Synchronous method, system and sealing device for coalbed methane displacement based on electric knock to increase penetration of co2

Abstract

The application provides a synchronous method and system for CO2 displacement of coal bed gas based on electric detonation penetration and a sealing device, realizes collaborative and synchronous operation of electric detonation penetration and CO2 displacement, greatly shortens an operation cycle, reduces engineering cost, makes a crack network formed by electric detonation penetration be immediately and efficiently utilized, avoids CO2 injection difficulty caused by crack closure, and significantly improves technical collaboration effect; meanwhile, synchronous injection of CO2 can enhance diffusion capacity by using a transient negative pressure area generated by electric detonation, solves the problems of low injection efficiency and small sweep range of CO2 in low-permeability coal seams, realizes double targets of coal bed gas production increase and CO2 geological storage, and has dual benefits of energy and environmental protection. The application highly integrates penetration, displacement and sealing, forms a complete solution, reduces field operation complexity, and has good engineering application prospect.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane development technology, specifically relating to a synchronous method, system and sealing device for CO2 displacement of coalbed methane based on electro-explosion vibration. Background Technology

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, has multiple strategic implications for increasing clean energy supply, ensuring safe coal mine production, and reducing greenhouse gas emissions through its efficient extraction. However, the typical characteristics of most coal seams in my country are "low permeability, low pressure, and low saturation," resulting in generally low CBM recovery rates and inefficient direct extraction, becoming a core bottleneck for the industry's development. To overcome this bottleneck, the industry has conducted extensive research on coal seam permeability enhancement and CBM displacement.

[0003] To improve coal seam permeability, the industry has mainly developed the following two types of permeability enhancement technologies:

[0004] Hydraulic fracturing technology: This is currently the most widely used method for improving permeability. Its principle is to inject high-pressure fluid to fracture coal and rock, forming a network of fractures. However, this method tends to form a single main fracture in hard or structurally complex coal seams, resulting in limited complexity of the fracture network and uneven permeability enhancement. Furthermore, it consumes a large amount of water, leading to water waste and potential formation contamination.

[0005] Blasting fracturing technology includes explosive blasting and high-energy pulse fracturing technologies such as electrohydraulic pulse and electro-detonation explored in recent years. Among them, high-intensity electro-detonation technology generates plasma channels through instantaneous electrode discharge, inducing strong shock waves and water hammer effects, which can produce a multi-directional and uniform micro-fracture network in coal and rock mass, and is theoretically more advantageous. However, this technology is still in the experimental stage and mainly has the following problems: (a) Insufficient energy controllability and safety, which may lead to wellbore damage or excessive development and penetration of fractures; (b) Usually used as a single permeability enhancement method, it has not formed an efficient and orderly synergistic system with subsequent gas displacement processes.

[0006] In terms of coalbed methane displacement to enhance oil recovery, CO2 (carbon dioxide) displacement of coalbed methane (CO2-ECBM) technology is considered a very promising approach. Since the adsorption capacity of CO2 in coal is usually 2-4 times that of CH4 (methane), CO2 injection can competitively replace adsorbed CH4, achieving the dual goals of increasing coalbed methane production and CO2 geological sequestration. However, the engineering application of this technology faces two major challenges: (1) Injection problem: Low-permeability coal seams make CO2 injection difficult, requiring extremely high injection pressure, and it is prone to fingering, resulting in low sweep efficiency; (2) Sealing and monitoring problem: Injected CO2 may escape along existing fractures or engineering fractures, requiring reliable sealing and isolation devices downhole to ensure the controllability of the displacement process and the safety of sequestration.

[0007] Currently, solutions for coal seam permeability enhancement and coalbed methane displacement are often fragmented. Permeability enhancement, injection displacement, and downhole sealing are typically performed using different equipment in stages, resulting in long operation cycles, high costs, and poor coordination between stages. In particular, there is a lack of an integrated downhole device capable of rapidly transitioning to controlled injection and sealing after high-voltage electro-detonation permeability enhancement. This prevents the fracture network created by permeability enhancement from being used promptly and efficiently in the CO2 displacement process, significantly reducing the synergistic effect of the technologies.

[0008] Therefore, there is an urgent need to develop a systematic solution that deeply integrates high-strength electric explosion permeability enhancement with CO2 displacement and storage technology, and is equipped with an efficient, reliable, and mobile integrated sealing device, in order to achieve safe, efficient, and green large-scale mining of coalbed methane. Summary of the Invention

[0009] To address the technical problems existing in the prior art, the first aspect of the present invention is to provide a synchronization method for CO2 displacement of coalbed methane based on electro-explosion vibration. The second aspect, based on the same inventive concept, also provides a sealing device for implementing the aforementioned synchronization method and synchronization system. The third aspect, based on the same inventive concept, also provides a synchronization system for implementing the aforementioned synchronization method for CO2 displacement of coalbed methane based on electro-explosion vibration.

[0010] In this embodiment of the invention, the method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability includes the following steps:

[0011] S1. Obtain the dynamic fracturing pressure, geostress profile, and coal and rock strength of the target coal seam;

[0012] S2. Based on the coal seam stress profile and coal-rock strength, determine the injection pressure window and set the CO2 injection pressure. Designed within the injection pressure window;

[0013] S3. Install the ground pulse power supply, downhole electric detonation tool, injection pump and monitoring sensor, conduct small-energy test explosion, and calculate the main detonation parameters after correcting the formation parameters based on the micro-vibration event monitoring data and pressure response curve generated by the test explosion. The downhole electric detonation tool is electrically connected to the ground pulse power supply through an integrated sealing device and is lowered to the target section of the coal seam along with the integrated sealing device.

