Multi-cavity structure carbon dioxide continuous phase transformation fracturing device and experimental method

Abstract

The application discloses a multi-cavity structure carbon dioxide continuous phase change fracturing device, which comprises a filling cavity with a filling cavity chamber in the inside, a main storage cavity with a main storage cavity chamber in the inside and connected with the filling cavity chamber at the upper end, a trigger cavity with a trigger cavity chamber in the inside and connected with the main storage cavity chamber at the lower end, a first control valve arranged between the filling cavity chamber and the main storage cavity chamber, a second control valve arranged between the trigger cavity chamber and the main storage cavity chamber, and an electric heating wire arranged in the trigger cavity chamber. The filling cavity is used for connecting a ground pipe column to realize injection of supercritical carbon dioxide. The first control valve is controlled to be opened, supercritical carbon dioxide enters the main storage cavity chamber from the filling cavity chamber to be safely stored, the second control valve is controlled to be opened, supercritical carbon dioxide enters the trigger cavity chamber from the main storage cavity chamber, phase change of the supercritical carbon dioxide occurs under instantaneous heating of the electric heating wire, and carbon dioxide phase change fracturing is carried out.

Description

TECHNICAL FIELD

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

[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 an important direction in the global energy field. However, unconventional oil and gas reservoirs generally have low porosity and low permeability, making it difficult to effectively develop them using traditional extraction techniques, which require the use of hydraulic fracturing and other stimulation measures.

[0003] Hydraulic fracturing technology involves injecting high-pressure fluid into the formation to create a network of fractures, thereby increasing oil and gas production. However, hydraulic fracturing technology also has some limitations, such as the need for large amounts of water resources, which limits its application in areas where water resources are scarce; the presence of chemical additives in the fracturing fluid poses a risk of groundwater pollution; and water-based fracturing fluid may react with the formation, causing formation damage and affecting oil and gas production.

[0004] In order to overcome the limitations of hydraulic fracturing technology, carbon dioxide fracturing technology has emerged in recent years. Carbon dioxide fracturing technology uses supercritical carbon dioxide as a fracturing fluid, which can significantly reduce water consumption, making it particularly suitable for areas where water resources are scarce. Additionally, carbon dioxide is a non-toxic and harmless gas that does not pollute groundwater. Carbon dioxide can mix with crude oil, reducing its viscosity and improving its flowability, thereby increasing oil and gas recovery.

[0005] However, traditional carbon dioxide fracturing technology also has some challenges. Traditional carbon dioxide fracturing technology can only perform a single fracturing operation, making it difficult to achieve multiple fracturing and affecting oil and gas production.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] To solve the above problems, the present application proposes a multi-cavity structure carbon dioxide continuous phase 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.

[0008] Specifically, the following technical solutions are adopted:

[0009] A multi-cavity structure carbon dioxide continuous phase fracturing device, comprising:

[0010] a filling cavity having a filling chamber inside;

[0011] A main storage cavity with a main storage chamber inside, the upper end of the main storage cavity is connected with the filling cavity, and the filling chamber is communicated with the main storage chamber;

[0012] A trigger cavity with a trigger chamber inside, the lower end of the main storage cavity is connected with the trigger cavity, and the trigger chamber is communicated with the main storage chamber;

[0013] A first control valve arranged on the communication passage between the filling chamber and the main storage chamber for controlling the opening / closing thereof;

[0014] A second control valve arranged on the communication passage between the trigger chamber and the main storage chamber for controlling the opening / closing thereof;

[0015] An electric heating wire arranged in the trigger chamber;

[0016] The filling cavity is used for connecting the ground pipe column to realize the injection of liquid / supercritical carbon dioxide, the first control valve is controlled to be opened, the liquid / supercritical carbon dioxide enters the main storage chamber from the filling chamber for safe storage, the second control valve is controlled to be opened, the liquid / supercritical carbon dioxide enters the trigger chamber from the main storage chamber, and phase change is caused under the instantaneous heating of the electric heating wire to realize carbon dioxide phase change fracturing.

