Microwave radiation and carbon dioxide foam fracturing combined enhanced anti-reflection system and method

Abstract

A microwave radiation and carbon dioxide foam fracturing combined enhanced permeability increasing system comprises a carbon dioxide foam fracturing device and a microwave radiation device. The carbon dioxide foam fracturing device comprises a fracturing fluid storage tank, the fracturing fluid storage tank is communicated with a fracturing pipe through a booster pump, the fracturing pipe is inserted into a drill hole in a coal seam, and a heating head is fixedly arranged on the portion, located on the outer side of the drill hole, of the fracturing pipe. The microwave radiation device comprises a microwave generating device and a microwave emitter, the microwave generating device is used for outputting microwaves, the microwave emitter is inserted into the drill hole and used for emitting the microwaves, a cooling head is arranged on the microwave generating device, and the cooling head is connected with the heating head through a heat pipe. According to the device, microwave radiation and carbon dioxide foam fracturing technologies are combined, rapid weakening, fracturing, chambering and catalytic desorption of a coal seam can be better achieved, and on the other hand, heat generated by the microwave generating device can be used for adjusting the temperature of carbon dioxide foam fracturing fluid.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide foam fracturing, and specifically relates to a system and method for combined enhanced permeability improvement by microwave radiation and carbon dioxide foam fracturing. Background Art

[0002] The carbon dioxide foam fracturing fluid is a "gas-liquid dispersion system" composed of liquid carbon dioxide at about -18°C, a fracturing fluid base fluid, and a foaming agent. During the injection process into the fracturing holes, this dispersion system absorbs the heat energy of friction, the temperature of the fracturing fluid base fluid, and the formation temperature, causing the temperature to rise. When the temperature exceeds 31.06°C, the liquid carbon dioxide begins to gasify, forms a foam with the foaming agent, and in a state of high-speed flow, forms a gas-liquid two-phase dispersion system with a certain viscosity with the fracturing fluid base fluid.

[0003] Due to the phase change characteristics of carbon dioxide, the coal seam temperature selected for carbon dioxide foam fracturing should be above 40°C. In a low-temperature environment, the foaming amount of carbon dioxide foam will be significantly reduced, the effect of foam fracturing will be reduced, resulting in low foam fracturing performance and low success rate of foam fracturing. For low-temperature coal seams, to implement carbon dioxide foam fracturing, the ratio of pumped carbon dioxide to fracturing fluid will be as high as over 50%. Heating such a high proportion of carbon dioxide to gasify it is difficult and costly. In addition, during the fracturing construction, the preflush fluid pumped in will cause the formation temperature near the fracturing holes to rapidly drop below the critical temperature for foaming. The above reasons make it difficult to apply this technology to low-temperature coal seams. Summary of the Invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a system and method for combined enhanced permeability improvement by microwave radiation and carbon dioxide foam fracturing, which combines microwave radiation and carbon dioxide foam fracturing technologies, can better achieve rapid weakening, fracturing, hole expansion, and desorption promotion of the coal seam. On the other hand, it can adjust the temperature of the carbon dioxide foam fracturing fluid using the heat generated by the microwave generating device, further enhancing the effect of carbon dioxide foam fracturing.

[0005] To achieve the above object, the specific solution adopted by the present invention is as follows: A system for combined enhanced permeability improvement by microwave radiation and carbon dioxide foam fracturing includes a carbon dioxide foam fracturing device and a microwave radiation device; The carbon dioxide foam fracturing device includes a fracturing fluid storage tank for storing carbon dioxide foam fracturing fluid. The fracturing fluid storage tank is connected to a fracturing pipe through a booster pump. The fracturing pipe is inserted into a borehole in the coal seam, and a heating head is fixedly arranged on the part of the fracturing pipe outside the borehole; The microwave radiation device includes a microwave generating device and a microwave emitter. The microwave generating device is used to output microwaves. The microwave emitter is inserted into the borehole for emitting microwaves. A cooling head is provided on the microwave generating device, and the cooling head is connected to the heating head through a heat pipe.

[0006] Preferably, the carbon dioxide foam fracturing device includes a flowback liquid storage tank. The flowback liquid storage tank is communicated with the fracturing pipe through a flowback valve. A fracturing valve is provided between the output end of the booster pump and the fracturing pipe.

