CN114412418A - Method for extracting coal bed gas of superposed coal bed gas reservoir in multidirectional closed loop manner - Google Patents

Method for extracting coal bed gas of superposed coal bed gas reservoir in multidirectional closed loop manner Download PDF

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Publication number
CN114412418A
CN114412418A CN202210072377.2A CN202210072377A CN114412418A CN 114412418 A CN114412418 A CN 114412418A CN 202210072377 A CN202210072377 A CN 202210072377A CN 114412418 A CN114412418 A CN 114412418A
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gas
coal bed
extraction
pipe
diameter
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CN114412418B (en
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徐吉钊
翟成
余旭
刘厅
孙勇
丛钰洲
郑仰峰
唐伟
李宇杰
朱薪宇
徐鹤翔
王帅
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China University of Mining and Technology CUMT
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China University of Mining and Technology CUMT
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/006—Production of coal-bed methane
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E21B43/164—Injecting CO2 or carbonated water
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/30—Specific pattern of wells, e.g. optimizing the spacing of wells
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/34—Arrangements for separating materials produced by the well
    • E21B43/38—Arrangements for separating materials produced by the well in the well
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
    • Y02P90/70—Combining sequestration of CO2 and exploitation of hydrocarbons by injecting CO2 or carbonated water in oil wells

Abstract

The invention discloses a method for extracting coal bed gas of a superposed coal bed gas reservoir in a multidirectional closed loop manner, wherein a horizontal well and four extraction wells are formed in the superposed coal bed gas reservoir; laying a closed-loop extraction system in a horizontal well and each extraction well; then, gasifying agents are sequentially injected into four horizontal sections of the horizontal well, and a large amount of radiant heat and CO can be generated through gasification reaction2Gas to generate a fracture network which connects the upper coal layer, the rock stratum and the lower coal layer and reduces CH when the temperature of the coal body rises4Gas adsorption and CO2Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured4Fast desorption of gas; CO after gasification reaction2Gas is divided intoCO produced after separation and power generation2The gas can be re-injected into the upper coal seam and pass through the CO again2Adsorption property promoting CH4Gas displacement, the whole working process forms a closed loop, and the extracted CH is exploited simultaneously4Gas passing through CH4The generator set converts the electric energy into electric energy for subsequent utilization, and the high-efficiency exploitation and utilization of coal bed gas resources are realized.

Description

Method for extracting coal bed gas of superposed coal bed gas reservoir in multidirectional closed loop manner
Technical Field
The invention relates to a method for extracting coal bed gas of a superposed coal bed gas reservoir in a multidirectional closed loop mode, which is particularly suitable for the high-efficiency coal bed gas extraction of a superposed coal bed gas reservoir with a large cross-over area.
Background
The development and utilization of the coal bed gas have important significance for improving the energy structure of China and realizing the emission reduction of greenhouse gas. The exploratory recoverable coal bed gas resource in China exceeds 10 trillion m3With the gradual depletion of shallow coal resources, the coal bed gas exploitation gradually advances to the deep part. China coal bed gas resources generally have the characteristics of low porosity, low permeability and the like, and the extremely poor pore permeability characteristic hinders effective seepage of the coal bed gas, so that the rapid development of the coal bed gas industry is severely restricted.
At present, the coal bed gas exploitation is mainly carried out by gas exploitation through a drainage pressure relief method and is carried out through a ground well dredgingAnd water reduces the pore water pressure of the reservoir, and when the reservoir pressure is lower than the critical desorption pressure, a large amount of desorption can occur to the coal bed gas, so that free gas in the reservoir is promoted to be transported to a shaft to form mixed gas flow, and then the mixed gas flow is extracted. The pore permeability characteristics of the coal bed gas reservoir determine the occurrence state and the flowing behavior of the coal bed gas, but most of the existing coal bed gas reservoirs generally have the characteristics of low porosity, low permeability and the like, and the desorption and the drainage of the coal bed gas are severely restricted. The related scholars propose to inject CO into the coalbed methane reservoir2The extraction efficiency of the coal bed gas is improved by means of hot steam and the like, the adsorbed coal bed gas is desorbed by means of gas competitive adsorption or thermal driving, and diffusion and seepage occur depending on a pressure gradient and a fracture network, so that the coal bed gas is finally promoted to flow into an extraction shaft. However, these techniques have certain limitations in practical applications, such as CO2CO injection needs to be considered2Cost of capture and transportation, and CO2After entering the coal seam fracture, the adsorption expansion performance of the coal seam fracture leads the internal pressure of the fracture to be continuously increased, and further the subsequent CO is enabled to be generated2Gas cannot be injected into the in-situ coal bed continuously; the temperature of the hot steam is high, so that a steam generator needs to be arranged in actual use to generate the required hot steam, the acquisition of the hot steam is complex, the required temperature maintaining difficulty coefficient in the injection process is high, and specific heat preservation equipment needs to be arranged, so that the injection cost of the hot steam is indirectly increased; on the other hand, the two technologies cannot realize closed-loop construction in the aspect of gas extraction of the superposed coal bed gas reservoir at present, namely, injected CO2After fracturing permeability increase and competitive adsorption are finished, the rest part is discharged out of the coal bed, injected hot steam is liquefied into water after exchanging heat with the in-situ coal bed and is finally remained in the coal bed or discharged by a water suction pump, the closed-loop recycling process cannot be realized, and in addition, the CO can not be recycled due to the fact that the CO is discharged out of the water suction pump2And gas is continuously injected, if the internal pressure of the coal bed cannot be well monitored, the internal pressure building of the reservoir is easily caused, and the potential safety hazard of construction is further enlarged.