[0017] As an optional embodiment of the present application, a pressure sensor and a temperature sensor are arranged in the main storage cavity for real-time monitoring of the pressure and temperature of the liquid / supercritical carbon dioxide in the main storage chamber;

[0018] The multi-cavity structure carbon dioxide continuous phase change fracturing device comprises a battery and a downhole control unit, the battery is installed in the filling cavity or the main storage cavity or the trigger cavity, and the pressure sensor, the temperature sensor, the first control valve and the second control valve are electrically connected with the battery; the pressure sensor, the temperature sensor, the first control valve and the second control valve each have a communication module for communication connection with the downhole control unit.

[0019] As an optional embodiment of the present application, the trigger cavity has an inlet acceleration zone, a middle phase change zone and an outlet diffusion zone in sequence from the direction close to the main storage cavity to the direction away from the main storage cavity, and the electric heating wire comprises a plurality of independently controllable area resistance wires arranged in the inlet acceleration zone, the middle phase change zone and the outlet diffusion zone, respectively.

[0020] As an optional embodiment of the present application, a diffusion adjusting structure is arranged in the trigger cavity, the diffusion adjusting 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, and the angle adjusting range of the guide plate is 15°-60°.

[0021] As an optional embodiment of the present application, the outer part of the trigger cavity is provided with a heat insulation structure or a heat dissipation structure, the heat insulation structure adopts a multi-layer ceramic fiber material, and the heat dissipation structure adopts a micro-channel radiator.

[0022] The application also provides an experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device, comprising the following steps:

[0023] Preparation for the experiment is performed, and an experimental site is arranged;

[0024] The multi-cavity carbon dioxide continuous phase change fracturing device is lowered into a target well with a pipe column, and the multi-cavity carbon dioxide continuous phase change fracturing device is accurately positioned to a target fracturing layer;

[0025] Liquid / supercritical carbon dioxide is injected into the filling cavity of the multi-cavity carbon dioxide continuous phase change fracturing device by a ground high-pressure pump, the first control valve is controlled to be opened, and the second control valve is controlled to be kept closed, the liquid / supercritical carbon dioxide enters the main storage cavity through the filling cavity and is safely stored in the main storage cavity;

[0026] When the set pressure value in the main storage cavity is monitored, the injection of liquid / supercritical carbon dioxide is controlled to be stopped, the first control valve is controlled to be closed, and the second control valve is controlled to be kept closed;

[0027] A ground trigger instruction is received, the second control valve is controlled to be opened, the liquid / supercritical carbon dioxide enters the trigger cavity from the main storage cavity, phase change occurs under the instantaneous heating of the electric heating wire, and carbon dioxide phase change fracturing is performed.

[0028] As an optional embodiment of the present application, the experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device comprises the following steps:

[0029] After one carbon dioxide phase change fracturing experiment is completed, when the residual pressure in the main storage cavity is monitored to fall back and stabilize, a new carbon dioxide phase change fracturing is performed;

[0030] The above steps are repeatedly performed until a predetermined fracturing scale or total energy amount is reached, and the experiment is ended;

[0031] Peak pressure, temperature, trigger time data of carbon dioxide phase change fracturing explosion in the experiment are recorded and returned to a ground control terminal, and are used to analyze crack formation or expansion.

[0032] As an optional embodiment of the present application, in the experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device, a pressure sensor and a temperature sensor are arranged in the target well, and are used to monitor the external well pressure and the external well temperature of the multi-cavity carbon dioxide continuous phase change fracturing device.

[0033] When the internal pressure and temperature of the multi-cavity structure carbon dioxide continuous phase fracturing device, and the external well pressure and external well temperature meet the preset threshold, control is performed to execute a new carbon dioxide phase fracturing.

[0034] As an optional embodiment of the application, in the experimental method of the multi-cavity structure carbon dioxide continuous phase fracturing device, intelligent monitoring and safety control are performed during the carbon dioxide phase fracturing process, and a downhole sensor and a multiple interlocking mechanism are used to ensure that each liquid / supercritical carbon dioxide filling and triggering is performed within a controllable range; the multiple interlocking mechanism includes pressure interlocking, temperature interlocking, time interlocking, and position interlocking.

[0035] As an optional embodiment of the application, in the experimental method of the multi-cavity structure carbon dioxide continuous phase fracturing device, the carbon dioxide injection amount, heating temperature, and triggering frequency parameters are adjusted according to the fracturing requirements of the target fracturing layer to achieve the best fracturing effect.

