CN114412419B - Efficient closed-loop extraction method for superposed coal bed gas reservoir - Google Patents
Efficient closed-loop extraction method for superposed coal bed gas reservoir Download PDFInfo
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- CN114412419B CN114412419B CN202210072385.7A CN202210072385A CN114412419B CN 114412419 B CN114412419 B CN 114412419B CN 202210072385 A CN202210072385 A CN 202210072385A CN 114412419 B CN114412419 B CN 114412419B
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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
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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
- E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
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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
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/164—Injecting CO2 or carbonated water
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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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- 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
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/40—Capture or disposal of greenhouse gases of CO2
Abstract
The invention discloses a method for efficiently extracting a closed loop of a superposed coal bed gas reservoir, which comprises the steps of firstly forming a horizontal well and an extraction well in the superposed coal bed gas reservoir; laying a closed-loop extraction system in a horizontal well and an extraction well; then, a gasifying agent is injected into the horizontal section of the horizontal well, and a large amount of radiant heat and CO are generated through gasification reaction 2 Gas to generate a fracture network which connects the upper coal layer, the rock layer and the lower coal layer and reduces CH by increasing the temperature of the coal body 4 Gas adsorption and CO 2 Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured 4 Fast desorption of gas; CO after gasification reaction 2 The gas is separated from CO generated by power generation 2 The gas can be re-injected into the upper coal seam and pass through the CO again 2 Adsorption property promoting CH 4 Gas displacement, the whole working process forms a closed loop, and the extracted CH is exploited simultaneously 4 Gas passing through CH 4 The 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
Technical Field
The invention relates to a method for efficiently extracting a superposed coal bed gas reservoir in a closed loop manner, which is particularly suitable for implementation work of efficient mining of an enriched coal bed gas superposed coal reservoir and green mining of a deep coal bed.
Background
The total amount of the shallow coal bed gas resources within 2000m exceeds 30 trillion m 3 The amount of recoverable resources exceeds 10 trillion m 3 . The efficient development and utilization of the coal bed gas can accelerate the realization of diversification of energy structures on one hand, and can ensure the safe exploitation of coal resources on the other hand, thereby realizing the double green exploitation of coal and the coal bed gas in the true sense.
At present, gas extraction is mainly carried out through a drainage pressure relief method in coal bed gas mining, pore water pressure of a reservoir is reduced through ground well drainage, and when the reservoir pressure is lower than critical desorption pressure, a large amount of desorption can occur in 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 reservoir 2 The 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, diffusion and seepage occur depending on a pressure gradient and a fracture network, and finally the coal bed gas flow is promoted to enter an extraction shaft. However, these techniques have certain limitations in practical applications, such as CO 2 CO injection needs to be considered 2 Cost of capture and transportation, and CO 2 After entering the coal seam crack, the adsorption expansion performance of the coal seam crack leads to the inside of the crackThe pressure continues to increase, thereby allowing subsequent CO 2 Gas 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 CO 2 After 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 pump 2 And 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 superposed coal bed gas reservoir gas extraction technology, how to provide a method can realize the efficient closed-loop extraction of the superposed coal bed gas reservoir on the basis of combining the coal bed gasification technology and the CO2 displacement technology, and can recycle CO 2 The gas can not only reduce the coal bed gas exploitation cost and improve the coal bed gas exploitation efficiency, but also can partially remove CO 2 The 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 efficiently extracting superposed coal bed gas reservoirs in a closed loop manner, which realizes the efficient closed loop extraction of the superposed coal bed gas reservoirs on the basis of combining a coal bed gasification technology and a CO2 displacement technology to ensure that CO is extracted in a closed loop manner 2 The 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 recycled 2 The 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 efficient closed-loop extraction of a superposed coal bed gas reservoir 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 an extraction well are respectively formed; wherein the horizontal section of the horizontal well is positioned in the lower coal seam and is parallel to the inclination of the lower coal seam;