[0014] S4. Start the ground pulse power supply and release electrical energy to the underground electric detonation tool through the cable in the integrated sealing device. This will generate a high-intensity shock wave in the underground water with a pressure peak exceeding the dynamic fracture pressure of the coal seam, forming a complex and interconnected three-dimensional fracture network in the coal seam.

[0015] During the dynamic lowering of the downhole electric detonation tool, an integrated sealing device ensures that the cable and the gas channel remain sealed.

[0016] S5. After a single or single-round electric detonation operation is completed, switch to injection mode within a preset time. The injection pump injects CO2 fluid of a preset phase into the three-dimensional fracture network through the air guide channel of the integrated sealing device.

[0017] S6. By adjusting the injection pump in real time, the CO2 injection pressure is increased. The injection pressure is controlled and stabilized within a preset window to prevent premature closure of the fractures. At the same time, the continuously injected CO2 diffuses along the newly formed fracture network and competes with the coalbed methane on the coal matrix surface for adsorption, thereby replacing and displacing methane.

[0018] S7. Through independent production wells or gas production channels in the same wellbore, coalbed methane displaced by CO2 is harvested, while downhole pressure and micro-vibration signals are monitored in real time.

[0019] The sealing device of this invention, used in the aforementioned synchronous method and system for CO2 displacement of coalbed methane based on electro-detonation, includes a shell body, a sealing component, a cable channel, a gas guiding channel, and an electro-detonation tool connection port located at the lower end of the shell body for connection with an underground electro-detonation tool. The shell body has an axially penetrating cavity. The cable channel and the gas guiding channel independently penetrate the sealing component and the shell body. The upper end of the gas guiding channel is connected to an injection pump for injecting displacement fluid. A cable connected to a surface pulse power supply is threaded through the cable channel and electrically connected to the underground electro-detonation tool. The sealing component is located within the cavity of the shell body to maintain long-term airtightness during the up-and-down movement of the underground electro-detonation tool.

[0020] The synchronization system of this invention is used to implement the above-described synchronization method for CO2 displacement of coalbed methane based on electro-explosion vibration. The synchronization system includes:

[0021] A high-intensity electric blast subsystem for generating and transmitting high-energy shock waves includes a ground pulse power supply, an underground electric blast tool, and an integrated sealing device for cable and gas guide as described in any one of claims 5-8. The underground electric blast tool can be lowered to the target section of the coal seam along with the integrated sealing device, and the integrated sealing device ensures that the cable and gas guide channel remain sealed during the dynamic lowering process.

[0022] The CO2 injection subsystem is used to deliver CO2 fluid of a preset phase to the permeable coal seam fracture network. It includes a CO2 storage tank, an injection pump and an injection pipeline. The output end of the injection pipeline is connected to the inlet of the gas guide channel. The CO2 storage tank is used to provide CO2 fluid of a preset phase and the injection pump is used to deliver the CO2 fluid of the preset phase to the gas guide channel through the injection pipeline.

[0023] The intelligent monitoring and feedback control subsystem includes pressure sensors and microseismic monitoring arrays deployed downhole, and a control host located on the surface. The control host has a built-in formation pressure and fracture network model, which is used to receive monitoring data, dynamically optimize electric blast parameters and injection parameters, and output control commands.

[0024] Compared with the prior art, the advantages of the superior technical solution of the present invention include:

[0025] 1. This invention achieves synergistic and simultaneous operation of electro-blast permeability enhancement and CO2 displacement, solving the problems of disconnect and poor synergy between existing permeability enhancement and CO2 displacement technologies. This significantly shortens the operation cycle and reduces engineering costs. By calibrating and correcting formation parameters through test blasts, and combining this with key threshold calculations (injection pressure window), precise matching of CO2 injection parameters is ensured. The fracture network formed by electro-blast permeability enhancement can be utilized instantly and efficiently, avoiding CO2 injection difficulties caused by fracture closure and significantly improving the synergistic effect of the technologies. At the same time, the synchronous injection of CO2 can utilize the instantaneous negative pressure zone generated by electro-blast to enhance diffusion capacity, solving the problems of low CO2 injection efficiency and small affected area in low-permeability coal seams. This achieves the dual goals of increasing coalbed methane production and geological CO2 sequestration, providing both energy and environmental benefits.

[0026] 2. This invention achieves high efficiency and controllability of CO2 displacement by controlling the CO2 injection phase, pressure window, and injection rhythm. By controlling the CO2 injection pressure between the fracture opening and closing pressures, the conductivity of the fracture is maintained while preventing CO2 escape due to excessive fracture expansion. This solves the problems of difficult-to-control injection pressure and fingering in existing CO2 displacement technologies. Dynamic adjustment of the injection rhythm, combined with the selection of optimal phases such as supercritical states, further improves CO2 utilization and CH4 replacement efficiency, while achieving efficient geological CO2 sequestration, meeting the development needs of green energy development and carbon emission reduction.

[0027] 3. This invention employs an integrated mobile sealing device combining a cable and a gas delivery pipe, enabling synchronous transmission of electrical energy and gas. This solves the problems of existing downhole devices being unable to simultaneously handle electrical energy transmission and gas delivery, and being prone to gas-electric interference and gas leakage, significantly improving the reliability and safety of the entire system. The integrated sealing device uses high-strength, high-pressure-resistant materials. The three-stage sealing structure and impact buffer structure of the sealing components work synergistically to effectively withstand the instantaneous impact of electric detonation and prevent CO2 leakage. The one-way isolation valve and pressure relief mechanism completely eliminate safety hazards such as back pressure transmission and pressure overload. In actual operation, the integrated sealing device carries the downhole electric detonation tool down with the oil rod to the target formation. Electrical pulse energy is provided to the downhole electric detonation tool via the cable, while the gas delivery channel delivers carbon dioxide gas downhole to accelerate the displacement of coalbed methane. The sealing components ensure that the device maintains long-term airtightness during the up-and-down movement of the downhole electric detonation tool, significantly improving the inherent safety and reliability of the entire operating system. Attached Figure Description

[0028] Figure 1 This is a flowchart of the synchronous method for CO2 displacement of coalbed methane based on electro-explosion vibration permeability enhancement in the embodiments.