Therefore, aiming at the defects of the existing overlapped coal bed gas reservoir gas extraction technology with a large cross-over area, how to provide a method is to combine the coal bed gasification technology and the CO2 displacement technologyIn addition, the high-efficiency closed-loop extraction of the superposed coal bed gas reservoir with a large cross-over area is realized, and CO can be recycled2The gas not only can reduce the exploitation cost of the coal bed gas and improve the exploitation efficiency of the coal bed gas, but also can partially remove CO2The gas is sealed in the superposed coal bed gas reservoir, so that the low-carbon exploitation of the coal bed gas is realized, and a new research idea is provided for the development of the power-assisted coal bed gas industry.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for extracting coal bed gas of a superposed coal bed gas reservoir in a multidirectional closed-loop manner, which realizes the efficient closed-loop extraction of the superposed coal bed gas reservoir with a larger cross-over area on the basis of combining a coal bed gasification technology and a CO2 displacement technology, so that CO is extracted in a CO-free closed-loop manner2The gas is recycled, the coal bed gas exploitation cost can be reduced, the coal bed gas exploitation efficiency is improved, and part of CO can be recycled2The gas is sealed in the superposed coal bed gas reservoir, so that the low-carbon exploitation of the coal bed gas is realized.
In order to achieve the purpose, the invention adopts the technical scheme that: a method for extracting coal bed gas of a superposed coal bed gas reservoir in a multidirectional closed loop mode comprises the following specific steps:
A. firstly, determining an overlapped coal bed gas reservoir to be extracted, wherein the overlapped coal bed gas reservoir consists of an upper coal bed, a rock stratum and a lower coal bed, the upper coal bed is positioned above the lower coal bed, the rock stratum is positioned between the upper coal bed and the lower coal bed, firstly, a drilling machine is utilized to respectively sequentially penetrate through the upper coal bed and the rock stratum and reach the lower coal bed for well drilling construction, and a horizontal well and four extraction wells are respectively formed; the four extraction wells are distributed on a circumference which takes the horizontal well as a circle center and takes a certain distance as a radius, and the circumference is uniformly divided by the four extraction wells, wherein the horizontal well consists of a vertical section and four horizontal sections, the four horizontal sections are all positioned in the lower coal seam and respectively face the four extraction wells, and the adjacent horizontal sections are mutually vertical;
B. a first plugging device and a second plugging device are arranged at the vertical section of the horizontal well, wherein the first plugging device is arranged at the wellhead of the horizontal well, the second plugging device is arranged at the position of a rock stratum, so that a first closed space is formed between the four horizontal sections of the horizontal well and the second plugging device, and a vertical space of the horizontal well is arranged between the first plugging device and the second plugging deviceThe straight section forms a second closed space; the well mouth of each extraction well is provided with a third plugging device for plugging each extraction well, and a gasification agent injection pump and CO are arranged on the ground2Injection pump, gas separator, CH4The device comprises a generator set, an extraction pump and a heat exchange unit, wherein the outlet of a gasification agent injection pump is connected with one end of a gasification agent injection pipe, the other end of the gasification agent injection pipe penetrates through a first plugging device and a second plugging device and then extends into a first closed space to the joint of a vertical section and a horizontal section, an igniter is arranged in the gasification agent injection pipe close to the other end, a pressure gauge is arranged at the joint of the gasification agent injection pipe and the outlet of the gasification agent injection pump, a four-way flow divider is arranged at the other end of the gasification agent injection pipe and comprises a connecting pipe, a shell and four telescopic injection devices, the telescopic directions of the four telescopic injection devices respectively face to the four horizontal sections, the telescopic injection devices comprise a first variable-diameter telescopic pipe, a second variable-diameter telescopic pipe, a third variable-diameter telescopic pipe and a fourth variable-diameter telescopic pipe, wherein the first variable-diameter telescopic pipe is positioned in the second variable-diameter telescopic pipe and can slide and extend out of the second variable-diameter telescopic pipe, the second variable-diameter telescopic pipe is positioned in the third variable-diameter telescopic pipe and can slide and extend out of the third variable-diameter telescopic pipe, the third variable-diameter telescopic pipe is positioned in the fourth variable-diameter telescopic pipe and can slide and extend out of the fourth variable-diameter telescopic pipe, one end of the connecting pipe is connected with the other end of the gasifying agent injection pipe, the other end of the connecting pipe is connected with the fourth variable-diameter telescopic pipes of the four telescopic injection devices through four connecting branch pipes respectively, and the four connecting branch pipes are all provided with one-way valves which are respectively a one-way valve a, a one-way valve b, a one-way valve c and a one-way valve d; at the beginning, the four one-way valves are all in a closed state, and the four telescopic injection devices are all in a fully contracted state; one ends of four gas extraction pipes respectively penetrate through the third plugging devices of the extraction wells to extend into the extraction wells, the other ends of the four gas extraction pipes are connected with the gas inlets