[0036] Compared with the prior art, the application has the following beneficial effects:

[0037] The multi-cavity structure carbon dioxide continuous phase fracturing device integrates the upper filling cavity, the main storage cavity, the triggering cavity, and the core components such as the first resettable control valve and the second control valve through modular design, realizes safe storage, precise control, and multiple controllable release of supercritical carbon dioxide, and breaks through the limitations of traditional one-time fracturing technology, can efficiently and accurately perform multiple fracturing operations, and significantly improves oil and gas recovery.

[0038] The multi-cavity structure carbon dioxide continuous phase fracturing device includes: the main storage cavity and the triggering cavity are designed separately using high-strength materials to ensure safe storage and precise release of carbon dioxide; the first resettable control valve and the second control valve, such as a high-speed valve, are innovatively used to replace traditional one-time rupture discs, multiple opening and closing and rapid response are realized; the electric heating wire instantaneous heating triggering mechanism is combined to accurately control the carbon dioxide phase change process, generate a high-energy shock wave to fracture the formation; at the same time, the modularity design and remote control technology improve the reliability, safety and adaptability of the device. This technology breaks through the limitations of traditional fracturing methods, provides an efficient, environmentally friendly and economic solution for unconventional oil and gas resource development.

[0039] In summary, the multi-cavity 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 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. Attached Figure Description

[0040] Figure 1 A schematic diagram illustrating the structural principle of a multi-cavity continuous phase change carbon dioxide fracturing device according to an embodiment of the present invention;

[0041] Figure 2 A flowchart of an experimental method for a multi-cavity carbon dioxide continuous phase change fracturing device according to an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of 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 some embodiments of the present invention, and not all embodiments.

[0043] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely illustrates some embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] It should be noted that, unless otherwise specified, the embodiments and features and technical solutions in the present invention can be combined with each other.

[0045] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0046] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. These terms are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0047] SeeFigure 1 As shown in this embodiment, a multi-cavity carbon dioxide continuous phase change fracturing device includes:

[0048] The filling cavity 100 has a filling chamber inside;

[0049] 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 chamber.

[0050] 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 chamber.

[0051] A first control valve 400 is disposed on the communication channel between the filling chamber and the main storage chamber, and is used to control its opening / closing;

[0052] The second control valve 700 is disposed on the communication channel between the trigger chamber and the main storage chamber, and is used to control its opening / closing;

[0053] An electric heating wire 800 is disposed in the trigger chamber;

[0054] The filling chamber 100 is used to connect to the ground tubing 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.

[0055] This embodiment presents a multi-chamber structure continuous phase change fracturing device for carbon dioxide. Through modular design, it integrates core components such as an upper filling chamber 100, a main storage chamber 200, a trigger chamber 300, and resettable triggerable first control valves 400 and 700, achieving safe storage, precise control, and multiple controllable releases of supercritical carbon dioxide. The device employs reusable first control valves 400 and 700, overcoming the limitations of traditional single-stage fracturing technology. It enables efficient and precise multiple fracturing operations, significantly improving oil and gas recovery rates.

[0056] This embodiment of a multi-chamber structure continuous phase change fracturing device for carbon dioxide includes: a main storage chamber 200 made of high-strength materials and a trigger chamber 300 designed separately to ensure the safe storage and precise release of carbon dioxide; innovative use of resettable first control valves 400 and second control valves 700, such as high-speed valves, to replace traditional disposable fracturing discs, enabling multiple opening and closing and rapid response; combined with an instantaneous heating triggering mechanism using heating wires to precisely control the carbon dioxide phase change process, generating high-energy shock waves to fracture the formation; and improved reliability, safety, and adaptability of the device through modular design and remote control technology. This technology overcomes the limitations of traditional fracturing methods, providing an efficient, environmentally friendly, and economical solution for unconventional oil and gas resource development.

[0057] In summary, the multi-cavity 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 socio-economic benefits.

