Carbon dioxide continuous phase change fracturing device with multi-cavity structure and experimental method

Abstract

The invention discloses a multi-cavity structure carbon dioxide continuous phase change fracturing device which comprises a filling cavity internally provided with a filling chamber; the upper end of the main storage cavity is connected with the filling cavity, and a main storage cavity communicated with the main storage cavity is formed in the main storage cavity; the lower end of the trigger cavity is connected with the trigger cavity, and a trigger cavity communicated with the main storage cavity is formed in the trigger cavity; a first control valve disposed between the filling chamber and the main storage chamber; a second control valve disposed between the trigger chamber and the main storage chamber; the electric heating wire is arranged in the trigger chamber; the filling cavity is used for being connected with a ground pipe column, achieving injection of supercritical carbon dioxide and controlling the first control valve to be opened, the supercritical carbon dioxide enters the main storage cavity from the filling cavity to be safely stored, the second control valve is controlled to be opened, and the supercritical carbon dioxide enters the trigger cavity from the main storage cavity to be safely stored. Phase change occurs under instantaneous heating of the electric heating wire, and carbon dioxide phase change fracturing is carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a multi-cavity structure carbon dioxide continuous phase change fracturing device and an experimental method. Background Art

[0002] With the increasing depletion of conventional oil and gas resources, the development of unconventional oil and gas resources, such as shale oil, tight oil, and coalbed methane, has become a key focus in the global energy sector. However, unconventional oil and gas reservoirs generally have low porosity and permeability, making them difficult to effectively exploit using traditional extraction technologies. Therefore, hydraulic fracturing and other production-enhancing measures are required.

[0003] Hydraulic fracturing technology increases oil and gas production by injecting high-pressure fluid into the formation, creating a network of fractures. However, hydraulic fracturing also has some limitations. For example, hydraulic fracturing consumes a large amount of water, which limits its application in water-scarce areas; the fracturing fluid contains chemical additives, which poses a risk of groundwater contamination; and water-based fracturing fluid may react with the formation, causing damage and affecting oil and gas production.

[0004] To overcome the limitations of hydraulic fracturing, CO2 fracturing has gained popularity in recent years. Using supercritical CO2 as a fracturing fluid, CO2 fracturing significantly reduces water consumption, making it particularly suitable for areas with water scarcity. Furthermore, CO2 is a non-toxic and harmless gas that does not pollute groundwater. CO2 is miscible with crude oil, reducing its viscosity and increasing its fluidity, thereby improving oil and gas recovery.

[0005] However, traditional carbon dioxide fracturing technology also has some challenges. Traditional carbon dioxide fracturing technology can usually only perform one fracturing operation and is difficult to achieve multiple fracturing, which affects oil and gas production.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a multi-chamber structure carbon dioxide continuous phase change fracturing device and experimental method, which breaks through the limitations of traditional one-time fracturing technology and aims to achieve multiple controllable operations of carbon dioxide fracturing, significantly improving single well production and oil and gas recovery rate.

[0008] Specifically, the following technical solutions are adopted: A multi-chamber carbon dioxide continuous phase change fracturing device comprising: A filling cavity having a filling chamber therein; A main storage cavity has a main storage chamber inside, the upper end of the main storage cavity is connected to the filling cavity, and the filling chamber is connected to the main storage chamber; A trigger cavity having a trigger chamber therein, the lower end of the main storage cavity being connected to the trigger cavity, and the trigger chamber being in communication with the main storage cavity; a first control valve, provided on the communication passage between the filling chamber and the main storage chamber, for controlling the opening / closing thereof; a second control valve, provided on the communication passage between the trigger chamber and the main storage chamber, for controlling the opening / closing thereof; An electric heating wire is arranged in the trigger chamber; The filling chamber is used to connect to the ground pipe string to achieve the injection of liquid / supercritical carbon dioxide. The first control valve is controlled to open, and the liquid / supercritical carbon dioxide enters the main storage chamber from the filling chamber for safe storage. The second control valve is controlled to open, and the liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber. Under the instantaneous heating of the electric heating wire, a phase change occurs, and carbon dioxide phase change fracturing is performed.

[0009] As an optional embodiment of the present invention, a pressure sensor and a temperature sensor are provided in the main storage chamber of the present invention for real-time monitoring of the pressure and temperature of the liquid / supercritical carbon dioxide in the main storage chamber; The multi-chamber structure carbon dioxide continuous phase change fracturing device includes a battery and a downhole control unit. The battery is installed in the filling chamber or the main storage chamber or the trigger chamber. The pressure sensor, temperature sensor, first control valve, and second control valve are all electrically connected to the battery; the pressure sensor, temperature sensor, first control valve, and second control valve each have a communication module for communicating with the downhole control unit.