[0007] Preferably, the microwave radiation device includes a power supply, a magnetron, a straight waveguide, a waveguide converter, and a coaxial waveguide connected in sequence. The waveguide converter is connected to the coaxial waveguide through a microwave transmission line. The coaxial waveguide is connected to the microwave emitter, and the cooling head is provided on the waveguide converter.

[0008] Preferably, the microwave radiation device includes a metal protective shell and a microwave protection tube. The magnetron and the straight waveguide are both arranged in the metal protective shell. The microwave protection tube is inserted into the borehole, and the microwave emitter is arranged in the microwave protection tube.

[0009] Preferably, the system further includes a temperature measuring device. The temperature measuring device includes a temperature sensor placed in the borehole, and the temperature sensor is connected to a control host through a signal transmission line.

[0010] Preferably, the system further includes a drainage device. The drainage device includes a drainage pipe inserted into the borehole, and the drainage pipe is communicated with underground gas drainage equipment through a drainage valve.

[0011] A method for jointly enhancing permeability by microwave radiation and carbon dioxide foam fracturing, based on the above-mentioned system for jointly enhancing permeability by microwave radiation and carbon dioxide foam fracturing, the method includes the following steps: Drill a borehole in a low-temperature and low-permeability coal seam, and the borehole reaches the roof of the coal seam; Send a temperature sensor, the microwave emitter, and the fracturing pipe into the borehole, and seal the borehole with a hole packer; Use the temperature sensor to monitor the temperature data inside the borehole; Adjust the microwave radiation device based on the temperature data, and use the microwave radiation device to emit microwaves to irradiate the borehole; Use the carbon dioxide foam fracturing device to input fracturing fluid into the borehole, and use the cooling head, the heat pipe, and the heating head to adjust the temperature of the fracturing fluid.

[0012] Preferably, during the process of injecting the fracturing fluid into the borehole, the borehole is irradiated with microwaves emitted by the microwave radiation device, so that the temperature inside the borehole is maintained at 39-41°C.

[0013] Preferably, the method further comprises the following steps: After the fracturing is completed, the fracturing fluid in the borehole is discharged. During the process of discharging the fracturing fluid, the borehole is irradiated with microwaves emitted by the microwave radiation device, so that the temperature inside the borehole is maintained at 195-205°C.

[0014] Preferably, the method further comprises the following steps: After the fracturing fluid is completely discharged, gas is extracted from the borehole.

[0015] The present invention combines microwave radiation and carbon dioxide foam fracturing technology, which can better achieve the rapid weakening, fracturing, hole enlargement and desorption promotion of coal seams. On the other hand, it can adjust the temperature of the carbon dioxide foam fracturing fluid by using the heat generated by the microwave generating device, further improving the effect of carbon dioxide foam fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0017] Figure 1 is a schematic structural diagram of the system of the present invention.

[0018] Reference numerals: 1 - control host, 2 - power supply, 3 - magnetron, 4 - metal protective shell, 5 - straight waveguide, 6 - waveguide converter, 7 - microwave transmission line, 8 - coaxial waveguide, 9 - microwave emitter, 10 - microwave protection tube, 11 - temperature sensor, 12 - signal transmission line, 13 - hole packer, 14 - coal seam, 15 - roof, 16 - borehole, 17 - extraction pipe, 18 - fracturing pipe, 19 - extraction valve, 20 - heating head, 21 - heat pipe, 22 - cooling head, 23 - fracturing fluid storage tank, 24 - booster pump, 25 - fracturing valve, 26 - return fluid storage tank, 27 - return valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] As Figure 1 shown, a system for jointly enhancing permeability by microwave radiation and carbon dioxide foam fracturing includes a carbon dioxide foam fracturing device and a microwave radiation device.

[0021] The carbon dioxide foam fracturing device includes a fracturing fluid storage tank 23 for storing carbon dioxide foam fracturing fluid. The fracturing fluid storage tank 23 is connected to a fracturing pipe 18 through a booster pump 24. The fracturing pipe 18 is inserted into a borehole 16 in the coal seam 14, and a heating head 20 is fixedly arranged on the part of the fracturing pipe 18 outside the borehole 16.

[0022] The microwave radiation device includes a microwave generating device and a microwave emitter 9. The microwave generating device is used to output microwaves. The microwave emitter 9 is inserted into the borehole 16 for emitting microwaves. A cooling head 22 is arranged on the microwave generating device, and the cooling head 22 is connected to the heating head 20 through a heat pipe 21.