[0058] This embodiment provides a multi-chamber structure carbon dioxide continuous phase change fracturing device. The main storage chamber 200 is equipped with a pressure sensor 500 and a temperature sensor 600 for real-time monitoring of the pressure and temperature of liquid / supercritical carbon dioxide in the main storage chamber.

[0059] The multi-cavity 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 cavity 100, the main storage cavity 200, or the trigger cavity 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 each have a communication module for communicating with the downhole control unit.

[0060] This embodiment describes a multi-cavity continuous phase change carbon dioxide fracturing device, and the functions of each structure are as follows:

[0061] (1) The upper filling chamber 100 is used to connect to the surface tubing and the injection of carbon dioxide is controlled by the first control valve 400. The first control valve 400 is driven by the actuator of the downhole control unit and can be remotely commanded to open and close, ensuring the safe injection of carbon dioxide.

[0062] (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 and ensure that it is maintained in a supercritical state.

[0063] (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 flows rapidly 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 fracture the formation.

[0064] (4) The first control valve 400 controls the carbon dioxide injection process and is driven by the downhole control unit actuator. It can be remotely commanded to switch on and off to ensure the safe and accurate injection of carbon dioxide.

[0065] (5) Pressure sensor 500 and temperature sensor 600 are located in the main storage chamber to monitor the temperature and pressure of supercritical carbon dioxide in real time to ensure that they are within a safe range.

[0066] (6) The second control valve 700 can be opened, closed and reset multiple times to ensure rapid response and resistance to high pressure impact, enabling the device to perform multiple pulse fracturing operations.

[0067] (7) The electric heating wire 800 is installed in the trigger chamber, which can heat carbon dioxide instantly and use circulating electricity to achieve multiple pulse heating, ensuring that carbon dioxide undergoes rapid phase change and generates high-energy shock waves.

[0068] (8) Battery 900 provides power to pressure sensor 500, temperature sensor 600, first control valve 400 and second control valve 700 to ensure that the device can operate stably in the downhole environment.

[0069] As an optional implementation of this embodiment, a multi-cavity carbon dioxide continuous phase change fracturing device is provided. The trigger chamber 300 has, sequentially, an inlet acceleration zone, a middle phase change zone, and an outlet diffusion zone along the direction 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, respectively disposed in the inlet acceleration zone, the middle phase change zone, and the outlet diffusion zone. In this embodiment, the electric heating wire 800 is installed within the trigger chamber 300 and arranged in a zoned manner for gradient heating of carbon dioxide, utilizing circulating electricity to achieve multiple pulse heating.

[0070] As an optional implementation of this embodiment, a multi-cavity carbon dioxide continuous phase change fracturing device of this embodiment is provided, wherein a diffusion adjustment structure 1000 is provided in the trigger cavity 300, the diffusion adjustment structure 1000 has a guide plate with an adjustable deflection angle, the guide plate is made of high temperature resistant ceramic composite material, and the deflection angle of the guide plate can be remotely adjusted according to the characteristics of the target formation, the angle adjustment range of the guide plate is 15°-60°.

[0071] As an optional implementation of this embodiment, in order to prevent local overheating or overcooling caused by multiple explosions, the trigger cavity 300 is provided with a heat insulation structure or a heat dissipation structure. The heat insulation structure is made of multi-layer ceramic fiber material, and the heat dissipation structure is made of microchannel heat sink.

[0072] This embodiment of a multi-cavity carbon dioxide continuous phase change fracturing device employs anti-interference technology in its pressure sensor 500, temperature sensor 600, and ground control terminal to avoid electromagnetic interference and ensure data accuracy and system reliability. The anti-interference technology includes digital filtering, photoelectric isolation, and redundant transmission.

[0073] In this embodiment, a multi-chamber structure carbon dioxide continuous phase change fracturing device is provided. 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.

[0074] In this embodiment, a multi-chamber structure carbon dioxide continuous phase change fracturing device is provided. 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.

[0075] This embodiment of a multi-cavity carbon dioxide continuous phase change fracturing device employs high-strength alloy steel, low-temperature resistant steel, reliable seals, and a high-efficiency heating system. It can cope with extreme downhole temperature changes (e.g., environments below -30°C) and ensure that liquid carbon dioxide is always kept within a preset temperature range. The seals are made of perfluoroether rubber, which maintains good sealing performance in a temperature range of -50°C to 200°C.