[0010] As an optional embodiment of the present invention, the trigger cavity of the present invention has an entrance acceleration zone, a middle phase change zone and an exit diffusion zone in sequence from close to the main storage cavity to away from the main storage cavity, and the electric heating wire includes a plurality of independently controllable regional resistance wires, which are respectively arranged in the entrance acceleration zone, the middle phase change zone and the exit diffusion zone.

[0011] As an optional embodiment of the present invention, a diffusion adjustment structure is provided in the trigger chamber of the present invention, and the diffusion adjustment structure has a guide plate with an adjustable deflection angle. The deflection angle of the guide plate is remotely adjusted according to the characteristics of the target formation, and the angle adjustment range of the guide plate is 15°-60°.

[0012] As an optional embodiment of the present invention, a heat insulation structure or a heat dissipation structure is provided outside the trigger cavity of the present invention. The heat insulation structure adopts a multi-layer ceramic fiber material, and the heat dissipation structure adopts a microchannel radiator.

[0013] The present invention also provides an experimental method for the multi-chamber structure carbon dioxide continuous phase change fracturing device, comprising: Prepare for the experiment and arrange the experimental site; The multi-chamber structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-chamber structure carbon dioxide continuous phase change fracturing device is accurately positioned at the target fracturing layer; Liquid / supercritical carbon dioxide is injected into the filling chamber of the downhole multi-chamber structure carbon dioxide continuous phase change fracturing device through a surface high-pressure pump, and the first control valve is controlled to open and the second control valve remains closed. The liquid / supercritical carbon dioxide enters the main storage chamber through the filling chamber for safe storage; When the set pressure value in the main storage chamber is monitored, the charging of liquid / supercritical carbon dioxide is stopped, the first control valve is controlled to close, and the second control valve is controlled to remain closed; Upon receiving a ground trigger command, the second control valve is controlled to open, and liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber, undergoes phase change under the instantaneous heating of the electric heating wire, and performs carbon dioxide phase change fracturing.

[0014] As an optional embodiment of the present invention, the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of the present invention includes: After one carbon dioxide phase change fracturing experiment is completed, when it is monitored that the residual pressure in the main storage chamber drops and stabilizes, a new carbon dioxide phase change fracturing is performed; Repeatedly execute until the predetermined fracturing scale or total energy is reached, and then end the experiment; The peak pressure, temperature, and trigger time data of the carbon dioxide phase change fracturing explosion are recorded during the experiment and transmitted back to the ground control terminal for analysis of crack formation or expansion.

[0015] As an optional embodiment of the present invention, in the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of the present invention, a pressure sensor and a temperature sensor are provided in the target well to monitor the external well pressure and external well temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device; When the internal pressure and temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device, as well as the external well pressure and external well temperature, all meet preset thresholds, a new carbon dioxide phase change fracturing is controlled to be performed.

[0016] As an optional embodiment of the present invention, in the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device described in the present invention, intelligent monitoring and safety control are carried out during the carbon dioxide phase change fracturing process, and downhole sensors and multiple interlocking mechanisms are used to ensure that each liquid / supercritical carbon dioxide filling and triggering is carried out within a controllable range; the multiple interlocking mechanisms include pressure interlock, temperature interlock, time interlock and position interlock.

[0017] As an optional embodiment of the present invention, in the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device described in the present invention, the carbon dioxide injection amount, heating temperature and trigger frequency parameters are adjusted according to the fracturing requirements of the target fracturing layer to achieve the best fracturing effect.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The multi-chamber carbon dioxide continuous phase-change fracturing device of the present invention integrates core components such as an upper filling chamber, a main storage chamber, a trigger chamber, and resettable first and second control valves through a modular design. This device achieves safe storage, precise control, and multiple controlled releases of supercritical carbon dioxide. The device utilizes reusable first and second control valves, breaking through the limitations of traditional one-time fracturing technology. It enables efficient and precise multiple fracturing operations, significantly improving oil and gas recovery rates.

[0019] The multi-chamber structure of the present invention is a continuous phase-change carbon dioxide fracturing device. Specifically, it includes: a main storage chamber and a trigger chamber separated by a high-strength material design to ensure safe storage and precise release of carbon dioxide; innovative use of resettable first and second control valves, such as high-speed valves, to replace traditional disposable rupture discs, enabling multiple opening and closing cycles and rapid response; combined with an instantaneous heating trigger mechanism using electric heating wires, it precisely controls the carbon dioxide phase change process, generating high-energy shock waves to fracture the formation; and, through modular design and remote control technology, improves the device's reliability, safety, and adaptability. This technology overcomes the limitations of traditional fracturing methods and provides an efficient, environmentally friendly, and economical solution for the development of unconventional oil and gas resources.