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 horizontal section 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; a third plugging device is arranged at the wellhead of the extraction well to plug the extraction well, and a gasification agent injection pump and CO are arranged on the ground 2 Injection pump, gas separator, CH 4 The system comprises a generator set, an extraction pump and a heat exchange unit, wherein an outlet of the 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, an igniter is arranged at the position, close to the other end, in the gasification agent injection pipe, a pressure gauge is arranged at the position, connected with the outlet of the gasification agent injection pump, of the gasification agent injection pipe, one end of a gas extraction pipe penetrates through a third plugging device and extends into an extraction well, the other end of the gas extraction pipe is connected with a gas inlet of the extraction pump, a gas outlet of the extraction pump is connected with a gas inlet of the heat exchange unit through a pipeline, a gas outlet of the heat exchange unit is connected with a gas inlet of a gas separator through a pipeline, and a CH (carbon-hydrogen) of the gas separator 4 The air outlet is communicated with CH through a pipeline 4 Inlet connection of generator set, CH 4 CO of exhaust port and gas separator of generator set 2 The gas outlets all pass through CO 2 Conveying pipeline and CO 2 Inlet connection of injection pump, CO 2 The outside of the conveying pipeline is wrapped with a condenser; CO2 2 Outlet of injection pump and CO 2 One end of the injection pipe is connected with CO 2 The other end of the injection pipe passes through the first plugging device to extendEntering a second closed space to finish the layout work of the system;
C. setting a pressure threshold, starting a gasifying agent injection pump, continuously injecting the mixed gasifying agent into the first closed space through a gasifying agent injection pipe under the pumping action of the gasifying agent injection pump, measuring the pressure value in the gasifying agent injection pipe in real time through a pressure gauge, indicating that the pressure value in the first closed space reaches the pressure threshold when the pressure value reaches the set pressure threshold, stopping the gasifying agent injection pump at the moment, and starting an igniter to ensure that the gasifying agent and CH in the first closed space 4 The gas is subjected to gasification reaction, and the gasification reaction can generate a large amount of radiant heat and CO 2 The 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 time 2 The gas will continuously increase the gas pressure in the first closed space, so that CO is generated 2 Gas enters the generated cracks to further impact and expand, finally, the generated cracks form a crack network, the crack network is used for communicating the upper coal seam, the rock stratum and the lower coal seam, meanwhile, a gasification area of the first closed space can form a pressure relief area with a certain volume due to gasification reaction, and under the dual effects of ground stress and pressure relief effect, the crack network in the upper coal seam and the rock stratum can further increase the porosity and the permeability; at the same time, the temperature of the coal body is increased to reduce CH 4 Gas adsorption and CO 2 Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured 4 Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from an extraction well through a gas extraction pipe, wherein the mixed gas comprises CH desorbed from a coal seam 4 Part of CO produced by gas and gasification reaction 2 The 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 separator 2 Gas and CH 4 Gas separation, separated CH 4 Gas entering CH 4 Generator set, startingCH 4 The generator set will CH 4 Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation 2 CO separated from gas by gas separator 2 All gases enter into CO 2 Conveying line due to CO 2 The condenser is wrapped outside the conveying pipeline; in CO 2 The gas being in CO 2 The temperature of the conveying pipeline is continuously reduced until liquid CO is formed 2 Then, liquid CO is introduced 2 By CO 2 Injection pump and CO 2 The injection pipe is injected into a second enclosed space in which liquid CO is present 2 After gasification, the gas enters the cracks in the upper coal layer and is treated with CH in the upper coal layer again 4 Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted 4 Converting the gas into electric energy for subsequent utilization, and generating CO 2 Gas and CO produced by gasification reaction 2 The 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 capsule body and four arc-shaped claw teeth, the high-pressure capsule body is positioned in the elastic shell, the four arc-shaped claw teeth are uniformly distributed outside the high-pressure capsule body, mucus is filled between the elastic shell and the high-pressure capsule 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 is pressed to flow out of the eyelet during the expansion of the high-pressure capsule, and the high-pressure plugging device can fill the incompletely attached part of the expanded 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 O 2 And steam. O is 2 After entering the coal bed, the coal bed is ignited by an igniter to be mixed with CH 4 The gas is gasified, and the water vapor can increase the internal temperature of the coal body and ensure CH 4 Gas and O 2 The 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 horizontal distance between the horizontal well and the extraction well is 200-300 m.
Furthermore, the other end of the gasifying agent injection pipe adopts a reducing outlet. The structure can increase the injection speed of the gasifying agent.