of the extraction pumps, the gas outlets of the extraction pumps are connected with the gas inlets of the heat exchange units through pipelines, the gas outlets of the heat exchange units are connected with the gas inlets of the gas separators through pipelines, and the CH of the gas separators are connected with the gas inlets of the gas separators through pipelines4The air outlet is communicated with CH through a pipeline4Inlet connection of generator set, CH4CO of exhaust port and gas separator of generator set2The gas outlets all pass through CO2Conveying pipeline and CO2Inlet connection of injection pump, CO2The outside of the conveying pipeline is wrapped with a condenser; CO22Outlet of injection pump and CO2One end of the injection pipe is connected with CO2The other end of the injection pipe penetrates through the first plugging device and extends into the second closed space, and the system is arranged; the telescopic injection device is in a shrinkage state when being installed, so that the four-way flow divider can be conveniently installed to a required position from the vertical section of the horizontal well, when a gasification agent is injected, the first diameter-variable telescopic pipe, the second diameter-variable telescopic pipe, the third diameter-variable telescopic pipe and the fourth diameter-variable telescopic pipe can sequentially extend out, so that the gasification agent is injected into the corresponding horizontal section, and the aperture of the first diameter-variable telescopic pipe is much smaller than that of the fourth diameter-variable telescopic pipe, so that the gasification agent can increase the injection speed of the gasification agent when finally sprayed out from the port of the first diameter-variable telescopic pipe after the telescopic injection device is pushed to extend, and the gasification agent further reaches the deepest part of the horizontal section;
C. setting a pressure threshold, starting a gasifying agent injection pump, continuously injecting the mixed gasifying agent into the four-way flow divider through the gasifying agent injection pipe under the pumping action of the gasifying agent injection pump, opening the one-way valve a at the moment, and pressurizing the corresponding telescopic injection device by the gasifying agent through the one-way valve a, and then the first variable diameter telescopic pipe, the second variable diameter telescopic pipe, the third variable diameter telescopic pipe and the fourth variable diameter telescopic pipe of the telescopic injection device all extend out to one horizontal section until the telescopic injection device completely extends out, the gasifying agent continuously enters the horizontal section through the end part of the first reducing telescopic pipe, the pressure value in the gasifying agent injection pipe is measured in real time through a pressure gauge, when the pressure value reaches the set pressure threshold value, the gasification agent injection pump is stopped, and the igniter is started, so that the gasification agent and CH in the current horizontal section are obtained.4The gas is gasified; then the gasification agent injection pump is started, the one-way valve a is closed, the one-way valve b is opened, and the process is repeated, so that the gasification agent and CH in the horizontal section corresponding to the one-way valve b4The gas is gasified; then, the check valves c and d are sequentially opened repeatedly in sequence, so that four levels are realizedGasifying agents in the sections are all equal to CH4The gas is gasified; the gasification reaction generates a large amount of radiant heat and CO2The gas and the radiant heat quickly raise the temperature of the coal in the lower coal layer, so that the coal is thermally cracked to generate cracks, and CO is generated at the same time2The gas will cause the gas pressure in the four horizontal segments to continue to increase, causing the CO to2Gas enters the generated fractures to further carry out impact expansion, finally the generated fractures form a fracture network, the fracture network connects the upper coal bed, the rock stratum and the lower coal bed, meanwhile, gasification areas in the four horizontal sections form a pressure relief area with a certain volume due to gasification reaction, and the fracture network in the upper coal bed and the rock stratum further increases the porosity and the permeability under the dual action of ground stress and pressure relief effect; at the same time, the temperature of the coal body is increased to reduce CH4Gas adsorption and CO2Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured4Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from four extraction wells through four gas extraction pipes, wherein the mixed gas comprises CH desorbed from a coal seam4Part of CO produced by gas and gasification reaction2The mixed gas passes through a heat exchange unit, the temperature of the mixed gas is reduced to normal temperature after heat exchange, and heat obtained by the heat exchange unit is used for providing heat energy for the subsequent preparation of water vapor; introducing the mixed gas at normal temperature into a gas separator, and separating CO by using the gas separator2Gas and CH4Gas separation, separated CH4Gas entering CH4Generator set, starting CH4The generator set will CH4Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation2CO separated from gas by gas separator2All gases enter into CO2Conveying line due to CO2The condenser is wrapped outside the conveying pipeline; in CO2The gas being in CO2The temperature of the conveying pipeline is continuously reduced until liquid CO is formed2Then, the liquid CO is introduced2By CO2Injection pump and CO2The injection pipe is injected into the second closed space in whichLiquid CO2After gasification, the gas enters the cracks in the upper coal layer and is treated with CH in the upper coal layer again4Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted4Converting the gas into electric energy for subsequent utilization, and generating CO2Gas and CO produced by gasification reaction2The gas can be continuously used in a closed loop.
