A method for gas extraction by linkage of three zones in a coal seam group

Abstract

The application discloses a method for gas extraction in three zones of coal seam group, which comprises the following steps: first, dividing the coal seam into underground coal gasification zone, pressure relief and permeability improvement zone and original extraction zone; in the initial stage of underground coal gasification, injecting high-temperature combustible gas generated by underground coal gasification into surface drilling, and the high-temperature combustible gas exchanges heat with the coal body, so that the temperature of the coal body is increased and the gas desorption is strengthened; under the continuous action of the coupling of high temperature and high pressure of the high-temperature combustible gas, the permeability of the coal body is improved; in the process of injecting the high-temperature combustible gas into the surface drilling, other adjacent boreholes continuously extract gas; under the condition of cyclic gas injection-gas extraction of the surface drilling, the coal body is subjected to the impact of positive pressure-negative pressure alternating pneumatic force, so that the coal body is further fractured; under the triple action of high-temperature strengthened gas desorption of the coal body, increased permeability of the coal body and gas displacement, the high-flow and high-quality extraction of deep coal seam gas is finally realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for extracting gas, in particular to a method for extracting gas in three zones of a coal seam group. BACKGROUND

[0002] Coal still accounts for the main part of primary energy consumption, and mine gas is still the No. 1 threat to coal production. During the process of coal mining in the coal mine area, the content and pressure of coal seam gas continue to increase, and the amount of gas emission increases, which leads to the continuous highlighting of the problem of coal production safety, and seriously restricts the development of the coal industry. The development of coal gas ground pre-extraction can reduce the content of underground coal seam gas before coal production, reduce the extraction pressure of underground gas, improve the extraction efficiency, and ensure the safety of mine production. However, with the continuous increase of the mining depth of the coal mine, the structure and permeability of the coal seam are deteriorated, the ground stress and gas content continue to increase; at the same time, the mining scale of the mine is rapidly expanded, and the amount of gas emission increases, which leads to the continuous highlighting of the problem of coal production safety, and the effect of the existing way of gas ground pre-extraction on deep coal mining is poor.

[0003] Therefore, how to provide a new method for effectively extracting gas from deep coal seams and achieving the required extraction effect is the research direction of the present application. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a method for extracting gas in three zones of a coal seam group, which utilizes the underground coal gasification method and uses the combustible gas generated by gasification to promote gas desorption, thereby effectively extracting gas from deep coal seams and achieving the required extraction effect.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a method for extracting gas in three zones of a coal seam group, comprising the following steps:

[0006] Step 1: According to the occurrence of the coal seam group in the coal mine area, the position of the underground coal gasification coal seam is determined, and the coal seam is divided into an underground coal gasification zone, a pressure relief and permeability improvement zone, and an original extraction zone according to the position of the underground coal gasification coal seam and the pressure relief influence range on other unexplored coal seams.

[0007] Step 2: From the ground to the underground coal gasification zone, the gas injection well and the gas production well required for underground coal gasification are constructed, and the first type of ground drilling is constructed to the pressure relief and permeability improvement zone, and the second type of ground drilling is constructed to the original extraction zone. After the ground drilling is constructed, the first type of ground drilling and the second type of ground drilling start the work of gas extraction.

[0008] Step three, underground coal gasification in the underground coal gasification zone, high temperature combustible gas is produced from the gas production well in the gasification process, and the gas is injected into each first type of ground drilling and each second type of ground drilling in turn, and the injection time of each ground drilling is 3-5h, and the cycle is continuously carried out in this way. In the process of injecting high temperature combustible gas into the ground drilling, the high temperature combustible gas exchanges heat with the coal body, so that the temperature of the coal body is increased, and then the coal body absorbs heat and accelerates the desorption of the gas adsorbed by the coal body; under the coupling action of high temperature and high pressure of the high temperature combustible gas, the coal body around each ground drilling is continuously cracked, and the permeability of the coal body is improved; when each ground drilling is not injected, the gas extraction is continuously carried out, and through the alternating injection of high temperature combustible gas and gas extraction, the coal body around the ground drilling is subjected to positive pressure-negative pressure alternating pneumatic force impact, so that the coal body is further cracked.

[0009] Step four, when the extraction flow of a certain first type of ground drilling which is not injected increases suddenly, it is indicated that the pressure relief influence range of the underground coal gasification process reaches the pressure relief and permeability improvement zone, then the injection of high temperature combustible gas into the first type of ground drilling is stopped, the injection of high temperature combustible gas into the second type of ground drilling is continued, and the coal body gasification work in the underground coal gasification zone is completed.

[0010] Further, the selection standard of the underground coal gasification coal seam in the step one is that according to the occurrence of the coal seam group in the coal mine area, the coal seam with thin thickness, high mining difficulty, high mining risk degree and high mining cost is selected as the underground coal gasification coal seam.

[0011] Further, in the step one, the underground coal gasification zone is the range of the selected coal seam for coal gasification; the pressure relief and permeability improvement zone is the mining protective layer of the underground coal gasification zone, so that the gas extraction efficiency is improved after the pressure relief and permeability improvement; the original extraction zone is the gas extraction area which is not affected by the underground coal gasification of the coal seam.