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 CH 4 And CO 2 Other 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 three aspects: first, a large amount of radiant heat and CO can be generated through the lower coal seam gasification process 2 The 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 CO 2 The 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, a cavity formed by gasification in a lower coal bed gasification area can form a pressure relief area with a certain volume, and under the dual action of ground stress and pressure relief effect, the formed fracture network in an upper coal bed and a rock stratum can further increase the porosity and permeability, and simultaneously, the CH is reduced by increasing the temperature of a coal body 4 Gas adsorption and CO 2 Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured 4 Fast desorption of gas; third, it is compressed by separationAfter CO 2 Gas and power generation CO 2 The 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 seam 2 Promoting the CH in the upper coal seam by the advantage of stronger adsorption property 4 The desorption displacement of gas can play a role in CO to a certain degree 2 Geological sealing, the whole working process forms a closed loop, and the extracted CH is exploited simultaneously 4 Gas passing through CH 4 The 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. Therefore, the method realizes the high-efficiency closed-loop extraction of the superposed coal bed gas reservoir on the basis of combining the coal bed gasification technology and the CO2 displacement technology, so that CO is extracted 2 The 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 recycled 2 The 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 shows CO in the present invention 2 The structure schematic diagram of the conveying pipeline and the condenser.
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 gasification agent injection pipe; 8-1-igniter; 8-2-pressure gauge; 9-CO 2 An injection pipe; 10-a third occluder; 11-a gasification agent injection pump; 12-CO 2 An injection pump; 13-gas extraction pipe; 14-a gas separator; 15-CO 2 A delivery line; 15-1-a condenser; 16-CH 4 A generator set; 17-a gasification zone; 18-fracture network; 19-high pressure occluder; 20-mucus; 21-eyelet; 22-arc shaped pawl teeth; 23-high pressure balloon; 24-heat exchanger unit.
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 an extraction well 5 are respectively formed; wherein the horizontal section of the horizontal well 4 is positioned in the lower coal seam 2 and is parallel to the inclination of the lower coal seam 2; the bottom of the extraction well 5 enters the lower coal seam within the range of 2-3 m, and the horizontal distance between the horizontal well 4 and the extraction well 5 is 200-300 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 horizontal section of the horizontal well 4 and the second plugging device 7, and a second closed space is formed between the first plugging device 6 and the vertical section of the horizontal well 4 between the second plugging device 7; a third plugging device 10 is arranged at the wellhead of the extraction well 5 to plug the extraction well 5, and a gasification agent injection pump 11 and CO are arranged on the ground 2 Injection pump 12, gas separator 14, CH 4 A generator set 16, an extraction pump and a heat exchange unit 24, wherein the outlet of a gasifying agent injection pump 11 is connected with one end of a gasifying agent injection pipe 8, the other end of the gasifying agent injection pipe 8 passes through a first plugging device 6 and a second plugging device 7 and then extends into a first closed space, as shown in fig. 4, an igniter 8-1 is arranged in the gasifying agent injection pipe 8 near the other end, the other end of the gasifying agent injection pipe 8 adopts a reducing outlet, a pressure gauge 8-2 is arranged at the connection position of the gasifying agent injection pipe 8 and the outlet of the gasifying agent injection pump 11, one end of a gas extraction pipe 13 passes through a third plugging device 10 and extends into a gas extraction well 5, the other end of the gas extraction pipe is connected with the gas inlet of the extraction pump, the gas outlet of the extraction pump is connected with the gas inlet of the heat exchange unit 24 through a pipeline, the gas outlet of the heat exchange unit 24 is connected with the gas inlet of a gas separator 14 through a pipeline, and the CH of the gas separator 14 4 The air outlet is communicated with CH through a pipeline 4 Inlet connection of the generator set 16, CH 4 GeneratorExhaust of the stack 16 