Furthermore, the first plugging device, the second plugging device and the third plugging device can adopt the existing plugging devices or the high-pressure plugging device of the invention, the high-pressure plugging device comprises an elastic shell, a high-pressure bag body and four arc-shaped claw teeth, the high-pressure bag body is positioned in the elastic shell, the four arc-shaped claw teeth are uniformly distributed outside the high-pressure bag body, mucus is filled between the elastic shell and the high-pressure bag body, and holes are formed in the elastic shell. By adopting the structure, the installation of the plugging device is convenient in an initial state, and then when plugging is carried out, the high-pressure bag body is injected with high-pressure water to be expanded, the volume of the high-pressure bag body is continuously increased in the shell, so that the four arc-shaped claw teeth are outwards expanded, finally, the four arc-shaped claw teeth can be wedged into a well wall rock stratum of a drilled well to be fastened along with the action of the continuous expansion force of the high-pressure bag body, and the high-pressure bag body can apply pressure to the shell after being completely expanded, and the high-pressure bag body compresses the well wall through the shell due to the fact that the shell is made of elastic materials, so that the high-pressure plugging device is completely attached to the well wall; in addition, mucus in the shell flows out of the holes under pressure in the expansion process of the high-pressure capsule, and the expanded high-pressure plugging device can fill the incompletely-jointed part of the high-pressure plugging device and the well wall and the broken part of the well wall, so that the plugging effect on the drilled well is finally ensured.
Further, the gasifying agent is composed of O2And water vapor. O is2After entering the coal seam, the coal seam is ignited by an igniter to be in contact with CH4The gas is gasified, and the water vapor can increase the internal temperature of the coal body and ensure CH4Gas and O2The gasification reaction of (3) proceeds stably.
Furthermore, the bottom of the extraction well enters the lower coal seam within the range of 2-3 m, and the radius between the horizontal well and the extraction well is 200-300 m.
Further, the pressure threshold value in the step C is 5 MPa.
Further, a filter group is arranged between the heat exchange unit and the gas separator and used for removing CH4And CO2Other gaseous impurities in the mixed gas.
Compared with the prior art, the high-efficiency closed-loop extraction method for the superposed coal bed gas reservoir has the application advantages in four aspects: first, a large amount of radiant heat and CO can be generated through the lower coal seam gasification process2The gas, the severe temperature changes that exist between the coal formation and the gasification zone can induce thermal cracking to occur, while the gasification produces CO2The gas can migrate along with the crack expansion, and the crack generated by thermal fracture can be further expanded and developed by the continuously increased gas volume, so that a multi-scale crack network which is mutually communicated is formed in the upper coal bed, the rock stratum and the lower coal bed, and a migration channel is provided for the subsequent extraction of the coal bed gas; secondly, the cavity formed in the gasification area of the lower coal seam due to gasification can form a pressure relief area with a certain volume, and the formed fracture network in the upper coal seam and the rock stratum can further increase the porosity and the permeability under the dual effects of the ground stress and the pressure relief effect, and simultaneously, the CH is reduced by increasing the temperature of the coal body4Gas adsorption and CO2Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured4Fast desorption of gas; third, CO after separation and compression2Gas and power generation CO2The gas can be re-injected into the upper coal seam to generate flow, CO, in the fracture network induced by gasification of the lower coal seam2Promoting the CH in the upper coal seam by the advantage of stronger adsorption property4The desorption displacement of gas can play a role of CO to a certain degree2Geological sealing, the whole working process forms a closed loop, and the extracted CH is exploited simultaneously4Gas passing through CH4The generator set converts the electric energy into electric energy for subsequent utilization, and the high-efficiency exploitation and utilization of coal bed gas resources are realized; fourthly, the four-way flow divider is arranged, so that four horizontal sections of the horizontal well can be sequentially subjected to gasification reaction, and coal of an overlapped coalbed methane reservoir with a large cross-over area can be further subjected to coal gasification reactionAnd (4) efficiently exploiting the bed gas. Therefore, the method realizes the high-efficiency closed-loop extraction of the superposed coal bed gas reservoir with a larger cross-over area on the basis of combining the coal bed gasification technology and the CO2 displacement technology, so that CO is extracted2The gas is recycled, the coal bed gas exploitation cost can be reduced, the coal bed gas exploitation efficiency is improved, and part of CO can be recycled2The gas is sealed in the superposed coal bed gas reservoir, so that the low-carbon exploitation of the coal bed gas is realized.
Drawings
FIG. 1 is a schematic layout of the present invention.
FIG. 2 is a schematic view of the high pressure occluder of the present invention in an initial state;
FIG. 3 is a schematic view of the expanded state of the high pressure occluding device of the present invention;
FIG. 4 is a schematic view showing the structure of a gasifying agent injecting pipe and an igniter in the present invention;
FIG. 5 is a top view of FIG. 4;
FIG. 6 is a schematic view of the four-way diverter of the present invention shown in a collapsed configuration;
fig. 7 is a schematic view of the four-way diverter of the present invention shown in an extended configuration.
In the figure: 1, putting a coal seam; 2, putting a coal seam; 3-a rock formation; 4-horizontal well; 5-extracting the well; 6-a first occluder; 7-a second occluder; 8-a third occluder; 9-a gasifying agent injection pipe; 9-1-igniter; 9-2-pressure gauge; 10-CO2An injection pipe; 11-a gasification agent injection pump; 12-CO2An injection pump; 13-gas extraction pipe; 14-heat exchanger unit; 15-a gas separator; 16-CH4A generator set; 17-CO2A delivery line; 18-fracture network; 19-a gasification zone; 20-high pressure occluder; 21-eyelet; 22-arc claw teeth; 23-high pressure bladder; 24-mucus; 25-a four-way diverter; 25-1-a first variable diameter telescopic pipe; 25-2-a second variable-diameter telescopic pipe; 25-3-a third variable-diameter telescopic pipe; 25-4-a fourth reducing telescopic pipe.