[0029] Figure 2 This is a schematic diagram of the synchronous system for CO2 displacement of coalbed methane based on electro-explosion vibration in the embodiment.

[0030] Figure 3 This is a cross-sectional schematic diagram of the cable and air-conducting integrated sealing device in the embodiment.

[0031] The reference numerals in the accompanying drawings include: rectifier 1, pressure regulator 2, power controller 3, booster 4, remote discharge switch 5, cable 6, filter 7, needle valve 8, injection pump 9, silencer 10, second pressure gauge 11, high-pressure regulator 12, first pressure gauge 13, three-way valve 14, third pressure gauge 15, water tank 16, CO2 storage tank 17, wellhead connector 18, gas guide channel 20, insulating barrier layer 21, elastic damping layer 24, metal elastic element 25, primary low-friction sealing ring 26, tertiary elastomer auxiliary sealing ring 27, secondary metal bellows sealing ring 28, one-way isolation valve 29, guide ring 30, pressure relief hole 31, electrode rod 32, pressure sensor 33, outer shell 34, electric detonation tool connection port 35. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] Example 1

[0034] This embodiment provides a method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability, such as... Figure 1 As shown, in a preferred embodiment, it includes the following steps:

[0035] S1. Stratigraphy and Engineering Assessment: Obtaining stratigraphic parameters, specifically through well logging, seismic exploration, etc., to obtain the dynamic fracture pressure, geostress profile, and coal and rock strength of the target coal seam.

[0036] S2. Critical Threshold Calculation: Based on the coal seam stress profile and coal-rock strength, determine the injection pressure window and set the CO2 injection pressure... The design is within the injection pressure window. Specifically:

[0037] Determine the injection pressure window: Calculate the fracture opening pressure With crack closure pressure , respectively serving as the upper and lower limits of the injection pressure window;

[0038]

[0039]

[0040] in, The minimum horizontal principal stress (MPa) in the fracture region; The dynamic tensile strength of coal and rock (MPa); This is the fracture closure pressure (MPa), the pressure at which a fracture recloses due to a decrease in external pressure. It is typically lower than the opening pressure and approximately equal to the minimum horizontal principal stress. ;

[0041] Injecting CO2 pressure The pressure is set within the injection pressure window to maintain the fracture conductivity.

[0042]

[0043] in, The CO2 injection pressure (MPa) is the actual pressure applied to the fracture to ensure that the fracture remains open.

[0044] S3. Test and Calibration: Install the ground pulse power supply, downhole electric detonation tool, injection pump and monitoring sensors, conduct a small-energy test explosion, and calculate the main detonation parameters after correcting the formation parameters based on the micro-vibration event monitoring data and pressure response curve generated by the test explosion. The downhole electric detonation tool is electrically connected to the ground pulse power supply through an integrated sealing device and is lowered to the target section of the coal seam together with the integrated sealing device.

[0045] The specific process of conducting low-energy test blasts and calculating main detonation parameters based on monitoring data is as follows: Low-energy test blasts are conducted in the target layer, performing one or several low-yield (e.g., 10%-30% of the design energy) electro-detonation operations. Based on the monitoring data of microseismic events generated by the test blasts (e.g., number of events, energy, distribution) and pressure response curves, key features including fracture radius and wave velocity attenuation signals are extracted. A geological model is constructed based on the original geological parameters, and parameters are continuously adjusted to ensure the simulation results match the measured data. Rock mechanics parameters are calibrated based on the adjusted parameters. Forward modeling is performed based on the calibrated parameters to simulate suitable electro-detonation parameters. The actual energy response coefficient η and fracture pressure gradient of the formation are inverted and corrected to optimize the main detonation operation plan. The required capacitor energy storage E, discharge voltage V, number of pulses N, and action time t for the main detonation operation are calculated, and the arrangement position and discharge spacing of the discharge electrodes of the downhole electro-detonation tool are confirmed.

[0046] S4. High-Intensity Electro-Explosion Vibration Enhancement: The surface pulse power supply is activated, releasing electrical energy to the underground electro-explosion tool via a cable within the integrated sealed device. This generates a high-intensity shock wave in the underground water, with a peak pressure exceeding the dynamic fracturing pressure of the coal seam, forming a complex and interconnected three-dimensional fracture network within the coal seam. Since there is water underground, the electro-explosion tool is lowered into the water. Using liquid as a medium, and because water has extremely low compressibility, when electrical energy is released in the liquid, it can efficiently convert electrical energy into powerful shock wave mechanical energy.

[0047] The high-intensity shock wave is generated by using a capacitor energy storage device to complete a high-voltage discharge within milliseconds to microseconds, forming a plasma channel between the downhole discharge electrodes to excite the water hammer effect and generate a high-intensity shock wave with a pressure peak range of 50-150 MPa and a pulse width of 10⁻⁻⁴ MPa. 7 Up to 10⁻ 5 Second.

[0048] During the dynamic lowering of the downhole electric detonation tool, an integrated sealing device ensures that the cable and the gas channel remain sealed.

