A multi-physical field coupling-based active gas induced extraction device and method

Abstract

The application discloses a kind of active gas induced extraction device and method based on multi-physical field coupling, belong to coal mine gas control technical field. For the problem of extraction efficiency attenuation caused by water lock effect, fracture closure and coal mass creep of horizontal well after hydraulic fracturing, the application adopts the time sequence coordination scheme of "ultrasonic dredging and thermal disturbance displacement": the composite generator integrated with ultrasonic active transducer and phase change energy storage temperature control module is lowered into failed horizontal well, first, the liquid lock blockage and microfracture are dredged through the mechanical vibration and cavitation effect of ultrasonic wave; then, the periodic cold and hot disturbance is applied by the solid-liquid phase change cycle of phase change material, and the adsorbed gas is actively driven to desorb and migrate. The application does not need to inject high-pressure fluid again, can effectively activate the failed fractured horizontal well, prolong the service life of horizontal well, improve the recovery rate of residual gas resources, and has the advantages of clean and efficient, no secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas control and coalbed methane production enhancement technology, specifically involving an active gas-induced extraction device and method based on multi-physics field coupling, which is applicable to secondary permeability enhancement and enhanced extraction operations of failed fracturing horizontal wells in deep high-gas and low-permeability coal seams. Background Technology

[0002] As my country's shallow coal resources are gradually depleted and coal mining depths continue to increase, deep coal seams generally exhibit characteristics of high gas pressure, high gas content, and low permeability, significantly increasing the risk of gas disasters and the difficulty of control. Currently, horizontal well segmented hydraulic fracturing technology is the mainstream technique for enhancing permeability and strengthening gas extraction in deep, low-permeability coal seams, and it has achieved certain results in field applications.

[0003] However, engineering practice shows that, affected by multiple factors, a large number of fractured horizontal wells generally experience a significant decline in extraction efficiency 1-2 years after commissioning: First, the retention of fracturing fluid creates a water-locking effect, blocking the pores and microfractures in the coal seam; second, under the action of geostress, the fractures undergo creep closure, and the seepage channels continue to shrink; third, the migration of solid particles such as coal dust blocks the pore throat, further reducing the permeability of the coal seam. Conventional remedial measures, such as secondary hydraulic fracturing and acidizing to remove blockages, have drawbacks such as high construction costs, complex procedures, easy exacerbation of water-locking damage, and progressively decreasing effectiveness. Moreover, chemical agents can easily cause secondary pollution of the groundwater environment.

[0004] In recent years, ultrasonic permeability enhancement technology has been gradually applied to the field of coalbed methane production enhancement. Utilizing the mechanical vibration and cavitation effect of ultrasound, it can effectively unclog seepage channels and expand microfractures. However, ultrasonic action alone can only improve pore connectivity and cannot continuously disrupt the gas adsorption equilibrium, resulting in limited displacement of adsorbed gas and insufficient sustainability of improved extraction efficiency. Thermally stimulated desorption technology can reduce gas adsorption by increasing temperature, but existing methods such as hot fluid injection and electric heating easily introduce external fluids, posing risks of secondary water lock and mineral expansion. Furthermore, the desorption driving force of continuous constant-temperature heating gradually weakens over time, leading to poor long-term effects.

[0005] Therefore, for horizontal wells that have failed due to fracturing, there is an urgent need to develop an active enhanced extraction technology that does not require secondary injection, is clean and efficient, and can simultaneously achieve channel unblocking and adsorption displacement, in order to solve the problems of rapid decline in extraction efficiency and high remediation costs of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an active gas-induced extraction device and method based on multi-physics field coupling. By using the temporal synergistic coupling of ultrasonic field and temperature field, the integrated effect of "seepage channel unblocking - gas adsorption and displacement" is achieved. Without injecting high-pressure fluid, the failed horizontal well is activated, the gas extraction effect is continuously enhanced, and the service life of the horizontal well is extended.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On the one hand, the present invention provides an active gas-induced extraction method based on multi-physics coupling, comprising the following steps: A. Failure Assessment and Mode Selection: Continuously monitor the gas extraction status of the target horizontal well, measuring the extracted gas concentration, extraction volume, and residual fracturing fluid level in the well. When the extracted gas concentration remains below 15% for more than one month, the well is considered to have entered the failure decay stage and is ready for operation.