[0020] In summary, the multi-chamber structure carbon dioxide continuous phase change fracturing device of the present invention has significant beneficial effects such as improving oil and gas recovery rate, reducing environmental impact, improving economic benefits, enhancing operational safety, and improving technical adaptability. It provides a highly efficient, environmentally friendly, economical, safe, and adaptable technical means for the development of unconventional oil and gas resources, and has broad application prospects and important social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the structural principle of a multi-chamber carbon dioxide continuous phase change fracturing device according to an embodiment of the present invention; Figure 2 Flow chart of an experimental method for a multi-chamber structure carbon dioxide continuous phase change fracturing device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0023] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents some embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features and technical solutions therein may be combined with each other.

[0025] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0026] In the description of the present invention, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is typically placed when in use, or the orientations or positional relationships commonly understood by those skilled in the art. Such terms are intended solely to facilitate the description of the present invention and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" and the like are used solely for distinction and should not be construed as indicating or implying relative importance.

[0027] See also Figure 1 As shown, a multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment includes: The filling cavity 100 has a filling chamber inside; The main storage cavity 200 has a main storage chamber inside. The upper end of the main storage cavity 200 is connected to the filling cavity 100, and the filling chamber is connected to the main storage cavity; The trigger cavity 300 has a trigger chamber inside. The lower end of the main storage cavity 200 is connected to the trigger cavity 300, and the trigger chamber is connected to the main storage cavity. a first control valve 400 , provided on the communication passage between the filling chamber and the main storage chamber, for controlling the opening / closing thereof; a second control valve 700 , provided on the communication passage between the trigger chamber and the main storage chamber, for controlling the opening / closing thereof; The electric heating wire 800 is arranged in the trigger chamber; The filling chamber 100 is used to connect to the ground pipe string to realize the injection of liquid / supercritical carbon dioxide. The first control valve 400 is controlled to open, and the liquid / supercritical carbon dioxide enters the main storage chamber from the filling chamber for safe storage. The second control valve 700 is controlled to open, and the liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber. Under the instantaneous heating of the electric heating wire 800, a phase change occurs, and carbon dioxide phase change fracturing is performed.

[0028] This embodiment of a multi-chamber carbon dioxide continuous phase-change fracturing device utilizes a modular design that integrates core components, including an upper filling chamber 100, a main storage chamber 200, a trigger chamber 300, and a resettable first and second control valves 400 and 700. This device achieves safe storage, precise control, and multiple, controlled releases of supercritical carbon dioxide. Utilizing reusable first and second control valves 400 and 700, this device overcomes the limitations of conventional one-time fracturing technology, enabling efficient and precise multiple fracturing operations and significantly improving oil and gas recovery.

[0029] This embodiment of a multi-chamber carbon dioxide continuous phase-change fracturing device specifically includes: a main storage chamber 200 and a trigger chamber 300, made of high-strength materials, separated to ensure safe storage and precise release of carbon dioxide; innovative use of a resettable first control valve 400 and a second control valve 700, such as high-speed valves, to replace traditional disposable rupture discs, enabling multiple opening and closing cycles and rapid response; combined with an instantaneous heating trigger mechanism using a heating wire, the device precisely controls the carbon dioxide phase change process, generating high-energy shock waves to fracture the formation; and, through modular design and remote control technology, enhances the device's reliability, safety, and adaptability. This technology overcomes the limitations of traditional fracturing methods and provides an efficient, environmentally friendly, and economical solution for the development of unconventional oil and gas resources.

[0030] In summary, the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment has significant beneficial effects such as improving oil and gas recovery rate, reducing environmental impact, improving economic benefits, enhancing operational safety, and improving technical adaptability. It provides an efficient, environmentally friendly, economical, safe, and highly adaptable technical means for the development of unconventional oil and gas resources, and has broad application prospects and important social and economic benefits.

[0031] In the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment, a pressure sensor 500 and a temperature sensor 600 are provided in the main storage chamber 200 for real-time monitoring of the pressure and temperature of the liquid / supercritical carbon dioxide in the main storage chamber.

[0032] The multi-chamber structure carbon dioxide continuous phase change fracturing device described in this embodiment includes a battery 900 and a downhole control unit. The battery 900 is installed in the filling chamber 100 or the main storage chamber 200 or the trigger chamber 300. The pressure sensor 500, the temperature sensor 600, the first control valve 400, and the second control valve 700 are all electrically connected to the battery 900; the pressure sensor 500, the temperature sensor 600, the first control valve 400, and the second control valve 700 respectively have a communication module for communicating with the downhole control unit.