and CO of the gas separator 14 2 The gas outlets all pass through CO 2 Conveying line 15 and CO 2 The inlet of the injection pump 12 is connected, as shown in FIG. 5, to CO 2 The outside of the conveying pipeline 15 is wrapped with a condenser 15-1; CO2 2 Outlet of injection pump 12 and CO 2 One end of the injection pipe 9 is connected with CO 2 The other end of the injection pipe 9 passes through the first plugging device and extends into the second closed space, and the system is laid; as shown in fig. 2 and 3, the first occluder 6, the second occluder 7 and the third occluder 10 are all high-pressure occluders 19, the high-pressure occluder 19 includes an elastic shell, a high-pressure capsule 23 and four arc-shaped claws 22, the high-pressure capsule 23 is located in the elastic shell, the four arc-shaped claws 22 are uniformly distributed outside the high-pressure capsule 23, mucus 20 is filled between the elastic shell and the high-pressure capsule 23, and the elastic shell is provided with holes 21; between the heat exchanger unit 24 and the gas separator 14, a filter bank is provided for removing CH 4 And CO 2 Other gaseous impurities in the mixed gas;
C. setting the pressure threshold value to be 5Mpa, and then starting a gasification agent injection pump 11, wherein the gasification agent is O 2 Mixing the mixed gasifying agent with water vapor, continuously injecting the gasifying agent into the first closed space through a gasifying agent injection pipe 8 under the pumping action of a gasifying agent injection pump 11, measuring the pressure value in the gasifying agent injection pipe 8 in real time through a pressure gauge 8-2, indicating that the pressure value in the first closed space reaches the pressure threshold value when the pressure value reaches the set pressure threshold value, stopping the gasifying agent injection pump 11 at the moment, and starting an igniter 8-1 to ensure that the gasifying agent and CH in the first closed space 4 The gas is subjected to gasification reaction, and the gasification reaction can generate a large amount of radiant heat and CO 2 The 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 time 2 The gas will continuously increase the gas pressure in the first closed space, so that CO is generated 2 Gas enters the generated cracks to further carry out impact expansion, finally the generated cracks form a crack network 18, the crack network 18 communicates the upper coal seam 1, the rock stratum 3 and the lower coal seam 2, and meanwhile, a gasification area 17 of the first closed space can be formed due to gasification reactionThe pressure relief area with a certain volume further increases the porosity and permeability of the fracture network 18 in the upper coal seam 1 and the rock stratum 3 under the double action of the ground stress and the pressure relief effect; at the same time, the temperature of the coal body is increased to reduce CH 4 Gas adsorption and CO 2 Under the dual action of gas competitive adsorption, CH in the upper coal seam 1 and the lower coal seam 2 is enabled 4 Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from the extraction well through a gas extraction pipe 13, wherein the mixed gas comprises CH desorbed from a coal seam 4 Part of CO produced by gas and gasification reaction 2 Then, the mixed gas passes through a heat exchanger unit 24, the temperature of the mixed gas is reduced to normal temperature after heat exchange, and the heat obtained by the heat exchanger unit 24 is used for providing heat energy for the subsequent preparation of water vapor; the normal temperature mixed gas enters a gas separator 14, and the gas separator 14 separates CO 2 Gas and CH 4 Gas separation, separated CH 4 Gas into CH 4 Genset 16, start CH 4 Genset 16 will CH 4 Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation 2 CO separated from the gas by the gas separator 14 2 All gases enter into CO 2 Conveying line 15 for CO 2 The condenser 15-1 is wrapped outside the conveying pipeline 15; in CO 2 The gas being in CO 2 The temperature of the transfer line 15 is continuously reduced until liquid CO is formed 2 Then, the liquid CO is introduced 2 By CO 2 Injection pump 12 and CO 2 The injection pipe 9 injects into the second closed space, in which the liquid CO is present 2 Enters the cracks in the upper coal layer 1 after gasification, and carries out treatment on CH in the upper coal layer 1 again 4 Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted 4 Converting the gas into electric energy for subsequent utilization, and generating CO 2 Gas and CO produced by gasification reaction 2 The gas can be continuously used in a closed loop.