[0008] The ultrasonic operation mode is selected based on the residual fracturing fluid in the well: when the fluid level is greater than 0.3 times the diameter of the horizontal well, a low-frequency, high-power ultrasonic mode is used to enhance cavitation and break fluid locks; when the fluid level is less than 0.3 times the diameter of the horizontal well or the well section is basically dry, a medium-to-high frequency ultrasonic mode is used, focusing on mechanical vibration to achieve secondary fracturing and permeability enhancement. The low-frequency, high-power ultrasonic frequency is 20~25kHz, with a single-segment power of not less than 2kW; the medium-to-high frequency ultrasonic frequency is 30~40kHz, with a single-segment power of 1~1.5kW.

[0009] B. Composite generator insertion and positioning: Use downhole television or ranging equipment to determine the specific location of the fracturing perforation section and fracture development section in the horizontal well. Send the composite generator into the target horizontal well through the integrated cable and adjust the insertion depth to ensure that the working section of the composite generator is accurately aligned with the fracturing perforation section or fracture development section.

[0010] C. Ultrasonic Permeability Enhancement and Unblocking Operation: Activate the surface ultrasonic generator system to drive the downhole ultrasonic active transducer, outputting ultrasonic waves according to the selected mode. During the operation, monitor the gas concentration changes in real time through the surface extraction system. When the gas concentration increases by more than 50%, it indicates that the wellbore fluid lock blockage has been effectively broken and the seepage channel has been significantly cleared.

[0011] Specifically, if the low-frequency high-power ultrasonic mode is selected, i.e. for well sections with a large amount of residual fracturing fluid, the ultrasonic action time is set to 90 minutes; if the medium-high frequency ultrasonic mode is selected, i.e. for well sections with virtually no residual fracturing fluid, the ultrasonic action time is set to 60 minutes.

[0012] D. Phase Change Energy Storage Thermal Disturbance Displacement Operation: After the ultrasonic operation is completed, the ultrasonic system is shut down, and the surface temperature control system is activated. Through the solid-liquid cycle phase change of the phase change material in the phase change energy storage temperature control module, periodic heating-cooling temperature disturbances are applied to the near-wellbore coal seam area of ​​the horizontal well, repeatedly disrupting the gas adsorption equilibrium and driving the continuous desorption and migration of adsorbed gas into the wellbore. When the gas extraction concentration stably rises to above 20%, it indicates that the failed horizontal well has been successfully activated. The phase change material filled in the phase change energy storage temperature control module is paraffin-based phase change material or calcium chloride hexahydrate, and the phase change temperature covers the original ambient temperature of the coal seam.

[0013] The duration of a single complete hot and cold cycle is controlled at 60-100 minutes, and the cycle is repeated 4-6 times. The temperature disturbance amplitude is controlled at 8-30℃, which can be adjusted according to the degree of coal seam metamorphism: a large amplitude disturbance of 20-30℃ is used for high-metamorphic and strongly adsorbed coal seams, and a small amplitude disturbance of 8-20℃ is used for low-metamorphic coal seams.

[0014] E. Continuous extraction and routine maintenance: Connect the activated horizontal well to the mine's conventional extraction pipeline for continuous gas extraction. To extend the activation period, start the composite generator monthly for 30 minutes of ultrasonic maintenance to inhibit fracture creep closure; at the same time, supplement thermal disturbance maintenance according to the decreasing trend of gas extraction concentration to maintain a stable desorption driving force.

[0015] On the other hand, the present invention provides an active gas-induced extraction device based on multi-physics coupling to implement the above method, including a composite generator lowered into a horizontal well, an ultrasonic generation system and a surface temperature control system installed on the ground.

[0016] The composite generator is a sealed, pressure-resistant cylindrical structure with an outer diameter smaller than the inner diameter of the target horizontal well and a length of approximately 2 meters. The cylinder is made of pressure-resistant stainless steel and can withstand a confining pressure of no less than 20 MPa. The composite generator integrates an ultrasonic active transducer and a phase change energy storage temperature control module, with the phase change energy storage temperature control module located outside the ultrasonic active transducer. A liquid level sensor is also installed to measure the liquid level within the horizontal well. Multiple sets of elastic centering stabilizers are evenly distributed around its outer perimeter to ensure axial centering of the device within the horizontal well section.

[0017] The ultrasonic active transducer is a piezoelectric ceramic transducer, which is electrically connected to the ground ultrasonic generation system via a pressure-resistant waterproof cable; the output power range of the ground ultrasonic generation system is 1~5kW, and the frequency and power can be adjusted.