[0076] In this embodiment, a multi-chamber structure carbon dioxide continuous phase change fracturing device is provided with pressure sensors in the main storage chamber 200 and the downhole environment. If an abnormality occurs, such as overpressure or overheating, the system will automatically prohibit triggering and slowly depressurize. Only when the pressure inside the chamber and the external well pressure are stable within a safe range can the next filling or triggering be performed. The safe range is set to 70% to 90% of the design pressure.

[0077] This embodiment of a multi-cavity continuous phase change fracturing device for carbon dioxide requires sufficient strength and toughness to withstand multiple impacts, and ensures a long service life in terms of design and material selection; the key components of the device are made of high-strength alloy steel with a fatigue life of ≥1000 cycles, such as 30CrMnSiNi2A.

[0078] like Figure 2 As shown, this embodiment also provides an experimental method for a multi-cavity carbon dioxide continuous phase change fracturing device, including:

[0079] Prepare for the experiment and set up the experimental site;

[0080] The multi-cavity structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-cavity structure carbon dioxide continuous phase change fracturing device is precisely positioned at the target fracturing layer.

[0081] Liquid / supercritical carbon dioxide is injected into the filling chamber of the downhole multi-chamber carbon dioxide continuous phase change fracturing device using a surface high-pressure pump. The first control valve 400 is opened and the second control valve 700 is kept closed. The liquid / supercritical carbon dioxide enters the main storage chamber 200 through the filling chamber 100 for safe storage.

[0082] When the set pressure value is detected in the main storage chamber 200, the filling of liquid / supercritical carbon dioxide is stopped, and the first control valve 400 is closed and the second control valve 700 remains closed.

[0083] Upon receiving a ground trigger command, the second control valve 700 is opened, allowing liquid / supercritical carbon dioxide to enter the trigger chamber from the main storage chamber. Under the instantaneous heating of the electric heating wire 800, a phase change occurs, resulting in carbon dioxide phase change fracturing.

[0084] This embodiment presents an experimental method for a multi-cavity structure carbon dioxide continuous phase change fracturing device. Based on the multi-cavity structure carbon dioxide continuous phase change fracturing device, continuous phase change fracturing of the target fracturing layer in the well is achieved. The stability and reliability of the carbon dioxide continuous phase change fracturing device are verified through experiments. At the same time, the experimental results can better guide the actual construction process and parameter settings to ensure the construction effect.

[0085] The experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device in this embodiment includes:

[0086] After a carbon dioxide phase change fracturing experiment is completed, when the residual pressure in the main storage chamber 200 is monitored to drop and stabilize, a new carbon dioxide phase change fracturing is performed.

[0087] Repeat the process until the predetermined fracturing scale or total energy is reached, then end the experiment.

[0088] Record the peak pressure, temperature, and trigger time data of carbon dioxide phase change fracturing blasting during the experiment, and transmit them back to the ground control terminal for analysis of crack formation or propagation.

[0089] After each carbon dioxide phase change fracturing operation, the multi-chamber structure carbon dioxide continuous phase change fracturing device is inspected and maintained, with particular attention to the integrity of the electric heating wire 800 in the trigger chamber and the sealing performance of the second control valve 700, to ensure that it can carry out the next fracturing operation.

[0090] The experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device in this embodiment adjusts parameters such as carbon dioxide injection volume, heating temperature, and triggering frequency according to actual needs to achieve the best fracturing effect; for example, for shale formations, the triggering frequency can be optimized to 20Hz to improve fracture propagation efficiency.

[0091] In the experimental method of the multi-cavity structure carbon dioxide continuous phase change fracturing device in this embodiment, a pressure sensor and a temperature sensor are installed in the target well to monitor the external well pressure and external well temperature of the multi-cavity structure carbon dioxide continuous phase change fracturing device.

[0092] When the internal pressure and temperature of the multi-cavity carbon dioxide continuous phase change fracturing device, as well as the external well pressure and temperature, all meet the preset thresholds, a new round of carbon dioxide phase change fracturing is controlled to be executed.