[0012] Further, in order to improve the efficient and high quality gas extraction in the original extraction zone, the step five is further included, that is, the gas extracted from the first type of ground drilling in the pressure relief and permeability improvement zone is injected into each second type of ground drilling in turn, and the gas extraction is continuously carried out when the second type of ground drilling is not injected, so that the enhanced gas extraction is realized by continuously circulating.

[0013] Further, the high temperature combustible gas is mainly composed of CO, H2 and CH4.

[0014] Compared with the prior art, the present application makes full use of the pressure relief and permeability improvement effect of underground coal gasification and the "heat-power" coupling impact of its products, and realizes the linkage of three zones, i.e. underground coal gasification zone, pressure relief and permeability improvement zone and original extraction zone, to achieve efficient and high-quality development of gas. In the initial stage of underground coal gasification, the high-temperature combustible gas generated by underground coal gasification is injected into the ground drilling, and heat transfer occurs between the high-temperature combustible gas and the coal body, so that the temperature of the coal body is increased, the heat absorbed by the gas adsorbed by the coal body is absorbed, and the gas desorption is accelerated; under the continuous action of the "high temperature + high pressure" coupling of the high-temperature combustible gas, the coal body around the ground drilling is continuously cracked, the original closed cracks in the coal body are expanded, the open cracks are further expanded, and the permeability of the coal body is improved; in the process of injecting the high-temperature combustible gas into the ground drilling, other adjacent boreholes continuously extract gas, and the stress direction of the coal body around the boreholes is consistent, which is more conducive to cracking the coal body. The high-temperature combustible gas injected into the ground drilling can also displace and carry the gas rich in the coal body. In addition, under the condition of cyclic injection of gas-gas extraction in the ground drilling, the coal body is subjected to alternating pneumatic force impact of positive pressure (i.e. high pressure generated by the injection of high-temperature combustible gas) - negative pressure (i.e. negative pressure generated during gas extraction), which facilitates further cracking of the coal body. Under the triple action of high-temperature strengthening of coal body gas desorption, increase of coal body permeability and displacement of gas, the gas is extracted at a large flow rate and quickly.

[0015] With the continuous progress of underground coal gasification, the overlying and underlying coal seams gradually change into pressure relief and permeability improvement zones, at this time, the injection of high-temperature combustible gas into the first type of ground drilling is stopped, and the ground drilling in the pressure relief and permeability improvement zone relies on pressure relief and permeability improvement to realize efficient and high-quality extraction of gas. The second type of ground drilling continuously injects high-temperature combustible gas to continue to strengthen gas extraction; after the underground coal gasification zone is completed, the gas extracted from the first type of ground drilling is continuously injected into the second type of ground drilling to strengthen the gas extraction in the original extraction zone.

[0016] In summary, the present application strengthens the gas extraction by the pressure relief and permeability improvement effect of underground coal gasification and the heat-power coupling impact of its products, and the linkage of three zones. The medium for strengthening the gas extraction is the high-temperature combustible gas generated by underground coal gasification or the extracted gas, which minimizes the entry of other gases into the gas extraction system and ensures the concentration and utilization quality of the extracted gas. In addition, the process of the present application is simple, easy to operate and low in cost, and by means of the occurrence conditions of coal seams and underground coal gasification technology, the present application integrates the protection layer mining, high-temperature strengthening of coal body gas desorption, increase of coal body permeability and displacement of gas, and realizes efficient and high-quality development of coal seam gas, which has wide practicability. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a construction schematic diagram of the present application.

[0018] In the figure: 1, gas injection well; 2, underground coal gasification area; 3, gas production well; 4, pressure relief and permeability enhancement area; 5, first type of surface drilling well; 6, second type of surface drilling well; 7, ground surface; 8, original gas extraction area. DETAILED DESCRIPTION

[0019] The present application will be further described below.

[0020] As shown in the figure, the present application comprises the following steps: Figure 1

[0021] Step one, according to the occurrence of coal seam group in coal mine area, select coal seam with thin thickness, high mining difficulty, high mining risk degree and high mining cost as underground coal gasification coal seam, divide the coal seam into underground coal gasification area 2, pressure relief and permeability enhancement area 4 and original gas extraction area 8 according to the position of underground coal gasification coal seam and the pressure relief influence range on other unmined coal seams; the underground coal gasification area 2 is the range of coal seam selected for coal gasification; the pressure relief and permeability enhancement area 4 is the mining protective layer of the underground coal gasification area 2, which improves the gas extraction efficiency after pressure relief and permeability enhancement; the original gas extraction area 8 is the gas extraction area not affected by the underground coal gasification of coal seam.

[0022] Step two, construct gas injection well 1 and gas production well 3 required for underground coal gasification from the ground to the underground coal gasification area 2, and construct first type of surface drilling well 5 to the pressure relief and permeability enhancement area 4, and construct second type of surface drilling well 6 to the original gas extraction area 8, after the construction of surface drilling well, the first type of surface drilling well 5 and the second type of surface drilling well 8 start the gas extraction work.