[0018] The outer shell of the phase change energy storage temperature control module is made of high thermal conductivity copper material, and the interior is filled with phase change material. The shell has an expansion space of no less than 15% of the module volume to accommodate the volume change of the phase change material. The phase change energy storage temperature control module is connected to the ground temperature control system through a temperature control pipeline. The heating power of the ground temperature control system is 5~8kW, the temperature control accuracy is ±0.2℃, and a PID control algorithm is used to achieve precise control of the phase change material temperature.

[0019] The integrated cable and pipeline have good bending ability, with a maximum allowable bending rate of not less than 2° / m, and can smoothly pass through the bending section of the horizontal well.

[0020] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a step-by-step coupled process of "ultrasonic unblocking followed by thermal desorption": First, ultrasonic waves are used to open the seepage channels, removing water locks and solid blockages, thus providing a pathway for gas migration; then, periodic thermal disturbances continuously disrupt the adsorption equilibrium, providing a continuous driving force for gas migration. The timing of these two processes creates a synergistic effect, resulting in a greater increase in extraction concentration and a longer effective duration compared to single ultrasonic or single thermal excitation, effectively activating failed horizontal wells.

[0021] 2. This invention relies entirely on the action of a pure physical field to achieve permeability enhancement and desorption, without the need to inject high-pressure water or chemical agents into the coal seam. It fundamentally avoids secondary water lock, clay mineral expansion and groundwater pollution problems, and is suitable for water-sensitive coal seams and mining areas with high environmental protection requirements.

[0022] 3. This invention integrates the ultrasonic transducer and the phase change temperature control module into the same cylindrical device, which can complete both processes in one go without repeatedly raising and lowering the tubing string. The construction process is simple, the operating cost is low, and it can quickly respond to the treatment needs of failed wells.

[0023] 4. The ultrasonic waves and phase change materials in this invention are both physical processes, with no consumables required; the phase change material is sealed in the housing and can be recycled, resulting in a long service life for the device; the extraction effect can be maintained through regular maintenance, significantly extending the service life of the horizontal well and improving the recovery rate of residual gas resources. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the overall implementation of the active gas-induced extraction method described in this invention.

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of the composite generator described in this invention.

[0026] In the diagram: 1-rock strata, 2-target coal seam, 3-target horizontal well, 4-composite generator, 4-1-ultrasonic active transducer, 4-2-phase change energy storage temperature control module, 5-pressure resistant waterproof cable, 6-temperature control pipeline, 7-ground ultrasonic generation system, 8-ground temperature control system. Detailed Implementation

[0027] The present invention will be further described below.

[0028] like Figure 1 As shown, the active gas-induced extraction system based on multi-physics coupling described in this invention mainly includes a target horizontal well 3, a composite generator 4, a pressure-resistant and waterproof cable 5, a temperature control pipeline 6, a surface ultrasonic generator system 7, and a surface temperature control system 8. The composite generator 4 is lowered into the fracturing section of the target horizontal well 3 in the target coal seam 2 via an integrated cable and pipeline, and is connected to the surface ultrasonic generator system 7 and temperature control system 8 respectively. The surface extraction system 1 realizes gas extraction through the wellbore pipeline.

[0029] like Figure 2 As shown, the composite generator 4 is the core downhole operation unit, featuring a cylindrical, sealed shell structure. The main body is made of 304 stainless steel, with an outer diameter of 108mm, suitable for horizontal wells with an inner diameter of 120mm or more. Each section is 2m long and has a rated pressure of 20MPa. The shell integrates an ultrasonic active transducer 4-1 and a phase change energy storage temperature control module 4-2; the phase change energy storage temperature control module 4-2 is located outside the ultrasonic active transducer 4-1. A liquid level sensor 4-4 is installed at the end of the shell to detect the residual fracturing fluid level in the well. Three sets of elastic centralizers 4-3 are evenly arranged circumferentially around the outer perimeter of the shell to ensure the device is centered within the horizontal well, allowing the ultrasonic and thermal effects to be evenly transmitted to the surrounding coal seams.

[0030] The ultrasonic active transducer 4-1 uses a piezoelectric ceramic resonator assembly with switchable operating frequency. It is connected to the ground ultrasonic generation system 7 via a pressure-resistant waterproof cable 5. The ground system can output an adjustable frequency of 20~40kHz and an adjustable power of 1~5kW.