[0049] S5, CO2 Synchronous Switching Injection: After a single or single-round electric detonation operation, the system switches to CO2 injection mode within a preset time (10 seconds). The injection pump injects CO2 fluid of a preset phase into the three-dimensional fracture network through the air guide channel of the integrated sealing device. The CO2 injection pressure... It is controlled within a range that is higher than the pore pressure of the coal seam but lower than the fracture closure pressure.

[0050] The CO2 fluid is in a supercritical state, the CO2 injection pressure is 8-25 MPa, and the interval between the injection process and the electric detonation operation is no more than 10 seconds, so as to utilize the instantaneous negative pressure zone generated by the shock wave to enhance the CO2 absorption and diffusion capabilities.

[0051] S6. Injection Maintenance and Displacement Maintenance Pressure: The CO2 injection pressure is maintained through real-time adjustment of the injection pump. The injection pressure is controlled and stabilized within a preset window to prevent premature closure of the fractures. Meanwhile, under the influence of concentration gradient and pressure, the continuously injected CO2 diffuses along the newly formed fracture network and competes with the coalbed methane (methane) on the coal matrix surface for adsorption, thereby replacing and displacing the methane (CH4) with CO2.

[0052] S7. Coalbed methane extraction and monitoring: Coalbed methane displaced by CO2 is extracted through independent production wells or gas extraction channels in the same wellbore, while downhole pressure and micro-vibration signals are monitored in real time.

[0053] The core of the synchronization method of this invention lies in the closed-loop synergy between high-intensity electro-detonation three-dimensional anti-reflection (three-dimensional strong anti-reflection) and CO2 synchronous displacement and replacement.

[0054] High-intensity electro-explosion three-dimensional permeability enhancement: In the target coal seam section, a high-intensity shock wave is excited by high-power pulse discharge, which causes shear, tensile and fatigue damage to the coal and rock mass, forming a complex and interconnected network fracture system.

[0055] CO2 synchronous displacement and replacement: CO2 fluid (liquid, supercritical, or miscible) is injected into the permeable fracture network through the same wellbore with almost zero delay after electro-detonation operation. Utilizing the instantaneous negative pressure zone and expanded fracture space generated by the electro-detonation shock wave, CO2 is rapidly absorbed and diffused, competitively replacing CH4 adsorbed on the coal matrix surface.

[0056] Example 2

[0057] This embodiment provides an integrated sealing device for both the cable and the gas guide (hereinafter referred to as the integrated sealing device), installed inside the wellbore, for implementing the synchronization method of Embodiment 1. Figure 2 and Figure 3 As shown, the integrated sealing device includes a housing body 34, a sealing assembly, a cable channel, a gas guide channel 20, and an electro-detonation tool connection port 35. The upper end of the housing body 34 is equipped with a wellhead connector 18 (using a flange connection, nominal pressure 30MPa) for connection to the wellhead or casing; the lower end of the housing body 34 has an electro-detonation tool connection port 35, which uses a threaded connection for connecting a downhole electro-detonation tool (composed of multiple discharge electrodes connected in series). The housing body 34 is made of high-strength, high-pressure resistant alloy material (such as 316L stainless steel), and has an overall cylindrical structure with an outer diameter adapted to the inner diameter of the downhole wellbore. Its length is 800-1200mm, ensuring stable operation of the integrated sealing device under complex downhole pressure environments (0-50MPa).

[0058] The outer casing 34 has an axially extending cavity for accommodating the internal sealing components, cable channels, and air ducts 20. The inner wall of the cavity is coated with a wear-resistant coating (such as a polytetrafluoroethylene coating) with a thickness of 0.5-1mm to reduce frictional wear between the sealing components and the inner wall of the cavity.

[0059] The cable channel and the gas guide channel 20 independently pass through the sealing assembly and the outer casing 34. The upper end of the gas guide channel 20 is connected to the injection pump 9 for injecting displacement fluid. The cable 6, connected to the surface pulse power supply, runs through the cable channel and is electrically connected to the downhole electro-detonation tool. The cable 6 runs through the cable channel axially along the integrated sealing device and is used to transmit high-energy electrical pulse signals to the downhole electro-detonation tool. The gas guide channel 20 is arranged parallel to the cable 6 and is used to deliver carbon dioxide fluid from the CO2 storage tank 17 or water from the water tank 16 to the downhole. The integrated sealing device, carrying the downhole electro-detonation tool, can be lowered or raised in the wellbore along with the downhole tool (such as oil rod). The wellbore opening is sealed by a sealing plug. During axial movement, the integrated sealing device maintains a stable seal to prevent [damage / loss].

[0060] In this invention, the cable channel is located at the center of the outer casing 34, and the gas guide channel 20 is a concentric annular channel surrounding the cable channel. An insulating barrier layer 21 is provided between the cable channel and the gas guide channel 20. The insulating barrier layer 21 is made of epoxy resin with a thickness of 5-8 mm and an insulation resistance ≥100 MΩ, achieving physical isolation and electrical insulation between the cable channel and the gas guide channel 20. This prevents CO2 fluid leakage into the cable channel from causing gas-electric interference and avoids the safety hazards caused by static electricity accumulation. This concentric dual-channel structure achieves integrated arrangement of power transmission and gas delivery within the limited wellbore space, while ensuring safe isolation between the two under electric blasting operation conditions.

