Liquid carbon dioxide phase change fracturing system based on self-regulation temperature control module

Abstract

The invention discloses a liquid carbon dioxide phase change fracturing system based on a self-regulation temperature control module, and belongs to the technical field of carbon dioxide phase change fracturing. The system comprises a liquid storage cavity, the self-regulation temperature control module, a two-stage safety pressure relief assembly and a release pipe; the self-regulation temperature control module comprises a flexible heating sheet, a temperature and pressure sensor and a temperature control sensor; an MCU is arranged in the temperature control sensor, and the MCU realizes three-stage temperature and pressure closed-loop regulation and control through a PID algorithm; the two-stage safety pressure relief assembly is composed of a constant-pressure rupture disc and an electromagnetic pressure relief valve and is in linkage with a multi-parameter monitoring signal to achieve abnormal pressure relief. According to the liquid carbon dioxide phase change fracturing system based on the self-regulation temperature control module, the problems that in the prior art, heating precision is low, safety protection is insufficient, and reusability is poor are solved, and the liquid carbon dioxide phase change fracturing system has the advantages of being accurate in temperature control, safe, reliable and low in cost and is suitable for fracturing operation of multiple scenes such as coal mines, metal mines and urban tunnels.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide phase change fracturing technology, and in particular to a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module. Background Technology

[0002] Carbon dioxide phase change fracturing technology, as a novel physical rock-breaking method, operates on the principle of filling a specially designed high-strength sealed fracturing tube with liquid carbon dioxide under high pressure. By activating an internal heating device, the liquid carbon dioxide absorbs heat and rapidly undergoes a liquid-gas phase change. Due to the physical properties of carbon dioxide, its volume can expand hundreds of times during this phase change, instantly creating a working pressure of 200-300 MPa or even higher inside the fracturing tube. When the internal pressure exceeds the bearing limit of the energy-releasing component (usually a pressure-controlled energy-releasing plate with a preset fracture strength), the component is instantly ruptured, and the accumulated high-pressure carbon dioxide gas is directionally ejected through a release pipe, acting on the target medium such as rock or concrete, causing cracks or fracturing, ultimately achieving the fracturing objective. It has advantages such as no open flame, no toxic or harmful gases, and low vibration, and has been widely used in mining, engineering blasting, and other fields.

[0003] However, existing technologies have significant drawbacks: low heating and temperature control accuracy, inability to dynamically adjust the heating rate; and insufficient safety protection, with no effective pressure relief measures under abnormal operating conditions. Therefore, there is an urgent need to develop a new fracturing system with precise temperature control, intelligent feedback, safety protection, and modular reusability. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, which solves the problems of low heating accuracy, insufficient safety protection, and poor reusability in the prior art. It has the advantages of precise temperature control, safety and reliability, and low cost, and is suitable for fracturing operations in various scenarios such as coal mines, metal mines, and urban tunnels.

[0005] To achieve the above objectives, the present invention provides a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, comprising: The liquid storage chamber is used to store liquid carbon dioxide. It is made of 20# or 30# seamless steel pipes and has a rated pressure of ≥350MPa. The liquid storage chamber is equipped with quick-release flange joints at both ends. The self-regulating temperature control module includes 3-4 sets of flexible heating elements, 2-3 high-pressure resistant integrated temperature and pressure sensors and temperature control sensors. The temperature control sensors are equipped with an explosion-proof MCU with a built-in PID dynamic control algorithm. The flexible heating elements are evenly distributed and closely attached to the outer wall of the liquid storage cavity at 90-120°. The temperature and pressure sensors extend into the liquid storage cavity through a sealed interface. The two-stage safety pressure relief assembly consists of a constant pressure rupture disc and an electromagnetic pressure relief valve connected in parallel. The constant pressure rupture disc is located in the flange groove between the liquid storage chamber and the release pipe, and the electromagnetic pressure relief valve is connected in parallel to the pressure relief port on the side wall of the liquid storage chamber. The release tube is connected to the liquid storage chamber at one end via a flange joint, and the other end is equipped with a directional energy focusing cover with an energy focusing angle of 50-70°. Furthermore, the temperature control sensor is equipped with an alarm light on top, a biodegradable protective cover at the bottom of the alarm light, a high-temperature resistant protective shell on the outside of the temperature control sensor, and a temperature measuring head at the bottom of the temperature control sensor.