[0033] This embodiment is a multi-chamber structure carbon dioxide continuous phase change fracturing device, and the functions of each structure are as follows: (1) The upper filling chamber 100 is used to connect to the surface pipe string and control the injection of carbon dioxide through the first control valve 400. The first control valve 400 is driven by the downhole control unit actuator and can be remotely commanded to open and close to ensure the safe injection of carbon dioxide.

[0034] (2) The main storage chamber 200 is used to safely store supercritical carbon dioxide. A pressure sensor 500 and a temperature sensor 600 are installed in the chamber to monitor the temperature and pressure of carbon dioxide in real time to ensure that it remains in a supercritical state.

[0035] (3) The trigger chamber 300 is connected to the main storage chamber through the second control valve 700. When the trigger chamber 300 is activated, supercritical carbon dioxide rapidly flows into the trigger chamber and undergoes a phase change under the instantaneous heating of the electric heating wire 800, generating a high-energy shock wave to fractur e the formation.

[0036] (4) The first control valve 400 controls the injection process of carbon dioxide and is driven by the downhole control unit actuator. It can be remotely controlled to open and close to ensure the safe and accurate injection of carbon dioxide.

[0037] (5) The pressure sensor 500 and the temperature sensor 600 are located in the main storage chamber to monitor the temperature and pressure of the supercritical carbon dioxide in real time to ensure that they are within a safe range.

[0038] (6) The second control valve 700 can be opened, closed and reset multiple times to ensure rapid response and resistance to high-pressure shock, enabling the device to perform multiple pulse fracturing.

[0039] (7) The electric heating wire 800 is installed in the trigger chamber, which can instantly heat the carbon dioxide and use circulating electricity to achieve multiple pulse heating to ensure that the carbon dioxide quickly changes phase and generates high-energy shock waves.

[0040] (8) The battery 900 provides power to the pressure sensor 500, the temperature sensor 600, the first control valve 400, and the second control valve 700, ensuring that the device can operate stably in the underground environment.

[0041] As an optional embodiment of this embodiment, a multi-chamber carbon dioxide continuous phase change fracturing device is provided. The trigger chamber 300 includes an inlet acceleration zone, a middle phase change zone, and an outlet diffusion zone, sequentially arranged from near the main storage chamber 200 to away from the main storage chamber 200. The electric heating wire 800 includes multiple independently controllable regional resistance wires, correspondingly arranged in the inlet acceleration zone, the middle phase change zone, and the outlet diffusion zone. The electric heating wire 800 of this embodiment is installed within the trigger chamber 300 and arranged in a zoned manner to provide gradient heating of carbon dioxide, utilizing circulating power to achieve multiple pulse heating.

[0042] As an optional implementation of this embodiment, a multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment is provided, wherein a diffusion adjustment structure 1000 is provided in the trigger chamber 300, and the diffusion adjustment structure 1000 has a guide plate with an adjustable deflection angle, and the guide plate is made of a high-temperature resistant ceramic composite material, and the deflection angle of the guide plate is remotely adjusted according to the characteristics of the target formation, and the angle adjustment range of the guide plate is 15°-60°.

[0043] As an optional implementation of this embodiment, a multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment is provided with a heat insulation structure or a heat dissipation structure on the outside of the trigger cavity 300 to prevent local overheating or overcooling caused by multiple explosions. The heat insulation structure adopts a multi-layer ceramic fiber material, and the heat dissipation structure adopts a microchannel radiator.

[0044] In the multi-chamber carbon dioxide continuous phase change fracturing device of this embodiment, the pressure sensor 500, the temperature sensor 600 and the ground control terminal all adopt anti-interference technology to avoid electromagnetic interference and ensure data accuracy and system reliability; the anti-interference technology includes digital filtering, optoelectronic isolation and redundant transmission.

[0045] In the multi-chamber carbon dioxide continuous phase change fracturing device of this embodiment, the first control valve 400 is a high-pressure ball valve or a needle valve, preferably a high-pressure ball valve with a ceramic sealing surface to improve wear resistance and sealing performance.

[0046] In the multi-chamber carbon dioxide continuous phase change fracturing device of this embodiment, the second control valve 700 is a high-speed ball valve or a high-pressure gate valve, preferably a hydraulically driven high-speed ball valve, which has higher reliability and anti-interference ability.

[0047] The multi-chamber structure of the carbon dioxide continuous phase change fracturing device of this embodiment is made of high-strength alloy steel, low-temperature resistant steel, reliable seals, and an efficient heating system. It can cope with extreme temperature changes downhole (for example, environments below -30°C) and ensure that the liquid carbon dioxide always remains within a preset temperature range. The seals are made of perfluoroether rubber and maintain good sealing performance in the temperature range of -50°C to 200°C.