[0023] When performing carbon dioxide fracturing on a low-temperature coal seam, first drill a borehole 16 in the coal seam 14 and make the borehole 16 reach the roof 15 of the coal seam 14. Then, use the booster pump 24 to transport the carbon dioxide foam fracturing fluid in the fracturing fluid storage tank 23 into the borehole 16, and use the carbon dioxide foam fracturing fluid to fracture the borehole 16. On the other hand, use the microwave generating device of the microwave radiation device to generate microwaves, and then emit them into the borehole 16 through the microwave emitter 9 to radiate the borehole 16. At the same time, the heat generated by the microwave generating device can be transported to the fracturing pipe 18 through the cooling head 22, the heat pipe 21, and the heating head 20, thereby changing the temperature of the carbon dioxide foam fracturing fluid in the fracturing pipe 18. The power of the microwave generating device can be adjusted according to the actual temperature inside the borehole 16, thereby changing the temperature of the microwave generating device, and further changing the heat transported to the carbon dioxide foam fracturing fluid through the cooling head 22, the heat pipe 21, and the heating head 20, so that the temperature of the carbon dioxide foam fracturing fluid can better fracture the borehole 16.

[0024] The present invention combines microwave radiation and carbon dioxide foam fracturing technologies, which can better achieve rapid weakening, fracturing, hole enlargement, and desorption promotion of coal seams. On the other hand, it can adjust the temperature of the carbon dioxide foam fracturing fluid by using the heat generated by the microwave generating device, further improving the effect of carbon dioxide foam fracturing.

[0025] In order to facilitate the rapid recovery of carbon dioxide foam fracturing fluid after the completion of fracturing, the carbon dioxide foam fracturing device includes a return fluid storage tank 26. The return fluid storage tank 26 is connected to the fracturing pipe 18 through a return valve 27. A fracturing valve 25 is provided between the output end of the booster pump 24 and the fracturing pipe 18. After the fracturing is completed, the booster pump 24 can be stopped and the fracturing valve 25 can be closed. At the same time, the return valve 27 is opened. At this time, since the pressure in the borehole 16 is much greater than the pressure inside the return fluid storage tank 26, the carbon dioxide foam fracturing fluid can smoothly enter the return fluid storage tank 26 through the return valve 27, realizing the recovery of the carbon dioxide foam fracturing fluid.

[0026] The specific structure of the microwave laying device is as follows: The microwave radiation device includes a power supply 2, a magnetron 3, a straight waveguide 5, a waveguide converter 6, and a coaxial waveguide 8 that are connected in sequence. The waveguide converter 6 is connected to the coaxial waveguide 8 through a microwave transmission line 7. The coaxial waveguide 8 is connected to a microwave emitter 9. A cooling head 22 is provided on the waveguide converter 6. When starting the carbon dioxide foam fracturing, the magnetron 3 generates microwaves. The microwaves are transmitted to the microwave emitter 9 through the straight waveguide 5, the waveguide converter 6, and the coaxial waveguide 8, and then are emitted to the inner wall of the borehole 16 through the microwave emitter 9, realizing the radiation of the borehole 16. The magnetron 3, the straight waveguide 5, the waveguide converter 6, and the coaxial waveguide 8 are all mature existing technologies and will not be elaborated here.

[0027] In order to protect the magnetron 3 and the straight waveguide 5 and extend the service life of the microwave radiation device, the microwave radiation device includes a metal protective shell 4 and a microwave protection tube 10. The magnetron 3 and the straight waveguide 5 are both arranged in the metal protective shell 4. The microwave protection tube 10 is inserted into the borehole 16, and the microwave emitter 9 is arranged in the microwave protection tube 10. Since the waveguide converter 6 needs to transfer heat to the fracturing pipe 18 through the cooling head 22, the heat pipe 21, and the heating head 20, in order to arrange the cooling head 22, at least a part of the waveguide converter 6 needs to extend out of the metal protective shell 4 or be entirely located outside the metal protective shell 4.

[0028] In order to be able to flexibly adjust the microwave radiation device according to the actual temperature inside the borehole 16 to improve the effect of carbon dioxide foam fracturing, the system further includes a temperature measuring device. The temperature measuring device includes a temperature sensor 11 placed in the borehole 16. The temperature sensor 11 is connected to a control host 1 through a signal transmission line 12. The temperature sensor 11 and the control host 1 are both mature existing technologies and will not be elaborated here. The control host 1 can also be connected to the magnetron 3 and each valve to achieve automatic control and improve the overall efficiency.