[0006] The MCU is electrically connected to the self-regulating temperature control module, the two-stage safety pressure relief component, and the temperature and pressure sensor, respectively, to realize temperature and pressure data acquisition, dynamic adjustment of heating power, and pressure relief control under abnormal operating conditions.

[0007] Preferably, the flexible heating element is made of silicone insulating material, with a temperature resistance range of -60~200℃ and a single element power of 180-220W. It is fixed to the outer wall of the liquid storage cavity by high-temperature resistant tape, with a gap of ≤0.5mm between it and the tube wall.

[0008] Preferably, the temperature range of the temperature and pressure sensor is 50~150℃, with an accuracy of ±0.5℃; the pressure range of the temperature and pressure sensor is 0~400MPa, with an accuracy of ±1%FS; and the MCU collects temperature and pressure data every 0.5 seconds and generates a bivariate curve.

[0009] Preferably, the temperature range of the temperature and pressure sensor is 50~150℃, with an accuracy of ±0.5℃; the pressure range of the temperature and pressure sensor is 0~400MPa, with an accuracy of ±1%FS; and the MCU collects temperature and pressure data every 0.5 seconds and generates a bivariate curve.

[0010] Preferably, the MCU adopts a mining-grade Exdl explosion-proof design and has a built-in three-stage temperature control and voltage boosting program, specifically: Preheating stage: target temperature 20~30℃, heating power 400~600W, temperature rise rate 1.0~1.5℃ / min, lasting 5-8min; Phase transition stage: The temperature is dynamically matched according to the target pressure, the heating power is adaptively adjusted from 300 to 800W, and the pressure increase rate is ≤15MPa / min; Pressure stabilization phase: When the pressure reaches 90% of the target value, the heating power is reduced to 200~300W, and the pressure is maintained to slowly rise to the target value for 2~3 minutes.

[0011] Preferably, the release tube is a tapered seamless steel tube with an inlet diameter matching the liquid storage chamber and an outlet diameter of 40-60 mm. The outer wall of the release tube is provided with anti-slip texture to enhance the adhesion with the sealing agent.

[0012] Preferably, the system also includes a gas concentration sensor, a mine inclinometer, and an acoustic detector. The gas concentration sensor is arranged upwind and downwind of the fracturing zone. When the gas concentration exceeds 1.0%, the MCU triggers the electromagnetic pressure relief valve and cuts off the heating circuit.

[0013] Preferably, the liquid storage chamber, self-regulating temperature control module, two-stage safety pressure relief component, and release pipe are connected separately via flanges or quick-release connectors. The core components have a reuse rate of ≥80% after testing and maintenance, and a single system can be reused 10 to 15 times.

[0014] This invention also provides a fracturing method for a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, comprising the following steps: S1. Construction and pretreatment of fractured holes, including drilling, hole cleaning, and hole sealing pretreatment; S2. System assembly and insertion: After completing component assembly and self-inspection, the system is hoisted into the hole and sealed. S3. Liquid carbon dioxide is quantitatively filled, with the filling amount being 70%~80% of the effective volume of the storage chamber, and the filling pressure is controlled at 6.0~8.0MPa; S4. Self-regulating temperature and pressure control: The MCU dynamically adjusts the heating power according to a three-stage program to achieve coordinated closed-loop temperature and pressure control. S5, Fracturing Energy Release: When the pressure reaches the set threshold, the constant pressure fracturing disc ruptures, and high-pressure gas is injected in a directional manner to induce fracturing. S6. Cooling and system reset after operation: After cooling to ambient temperature, the components are recovered, inspected and maintained, and then reset for later use.

[0015] Preferably, in step S4, when the temperature rise rate exceeds 1.5℃ / min or the pressure rise rate exceeds 15MPa / min, the MCU reduces the heating power by 50~100W each time; when the temperature rise rate is less than 1.0℃ / min, the MCU increases the heating power by 50~100W each time until the parameters return to the set range.