[0048] In the multi-chamber carbon dioxide continuous phase change fracturing device of this embodiment, pressure sensors are installed in the main storage chamber 200 and the downhole environment. Once an abnormality occurs, such as overpressure or overheating, the system automatically prohibits triggering and slowly relieves pressure. The next filling or triggering can only be performed when the intra-chamber pressure and the external well pressure are stable within a safe range; the safety range is set to 70% to 90% of the design pressure.

[0049] The multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment needs to have sufficient strength and toughness as a whole to withstand multiple impacts, and the design and material selection must ensure repeated service life; the key components of the device are made of high-strength alloy steel with a fatigue life of ≥1000 times, such as 30CrMnSiNi2A.

[0050] like Figure 2 As shown, this embodiment also provides an experimental method for a multi-chamber structure carbon dioxide continuous phase change fracturing device, including: Prepare for the experiment and arrange the experimental site; The multi-chamber structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-chamber structure carbon dioxide continuous phase change fracturing device is accurately positioned at the target fracturing layer; Liquid / supercritical carbon dioxide is injected into the filling chamber of the downhole multi-chamber structure carbon dioxide continuous phase change fracturing device through a surface high-pressure pump. The first control valve 400 is controlled to open and the second control valve 700 remains closed. The liquid / supercritical carbon dioxide enters the main storage chamber 200 through the filling chamber 100 for safe storage. When the set pressure value in the main storage chamber 200 is monitored, the charging of liquid / supercritical carbon dioxide is stopped, the first control valve 400 is controlled to be closed, and the second control valve 700 is controlled to remain closed; Upon receiving a ground trigger command, the second control valve 700 is controlled to open, and liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber, undergoes phase change under the instantaneous heating of the electric heating wire 800, and performs carbon dioxide phase change fracturing.

[0051] The present embodiment provides an experimental method for a multi-chamber structure carbon dioxide continuous phase change fracturing device, which realizes continuous phase change fracturing of a target fracturing layer downhole based on the multi-chamber structure carbon dioxide continuous phase change fracturing device. The stability and reliability of the carbon dioxide continuous phase change fracturing device are verified through experiments. At the same time, based on the experimental results, the actual construction process and parameter settings can be better guided to ensure the construction effect.

[0052] The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment includes: After one carbon dioxide phase change fracturing experiment is completed, when it is monitored that the residual pressure in the main storage chamber 200 drops and stabilizes, a new carbon dioxide phase change fracturing experiment is performed; Repeatedly execute until the predetermined fracturing scale or total energy is reached, and then end the experiment; The peak pressure, temperature, and trigger time data of the carbon dioxide phase change fracturing explosion are recorded during the experiment and transmitted back to the ground control terminal for analysis of crack formation or expansion.

[0053] After each carbon dioxide phase change fracturing operation, the multi-chamber structure carbon dioxide continuous phase change fracturing device is inspected and maintained, especially the integrity of the electric heating wire 800 in the trigger chamber and the sealing performance of the second control valve 700 are checked to ensure that it can carry out the next fracturing operation.

[0054] The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment adjusts parameters such as carbon dioxide injection volume, heating temperature, and trigger frequency according to actual needs to achieve the best fracturing effect; for example, for shale layers, the trigger frequency can be optimized to 20Hz to improve the efficiency of crack expansion.

[0055] In the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment, a pressure sensor and a temperature sensor are set in the target well to monitor the external well pressure and external well temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device; When the internal pressure and temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device, as well as the external well pressure and external well temperature, all meet preset thresholds, a new carbon dioxide phase change fracturing is controlled to be performed.

[0056] Both the main storage chamber and the downhole environment are equipped with pressure sensors. Once an abnormality occurs, such as overpressure or overheating, the system automatically prohibits triggering and slowly relieves pressure. The next filling or triggering can only be performed when the pressure in the chamber and the external well pressure are stable within a safe range; the safety range is set at 70% to 90% of the design pressure.

[0057] The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment is as follows: during the carbon dioxide phase change fracturing process, intelligent monitoring and safety control are carried out, and downhole sensors and multiple interlock mechanisms are used to ensure that each liquid / supercritical carbon dioxide filling and triggering is carried out within a controllable range; the multiple interlock mechanisms include pressure interlock, temperature interlock, time interlock and position interlock.

[0058] The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment adjusts the carbon dioxide injection rate, heating temperature and trigger frequency parameters according to the fracturing requirements of the target fracturing layer to achieve the best fracturing effect.