Detailed Description
The present invention will be further explained below.
As shown in fig. 1, the method comprises the following specific steps:
A. firstly, determining an overlapped coal bed gas reservoir to be extracted, wherein the overlapped coal bed gas reservoir consists of an upper coal bed 1, a rock stratum 3 and a lower coal bed 2, the upper coal bed 1 is positioned above the lower coal bed 2, the rock stratum 3 is positioned between the upper coal bed 1 and the lower coal bed 2, firstly, a drilling machine is utilized to respectively sequentially penetrate through the upper coal bed 1 and the rock stratum 3 and reach the lower coal bed 2 for well drilling construction, and a horizontal well 4 and four extraction wells 5 are respectively formed; the four extraction wells 5 are distributed on a circumference which takes the horizontal well 4 as the circle center and has a radius of 200-300 m, and the four extraction wells 5 equally divide the circumference, wherein the horizontal well 4 consists of a vertical section and four horizontal sections, the four horizontal sections are all positioned in the lower coal seam 2 and respectively face the four extraction wells 5, and the adjacent horizontal sections are mutually vertical; the bottom of each extraction well 5 enters the lower coal seam within the range of 2-3 m;
B. a first plugging device 6 and a second plugging device 7 are arranged at the vertical section of the horizontal well 4, wherein the first plugging device 6 is positioned at the wellhead of the horizontal well 4, the second plugging device 7 is positioned at the position of the rock stratum 3, so that a first closed space is formed between the four horizontal sections of the horizontal well 6 and the second plugging device 7, and a second closed space is formed between the vertical section of the horizontal well 4 between the first plugging device 6 and the second plugging device 7; the well mouth of each extraction well 5 is provided with a third plugging device 8 for plugging each extraction well 5, and a gasification agent injection pump 11 and CO are arranged on the ground2Injection pump 12, gas separator 15, CH4A generator set 16, an extraction pump and a heat exchange unit 14, wherein the outlet of a gasification agent injection pump 11 is connected with one end of a gasification agent injection pipe 9, the other end of the gasification agent injection pipe 9 passes through a first plugging device 6 and a second plugging device 7 and then extends into a first closed space to the joint of a vertical section and a horizontal section, as shown in figures 4 and 5, an igniter 9-1 is arranged in the gasification agent injection pipe 9 close to the other end, a pressure gauge 9-2 is arranged at the joint of the gasification agent injection pipe 9 and the outlet of the gasification agent injection pump 11, a four-way flow divider 25 is arranged at the other end of the gasification agent injection pipe 9, as shown in figures 6 and 7, the four-way flow divider 25 comprises a connecting pipe, a shell and four telescopic injection devices, the telescopic directions of the four telescopic injection devices respectively face to the four horizontal sections, and the telescopic injection devices comprise a first diameter-variable telescopic pipe 25-1 and a second diameter-variable telescopic pipe 25-2, A third diameter-changing telescopic pipe 25-3 and a fourth diameter-changing telescopic pipe 25-4, wherein the first diameter-changing telescopic pipe 25-1 is positioned in the second diameter-changing telescopic pipe 25-2The second variable-diameter telescopic pipe 25-2 is positioned in a third variable-diameter telescopic pipe 25-3 and can slide and extend out of the third variable-diameter telescopic pipe 25-3, the third variable-diameter telescopic pipe 25-3 is positioned in a fourth variable-diameter telescopic pipe 25-4 and can slide and extend out of the fourth variable-diameter telescopic pipe 25-4, one end of a connecting pipe is connected with the other end of a gasifying agent injection pipe 9, the other end of the connecting pipe is respectively connected with the fourth variable-diameter telescopic pipes 25-4 of four telescopic injection devices through four connecting branch pipes, and one-way valves, namely a, a one-way valve b, a one-way valve c and a one-way valve d, are respectively arranged on the four connecting branch pipes; at the beginning, the four one-way valves are all in a closed state, and the four telescopic injection devices are all in a fully contracted state; one ends of four gas extraction pipes 13 respectively penetrate through the third plugging devices 8 of the extraction wells 5 to extend into the extraction wells, the other ends of the four gas extraction pipes are connected with the gas inlets of the extraction pumps, the gas outlets of the extraction pumps are connected with the gas inlets of the heat exchange unit 14 through pipelines, the gas outlets of the heat exchange unit 14 are connected with the gas inlets of the gas separators 15 through pipelines, and filter groups are arranged between the heat exchange unit 14 and the gas separators 15 and used for removing CH4And CO2Other gaseous impurities in the mixed gas; CH of gas separator 154The air outlet is communicated with CH through a pipeline4Inlet connection of the generator set 16, CH4CO of the exhaust of the power plant 16 and of the gas separator 152The gas outlets all pass through CO2Conveying line 17 and CO2Inlet connection of the injection pump 12, CO2The outside of the conveying pipeline 17 is wrapped with a condenser for passing CO2CO of the transfer line 172The gas is cooled and liquefied into liquid; CO22Outlet of injection pump 12 and CO2One end of the injection pipe 10 is connected with CO2The other end of the injection pipe 10 penetrates through the first plugging device 6 and extends into the second closed space, and the system is laid; the telescopic injection device is in a shrinkage state when being installed by adopting the structure, so that the four-way flow divider 25 can be conveniently installed to a required position from the vertical section of the horizontal well, and when the gasification agent is injected, the first diameter-changing telescopic pipe 25-1, the second diameter-changing telescopic pipe 25-2, the third diameter-changing telescopic pipe 25-3 and the fourth diameter-changing telescopic pipe 25-4 can be sequentially extended out, so that the gasification agent is injected into the corresponding horizontal section, and the gasification agent is injected into the corresponding horizontal sectionAnd because the aperture of the first reducing expansion pipe 25-1 is much smaller than that of the fourth reducing expansion pipe 25-4, after the expansion injection device is pushed to extend, the gasification agent can be sprayed out from the port of the first reducing expansion pipe 25-1, the spraying speed of the gasification agent can be increased, and the gasification agent can further reach the deepest part of the horizontal section;