[0016] Therefore, the present invention employs the above-mentioned liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, and the technical effects are as follows: Precise temperature control and stable crack initiation: Through the synergistic effect of PID dynamic algorithm and flexible heating element, the accuracy of temperature and pressure control is significantly improved, adapting to the crack initiation requirements under different geological conditions, ensuring that crack expansion is controllable and the fracture range is predictable; Safe and reliable, adaptable to complex environments: The dual-stage safety pressure relief component responds quickly, and the multi-parameter linkage protection can effectively avoid risks such as gas outbursts and equipment damage, and meets the ExdI level explosion-proof standard for mining. High reusability and reduced cost: The split quick-release structure allows core components to be reused 10-15 times, reducing solid waste generation and lowering the cost of cracking per batch. Easy to operate and highly intelligent: Fully automated control, supports on-site and remote monitoring, reduces the intensity of manual intervention and improves work efficiency.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a liquid carbon dioxide phase change cracking system based on a self-regulating temperature control module according to the present invention; Figure 2 This is a front view and a cross-sectional view of a temperature control sensor in an embodiment of a liquid carbon dioxide phase change-induced cracking system based on a self-regulating temperature control module according to the present invention.

[0019] Figure Labels 1. Liquid storage chamber; 2. Temperature and pressure sensor; 3. Constant pressure rupture disc; 4. Sealing gasket; 5. Electromagnetic pressure relief valve; 6. Release pipe; 7. Directional energy focusing cover; 8. Detonator; 9. Temperature control sensor; 10. Warning light; 11. Biodegradable protective cover; 12. High temperature resistant protective shell; 13. Temperature measuring mold head; 14. MCU. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "comprising" or "including," and similar terms used in this invention, mean that the element or object preceding the term encompasses the elements or objects listed following the term and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0022] Example 1 like Figure 1 As shown, the present invention provides a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, including a liquid storage chamber 1, a self-regulating temperature control module, a two-stage safety pressure relief assembly, a release tube 6, and an MCU 14.

[0023] All core components of the system must meet the ExdI level explosion-proof standard for mining and the requirements of the "Coal Mine Safety Regulations" for underground pressure equipment. The specific selection and parameters are as follows: Storage chamber 1: Made of 20# or 35# seamless alloy steel pipe, with an inner diameter of 80-100mm, a wall thickness of 10-14mm, a length of 2.0-3.0m, and a rated pressure of ≥350MPa; both ends are equipped with quick-release flange joints and high-pressure resistant sealing gaskets 4, made of nitrile rubber or fluororubber, which facilitates quick assembly and disassembly on site and is suitable for narrow working spaces downhole.

[0024] The self-regulating temperature control module includes 3-4 sets of flexible heating elements, each with a power of 180-220W and a temperature range of -60~200℃. These elements are made of silicone rubber insulation and are evenly distributed along the outer wall of the storage chamber 1 at 90°-120° to ensure heating uniformity. It is equipped with 2-3 integrated mine-use high-pressure temperature and pressure sensors 2, with a temperature range of -50~150℃ and an accuracy of ±0.5℃; and a pressure range of 0~400MPa and an accuracy of ±1%FS. The sensor probes extend into the storage chamber 1 through a sealed interface to directly collect the temperature and pressure data within the chamber. It also integrates an explosion-proof temperature control sensor 9 and a built-in MCU 14 with a PID dynamic control algorithm, which can be linked with the heating elements, temperature and pressure sensors 2, and pressure relief components via mine-use cables.

[0025] Safety pressure relief assembly: Adopts a dual-stage protection structure of "constant pressure rupture disc + electromagnetic pressure relief valve". The constant pressure rupture disc 3 is made of Hastelloy or stainless steel, and the burst pressure can be set to 200-300MPa according to the rupture requirements, with an error controlled within ±5MPa; the electromagnetic pressure relief valve 5 is a two-position, two-way type with a rated diameter of 12-18mm, a response time ≤0.1s, a working pressure of 0-350MPa, and an explosion-proof rating consistent with the MCU, featuring automatic shutdown upon power failure and rapid opening upon power restoration.