[0093] Pressure sensors are installed in both the main storage chamber and the downhole environment. In the event of an abnormality, such as overpressure or overheating, the system will automatically prevent triggering and slowly depressurize. The next filling or triggering can only be performed when the pressure inside the chamber and the external well pressure are stable within a safe range. The safe range is set to 70% to 90% of the design pressure.

[0094] The experimental method of the multi-cavity structure carbon dioxide continuous phase change fracturing device in this embodiment includes intelligent monitoring and safety control during the carbon dioxide phase change fracturing process. In conjunction with downhole sensors and multiple interlocking mechanisms, it is ensured that each liquid / supercritical carbon dioxide filling and triggering is carried out within a controllable range. The multiple interlocking mechanisms include pressure interlocking, temperature interlocking, time interlocking, and position interlocking.

[0095] The experimental method of the multi-cavity carbon dioxide continuous phase change fracturing device in this embodiment adjusts the carbon dioxide injection volume, heating temperature, and triggering frequency parameters according to the fracturing requirements of the target fracturing layer to achieve the best fracturing effect.

[0096] The specific implementation method of the experimental method for the multi-cavity structure carbon dioxide continuous phase change fracturing device in this embodiment includes the following steps:

[0097] (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 pressure and temperature sensors, second control valve 700, electric heating wire 800, etc., to ensure that the equipment is in normal working condition; specially 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 (pressure resistance ≥150MPa) of the second control valve 700.

[0098] (2) Device running and positioning: The device is run into the target well along with the tubing string and is precisely positioned to the target fracturing layer. The downhole electrical control system enters standby mode. The main storage chamber 200 may initially be empty or contain only a small amount of carbon dioxide. 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 ≥120MPa).

[0099] (3) Injecting supercritical carbon dioxide: The surface high-pressure pump injects supercritical carbon dioxide downhole and opens the first control valve 400. The carbon dioxide enters the main storage chamber through the first control valve 400. After reaching the design quantity and pressure, the first control valve 400 is closed and the main storage chamber is sealed. During the injection process, the carbon dioxide status 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℃).

[0100] (4) Real-time pressure monitoring: The temperature and pressure of supercritical carbon dioxide are monitored in real time by pressure sensor 500 and temperature sensor 600 installed in the main storage chamber; at the same time, the data is transmitted to the ground control system to dynamically adjust the fracturing parameters (such as carbon dioxide injection volume and heating temperature) in combination with geological conditions.

[0101] (5) Triggering blasting: The downhole control unit receives the triggering command from the ground. After confirming that the pressure and temperature are within the safe range, it executes the triggering action. The second control valve 700 opens instantaneously (response time <10ms) and the electric heating wire 800 is started to heat the carbon dioxide in the triggering chamber in a very short time (the temperature rises by more than 200°C). The high-pressure carbon dioxide gas flow and the expansion shock wave are released to the formation, generating cracks. The triggering duration is usually tens to hundreds of milliseconds. Then the second control valve 700 closes again. During this process, the independent design of the triggering chamber 300 avoids the main storage chamber 200 from being subjected to instantaneous high-pressure impact, improving the safety and reusability of the device.

[0102] (6) Downhole pressure drop: After the triggering is completed, the residual pressure in the downhole and main storage chamber 200 will gradually drop and stabilize; the pressure change curve is monitored by pressure sensor 500 to evaluate the fracturing effect.

[0103] (7) Open the upper first control valve 400 again to allow supercritical carbon dioxide from the ground to enter the cavity and replenish the required pressure and volume. After filling, close the valve and the device enters the ready-to-explode state again. The process is the same as the first triggering process and 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 continuous operation of "injection-fracturing-re-injection-re-fracturing", and the single well operation efficiency is increased by 5 to 8 times.

[0104] (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 (phase change efficiency >95%) of the electric heating wire 800 in the trigger chamber and the sealing performance decay of the resettable trigger valve are analyzed.

[0105] (9) Clean up the site: After checking that the equipment is in good condition, shut it down and clean the ground; focus on checking the heat insulation coating on the inner wall of the trigger chamber and the wear of the resettable trigger valve, and replace it if necessary. Example

[0106] 1. Experimental Preparation

[0107] A low-permeability oil and gas well was selected as the experimental subject. This well has low formation permeability, and traditional hydraulic fracturing is ineffective, resulting in limited production increases. The target formation depth is 2500 meters, with a formation pressure of 35 MPa and a temperature of 85°C. A multi-chamber structure CO2 continuous phase change fracturing device was assembled in the laboratory. This 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.