[0061] The sealing assembly is housed within the cavity of the outer casing 34 to maintain long-term airtightness during the up-and-down movement of the downhole electro-detonation tool. Specifically, the sealing assembly includes, sequentially arranged axially, a primary low-friction sealing ring 26 to reduce movement resistance, a secondary metal bellows sealing ring 28 to absorb axial displacement and withstand transient pressure impacts from electro-detonation, and a tertiary elastomer auxiliary sealing ring 27 to compensate for micro-deformation and provide a static seal. The primary low-friction sealing ring 26 is made of PTFE to reduce frictional resistance during the axial movement of the integrated sealing device, ensuring smooth movement; the secondary metal bellows sealing ring 28 is made of stainless steel to withstand higher pressures and absorb transient axial impacts from electro-detonation; and the tertiary elastomer auxiliary sealing ring 27 is made of fluororubber with an annular groove on its sealing surface to enhance the sealing effect, compensate for minor displacements and machining tolerances, and further improve overall airtightness.

[0062] In another preferred embodiment of the present invention, an impact buffer structure is provided on the outer side of the sealing assembly for absorbing and attenuating the microsecond-level high-voltage shock wave generated by the electric detonation. The impact buffer structure includes a metallic elastic element 25 and a high-modulus elastic damping layer 24 surrounding the metallic elastic element 25. The metallic elastic element 25 undergoes elastic deformation under transient impact to absorb energy, and the elastic damping layer 24 is used to attenuate the high-frequency shock wave and reduce the damage to the sealing assembly caused by the impact. The metallic elastic element is made of spring steel and is arranged in a ring array (6-8 elements), with an elastic modulus of 200-210 GPa. The elastic damping layer is made of polyurethane, which can effectively attenuate the peak pressure of the electric detonation shock wave and prevent the sealing assembly from being damaged by the transient impact.

[0063] Preferably, a one-way isolation valve 29 is installed in the gas guide channel 20. The one-way isolation valve 29 adopts a ball valve structure, with a nominal pressure of 30-50MPa, an opening pressure of 0.1-0.2MPa, and a closing response time of ≤10ms, to ensure that the high pressure back pressure generated by the electric detonation cannot flow back to the injection pipeline.

[0064] More preferably, a pressure relief mechanism for depressurization is also provided at a predetermined position in the air guide channel 20. This mechanism is an overpressure directional pressure relief plate (a pressure relief safety valve mechanism with a burst pressure of 25-30 MPa) located in the pressure relief hole 31 on the wall of the air guide channel 20. When the internal pressure exceeds a set threshold, it preferentially fails, achieving directional pressure relief through the overpressure directional pressure relief plate, thereby improving the overall safety of the system. Alternatively, a sacrificial sealing section made of a pressure-resistant material can be provided on the wall of the air guide channel 20. This sacrificial sealing section is made of aluminum alloy with a thickness of 3-5 mm and a burst pressure of 28-32 MPa, allowing for rapid pressure relief during pressure overload, ensuring the safety of the device.

[0065] More preferably, a guide ring 30 (made of brass, 8-10mm thick) is also provided inside the housing body 34 to resist impact loads, reduce friction, ensure that the sealing assembly moves linearly along the axial direction inside the housing body 34, maintain high coaxiality with the housing body 34, and ensure that the sealing assembly operates smoothly and accurately inside the housing body 34.

[0066] Example 3

[0067] This embodiment provides a CO2 displacement coalbed methane synchronization system based on high-intensity electric blast permeability enhancement (hereinafter referred to as the synchronization system). This synchronization system is a dedicated supporting system for implementing the CO2 displacement coalbed methane synchronization method based on high-intensity electric blast permeability enhancement in Embodiment 1. It can realize the integrated and coordinated operation of electric blast permeability enhancement, CO2 displacement injection and intelligent control of the operation process.

[0068] like Figure 2As shown, the synchronization system includes a high-intensity electric detonation subsystem, a CO2 injection subsystem, and an intelligent monitoring and feedback control subsystem.

[0069] The high-strength electric blast subsystem, as the core unit for the generation and transmission of high-energy shock waves, is used to output high-energy shock waves to the target coal seam section to meet the permeability enhancement requirements. Specifically, it includes a ground pulse power supply, an underground electric blast tool, and the cable and gas-conducting integrated sealing device of the aforementioned embodiment 2. The underground electric blast tool can be synchronously lowered to the target coal seam section through the integrated sealing device. Relying on the dynamic moving seal of the integrated sealing device, it ensures that the cable 6 and the gas-conducting channel 20 always maintain reliable airtightness and electrical isolation under the complex working conditions of the underground tool's axial dynamic lowering and retrieval and the transient impact of electric blast. The ground pulse power supply includes a rectifier 1, a voltage regulator 2, a power controller 3, a booster 4, and a remote discharge switch 5. The matching cable 6 is a high-voltage cable. The input end of the cable 6 is electrically connected to the output end of the ground pulse power supply. The cable 6 is axially threaded through the central cable channel of the integrated sealing device and connected to the downhole electric detonation tool. The downhole electric detonation tool is equipped with multiple series-connected discharge electrodes, which can convert electrical energy into shock wave energy. During operation, the power controller 3 and the voltage regulator 2 work together to achieve precise fine-tuning of the electric detonation discharge energy and discharge frequency. The remote discharge switch 5 is used to achieve remote and precise control of the current on and off during electric detonation operations.