[0026] Release tube and energy-concentrating structure: The release tube 6 is a tapered seamless steel tube with an inlet diameter that matches the liquid storage chamber 1 and an outlet diameter of 40-60mm; the outlet end is equipped with a directional energy-concentrating cover 7 with an energy-concentrating angle of 50°-70° and made of low-carbon steel, which can guide the directional injection of high-pressure gas and control the direction of crack propagation; the outer wall of the release tube is provided with anti-slip texture to facilitate the adhesion of the sealing agent in the crack-causing cavity gap.

[0027] The end of the liquid storage chamber 1 away from the release pipe 6 is connected to an initiator 8, which is used to make the liquid carbon dioxide absorb heat and rapidly undergo a liquid-gas phase change.

[0028] like Figure 2As shown, the temperature control sensor 9 is equipped with an alarm light 10 on top, a biodegradable protective cover 11 at the bottom of the alarm light 10, and a high-temperature resistant protective shell 12 on the outside of the temperature control sensor 9 to ensure the normal operation of the temperature control sensor 9. The temperature control sensor 9 is equipped with a temperature measuring mold head 13 at the bottom, which is connected to the liquid storage chamber 1 to monitor the temperature inside the liquid storage chamber 1.

[0029] Detailed on-site implementation process: Step 1: Construction of fractured holes and pretreatment of ducts; Drilling design: Based on the thickness and stress distribution characteristics of the coal seam or rock stratum to be fractured, determine the parameters of the fracture-inducing borehole: borehole diameter 90-120mm with reserved sealing space, borehole depth to penetrate the stress concentration zone or target fracture-inducing layer, reaching 2-3m into stable rock strata, borehole spacing 3-5m, arranged in a fan shape or row, with an angle of 30°-60° to the strike of the rock strata, avoiding roadway support structures and pipelines.

[0030] Drilling: Mining hydraulic drilling rigs or pneumatic drilling rigs are used for drilling. The drilling speed is controlled during the drilling process to avoid the collapse of the borehole wall. If broken rock strata are encountered, casing is required for wall protection. The casing material is PVC or seamless steel pipe, and the inner diameter is matched with the borehole.

[0031] Hole cleaning: After drilling is completed, use high-pressure air or high-pressure water to blow away rock cuttings and dust inside the hole for 3-5 minutes until no obvious impurities are discharged from the hole opening; then use a borehole inspection instrument to check the verticality and integrity of the hole to ensure that there is no serious deviation or collapse of the hole.

[0032] Pre-treatment for sealing holes: Apply an interface agent to the opening section of the cracked hole to enhance the adhesion between the sealing agent and the hole wall; prepare polyurethane sealing agent or cement-based sealing material for later use.

[0033] Step 2: System assembly and manhole layout; Component Assembly: System assembly is carried out on the downhole assembly platform: ① Connect the storage chamber 1 and the release pipe 6 through a flange joint, install the sealing gasket 4 and tighten the bolts; ② Attach the flexible heating element to the outer wall of the storage chamber 1 and fix it with high-temperature resistant tape to ensure that the heating element is tightly attached to the pipe wall; ③ Install the temperature and pressure sensor 2 at both ends of the storage chamber through the sealed interface, and connect the temperature and pressure sensor 2 cable to the MCU 14 through the explosion-proof connector; ④ Install the constant pressure rupture disc 3 into the flange groove between the storage chamber 1 and the release pipe 6, and connect the electromagnetic pressure relief valve 5 in parallel to the pressure relief port on the side wall of the storage chamber 1.

[0034] System self-test: After assembly, the status of each component is checked through the self-test function of MCU 14: ① Heating element test: 10% of the rated power is applied to check whether the heating element heats up evenly (using an infrared thermometer to detect, temperature difference ≤2℃); ② Sensor test: Simulate temperature and pressure signals to check whether the data acquisition of MCU 14 is normal; ③ Pressure relief component test: Low-pressure gas is introduced into the liquid storage chamber 1 to trigger the electromagnetic pressure relief valve 5, and check whether the valve opens and closes smoothly and without leakage.