[0029] After using carbon dioxide foam fracturing, the gas in coal seam 14 will overflow. In order to extract this gas and avoid potential safety hazards, the system further includes a gas extraction device. The gas extraction device includes an extraction pipe 17 inserted into borehole 16, and the extraction pipe 17 is connected to the underground gas extraction equipment through an extraction valve 19.

[0030] The present invention also provides a method for jointly enhancing permeability by microwave radiation and carbon dioxide foam fracturing. Based on the above-mentioned system for jointly enhancing permeability by microwave radiation and carbon dioxide foam fracturing, the method includes S1 to S7.

[0031] S1. Drill borehole 16 in the low-temperature and low-permeability coal seam 14, and the borehole 16 reaches the roof 15 of the coal seam 14.

[0032] S2. Feed a temperature sensor 11, a microwave emitter 9, and a fracturing pipe 18 into the borehole 16, and seal the borehole 16 using a hole packer 13.

[0033] S3. Use the temperature sensor 11 to monitor the temperature data inside the borehole 16.

[0034] S4. Adjust the microwave radiation device based on the temperature data, and use the microwave radiation device to emit microwaves to irradiate the borehole 16.

[0035] S5. Use the carbon dioxide foam fracturing device to input fracturing fluid into the borehole 16, and adjust the temperature of the fracturing fluid using a cooling head 22, a heat pipe 21, and a heating head 20. More specifically, during the process of inputting the fracturing fluid into the borehole 16, use the microwave radiation device to emit microwaves to irradiate the borehole 16, so that the temperature inside the borehole 16 is maintained at 39 - 41 °C. When the temperature sensor 11 inside the borehole 16 shows a temperature higher than 40 °C, the control host 1 receives the signal and automatically reduces the output power of the microwave radiation device through the PLC controller until the temperature shown by the temperature sensor 11 inside the borehole 16 reaches 40 °C; when the temperature sensor 11 inside the borehole shows a temperature lower than 40 °C, the control host 1 receives the signal and increases the output power of the microwave radiation device through the PLC until the temperature shown by the temperature sensor 11 inside the borehole 16 reaches 40 °C. At this temperature, the liquid carbon dioxide in the foam fracturing fluid starts to vaporize, forming a stable carbon dioxide foam fracturing fluid.

[0036] S6. After the fracturing is completed, the fracturing fluid in the borehole 16 is discharged. During the process of discharging the fracturing fluid, the borehole 16 is irradiated with microwaves emitted by a microwave radiation device, so that the temperature inside the borehole 16 is maintained at 195 - 205 °C. Specifically, when the control host 1 shows that the foam pressure in the borehole 16 significantly decreases, the booster pump 24 and the fracturing valve 25 are closed, and the discharge return valve 27 is opened. Since the pressure in the borehole 16 is greater than the internal pressure of the discharge return liquid storage tank 26, the fracturing fluid begins to be discharged from the borehole 16 to the discharge return liquid storage tank 26. Further, when the temperature sensor 11 in the borehole 16 shows a temperature lower than 200 °C, the control host 1 receives the signal and increases the output power of the microwave radiation device through the PLC until the temperature shown by the temperature sensor 11 in the borehole 16 reaches 200 °C. This high-temperature environment causes the carbon dioxide foam to rapidly rupture, accelerating the recovery of the carbon dioxide foam fracturing fluid.

[0037] S7. After the fracturing fluid is completely discharged, gas is extracted from the borehole 16.

[0038] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0039] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for combined microwave radiation and carbon dioxide foam fracturing to enhance transparency, characterized in that: It includes a carbon dioxide foam fracturing device and a microwave radiation device; The carbon dioxide foam fracturing device comprises a fracturing fluid storage tank (23), the fracturing fluid storage tank (23) being used to store carbon dioxide foam fracturing fluid, the fracturing fluid storage tank (23) being connected to a fracturing pipe (18) via a booster pump (24), the fracturing pipe (18) being inserted into a borehole (16) on a coal seam (14), and a heating head (20) being fixedly provided on a portion of the fracturing pipe (18) located outside the borehole (16); The microwave radiation device comprises a microwave generating device and a microwave emitter (9), wherein the microwave generating device is used to output microwaves, and the microwave emitter (9) is inserted into the borehole (16) to emit microwaves, and the microwave generating device is provided with a cooling head (22), and the cooling head (22) is connected to the heating head (20) via a heat pipe (21).