[0059] The specific implementation of the experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device of this embodiment includes the following steps: (1) Experimental preparation and site layout: Investigate the parameters of the simulated downhole environment or the actual downhole operation site to ensure that the experimental environment meets the design requirements; debug the parameters of the experimental equipment, including the pressure and temperature sensors, the second control valve 700, the electric heating wire 800, etc., to ensure that the equipment is in normal working condition; especially debug the heating power (up to kilowatt level) and response time (≤50ms) of the electric heating wire 800 in the trigger chamber, as well as the sealing performance of the second control valve 700 (pressure resistance ≥150MPa).

[0060] (2) Lowering and positioning of the device: The device is lowered into the target well along with the tubing string and accurately positioned at the target fracturing layer. The downhole electrical control system enters the standby state. The main storage chamber 200 may be empty or contain only a small amount of carbon dioxide at first. At the same time, the adaptive expansion sealing ring outside the trigger chamber is activated to ensure that the device forms a reliable seal with the well wall (sealing pressure ≥ 120 MPa).

[0061] (3) Injecting supercritical carbon dioxide: The surface high-pressure pump injects supercritical carbon dioxide into the well and opens the first control valve 400. The supercritical carbon dioxide enters the main storage chamber through the first control valve 400. After reaching the designed amount and pressure, the first control valve 400 is closed and the main storage chamber is sealed. During the injection process, the state of carbon dioxide is monitored in real time by the pressure sensor 500 and the temperature sensor 600 to ensure that it is in a supercritical state (pressure ≥7.38 MPa, temperature ≥31.1°C).

[0062] (4) Real-time pressure monitoring: The temperature and pressure of the supercritical carbon dioxide are monitored in real time by the pressure sensor 500 and the temperature sensor 600 installed in the main storage chamber. At the same time, the data is transmitted to the ground control system, and the fracturing parameters (such as carbon dioxide injection volume and heating temperature) are dynamically adjusted according to the geological conditions.

[0063] (5) Triggering blasting: The downhole control unit receives the ground trigger command and executes the triggering action after confirming that the pressure and temperature are within the safe range. The second control valve 700 opens instantaneously (response time <10ms) and the electric heating wire 800 is simultaneously started to heat, causing the carbon dioxide in the trigger chamber to undergo phase change and expansion in a very short time (the temperature rises by more than 200°C). The high-pressure carbon dioxide gas flow and expansion shock wave are released into the formation, generating cracks. The triggering duration is usually tens to hundreds of milliseconds; then the second control valve 700 is closed again; during this process, the independent design of the trigger chamber 300 prevents the main storage chamber 200 from being subjected to instantaneous high-pressure shock, thereby improving the safety and reusability of the device.

[0064] (6) Downhole pressure drop: After the trigger is completed, the residual pressure in the downhole and the main storage chamber 200 will gradually drop and stabilize; the pressure change curve is monitored by the pressure sensor 500 to evaluate the fracturing effect.

[0065] (7) Open the upper first control valve 400 again to allow the surface supercritical carbon dioxide to enter the cavity and replenish it to the required pressure and volume. After the filling is completed, close the valve and the device enters the ready-to-explode state again. The same as the first triggering process, it is repeated: open the second control valve 700 → start the instantaneous phase change → impact fracturing again → close the second control valve 700 → pressure drops → wait for the next time until the predetermined fracturing scale or total energy is reached; this process can realize the continuous operation of "injection-fracturing-reinjection-refracturing", and the single well operation efficiency is increased by 5 to 8 times.

[0066] (8) Experimental data acquisition and analysis: The sensor records the peak pressure, temperature, trigger time and other data of the explosion and transmits them back to the ground for analysis of crack formation or expansion; in particular, the heating efficiency of the electric heating wire 800 in the trigger chamber (phase change efficiency>95%) and the attenuation of the sealing performance of the resettable trigger valve are analyzed.

[0067] (9) Cleaning the site: After checking that the equipment is in good condition, shut it down and clean the ground; focus on checking the wear of the thermal insulation coating on the inner wall of the trigger chamber and the resettable trigger valve, and replace them if necessary. Example

[0068] 1. Experimental Preparation A low-permeability oil and gas well was selected as the experimental subject. The formation permeability was low, making traditional hydraulic fracturing ineffective and limiting production increases. The target depth was 2,500 meters, the formation pressure was 35 MPa, and the temperature was 85°C. A multi-chamber CO2 continuous phase-change fracturing device was assembled in the laboratory. The device includes a filling chamber 100, a main storage chamber 200, a trigger chamber 300, a first control valve 400, and a second control valve 700. Pressure and temperature sensors were installed and calibrated to ensure real-time monitoring of pressure and temperature changes within the main storage chamber.