[0035] System entry into the borehole: Use mining hoisting equipment to slowly hoist the system into the fracturing borehole at a hoisting speed of 0.2-0.5 m / s to avoid collisions between the system and the borehole wall that could damage the sensors or heating elements; adjust the direction of the release pipe 6 so that the energy-concentrating cover 7 is aligned with the target fracturing area; after the system is in place, inject a sealing agent into the borehole opening section. The sealing agent must cover the gap between the system and the borehole wall and form a sealed section after curing to prevent gas leakage during fracturing.

[0036] Step 3: Liquid carbon dioxide filling; Preparation before filling: Connect the mine explosion-proof liquid carbon dioxide filling equipment to the filling interface of the storage chamber 1 through the filling hose; check whether the pressure gauge and safety valve of the filling equipment are within the calibration validity period, and whether the hose is damaged or aged; perform vacuum treatment on the storage chamber 1 to remove air from the chamber and avoid air resistance or pressure fluctuations during phase change.

[0037] Quantitative filling: Determine the amount of liquid carbon dioxide to be filled based on the volume of the storage chamber 1 and the fracturing requirements. It is usually 70%-80% of the effective volume of the storage chamber. Start the filling equipment and control the filling pressure to 6.0-8.0 MPa. Monitor the pressure and temperature of the storage chamber 1 in real time during the filling process to avoid overpressure filling. The machine will automatically stop when the pressure exceeds 8.0 MPa.

[0038] Sealing after filling: After filling, close the filling valve between the filling equipment and the liquid storage chamber 1, and disassemble the filling hose; check the sealing of the filling interface with soapy water to ensure there is no leakage; read the initial temperature and pressure data of the liquid storage chamber 1 through MCU 14. The initial temperature should be consistent with the ambient temperature, and the initial pressure should be 6.0-8.0MPa. Record the initial state.

[0039] Step 4: Self-regulating temperature and pressure control with coordinated temperature and pressure regulation; Temperature control parameter setting: Temperature and pressure control parameters are set through the MCU 14's operating interface: ① Initial heating stage: target temperature 20-30℃, heating power 400-600W, temperature rise rate 1.0-1.5℃ / min, duration 5-8min; ② Phase change heating stage: set the target pressure according to the fracturing pressure requirement, the MCU 14 automatically matches the target temperature, the heating power is dynamically adjusted from 300-800W, and the pressure rise rate is ≤15MPa / min; ③ Pressure stabilization stage: when the pressure reaches 90% of the target value, reduce the heating power to 200-300W, maintain the pressure to slowly increase to the target value, duration 2-3min, to ensure sufficient phase change of carbon dioxide in the cavity.

[0040] Dynamic control process: After the temperature control program is started, MCU 14 collects intracavity temperature and pressure data every 0.5 seconds and corrects the heating power in real time through a PID algorithm: ① If the temperature rise rate exceeds the set value or the pressure rise rate exceeds 15MPa / min, the heating power is automatically reduced by 50-100W each time until the parameters return to the set range; ② If the temperature rise rate is lower than the set value or the pressure rise is slow, the heating power is automatically increased by 50-100W each time, while checking whether the heating element is working properly; ③ If abnormal temperature and pressure data occur, such as a sudden temperature rise or a sudden pressure drop, heating is immediately stopped, and the alarm light 10 is triggered for audible and visual alarm, waiting for manual troubleshooting.

[0041] Temperature and pressure coordinated monitoring: During the temperature control and pressure increase process, the temperature and pressure change curves are recorded simultaneously and displayed in real time through the intrinsically safe mining display screen. The intrinsically safe mining display screen is electrically connected to the temperature control sensor 9. If remote monitoring is required, the data can be transmitted to the ground monitoring center through the wireless transmission module to ensure that ground personnel can keep abreast of the fracturing progress in real time.

[0042] Step 5: Fracturing Energy Release and Safety Monitoring; Fracturing trigger: When the MCU 14 detects that the pressure inside the cavity reaches the set fracturing pressure and the temperature is stable within the target range, it automatically stops heating. The constant pressure fracturing disc 3 ruptures instantaneously under pressure. High-pressure carbon dioxide gas is injected directionally through the release pipe 6 and the directional energy focusing hood 7, acting on the rock strata or coal body of the borehole wall to form radial impact stress and tensile stress, causing cracks to be generated in the target area.