[0108] 2. Equipment lowering and positioning

[0109] The device is lowered into the target well section and accurately positioned at the target formation to ensure that the fracturing energy can be effectively released.

[0110] 3. Supercritical carbon dioxide injection

[0111] Liquid carbon dioxide is injected into the main storage chamber 200 through a ground-based pipeline to achieve a pressure of 40 MPa.

[0112] 4. Triggering fracturing

[0113] 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 a high-energy shock wave, which fracturing the formation.

[0114] 5. Repeated triggering, multiple fracturing operations.

[0115] Repeat the triggering process, performing multiple fracturing operations with a 5-minute interval between each. After triggering, the residual pressure downhole and in the main storage chamber will gradually decrease and stabilize. Open the first control valve 400 again to allow surface liquid carbon dioxide to enter the chamber, replenishing the required pressure and volume. After filling, close the first control valve 400, and the device returns to the ready-to-fire state. Repeat the same process as the first triggering: open the second control valve 700 → initiate instantaneous phase change → perform another impact fracturing → close the second control valve 700 → pressure decrease → wait for the next attempt, until the predetermined fracturing scale or total energy is reached.

[0116] 6. Evaluation of fracturing effectiveness

[0117] Following fracturing, downhole sensor monitoring showed a 50% increase in formation permeability and a 30% increase in oil and gas production. Multiple fracture networks were successfully formed, effectively improving formation permeability. The carbon dioxide phase change process was precisely controlled, achieving a utilization rate of over 90%. Compared to traditional hydraulic fracturing, this method saved 80% of water resources and reduced operating costs by 20%. Example

[0118] 1. Experimental Preparation

[0119] A shale gas well was selected as the experimental target. The formation was dense, making it difficult to create effective fractures using traditional fracturing techniques. The target formation depth was 3000 meters, with a formation pressure of 40 MPa and a temperature of 95°C. A multi-chamber continuous phase change fracturing (CVF) device was assembled in the laboratory, including 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.

[0120] 2. Equipment lowering and positioning

[0121] The device is lowered into the target well section and accurately positioned at the target formation to ensure that the fracturing energy can be effectively released.

[0122] 3. Supercritical carbon dioxide injection

[0123] Liquid carbon dioxide is injected into the main storage chamber 200 through a ground-based pipeline to achieve a pressure of 50 MPa.

[0124] 4. Triggering fracturing

[0125] A trigger signal is sent to open the resettable trigger valve, allowing carbon dioxide to enter the trigger chamber. The heating wire instantly heats the carbon dioxide, causing it to undergo a rapid phase change and generate a high-energy shock wave, which fracturing the formation.

[0126] 5. Repeated triggering, multiple fracturing operations

[0127] The triggering process is repeated, performing multiple fracturing operations with 10-minute intervals between each. After triggering, the residual pressure downhole and in the main storage chamber gradually decreases and stabilizes. Subsequently, the first control valve 400 is reopened to replenish the chamber with surface liquid carbon dioxide until the required pressure and volume are reached. After filling, the first control valve 400 is closed, and the device re-enters the ready-to-fire state. The following steps are repeated: open the second control valve 700 → initiate instantaneous phase change → perform another impact fracturing → close the second control valve 700 → pressure decreases → wait for the next trigger, until the predetermined fracturing scale or total energy is reached.

[0128] 6. Evaluation of fracturing effect

[0129] Following fracturing, downhole sensor monitoring showed a 40% increase in shale gas production, successfully forming a complex fracture network and effectively improving shale gas yield. Some carbon dioxide was retained in the formation, achieving geological carbon dioxide sequestration and reducing greenhouse gas emissions. Compared to traditional fracturing techniques, this technology reduces water consumption by 90%, significantly lowering the risk of environmental pollution.