as shown in fig. 2 and 3, the first occluder 6, the second occluder 7 and the third occluder 8 are all high-pressure occluders, each high-pressure occluder includes an elastic shell, a high-pressure capsule 23 and four arc-shaped claw teeth 22, the high-pressure capsule 23 is located in the elastic shell, the four arc-shaped claw teeth 22 are uniformly distributed outside the high-pressure capsule 23, mucus 24 is filled between the elastic shell and the high-pressure capsule 23, and the elastic shell is provided with holes 21. By adopting the structure in an initial state, the installation of the plugging device is convenient, when plugging is carried out, high-pressure water is injected into the high-pressure capsule 23 to enable the high-pressure capsule 23 to start to expand, the volume of the high-pressure capsule 23 is continuously increased in the shell, so that the four arc-shaped claw teeth 22 are outwards expanded, finally, the four arc-shaped claw teeth 22 can be wedged into a well wall rock stratum of a drilled well to be fastened along with the continuous expansion force action of the high-pressure capsule 23, meanwhile, the high-pressure capsule 23 can be pressed on the shell after being completely expanded, and the high-pressure capsule 23 is made of an elastic material to tightly press the well wall through the shell, so that the high-pressure plugging device 23 is completely attached to the well wall; in addition, mucus 24 in the shell flows out from the hole 21 under pressure in the expansion process of the high-pressure capsule 23, and can fill the incompletely attached part of the expanded high-pressure stopper 20 and the well wall and the broken part of the well wall, so that the blocking effect on the drilled well is finally ensured;
C. setting the pressure threshold value to be 5MPa, and then starting a gasification agent injection pump 11, wherein the gasification agent is O2Mixing with steam, continuously injecting the mixed gasifying agent into the four-way flow divider 25 through the gasifying agent injection pipe 9 under the pumping action of the gasifying agent injection pump, opening the one-way valve a at the moment, and pressurizing the corresponding telescopic injection device through the one-way valve a by the gasifying agent, so that the first diameter-changing telescopic pipe 25-1, the second diameter-changing telescopic pipe 25-2, the third diameter-changing telescopic pipe 25-3 and the fourth diameter-changing telescopic pipe 25-4 of the telescopic injection device are all in one horizontal sectionExtending until the gasification agent and the CH in the current horizontal section are completely extended, continuously entering the horizontal section through the end part of the first reducing telescopic pipe 25-1, measuring the pressure value in the gasification agent injection pipe in real time through a pressure gauge 9-2, stopping the gasification agent injection pump 11 when the pressure value reaches a set pressure threshold value, and starting an igniter 9-1 to ensure that the gasification agent and the CH in the current horizontal section are gasified and completely extended4The gas is gasified; then the gasification agent injection pump 11 is started, the one-way valve a is closed, the one-way valve b is opened, and the process is repeated, so that the gasification agent and CH in the horizontal section corresponding to the one-way valve b4The gas is gasified; then the one-way valve c and the one-way valve d are opened in sequence repeatedly, so that the gasifying agents in the four horizontal sections are all equal to CH4The gas is gasified; the gasification reaction generates a large amount of radiant heat and CO2The temperature of the coal body in the lower coal layer 2 is rapidly raised by the gas and the radiant heat, so that the coal body is thermally cracked to generate cracks, and CO generated at the same time2The gas will cause the gas pressure in the four horizontal segments to continue to increase, causing the CO to2Gas enters the generated cracks to further impact and expand, finally the generated cracks form a crack network 18, the crack network 18 is used for communicating the upper coal seam 1, the rock stratum 3 and the lower coal seam 2, meanwhile, gasification regions 19 in the four horizontal sections form pressure relief regions with certain volumes due to gasification reaction, and under the dual action of ground stress and pressure relief effects, the crack network 18 in the upper coal seam 1 and the rock stratum 3 can further increase the porosity and the permeability; at the same time, the temperature of the coal body is increased to reduce CH4Gas adsorption and CO2Under the dual action of gas competitive adsorption, CH in the upper coal seam 1 and the lower coal seam 2 is enabled4Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from four extraction wells 5 through four gas extraction pipes 13, wherein the mixed gas comprises CH desorbed from a coal seam4Part of CO produced by gas and gasification reaction2Then, the mixed gas passes through a heat exchanger unit 14, the temperature of the mixed gas is reduced to normal temperature after heat exchange, and heat obtained by the heat exchanger unit 14 is used for providing heat energy for the subsequent preparation of water vapor; the mixed gas at normal temperature enters a gas separator 15, and the gasSeparator 15 separates CO2Gas and CH4Gas separation, separated CH4Gas entering CH4Genset 16, start CH4Genset 16 will CH4Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation2CO separated from gas by gas separator 152All gases enter into CO2Conveying line 17 for CO2The condenser is wrapped outside the conveying pipeline 17; in CO2The gas being in CO2The temperature of the transfer line 17 is continuously reduced until liquid CO is formed2Then, the liquid CO is introduced2By CO2Injection pump 12 and CO2The injection pipe 10 injects into the second enclosed space, in which the liquid CO is present2Enters the cracks in the upper coal layer 1 after gasification, and carries out treatment on CH in the upper coal layer 1 again4Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted4Converting the gas into electric energy for subsequent utilization, and generating CO2Gas and CO produced by gasification reaction2The gas can be continuously used in a closed loop.