[0043] Real-time safety monitoring: During the fracturing process, the on-site status is monitored using the following equipment: ① A mine inclinometer is placed in the roadway or rock stratum 3-5m around the fracture hole to monitor the displacement of the surrounding rock in real time. If the displacement exceeds 30mm, emergency measures are immediately activated. ② Acoustic wave detector to monitor the rate and extent of crack propagation, ensuring that cracks only propagate in the target area and do not affect the surrounding support structure; ③ Gas concentration sensors are placed upwind and downwind of the fracturing area. If the gas concentration exceeds 1.0%, the system power is immediately cut off, the local ventilation fan is turned on, and the operation can continue only after the concentration drops to a safe range.

[0044] Emergency Handling: If the following abnormal situations occur, MCU 14 will automatically trigger emergency pressure relief: ① The pressure inside the cavity exceeds the safety limit; ② The temperature exceeds 60℃; ③ The gas concentration exceeds 1.0% and cannot be reduced by ventilation; In case of emergency pressure relief, the electromagnetic pressure relief valve 5 opens quickly, reducing the pressure inside the cavity to below 100MPa, while simultaneously cutting off the heating circuit to prevent the risk from escalating.

[0045] Step Six: Post-operation cooling and system reset maintenance; Cooling: After the fracturing energy is released, keep the electromagnetic pressure relief valve 5 open for 30-60 minutes to allow the high-pressure gas remaining in the liquid storage chamber 1 to be fully released, and at the same time, allow it to cool naturally to the ambient temperature. If accelerated cooling is required, room temperature water can be sprayed on the outer wall of the liquid storage chamber 1 to avoid sudden cooling that could cause deformation of the pipe wall. The cooling time can be shortened to 15-20 minutes.

[0046] System recovery: After the temperature and pressure of the storage chamber 1 drop to a safe range, remove the sealing agent at the orifice and use hoisting equipment to remove the system from the fracture hole; avoid collisions with the system during the recovery process to prevent damage to components such as sensors and heating elements.

[0047] Component Inspection and Maintenance: Each recovered system component is inspected individually: ① Liquid Storage Chamber 1: Check the inner wall for corrosion, deformation, or cracks. Use an ultrasonic flaw detector to check the wall thickness. If defects are found, repair or replacement is required; ② Heating Element: Check the appearance for damage or aging. Test the heating power. If the damage rate exceeds 10%, the entire unit must be replaced; ③ Sensor: Calibrate the temperature and pressure detection accuracy. If the error exceeds ±1%FS, recalibrate or replace; ④ Pressure Relief Assembly: Replace the pressure relief disc 3 with a new one. Check the sealing and response speed of the electromagnetic pressure relief valve 5 to ensure there is no leakage or jamming.

[0048] System Reset: Reassemble the qualified components and perform a second self-test to ensure that the system performance is restored to its initial state and can be used for the next fracturing operation; classify and recycle or scrap the damaged components to avoid mixing with normal components and affecting the system reliability.

[0049] Therefore, the present invention adopts the above-mentioned liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module, which solves the problems of low heating accuracy, insufficient safety protection and poor reusability in the prior art. It has the advantages of precise temperature control, safety and reliability and low cost, and is suitable for fracturing operations in multiple scenarios such as coal mines, metal mines and urban tunnels.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A liquid carbon dioxide phase change-induced cracking system based on a self-regulating temperature control module, characterized in that, include: The liquid storage chamber is used to store liquid carbon dioxide, and quick-release flange joints are provided at both ends of the liquid storage chamber; The self-regulating temperature control module includes a flexible heating element, a temperature and pressure sensor, and a temperature control sensor; the temperature control sensor has an MCU inside; the flexible heating element is evenly distributed and closely attached to the outer wall of the liquid storage cavity, and the temperature and pressure sensor extends into the liquid storage cavity through a sealed interface; The two-stage safety pressure relief assembly consists of a constant pressure rupture disc and an electromagnetic pressure relief valve connected in parallel. The constant pressure rupture disc is located in the flange groove between the liquid storage chamber and the release pipe, and the electromagnetic pressure relief valve is connected in parallel to the pressure relief port on the side wall of the liquid storage chamber. The release tube is connected to the liquid storage chamber at one end via a flange joint, and the other end is equipped with a directional energy-concentrating cover; The MCU is electrically connected to the self-regulating temperature control module, the two-stage safety pressure relief component, and the temperature and pressure sensor, respectively, to realize temperature and pressure data acquisition, dynamic adjustment of heating power, and pressure relief control under abnormal operating conditions.