[0130] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. A multi-cavity carbon dioxide continuous phase change fracturing device, characterized in that, include: The filling cavity has a filling chamber inside; The 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. The trigger cavity has a trigger chamber inside. The lower end of the main storage cavity is connected to the trigger cavity, and the trigger chamber is connected to the main storage chamber. A first control valve is disposed on the communication channel between the filling chamber and the main storage chamber, and is used to control its opening / closing; The second control valve is located on the communication channel between the trigger chamber and the main storage chamber, and is used to control its opening / closing; An electric heating wire is disposed in the trigger chamber; The multi-cavity structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-cavity structure carbon dioxide continuous phase change fracturing device is precisely positioned at the target fracturing layer. The filling chamber is used to connect to the ground tubing to realize 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. Pressure and temperature sensors are installed in the main storage chamber to monitor the pressure and temperature of the liquid / supercritical carbon dioxide in the main storage chamber in real time. 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, main storage chamber, or 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. The trigger cavity has an inlet acceleration zone, a middle phase change zone, and an outlet diffusion zone in sequence along the direction from the main storage cavity to the direction away from the main storage cavity. The electric heating wire includes multiple independently controlled regional resistance wires, which are respectively arranged in the inlet acceleration zone, the middle phase change zone, and the outlet diffusion zone. The trigger cavity is equipped with a diffusion adjustment structure, which has a guide plate with an adjustable deflection angle. The deflection angle of the guide plate can be remotely adjusted according to the characteristics of the target formation. The angle adjustment range of the guide plate is 15°-60°. The trigger cavity is provided with a heat insulation structure or a heat dissipation structure. The heat insulation structure is made of multi-layer ceramic fiber material, and the heat dissipation structure is made of microchannel heat sink.

2. An experimental method for a multi-cavity carbon dioxide continuous phase change fracturing device as described in claim 1, characterized in that, include: Prepare for the experiment and set up the experimental site; The multi-cavity structure carbon dioxide continuous phase change fracturing device is lowered into the target well along with the tubing string, and the multi-cavity structure carbon dioxide continuous phase change fracturing device is precisely 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 using a pressure pump. The first control valve is opened while the second control valve remains closed. The liquid / supercritical carbon dioxide then enters the main storage chamber for safe storage through the filling chamber. When the set pressure value is detected in the main storage chamber, the filling of liquid / supercritical carbon dioxide is stopped, the first control valve is closed, and the second control valve remains closed. Upon receiving a ground trigger command, the second control valve is opened, allowing liquid / supercritical carbon dioxide to enter the trigger chamber from the main storage chamber. Under the instantaneous heating of the electric heating wire, a phase change occurs, resulting in carbon dioxide phase change fracturing.

3. The experimental method for the multi-cavity carbon dioxide continuous phase change fracturing device according to claim 2, characterized in that, include: After a carbon dioxide phase change fracturing experiment is completed, when the residual pressure in the main storage chamber is monitored to drop and stabilize, a new carbon dioxide phase change fracturing is performed. Repeat the process until the predetermined fracturing scale or total energy is reached, then end the experiment. Record the peak pressure, temperature, and trigger time data of carbon dioxide phase change fracturing blasting during the experiment, and transmit them back to the ground control terminal for analysis of crack formation or propagation.

4. The experimental method for the multi-cavity carbon dioxide continuous phase change fracturing device according to claim 3, characterized in that, Pressure and temperature sensors are installed in the target well to monitor the external well pressure and temperature of the multi-cavity carbon dioxide continuous phase change fracturing device. When the internal pressure and temperature of the multi-cavity carbon dioxide continuous phase change fracturing device, as well as the external well pressure and temperature, all meet the preset thresholds, a new round of carbon dioxide phase change fracturing is controlled to be executed.

5. The experimental method for the multi-cavity carbon dioxide continuous phase change fracturing device according to claim 2, characterized in that, During the carbon dioxide phase change fracturing process, intelligent monitoring and safety control are implemented, in conjunction with downhole sensors and multiple interlocking mechanisms, to ensure that each liquid / supercritical carbon dioxide filling and triggering is carried out within the control range; the multiple interlocking mechanisms include pressure interlocking, temperature interlocking, time interlocking and position interlocking.

6. The experimental method for the multi-cavity carbon dioxide continuous phase change fracturing device according to claim 2, characterized in that, Adjust 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.

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