circuit is connected to each cooling chamber through a water pipeline. The circulating water circuit circulates water from bottom to top, and a diverter is used for diversion and merging of water in each cooling chamber.

3. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 1 is characterized in that: The pump injection module includes a high-precision injection pump, an oil-water isolator and a multiphase fluid pump injection system; The high-precision injection pump is the power source of the pump injection module; the oil-water isolator is a piston container, and the two spaces separated by the piston are respectively connected to the injection pump and the sample injection pipe, among which the space connected to the sample injection pipe stores liquid fracturing medium.

4. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 3 is characterized in that: The pressure and flow measurement and control module includes a pressure sensor arranged at the liquid outlet end of the oil-water isolator, which is used to monitor the pressure of the fluid pumped into the sample; a flow sensor, which is used to monitor the pumping flow; and a displacement sensor, which is used to monitor the displacement stroke of the oil-water isolator piston and further calculate the pumping flow.

5. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 3 is characterized in that: The fracturing medium includes at least one of a proppant, a temporary plugging agent, a water-based fracturing fluid and an oil-based fracturing fluid. The water-based fracturing fluid and the oil-based fracturing fluid are used to control at least one physical and chemical property of the pumping fluid, including viscosity, pH and fluid loss characteristics.

6. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 3, characterized in that: The pumping module is also equipped with storage tanks and pumping devices for CO2, N2 and steam gaseous and supercritical multiphase fluids, which are used for fracturing with multiphase fluids as fracturing media; it is also equipped with a fracturing medium heating and steam exciter heating system, which is used for fracturing physical simulation with high-temperature fluids as fracturing media.

7. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 1, characterized in that: The optical monitoring device includes a fiber Bragg grating (FBG); the fiber Bragg grating is pre-buried inside and on the surface of the sample structure, a high-strength transparent glass plate is arranged on the fiber Bragg grating, and a camera is arranged behind the high-strength transparent glass plate for observation.

8. The high-temperature and high-pressure true triaxial fracturing physical simulation experimental system according to claim 1, characterized in that: The sample loading module includes two sets of vertical sample loading slides, and the two sets of sample loading slides correspond to a platform respectively to form a double-layer slidable combined platform for placing the sample.

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