[0023] Step three, carry out underground coal gasification to the underground coal gasification area 2, high temperature combustible gas composed mainly of CO, H2 and CH4 is produced from the gas production well 3 in the gasification process; and the gas is injected into each first type of surface drilling well 5 and each second type of surface drilling well 6 in turn, the injection time of each surface drilling well is 3-5h, and the cycle is continued in this way, in the process of injecting high temperature combustible gas into surface drilling well, heat transfer occurs between high temperature combustible gas and coal body, which makes the temperature of coal body rise, and then the coal body adsorbed gas absorbs heat and accelerates its desorption; under the coupling effect of high temperature and high pressure of high temperature combustible gas, the coal body around each surface drilling well cracks continuously, which improves the permeability of coal body; each surface drilling well continuously carries out gas extraction when no gas is injected, through the way of alternately injecting high temperature combustible gas and extracting gas, the coal body around surface drilling well is subjected to positive pressure-negative pressure alternating pneumatic force impact, which promotes the coal body to further crack.

[0024] ​Step four, when the extraction flow of a first type of ground drilling well 5 without gas injection suddenly increases greatly, it indicates that the pressure relief influence range of the underground coal gasification process reaches the pressure relief and permeability improvement zone 4, then stop injecting high temperature combustible gas into the first type of ground drilling well 5, continue to maintain the circulating injection of high temperature combustible gas into the second type of ground drilling well 6, until the coal gasification work of the underground coal gasification zone 2 is completed.

[0025] Step five, in order to improve the efficient and high quality gas extraction of the original extraction zone, the gas extracted from the first type of ground drilling well 5 in the pressure relief and permeability improvement zone 4 is injected into each second type of ground drilling well 6 in turn, the second type of ground drilling well 6 continues to extract gas without gas injection, so as to realize the intensified gas extraction by continuous circulation.

[0026] The above is only the preferred embodiment of the present application, it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for gas extraction in three zones of a coal seam group, characterized in that, The method comprises the following steps: Step one, according to the occurrence of coal seams in the coal mining area, the position of the underground coal gasification coal seam is determined, and the coal seam is divided into the underground coal gasification area, the pressure relief and permeability enhancement area and the original extraction area according to the position of the underground coal gasification coal seam and the influence range of pressure relief on other unmined coal seams; Step two, the gas injection well and the gas production well required by the underground coal gasification are constructed from the ground to the underground coal gasification area, the first type of ground drilling is constructed to the pressure relief and permeability enhancement area, and the second type of ground drilling is constructed to the original extraction area, after the ground drilling is constructed, the first type of ground drilling and the second type of ground drilling start the gas extraction work; Step three, the underground coal gasification is carried out in the underground coal gasification area, the high-temperature combustible gas is produced from the gas production well in the gasification process, and the gas is injected into each first type of ground drilling and each second type of ground drilling in turn, the injection time of each ground drilling is 3-5h, and the cycle is continuously carried out, in the process that the high-temperature combustible gas is injected into the ground drilling, the high-temperature combustible gas is heat transferred with the coal body, the temperature of the coal body is increased, and then the heat absorbed by the coal body is absorbed and the desorption of the coal body is accelerated; under the coupling action of the high temperature and high pressure of the high-temperature combustible gas, the coal body around each ground drilling is continuously cracked, and the permeability of the coal body is improved; the gas extraction is continuously carried out when each ground drilling is not injected with gas, and the coal body around the ground drilling is impacted by the positive pressure-negative pressure alternating pneumatic force in the alternating mode of the high-temperature combustible gas injection and the gas extraction, so that the coal body is further cracked; Step four, when the extraction flow of a certain first type of ground drilling which is not injected with gas suddenly increases greatly, it is indicated that the pressure relief influence range of the underground coal gasification process reaches the pressure relief and permeability enhancement area, then the injection of the high-temperature combustible gas into the first type of ground drilling is stopped, the cyclic injection of the high-temperature combustible gas into the second type of ground drilling is continuously kept, and the coal body gasification work in the underground coal gasification area is completed; Step five, the gas extracted from the first type of ground drilling in the pressure relief and permeability enhancement area is injected into each second type of ground drilling in turn, and the gas extraction is continuously carried out when the second type of ground drilling is not injected with gas, so that the strengthened gas extraction is continuously cycled.

2. The method of claim 1, wherein, The selection standard of the underground coal gasification coal seam in step one is that according to the occurrence of coal seams in the coal mining area, the coal seam with thin thickness, large mining difficulty, large mining danger degree and high mining cost is selected as the underground coal gasification coal seam.

3. The method of claim 1, wherein, In step one, the underground coal gasification area is the range of the coal seam selected for coal gasification; the pressure relief and permeability enhancement area is the mining protective layer of the underground coal gasification area, so that the gas extraction efficiency is improved after the pressure relief and permeability enhancement; and the original extraction area is the gas extraction area which is not affected by the underground coal gasification of the coal seam.

4. The method for coal group occurrence three-zone linkage gas extraction according to claim 1, characterized in that, The high-temperature combustible gas comprises CO, H2 and CH4 gas.

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