The gasification agent injection pump 11, CO2Injection pump 12, gas separator 15, CH4The generator set 16, the extraction pump, the heat exchanger set 14, the one-way valve a, the one-way valve b, the one-way valve c and the one-way valve d are all existing equipment or devices, wherein CO2The maximum injection pressure of the injection pump 12 can reach 70MPa, and the maximum injection pressure of the gasification agent injection pump 11 can reach 40 MPa; the gas separator 15 can not only separate CH4And CO2The gas is subjected to single gas separation, and the purification and compression functions of the single gas are realized.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims (6)

1. A method for extracting coal bed gas of a superposed coal bed gas reservoir in a multidirectional closed loop mode is characterized by comprising the following specific steps:
A. firstly, determining an overlapped coal bed gas reservoir to be extracted, wherein the overlapped coal bed gas reservoir consists of an upper coal bed, a rock stratum and a lower coal bed, the upper coal bed is positioned above the lower coal bed, the rock stratum is positioned between the upper coal bed and the lower coal bed, firstly, a drilling machine is utilized to respectively sequentially penetrate through the upper coal bed and the rock stratum and reach the lower coal bed for well drilling construction, and a horizontal well and four extraction wells are respectively formed; the four extraction wells are distributed on a circumference which takes the horizontal well as a circle center and takes a certain distance as a radius, and the circumference is uniformly divided by the four extraction wells, wherein the horizontal well consists of a vertical section and four horizontal sections, the four horizontal sections are all positioned in the lower coal seam and respectively face the four extraction wells, and the adjacent horizontal sections are mutually vertical;
B. a first plugging device and a second plugging device are arranged at the vertical section of the horizontal well, wherein the first plugging device is positioned at the wellhead of the horizontal well, the second plugging device is positioned at the position of a rock stratum, so that a first closed space is formed between the four horizontal sections of the horizontal well and the second plugging device, and a second closed space is formed between the vertical section of the horizontal well between the first plugging device and the second plugging device; the well mouth of each extraction well is provided with a third plugging device for plugging each extraction well, and a gasification agent injection pump and CO are arranged on the ground2Injection pump, gas separator, CH4The device comprises a generator set, an extraction pump and a heat exchange unit, wherein the outlet of a gasification agent injection pump is connected with one end of a gasification agent injection pipe, the other end of the gasification agent injection pipe penetrates through a first plugging device and a second plugging device and then extends into a first closed space to the joint of a vertical section and a horizontal section, an igniter is arranged in the gasification agent injection pipe close to the other end, a pressure gauge is arranged at the joint of the gasification agent injection pipe and the outlet of the gasification agent injection pump, a four-way flow divider is arranged at the other end of the gasification agent injection pipe and comprises a connecting pipe, a shell and four telescopic injection devices, the telescopic directions of the four telescopic injection devices respectively face to the four horizontal sections, the telescopic injection devices comprise a first variable-diameter telescopic pipe, a second variable-diameter telescopic pipe, a third variable-diameter telescopic pipe and a fourth variable-diameter telescopic pipe, wherein the first variable-diameter telescopic pipe is positioned in the second variable-diameter telescopic pipe and can slide and extend out of the second variable-diameter telescopic pipe, second variable diameter telescopicThe pipe is arranged in a third variable-diameter telescopic pipe and can slide and extend out of the third variable-diameter telescopic pipe, the third variable-diameter telescopic pipe is arranged in a fourth variable-diameter telescopic pipe and can slide and extend out of the fourth variable-diameter telescopic pipe, one end of a connecting pipe is connected with the other end of a gasifying agent injection pipe, the other end of the connecting pipe is connected with the fourth variable-diameter telescopic pipe of four telescopic injection devices through four connecting branch pipes respectively, and the four connecting branch pipes are all provided with one-way valves which are respectively a one-way valve a, a one-way valve b, a one-way valve c and a one-way valve d; at the beginning, the four one-way valves are all in a closed state, and the four telescopic injection devices are all in a fully contracted state; one ends of four gas extraction pipes respectively penetrate through the third plugging devices of the extraction wells to extend into the extraction wells, the other ends of the four gas extraction pipes are connected with the gas inlets of the extraction pumps, the gas outlets of the extraction pumps are connected with the gas inlets of the heat exchange units through pipelines, the gas outlets of the heat exchange units are connected with the gas inlets of the gas separators through pipelines, and the CH of the gas separators are connected with the gas inlets of the gas separators through pipelines4The air outlet is communicated with CH through a pipeline4Inlet connection of generator set, CH4CO of exhaust port and gas separator of generator set2The gas outlets all pass through CO2Conveying pipeline and CO2Inlet connection of injection pump, CO2The outside of the conveying pipeline is wrapped with a condenser; CO22Outlet of injection pump and CO2One end of the injection pipe is connected with CO2The other end of the injection pipe penetrates through the first plugging device and extends into the second closed space, and the system is arranged;