[0070] The CO2 injection subsystem is used to stably deliver CO2 fluid of a preset phase to the enhanced coal seam fracture network. Specifically, it includes a CO2 storage tank, an injection pump 9, and an injection pipeline. The output end of the injection pipeline is sealed and connected to the inlet of the gas guide channel 20. The CO2 storage tank stores and provides CO2 fluid of a preset phase, such as supercritical CO2. The injection pump 9 pressurizes the CO2 fluid, ensuring it is stably delivered to the gas guide channel 20 through the injection pipeline at a preset pressure. The CO2 storage tank has a built-in pressure reducing valve, and its outlet is connected to the injection pipeline. Along the fluid delivery direction, the injection pipeline is sequentially connected with a first pressure gauge 13, a high-pressure regulating valve 12, a second pressure gauge 11, the injection pump 9, a needle valve 8, and a filter 7. The injection pump 9 is equipped with a silencer 10 to effectively reduce noise pollution during operation, thus improving the system's multifunctionality and operational adaptability. Preferably, a water tank 16 is also provided in parallel with the CO2 storage tank. The water tank 16 is also equipped with a pressure reducing valve. Its outlet is connected to the injection pipeline through a branch pipeline, which can inject water medium into the wellbore according to the actual needs of downhole operations. A third pressure gauge 15 and a three-way valve 14 are arranged in sequence along the fluid delivery direction on the branch pipeline. The three-way valve 14 can also be connected to other fluid sources to realize flexible injection and switching of multiple media.

[0071] The intelligent monitoring and feedback control subsystem, as the control core of the entire synchronization system, serves as the "brain" of the system, enabling real-time monitoring, data analysis, and dynamic parameter optimization during operations. Specifically, it includes a pressure sensor 33 deployed underground, a microseismic monitoring array, and a control host located on the surface. The pressure sensor 33 is integrated into the housing 34 of the integrated sealing device, accurately collecting real-time underground pressure data. The microseismic monitoring array is conventionally installed around the target coal seam to collect microseismic signals related to coal seam fracture development. The surface control host uses a PLC controller with a pre-built formation pressure and fracture network model. It receives real-time underground monitoring data from the pressure sensor 33 and the microseismic monitoring array, and performs rapid analysis and processing of the data based on the built-in model. This dynamically optimizes the electric blast parameters and CO2 injection parameters, while simultaneously outputting precise control commands to the high-intensity electric blast subsystem and the CO2 injection subsystem, achieving coordinated operation and closed-loop intelligent control of the entire process.

[0072] Example 4

[0073] This embodiment uses a deep, low-permeability coalbed methane well as an example to illustrate the closed-loop collaborative operation of "electro-explosion-CO2 injection".

[0074] 1) Well condition and basic parameter acquisition (formation assessment and design)

[0075] A coalbed methane well in a certain mining area was selected as the subject of the study. The well depth is approximately 1100 m, the target coal seam thickness is approximately 5.5 m, and the original permeability is 0.05–0.2 mD. Key parameters, including coal seam pore pressure (formation pressure), were obtained through well logging interpretation, laboratory coal sample mechanical tests, and small-scale fracturing / leakage tests. Stable pressure during well operations (bottom hole control pressure) Minimum horizontal principal stress in the fractured region (key parameter controlling fracture closure pressure) Dynamic tensile strength of coal and rock (under dynamic load conditions) .

[0076] Based on the above parameters, the minimum opening pressure window required by the shock wave to correspond to the dynamic fracturing threshold of the coal seam is determined. (Fracturing opening pressure) It can be estimated using the following formula:

[0077] ;

[0078] Therefore, the minimum effective overpressure of this well is calculated as follows:

[0079] .

[0080] To form a complex, interconnected network of fracture systems (three-dimensional enhanced permeability), an impact margin factor M = 4 is used in the engineering process to obtain the target overpressure:

[0081] ;

[0082] Therefore, the target shock wave peak pressure at the bottom of the well is:

[0083] .

[0084] To convert the "target overpressure" into "electric shock discharge energy", an energy-pressure calibration relationship is established through downhole test explosions. First, a downhole calibration (test explosion) is performed, and the peak value of the impact overpressure is recorded using a pressure sensor.

[0085] Setting the test explosion energy: The corresponding overpressure was measured:

[0086] Establish commonly used energy-pressure calibration relationships in engineering. It is the calibration coefficient:

[0087]

[0088] Based on this calculation, the target overpressure is achieved. Required energy per burst:

[0089]

[0090] Therefore, the energy of a single electric detonation discharge is determined to be 60–70 kJ / discharge.

[0091] The discharge energy and frequency are finely adjusted by the power controller 3 and the voltage regulator 2 to stabilize the shock wave pressure at the dynamic fracturing threshold of the coal seam. In terms of specific power supply implementation, the energy for a single event can be achieved through capacitor energy storage.

[0092]

[0093] For example, setting the charging voltage Take capacitor This allows for a single discharge energy of approximately 65 kJ.

[0094] This embodiment employs a "three-dimensional arrangement + cyclic loading" method for implementing electric blasting in the target coal seam section. The three-dimensional arrangement consists of three layers: upper, middle, and lower (arranged along the coal seam thickness direction).

[0095]

[0096] The initial number of detonations per floor was set to 5, and the number of additional detonations was determined based on monitoring feedback. The final number of detonations per floor was:

[0097]

[0098] Total number of detonation events: By finely adjusting the discharge energy and frequency through the power controller 3 and the voltage regulating device 2, the peak pressure at the bottom of the shock wave is kept stable at 58MPa, which triggers high-intensity shock waves to cause shear, tensile and fatigue damage to the coal and rock mass, forming a complex and interconnected network fracture system.

[0099] 2) High-intensity electro-explosion vibration three-dimensional anti-reflection operation

[0100] In practice, the integrated sealing device is lowered to the target fracture zone along with the oil rod. The upper end of the device is connected to the wellhead or casing, and the lower end is connected to the downhole electric detonation tool. The electric detonation operation is carried out according to the preset three-dimensional layout scheme using the high-power ground pulse power supply of the high-strength electric detonation subsystem and the downhole electric detonation tool (multiple high-strength discharge electrodes set in series). The device uses capacitor energy storage (charging voltage V=12KV, capacitor C≈0.9mF, achieving approximately 65kJ of single discharge energy).