The gasification agent injection pump 11, CO 2 Injection pump 12, gas separator 14, CH 4 Generating set 16 and extraction pumpAnd the heat exchanger unit 24 are conventional units, in which CO is present 2 The 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 14 can not only separate CH 4 And CO 2 The 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 (7)
1. A method for efficient closed-loop extraction of a superposed coal bed gas reservoir 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 an extraction well are respectively formed; wherein the horizontal section of the horizontal well is positioned in the lower coal seam and is parallel to the tendency of the lower coal seam;
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 horizontal section 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; a third plugging device is arranged at the wellhead of the extraction well to plug the extraction well, and a gasification agent injection pump and CO are arranged on the ground 2 Injection pump, gas separator, CH 4 The 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, an igniter is arranged at the position, close to the other end, in the gasification agent injection pipe, and the gasification agent injection pipe are connected with each otherA pressure gauge is arranged at the outlet connection part of the pump, one end of a gas extraction pipe penetrates through the third plugging device and extends into the extraction well, the other end of the gas extraction pipe is connected with a gas inlet of the extraction pump, a gas outlet of the extraction pump is connected with a gas inlet of the heat exchange unit through a pipeline, a gas outlet of the heat exchange unit is connected with a gas inlet of the gas separator through a pipeline, and CH of the gas separator is connected with CH of the gas separator 4 The air outlet is communicated with CH through a pipeline 4 Inlet connection of the generator set, CH 4 CO of exhaust port and gas separator of generator set 2 The gas outlets all pass through CO 2 Conveying pipeline and CO 2 Inlet connection of injection pump, CO 2 The outside of the conveying pipeline is wrapped with a condenser; CO2 2 Outlet of injection pump and CO 2 One end of the injection pipe is connected with CO 2 The 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 gasifying agent injection pump, continuously injecting the mixed gasifying agent into the first closed space through a gasifying agent injection pipe under the pumping action of the gasifying agent injection pump, measuring the pressure value in the gasifying agent injection pipe in real time through a pressure gauge, indicating that the pressure value in the first closed space reaches the pressure threshold when the pressure value reaches the set pressure threshold, stopping the gasifying agent injection pump at the moment, and starting an igniter to ensure that the gasifying agent and CH in the first closed space 4 The gas is subjected to gasification reaction, and the gasification reaction can generate a large amount of radiant heat and CO 2 The 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 time 2 The gas will continuously increase the gas pressure in the first closed space, so that CO is generated 2 Gas enters the generated cracks to further impact and expand, finally, the generated cracks form a crack network, the crack network is used for communicating the upper coal seam, the rock stratum and the lower coal seam, meanwhile, a gasification area of the first closed space can form a pressure relief area with a certain volume due to gasification reaction, and under the dual effects of ground stress and pressure relief effect, the crack network in the upper coal seam and the rock stratum can further increase the porosity and the permeability; at the same time, the temperature of the coal body is increased to reduce CH 4 Gas suctionAttachment and CO 2 Under the dual action of gas competitive adsorption, the CH in the upper coal seam and the lower coal seam is ensured 4 Fast desorption of gas;
D. after waiting for a period of time, starting an extraction pump to extract mixed gas from an extraction well through a gas extraction pipe, wherein the mixed gas comprises CH desorbed from a coal seam 4 Part of CO produced by gas and gasification reaction 2 The 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 separator 2 Gas and CH 4 Gas separation, separated CH 4 Gas into CH 4 Generator set, starting CH 4 The generator set will CH 4 Gas is combusted to generate electricity, so that the utilization of coal bed gas is realized; CO produced by power generation 2 CO separated from gas by gas separator 2 All gases enter into CO 2 Conveying line due to CO 2 The condenser is wrapped outside the conveying pipeline; in CO 2 The gas being in CO 2 The temperature of the conveying pipeline is continuously reduced until liquid CO is formed 2 Then, the liquid CO is introduced 2 By CO 2 Injection pump and CO 2 The injection pipe is injected into a second enclosed space in which liquid CO is present 2 After gasification, the gas enters the cracks in the upper coal layer and is treated with CH in the upper coal layer again 4 Displacing the gas;
E. the closed-loop extraction is continuously carried out according to the mode, and the extracted CH can be extracted 4 Converting the gas into electric energy for subsequent utilization, and generating CO 2 Gas and CO produced by gasification reaction 2 The gas can be continuously used in a closed loop.
2. The method for efficient closed-loop extraction of 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 arranged in the elastic shells, the four arc-shaped claw teeth are uniformly 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 efficient closed-loop extraction of stacked coal bed gas reservoirs according to claim 1, wherein the gasifying agent is O 2 And water vapor.
4. The method for efficient closed-loop extraction of the superposed coal bed gas reservoir according to claim 1, wherein the bottom of the extraction well enters the lower coal bed within a range of 2-3 m, and the horizontal distance between the horizontal well and the extraction well is 200-300 m.
5. The method for efficient closed-loop extraction of the superposed coal bed gas reservoir according to claim 1, wherein a reducing outlet is adopted at the other end of the gasifying agent injection pipe.
6. The method for efficient closed-loop extraction of the superposed coalbed methane reservoir according to claim 1, wherein the pressure threshold in the step C is 5 MPa.
7. The method for efficient closed-loop extraction of the superposed coalbed methane reservoir according to claim 1, wherein a filter group is arranged between the heat exchange unit and the gas separator and used for removing CH 4 And CO 2 Other gaseous impurities in the mixed gas.
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