2. The liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The flexible heating element is made of silicone insulating material, with a temperature resistance range of -60~200℃ and a single element power of 180-220W. It is fixed to the outer wall of the liquid storage cavity with high-temperature resistant tape, and the gap between the heating element and the tube wall is ≤0.5mm.

3. The liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The temperature range of the temperature and pressure sensor is 50~150℃, with an accuracy of ±0.5℃; the pressure range of the temperature and pressure sensor is 0~400MPa, with an accuracy of ±1%FS.

4. The liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The constant pressure rupture disc is made of Hastelloy or stainless steel, with a burst pressure set at 200~300MPa and an error of ≤±5MPa; the electromagnetic pressure relief valve is a two-position two-way type with a rated diameter of 12~18mm, a response time of ≤0.1s, and an explosion-proof rating consistent with that of the MCU.

5. A liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The MCU adopts a mining-grade Exdl explosion-proof design and has a built-in three-stage temperature control and voltage boosting program, specifically: Preheating stage: target temperature 20~30℃, heating power 400~600W, temperature rise rate 1.0~1.5℃ / min, lasting 5-8min; Phase transition stage: The temperature is dynamically matched according to the target pressure, the heating power is adaptively adjusted from 300 to 800W, and the pressure increase rate is ≤15MPa / min; Pressure stabilization phase: When the pressure reaches 90% of the target value, the heating power is reduced to 200~300W, and the pressure is maintained to slowly rise to the target value for 2~3 minutes.

6. The liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The release tube is a tapered seamless steel tube with an inlet diameter matching the liquid storage chamber and an outlet diameter of 40-60mm. The outer wall of the release tube is provided with anti-slip texture to enhance the adhesion with the sealing agent.

7. A liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The system also includes a gas concentration sensor, a mine inclinometer, and an acoustic detector. The gas concentration sensor is positioned upwind and downwind of the fracturing zone. When the gas concentration exceeds 1.0%, the MCU triggers the electromagnetic pressure relief valve and cuts off the heating circuit.

8. A liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 1, characterized in that: The liquid storage chamber, self-regulating temperature control module, two-stage safety pressure relief assembly, and release pipe are connected separately via flanges or quick-release connectors.

9. A fracturing method for a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Construction and pretreatment of fractured holes, including drilling, hole cleaning, and hole sealing pretreatment; S2. System assembly and insertion: After completing component assembly and self-inspection, the system is hoisted into the hole and sealed. S3. Liquid carbon dioxide is quantitatively filled, with the filling amount being 70%~80% of the effective volume of the storage chamber, and the filling pressure is controlled at 6.0~8.0MPa; S4. Self-regulating temperature and pressure control: The MCU dynamically adjusts the heating power according to a three-stage program to achieve coordinated closed-loop temperature and pressure control. S5, Fracturing Energy Release: When the pressure reaches the set threshold, the constant pressure fracturing disc ruptures, and high-pressure gas is injected in a directional manner to induce fracturing. S6. Cooling and system reset after operation: After cooling to ambient temperature, the components are recovered, inspected and maintained, and then reset for later use.

10. The fracturing method of a liquid carbon dioxide phase change fracturing system based on a self-regulating temperature control module according to claim 9, characterized in that: In step S4, when the temperature rise rate exceeds 1.5℃ / min or the pressure rise rate exceeds 15MPa / min, the MCU reduces the heating power by 50~100W each time; when the temperature rise rate is below 1.0℃ / min, the MCU increases the heating power by 50~100W each time until the parameters return to the set range.

Images