[0101] The electric detonation operation adopted a cyclic loading method, and a total of 21 detonations (N) were carried out at 3 detonation layers. total =N pos ×N each =3×7=21 times), by finely adjusting the discharge energy and frequency through the power controller 3 and the voltage regulating device 2, the peak pressure at the bottom of the shock wave is kept stable at 58MPa, which triggers high-intensity shock waves to cause shear, tensile and fatigue damage to the coal and rock mass, forming a complex and interconnected network fracture system.

[0102] During this process, the impact buffer structure (metal elastic element and elastic damping layer) of the integrated sealing device absorbs and attenuates the microsecond-level high-pressure shock wave generated by the electric detonation, protecting the seal from damage; the sealing components (first-level low-friction sealing ring, second-level metal bellows sealing ring, and third-level elastomer auxiliary sealing ring) maintain stable airtightness during the axial micro-movement of the device.

[0103] 3) Simultaneous CO2 displacement and replacement

[0104] To achieve "synchronous and efficient drive", the switching time between electric detonation and CO2 injection is controlled within 5-10 seconds after each electric detonation operation. Through the CO2 injection and fluid management subsystem, CO2 of a preset phase is injected into the permeable fracture network through the gas guide channel of the integrated sealing device. In this embodiment, supercritical CO2 is selected, and the phase and injection pressure meet the range of 8-25 MPa.

[0105] Meanwhile, to prevent premature fracture closure, the injection pressure should be controlled within a window that is "higher than the fracture closure pressure and lower than the fracture opening pressure." Therefore, the injection pressure for this well is set as follows: ,satisfy: .

[0106] The instantaneous negative pressure zone and expanded fracture space generated by electric detonation promote the rapid absorption and diffusion of CO2, competitively displacing CH4 adsorbed on the coal matrix surface. During injection, the injection pressure is monitored in real time by a first and second pressure gauge, and the downhole pressure is monitored by a pressure sensor. The injection duration (1-3 minutes each time) is adjusted based on the monitoring data. A one-way isolation valve in the gas guide channel prevents the back pressure generated by electric detonation from being transmitted back to the wellhead. The pressure relief hole at the preset position fails preferentially when the internal pressure exceeds the set threshold, achieving directional pressure relief and ensuring operational safety. An insulating barrier layer provides electrical isolation between the cable channel and the gas guide channel, avoiding the potential danger of gas-electric coupling.

[0107] 4) Intelligent Looping and Optimization

[0108] In another preferred embodiment, an intelligent monitoring and feedback control subsystem can be used to collect pressure data from downhole pressure sensors, microseismic signals, and CO2 injection parameters in real time. Based on formation pressure and mechanical models, the operational effectiveness can be analyzed in real time. If insufficient fracture development is detected, the single energy of the electric detonation or the number of detonations in a single layer can be appropriately increased. If abnormal CO2 injection pressure is detected, the high-pressure regulating valve can be adjusted to ensure that the injection pressure is maintained within a preset window. If abnormal microseismic signals are detected, operations can be suspended, safety hazards can be investigated, and the timing of the cycle can be adjusted.

[0109] Through the above intelligent adjustments, the parameters of the next round of "electric blasting-CO2 injection" cycle are optimized, ensuring that the entire operation process dynamically adapts to the formation conditions, continuously improving the permeability enhancement effect and CO2 displacement efficiency, and ultimately achieving the synergistic goal of efficient coalbed methane extraction and CO2 geological storage.

[0110] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability, characterized in that, Includes the following steps: S1. Obtain the dynamic fracturing pressure, geostress profile, and coal and rock strength of the target coal seam; S2. Based on the coal seam stress profile and coal-rock strength, determine the injection pressure window and set the CO2 injection pressure. Designed within the injection pressure window; S3. Install the ground pulse power supply, downhole electric detonation tool, injection pump and monitoring sensor, conduct small-energy test explosion, and calculate the main detonation parameters after correcting the formation parameters based on the micro-vibration event monitoring data and pressure response curve generated by the test explosion. The downhole electric detonation tool is electrically connected to the ground pulse power supply through an integrated sealing device and is lowered to the target section of the coal seam along with the integrated sealing device. S4. Start the ground pulse power supply and release electrical energy to the underground electric detonation tool through the cable in the integrated sealing device. This will generate a high-intensity shock wave in the underground water with a pressure peak exceeding the dynamic fracture pressure of the coal seam, forming a complex and interconnected three-dimensional fracture network in the coal seam. During the dynamic lowering of the downhole electric detonation tool, the integrated sealing device ensures that the cable and the gas guide channel remain sealed. S5. After a single or single-round electric detonation operation is completed, switch to CO2 injection mode within a preset time. The injection pump injects CO2 fluid of a preset phase into the three-dimensional fracture network through the air guide channel of the integrated sealing device. S6. By adjusting the injection pump in real time, the CO2 injection pressure is increased. The injection pressure is controlled and stabilized within a preset window to prevent premature closure of the fractures. At the same time, the continuously injected CO2 diffuses along the newly formed fracture network and competes with the coalbed methane on the coal matrix surface for adsorption, thereby replacing and displacing methane. S7. Through independent production wells or gas production channels in the same wellbore, coalbed methane displaced by CO2 is harvested, while downhole pressure and micro-vibration signals are monitored in real time.

2. The method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability as described in claim 1, characterized in that, In step S2, the specific method for determining the injection pressure window based on the coal seam stress profile and coal-rock strength is as follows: Calculate the fracture opening pressure With crack closure pressure , respectively serving as the upper and lower limits of the injection pressure window; in, This represents the minimum horizontal principal stress in the fracture region; The dynamic tensile strength of coal and rock; The crack closure pressure is the pressure at which a crack closes again due to a decrease in external pressure. Injecting CO2 pressure Set within the injection pressure window: in, The CO2 injection pressure is the actual pressure applied to the fracture to ensure that the fracture remains open.