2. A system for combined microwave radiation and carbon dioxide foam fracturing and enhanced transmission as claimed in claim 1, characterized in that: The carbon dioxide foam fracturing device comprises a return fluid storage tank (26), the return fluid storage tank (26) being connected to the fracturing pipe (18) via a return fluid valve (27), and a fracturing valve (25) being provided between the output end of the booster pump (24) and the fracturing pipe (18).

3. The system of microwave radiation and carbon dioxide foam fracturing combined with enhanced permeability enhancement as claimed in claim 1, characterized in that: The microwave radiation device comprises a power supply (2), a magnetron (3), a straight waveguide (5), a waveguide converter (6) and a coaxial waveguide (8) which are connected in sequence; the waveguide converter (6) and the coaxial waveguide (8) are connected via a microwave transmission line (7); the coaxial waveguide (8) is connected to the microwave transmitter (9); and the cooling head (22) is arranged on the waveguide converter (6).

4. A system for combined microwave radiation and carbon dioxide foam fracturing and enhanced permeability enhancement as claimed in claim 3, characterized in that: The microwave radiation device comprises a metal protective shell (4) and a microwave protective tube (10), the magnetron (3) and the straight waveguide (5) are both arranged in the metal protective shell (4), the microwave protective tube (10) is inserted into the drilled hole (16), and the microwave transmitter (9) is arranged in the microwave protective tube (10).

5. The system of microwave radiation and carbon dioxide foam fracturing combined with enhanced transmission enhancement as claimed in claim 1, characterized in that: The system further comprises a temperature measuring device, wherein the temperature measuring device comprises a temperature sensor (11) inserted into the borehole (16), and the temperature sensor (11) is connected to a control host (1) via a signal transmission line (12).

6. The system of microwave radiation and carbon dioxide foam fracturing combined with enhanced transmission enhancement as claimed in claim 1, characterized in that: The system further comprises an extraction device, wherein the extraction device comprises an extraction pipe (17) inserted into the borehole (16), and the extraction pipe (17) is connected to the underground gas extraction equipment via an extraction valve (19).

7. A method for strengthening and enhancing permeability by combining microwave radiation and carbon dioxide foam fracturing, characterized in that: Based on a system for combined enhanced permeability enhancement of microwave radiation and carbon dioxide foam fracturing as claimed in any one of claims 1 to 6, the method comprises the following steps: A borehole (16) is machined in a low-temperature and low-permeability coal seam (14), wherein the borehole (16) reaches a roof (15) of the coal seam (14); Inserting a temperature sensor (11), the microwave transmitter (9) and the fracturing pipe (18) into the borehole (16), and sealing the borehole (16) using a sealer (13); Using the temperature sensor (11) to monitor temperature data inside the borehole (16); Adjusting the microwave radiation device based on the temperature data, and utilizing the microwave radiation device to emit microwaves to irradiate the borehole (16); The carbon dioxide foam fracturing device is used to input fracturing fluid into the borehole (16), and the cooling head (22), the heat pipe (21) and the heating head (20) are used to adjust the temperature of the fracturing fluid.

8. The method of combining microwave radiation and carbon dioxide foam fracturing to enhance transmission as claimed in claim 7, characterized in that: During the process of injecting the fracturing fluid into the borehole (16), the microwave irradiation device is used to emit microwaves to irradiate the borehole (16), so that the temperature inside the borehole (16) is maintained at 39-41°C.

9. The method of combining microwave radiation and carbon dioxide foam fracturing to enhance transmission as claimed in claim 7, characterized in that: The method further comprises the steps of: After fracturing is completed, the fracturing fluid in the borehole (16) is discharged, and during the process of discharging the fracturing fluid, the microwave irradiation device is used to emit microwaves to irradiate the borehole (16), so that the temperature inside the borehole (16) is maintained at 195-205°C.

10. The method of combining microwave radiation and carbon dioxide foam fracturing to enhance transmission as claimed in claim 9, characterized in that: The method further comprises the steps of: After the fracturing fluid is completely discharged, gas is extracted from the borehole (16).

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