[0069] 2. Lowering and positioning of the device The device is lowered into the target well section and accurately positioned at the target layer to ensure that the fracturing energy can be effectively released.

[0070] 3. Supercritical CO2 injection Liquid carbon dioxide is injected into the main storage chamber 200 through the surface pipe string to make the pressure reach 40 MPa.

[0071] 4. Triggering fracking A trigger signal is sent to open the second control valve 700, allowing carbon dioxide to enter the trigger chamber 300. The electric heating wire 800 instantly heats the carbon dioxide, causing it to undergo a rapid phase change and generate high-energy shock waves, thereby fracturing the formation.

[0072] 5. Repeated triggering and multiple fracturing Repeat the triggering process and perform multiple fracturing operations, with an interval of 5 minutes between each operation. After the triggering is completed, the residual pressure in the well and the main storage chamber will gradually drop and stabilize. Open the first control valve 400 again to allow liquid carbon dioxide from the surface to enter the cavity and replenish the required pressure and volume. After the filling is completed, close the first control valve 400 and the device enters the ready-to-explode state again. The same as the first triggering process, repeatedly execute: open the second control valve 700 → start the instantaneous phase change → impact fracturing again → close the second control valve 700 → pressure drops → wait for the next time, until the predetermined fracturing scale or total energy is reached.

[0073] 6. Fracturing effect evaluation After fracturing, downhole sensors monitored a 50% increase in formation permeability and a 30% increase in oil and gas production. Multiple fracture networks were successfully created, effectively increasing formation permeability. The CO2 phase transition process was precisely controlled, achieving a utilization rate of over 90%. Compared to traditional hydraulic fracturing, this method saves 80% of water resources and reduces operating costs by 20%. Example

[0074] 1. Experimental Preparation A shale gas well was selected as the experimental target. The well's formation is dense, making it difficult to form effective fractures using traditional fracturing techniques. The target layer depth is 3,000 meters, the formation pressure is 40 MPa, and the temperature is 95°C. A multi-chamber CO2 continuous phase-change fracturing device was assembled in the laboratory. It includes a charging chamber 100, a main storage chamber 200, a trigger chamber 300, and a first control valve 400 and a second control valve 700. Pressure and temperature sensors were installed and calibrated to ensure real-time monitoring of pressure and temperature changes within the main storage chamber.

[0075] 2. Lowering and positioning of the device The device is lowered into the target well section and accurately positioned at the target layer to ensure that the fracturing energy can be effectively released.

[0076] 3. Supercritical carbon dioxide injection Liquid carbon dioxide is injected into the main storage chamber 200 through the surface pipe string to make the pressure reach 50 MPa.

[0077] 4. Triggering fracking A trigger signal is sent to open the resettable trigger valve, allowing CO2 to enter the trigger chamber. The heating wire instantly heats the CO2, causing it to undergo a rapid phase change and generate a high-energy shock wave, fracturing the formation.

[0078] 5. Repeated triggering and multiple fracturing Repeat the triggering process and perform multiple fracturing operations, with an interval of 10 minutes between each operation. After the triggering is completed, the residual pressure in the well and the main storage chamber will gradually drop and stabilize. Subsequently, the first control valve 400 is opened again to replenish the surface liquid carbon dioxide into the cavity until the required pressure and volume are reached. After the filling is completed, the first control valve 400 is closed and the device enters the ready-to-explode state again. Repeat the following steps: open the second control valve 700 → start the instantaneous phase change → impact fracturing again → close the second control valve 700 → pressure drops → wait for the next trigger until the predetermined fracturing scale or total energy is reached.

[0079] 6. Fracturing effect evaluation After fracturing, downhole sensors monitored a 40% increase in shale gas production. A complex fracture network was successfully formed, effectively increasing shale gas production. Some carbon dioxide was retained in the formation, achieving geological sequestration and reducing greenhouse gas emissions. Compared with traditional fracturing techniques, this technology reduces water consumption by 90%, significantly reducing the risk of environmental pollution.

[0080] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Although this specification has described the present invention in detail with reference to the above embodiments, the present invention is not limited to the above specific implementation methods. Therefore, any modification or equivalent replacement of the present invention; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the invention are included in the scope of the claims of the present invention.