3. The method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability according to claim 1, characterized in that, In step S3, a small-energy test explosion is conducted. Based on the monitoring data of the microseismic events and the pressure response curve generated by the test explosion, the formation parameters are corrected, and the main blast parameters are calculated. The specific process is as follows: Small-energy test blasts are conducted in the target formation, performing one or more low-yield electro-blast operations. Based on the microseismic event monitoring data and pressure response curves generated by the test blasts, key features including fracture radius and wave velocity attenuation signals are extracted. A geological model is constructed based on the original geological parameters, and the parameters are continuously adjusted to ensure that the simulation results match the measured data. The rock mechanics parameters are calibrated based on the adjusted parameters, and forward modeling is performed based on the calibrated parameters to simulate suitable electro-blast parameters. The actual energy response coefficient η and fracture pressure gradient of the formation are inverted and corrected to optimize the main blast scheme. The capacitor energy storage E, discharge voltage V, number of pulses N, and action time t required for the main blast operation are calculated, and the arrangement position and discharge spacing of the discharge electrodes of the downhole electro-blast tool are confirmed.

4. The method for simultaneous CO2 displacement of coalbed methane based on electro-explosion vibration-enhanced permeability according to claim 1, characterized in that, In step S4, the high-intensity shock wave is generated as follows: a high-voltage discharge is completed within milliseconds to microseconds using a capacitor energy storage device, forming a plasma channel between the downhole discharge electrodes to excite the water hammer effect and generate the high-intensity shock wave, with a pressure peak range of 50-150 MPa and a pulse width of 10⁻⁻⁶. 7 Up to 10⁻ 5 Second; In step S5, the CO2 fluid is in a supercritical state, the CO2 injection pressure is 8-25 MPa, and the interval between the injection process and the electric detonation operation is no more than 10 seconds, so as to utilize the instantaneous negative pressure zone generated by the shock wave to enhance the CO2 absorption and diffusion capabilities.

5. A cable and air-conducting integrated sealing device for implementing the synchronization method according to any one of claims 1-4, characterized in that, The integrated sealing device includes a housing body, a sealing component, a cable channel, a gas guide channel, and an electric detonation tool connection port located at the lower end of the housing body for connecting with a downhole electric detonation tool. The outer shell body has a through cavity in the axial direction; The cable channel and the air guide channel independently pass through the sealing assembly and the outer shell body. The upper end of the air guide channel is connected to the injection pump for injecting displacement fluid. The cable connected to the ground pulse power supply is run through the cable channel and electrically connected to the downhole electric detonation tool. The sealing assembly is disposed within the cavity of the outer shell body and is used to maintain the long-term airtightness of the downhole electric detonation tool during its up-and-down movement.

6. The cable and air-conducting integrated sealing device according to claim 5, characterized in that, The air duct is a concentric annular channel surrounding the cable channel, with an insulating barrier layer between them.

7. The cable and air-conducting integrated sealing device according to claim 5, characterized in that, The sealing assembly includes a primary low-friction sealing ring arranged sequentially along the axial direction to reduce movement resistance, a secondary metal bellows sealing ring to absorb axial displacement and withstand transient pressure impacts from electric shock, and a tertiary elastomer auxiliary sealing ring to compensate for micro-deformation and provide static sealing.

8. The cable and air-conducting integrated sealing device according to claim 5, characterized in that, The outer side of the sealing assembly is provided with an impact buffer structure for absorbing and attenuating the microsecond-level high-voltage shock wave generated by the electric detonation. The impact buffer structure includes a metal elastic element for elastic deformation under transient impact to absorb energy, and an elastic damping layer surrounding the metal elastic element for attenuating the energy of the high-frequency shock wave.

9. The cable and air-conducting integrated sealing device according to claim 5, characterized in that, The gas guiding channel is equipped with a one-way isolation valve to prevent the reverse flow of high-pressure fluid downhole; And / or the pipe wall of the air guide channel is also provided with a pressure relief mechanism for pressure relief, the pressure relief mechanism being an overpressure directional pressure relief plate provided in a pressure relief hole in the pipe wall of the air guide channel, or a sacrificial sealing section made of a material that can be broken by pressure provided on the pipe wall of the air guide channel.

10. A CO2 displacement coalbed methane synchronization system based on high-intensity electro-explosion permeability enhancement, used to implement the synchronization method according to any one of claims 1-4, characterized in that, The synchronization system includes: A high-intensity electric blast subsystem for generating and transmitting high-energy shock waves includes a ground pulse power supply, an underground electric blast tool, and an integrated sealing device for cable and gas guide as described in any one of claims 5-8. The underground electric blast tool can be lowered to the target section of the coal seam along with the integrated sealing device, and the integrated sealing device ensures that the cable and gas guide channel remain sealed during the dynamic lowering process. A CO2 injection subsystem is used to deliver CO2 fluid of a preset phase to the permeable coal seam fracture network. It includes a CO2 storage tank, an injection pump and an injection pipeline. The output end of the injection pipeline is connected to the inlet of the gas guiding channel. The CO2 storage tank is used to provide CO2 fluid of a preset phase and the injection pump is used to deliver the CO2 fluid of the preset phase to the gas guiding channel through the injection pipeline. The intelligent monitoring and feedback control subsystem includes pressure sensors and microseismic monitoring arrays deployed downhole, and a control host located on the surface. The control host has a built-in formation pressure and fracture network model, which is used to receive monitoring data, dynamically optimize electric blast parameters and injection parameters, and output control commands.

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