C. setting a pressure threshold, starting a gasification agent injection pump, enabling the mixed gasification agent to continuously inject the gasification agent into a four-way flow divider through a gasification agent injection pipe under the pumping action of the gasification agent injection pump, opening a one-way valve a at the moment, enabling the gasification agent to continuously pressurize a corresponding telescopic injection device through the one-way valve a, further enabling a first diameter-changing telescopic pipe, a second diameter-changing telescopic pipe, a third diameter-changing telescopic pipe and a fourth diameter-changing telescopic pipe of the telescopic injection device to extend into one horizontal section until the gasification agent completely extends out, enabling the gasification agent to continuously enter the horizontal section through the end part of the first diameter-changing telescopic pipe, measuring the pressure value in the gasification agent injection pipe in real time through a pressure gauge, and stopping gas injection when the pressure value reaches the set pressure threshold at the momentThe gasifying agent is injected into the pump, and the igniter is started, so that the gasifying agent and CH in the current horizontal section4The gas is gasified; then the gasification agent injection pump is started, the one-way valve a is closed, the one-way valve b is opened, and the process is repeated, so that the gasification agent and CH in the horizontal section corresponding to the one-way valve b4The gas is gasified; then the one-way valve c and the one-way valve d are opened in sequence repeatedly, so that the gasifying agents in the four horizontal sections are all equal to CH4The gas is gasified; the gasification reaction generates a large amount of radiant heat and CO2The gas and the radiant heat quickly raise the temperature of the coal in the lower coal layer, so that the coal is thermally cracked to generate cracks, and CO is generated at the same time2The gas will cause the gas pressure in the four horizontal segments to continue to increase, causing the CO to2Gas enters the generated fractures to further carry out impact expansion, finally the generated fractures form a fracture network, the fracture network connects the upper coal bed, the rock stratum and the lower coal bed, meanwhile, gasification areas in the four horizontal sections form a pressure relief area with a certain volume due to gasification reaction, and the fracture network in the upper coal bed and the rock stratum further increases the porosity and the permeability under the dual action of ground stress and pressure relief effect; at the same time, the temperature of the coal body is increased to reduce CH4Gas adsorption and CO2Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured4Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from four extraction wells through four gas extraction pipes, wherein the mixed gas comprises CH desorbed from a coal seam4Part of CO produced by gas and gasification reaction2The mixed gas passes through a heat exchange unit, the temperature of the mixed gas is reduced to normal temperature after heat exchange, and heat obtained by the heat exchange unit is used for providing heat energy for the subsequent preparation of water vapor; introducing the mixed gas at normal temperature into a gas separator, and separating CO by using the gas separator2Gas and CH4Gas separation, separated CH4Gas entering CH4Generator set, starting CH4The generator set will CH4Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation2Gas (es)CO separated from gas separator2All gases enter into CO2Conveying line due to CO2The condenser is wrapped outside the conveying pipeline; in CO2The gas being in CO2The temperature of the conveying pipeline is continuously reduced until liquid CO is formed2Then, the liquid CO is introduced2By CO2Injection pump and CO2The injection pipe is injected into a second enclosed space in which liquid CO is present2After gasification, the gas enters the cracks in the upper coal layer and is treated with CH in the upper coal layer again4Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted4Converting the gas into electric energy for subsequent utilization, and generating CO2Gas and CO produced by gasification reaction2The gas can be continuously used in a closed loop.
2. The method for extracting the coal bed gas in the multi-direction closed loop mode from the superposed coal bed gas reservoir according to claim 1, wherein the first plugging device, the second plugging device and the third plugging device are all high-pressure plugging devices, each high-pressure plugging device comprises an elastic shell, a high-pressure bag body and four arc-shaped claw teeth, the high-pressure bag bodies are located in the elastic shells, the four arc-shaped claw teeth are evenly distributed outside the high-pressure bag bodies, mucus is filled between the elastic shells and the high-pressure bag bodies, and holes are formed in the elastic shells.
3. The method for extracting coal bed gas in the multi-direction closed loop of the superposed coal bed gas reservoir according to claim 1, wherein the gasifying agent is O2And water vapor.
4. The method for extracting the coal bed gas of the superposed coal bed gas reservoir in the multidirectional closed loop mode is characterized in that the bottom of the extraction well enters the lower coal bed within the range of 2-3 m, and the radius between the horizontal well and the extraction well is 200-300 m.
5. The method for extracting the coal bed gas of the superposed coal bed gas reservoir in the multidirectional closed loop mode is characterized in that the pressure threshold value in the step C is 5 MPa.
6. The method for extracting coal bed gas in the multidirectional closed loop mode from the stacked coal bed gas reservoir as claimed in claim 1, wherein a filter group is arranged between the heat exchange unit and the gas separator and used for removing CH4And CO2Other gaseous impurities in the mixed gas.
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