[0031] The phase change energy storage temperature control module 4-2 has a copper outer shell with a wall thickness of 3mm. It is internally filled with paraffin-based phase change material with a phase change temperature of 35℃, covering the typical original temperature of deep coal seams (25~30℃). A 15% volume expansion cavity is reserved at the top of the shell to accommodate the volume expansion during the phase change melting process. The module is connected to the ground temperature control system 8 via temperature control pipeline 6. The ground temperature control system uses electric heating + circulating cooling, combined with PID control to achieve precise temperature regulation with a control accuracy of ±0.2℃. The integrated cable connecting the composite generator 4 has an overall bending rate of up to 2° / m, allowing it to smoothly pass through the directional drilling section of horizontal wells with a curvature radius of over 100m.

[0032] The method flow of the present invention will be described in detail below with reference to specific embodiments: Example 1: In a deep, high-gas mine, the main coal seam is anthracite (high-rank, highly absorbent), with an initial temperature of 28°C. Horizontal wells are used for pre-gas extraction via segmented hydraulic fracturing. After 18 months of operation, the extracted gas concentration remained below 12% for more than 35 days, indicating the well had entered a failure decay stage. The method of this invention was used for activation, with the following steps: A. Preliminary Assessment and Parameter Selection: Through downhole flow rate testing and fluid level detection, the residual fracturing fluid level in the target section of the horizontal well was measured to be 42 mm. The inner diameter of the horizontal well casing is 120 mm, and the fluid level is approximately 0.35 times the well diameter, which is greater than 0.3 times the threshold. Therefore, a low-frequency, high-power ultrasonic mode was selected, with the frequency set at 22 kHz, the single-segment power at 2.2 kW, and the ultrasonic treatment duration at 90 min. The coal seam is high-rank anthracite with strong adsorption properties; therefore, the temperature disturbance amplitude was set at 25℃, the duration of a single hot-cold cycle was 80 min, and a total of 5 cycles were performed.

[0033] B. Equipment placement and positioning: Downhole television is used to image and locate the fractured section of the horizontal well to identify three fractured sections; the composite generator is sent into the horizontal well through coiled tubing and then aligned with each fractured section for sequential operation.

[0034] C. Ultrasonic Unblocking and Permeability Enhancement: The surface ultrasonic generator system is activated, outputting 22kHz, 2.2kW ultrasonic waves to the target well section. During the operation, the gas concentration is monitored in real time through the surface extraction pipeline. After 65 minutes of operation, the gas concentration increased from the initial 11.2% to 17.8%, an increase of 58.9%, indicating that the liquid lock blockage has been effectively broken. The ultrasonic system is then shut down after 90 minutes of continuous operation.

[0035] D. Phase Change Thermal Disturbance Displacement: After the ultrasonic operation, the surface temperature control system is activated to control the phase change energy storage module to undergo periodic hot and cold cycles: during the heating phase, the phase change material is heated to 53℃ (25℃ higher than the original temperature) and held at that temperature for 20 minutes; then cooled to 28℃ and held at that temperature for 20 minutes; the heating and cooling transition phases each last 20 minutes, with a single complete cycle lasting 80 minutes. This cycle is repeated 5 times, with a total thermal disturbance duration of 400 minutes. After the operation, continuous monitoring for 3 days shows that the gas extraction concentration is stably maintained at 23%~26%, successfully recovering to above 20%, and the failed horizontal well has been reactivated.

[0036] E. Routine Maintenance: Connect the well to the mine's conventional extraction system for continuous extraction; to maintain effectiveness, conduct 30-minute ultrasonic maintenance once a month and thermal disturbance maintenance twice a quarter. After 6 months of operation, the extraction concentration remained stable at over 18%, and compared to a failed well under the same conditions that was not maintained, the extraction efficiency increased by more than 120%, and the service life of the horizontal well was significantly extended.

[0037] Example 2: The main coal seam of a low-gas mine is gas coal (low-rank), with an original temperature of 22℃. After 12 months of horizontal well fracturing and production, the extraction concentration dropped to 13%, and there was virtually no residual fracturing fluid in the well section. The method of this invention was used for operation: the steps were basically the same as in Example 1, except that: a medium-high frequency ultrasonic mode was selected, with a frequency of 35kHz, a power of 1.2kW, and an action time of 60min; the temperature disturbance amplitude was set to 15℃, a single cycle was 70min, and the cycle was repeated 4 times.