Claims

1. A multi-chamber structure carbon dioxide continuous phase change fracturing device, characterized in that: include: A filling cavity having a filling chamber therein; A main storage cavity has a main storage chamber inside, the upper end of the main storage cavity is connected to the filling cavity, and the filling chamber is connected to the main storage chamber; A trigger cavity having a trigger chamber therein, the lower end of the main storage cavity being connected to the trigger cavity, and the trigger chamber being in communication with the main storage cavity; a first control valve, provided on the communication passage between the filling chamber and the main storage chamber, for controlling the opening / closing thereof; a second control valve, provided on the communication passage between the trigger chamber and the main storage chamber, for controlling the opening / closing thereof; An electric heating wire is arranged in the trigger chamber; The filling chamber is used to connect to the ground pipe string to achieve the injection of liquid / supercritical carbon dioxide. The first control valve is controlled to open, and the liquid / supercritical carbon dioxide enters the main storage chamber from the filling chamber for safe storage. The second control valve is controlled to open, and the liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber. Under the instantaneous heating of the electric heating wire, a phase change occurs, and carbon dioxide phase change fracturing is performed.

2. The multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 1, characterized in that: A pressure sensor and a temperature sensor are provided in the main storage chamber for real-time monitoring of the pressure and temperature of the liquid / supercritical carbon dioxide in the main storage chamber; The multi-chamber structure carbon dioxide continuous phase change fracturing device includes a battery and a downhole control unit. The battery is installed in the filling chamber or the main storage chamber or the trigger chamber. The pressure sensor, temperature sensor, first control valve, and second control valve are all electrically connected to the battery; the pressure sensor, temperature sensor, first control valve, and second control valve each have a communication module for communicating with the downhole control unit.

3. The multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 1, characterized in that: The trigger cavity has an entrance acceleration zone, a middle phase change zone and an exit diffusion zone in sequence from close to the main storage cavity to away from the main storage cavity. The electric heating wire includes a plurality of independently controllable regional resistance wires, which are respectively arranged in the entrance acceleration zone, the middle phase change zone and the exit diffusion zone.

4. The multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 1, characterized in that: A diffusion adjustment structure is provided in the trigger cavity. The diffusion adjustment structure has a guide plate with an adjustable deflection angle. The deflection angle of the guide plate is remotely adjusted according to the target formation characteristics. The angle adjustment range of the guide plate is 15°-60°.

5. The multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 1, characterized in that: A heat insulation structure or a heat dissipation structure is arranged outside the trigger cavity. The heat insulation structure adopts a multi-layer ceramic fiber material, and the heat dissipation structure adopts a micro-channel radiator.

6. An experimental method for the multi-chamber structure carbon dioxide continuous phase change fracturing device according to any one of claims 1 to 5, characterized in that: include: Prepare for the experiment and arrange the experimental site; The multi-chamber structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-chamber structure carbon dioxide continuous phase change fracturing device is accurately positioned at the target fracturing layer; Liquid / supercritical carbon dioxide is injected into the filling chamber of the downhole multi-chamber structure carbon dioxide continuous phase change fracturing device through a surface high-pressure pump, and the first control valve is controlled to open and the second control valve remains closed. The liquid / supercritical carbon dioxide enters the main storage chamber through the filling chamber for safe storage; When the set pressure value in the main storage chamber is monitored, the charging of liquid / supercritical carbon dioxide is stopped, the first control valve is controlled to close, and the second control valve is controlled to remain closed; Upon receiving a ground trigger command, the second control valve is controlled to open, and liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber, undergoes phase change under the instantaneous heating of the electric heating wire, and performs carbon dioxide phase change fracturing.

7. The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 6 is characterized in that: include: After one carbon dioxide phase change fracturing experiment is completed, when it is monitored that the residual pressure in the main storage chamber drops and stabilizes, a new carbon dioxide phase change fracturing is performed; Repeatedly execute until the predetermined fracturing scale or total energy is reached, and then end the experiment; The peak pressure, temperature, and trigger time data of the carbon dioxide phase change fracturing explosion are recorded during the experiment and transmitted back to the ground control terminal for analysis of crack formation or expansion.

8. The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 7 is characterized in that: A pressure sensor and a temperature sensor are provided in the target well to monitor the external well pressure and external well temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device; When the internal pressure and temperature of the multi-chamber structure carbon dioxide continuous phase change fracturing device, as well as the external well pressure and external well temperature, all meet preset thresholds, a new carbon dioxide phase change fracturing is controlled to be performed.

9. The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 6, characterized in that: During the carbon dioxide phase-change fracturing process, intelligent monitoring and safety control are carried out, coordinated with downhole sensors and multiple interlock mechanisms to ensure that each liquid / supercritical carbon dioxide filling and triggering is carried out within a controllable range; the multiple interlock mechanisms include pressure interlock, temperature interlock, time interlock and position interlock.

10. The experimental method of the multi-chamber structure carbon dioxide continuous phase change fracturing device according to claim 6, characterized in that: Adjust the CO2 injection rate, heating temperature and trigger frequency parameters according to the fracturing requirements of the target fracturing layer to achieve the best fracturing effect.

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