[0038] After the operation, the gas extraction concentration steadily rose to 21%, achieving the expected activation effect.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An active gas-induced extraction method based on multiphysics coupling, characterized in that, Includes the following steps: A. Monitor the gas extraction status of the target horizontal well, and determine the extracted gas concentration, extraction volume, and residual fracturing fluid in the horizontal well. When the extraction concentration of the horizontal well remains below 15% for more than one month, the horizontal well is considered to have entered the failure decay stage. Select the ultrasonic operation mode based on the residual fracturing fluid volume: when the fluid level is greater than 0.3 times the diameter of the horizontal well, use the low-frequency high-power ultrasonic mode; when the fluid level is less than 0.3 times the diameter of the horizontal well or the well section is dry, use the medium-high frequency ultrasonic mode. B. To locate the fractured perforated section or fractured section of the horizontal well, a composite generator integrating an ultrasonic active transducer and a phase change energy storage temperature control module is sent into the target horizontal well via a cable, so that the working section of the composite generator is aligned with the fractured perforated section or fractured section. C. Start the ultrasonic active transducer and perform ultrasonic operation according to the mode selected in step A; monitor the extracted gas concentration in real time during the operation. When the gas concentration increases by more than 50%, it is determined that the seepage channel around the well is effectively cleared. D. After the ultrasonic operation is completed, the phase change energy storage temperature control module is activated to apply periodic heating-cooling temperature disturbances in the near-well area of ​​the horizontal well, repeating multiple heating and cooling cycles; when the gas extraction concentration steadily rises to above 20%, the failed horizontal well is deemed to have been reactivated. E. Connect the activated horizontal well to the extraction pipeline for normal gas extraction; periodically start the composite generator for ultrasonic maintenance and thermal disturbance maintenance to inhibit fracture closure and maintain extraction effect.

2. The method according to claim 1, characterized in that, In step A, the frequency of the low-frequency high-power ultrasound is 20~25kHz, and the power of a single segment is not less than 2kW; the frequency of the medium-high frequency ultrasound is 30~40kHz, and the power of a single segment is 1~1.5kW.

3. The method according to claim 1, characterized in that, In step C, if the low-frequency high-power ultrasound mode is selected, the duration of ultrasound action is 90 minutes; if the medium-high frequency ultrasound mode is selected, the duration of ultrasound action is 60 minutes.

4. The method according to claim 1, characterized in that, In step D, the duration of a single complete heating and cooling cycle is 60-100 minutes, and the number of cycles is 4-6; the temperature disturbance amplitude is controlled within 8-30℃.

5. The method according to claim 4, characterized in that, For high-ranking, highly adsorbent coal seams, the temperature disturbance amplitude is set to 20~30℃; for low-ranking coal seams, the temperature disturbance amplitude is set to 8~20℃.

6. The method according to claim 1, characterized in that, In step E, the composite generator is started monthly for 30 minutes of ultrasonic maintenance; thermal disturbance maintenance is added as needed based on the decreasing trend of gas extraction concentration.

7. The method according to claim 1, characterized in that, The phase change material filled in the phase change energy storage temperature control module is paraffin-based phase change material or calcium chloride hexahydrate, and the phase change temperature covers the original ambient temperature of the coal seam.

8. An active gas-induced extraction device based on multiphysics coupling, characterized in that, The system includes a composite generator lowered into a horizontal well, a surface ultrasonic generation system, and a surface temperature control system. The composite generator has a pressure-resistant cylindrical structure and integrates an ultrasonic active transducer and a phase change energy storage temperature control module. The phase change energy storage temperature control module is located outside the ultrasonic active transducer. The ultrasonic active transducer is connected to the surface ultrasonic generation system via a pressure-resistant waterproof cable. The phase change energy storage temperature control module is connected to the surface temperature control system via a temperature control pipeline. A liquid level sensor is installed on the composite generator to measure the liquid level in the horizontal well.

9. The apparatus according to claim 8, characterized in that, The outer diameter of the composite generator is smaller than the inner diameter of the target horizontal well, and the cylinder is made of pressure-resistant stainless steel, which can withstand a confining pressure of not less than 20MPa; the outer shell of the phase change energy storage temperature control module is made of copper thermally conductive material, and the shell is provided with an expansion reserve space with a volume not less than 15% of the module volume.

10. The apparatus according to claim 8, characterized in that, The composite generator is equipped with multiple sets of elastic centering stabilizers on its outer periphery to keep the composite generator axially centered in the horizontal well; the ultrasonic active transducer is a piezoelectric ceramic transducer; the output power of the surface ultrasonic generation system is 1~5kW; the heating power of the surface temperature control system is 5~8kW, and the temperature regulation of the phase change material is achieved through PID control.

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