Method for increasing yield of coal seam gas through cooperation of water jet slotting and hot flue gas displacement

Abstract

The invention discloses a method for increasing the yield of coal seam gas through cooperation of water jet slotting and hot flue gas displacement, which comprises the following steps: firstly, drilling in a low-permeability coal seam to form a slotting gas injection drill hole and an extraction drill hole, and performing high-pressure hydraulic slotting on the slotting gas injection drill hole to form an annular slotting groove; then a gas injection pipe and an extraction pipe are arranged in the slotted gas injection drill hole and the extraction drill hole correspondingly, and hole sealing operation is completed; the method comprises the following steps: firstly, extracting free gas in the slotted gas injection drill hole, then injecting hot flue gas into the slotted gas injection drill hole, and promoting desorption and flow of gas in coal body hole fractures by utilizing high temperature property and displacement property of the hot flue gas to form a new gas migration channel. And finally, the desorbed gas is subjected to secondary extraction in the extraction drill hole. Water jet slotting and hot flue gas displacement are combined, the breathability of the coal seam is preliminarily improved through high-pressure water jet by means of hydraulic slotting, generation of new pores is promoted through hot flue gas injection, gas is driven to flow out, a large amount of CO2 is sealed in the coal seam, and the gas extraction efficiency of the coal seam difficult to extract is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine production, and particularly relates to the extraction of coal bed methane (gas), and specifically is a method for increasing the production of coal bed gas by coordinating water jet cutting with hot flue gas displacement. Background Art

[0002] The gas in deep coal seams is characterized by high stress, low permeability, microporosity, and strong adsorption. Mining faces the problems of low coal seam permeability, difficult gas desorption and flow, and low extraction rate, resulting in most of the gas remaining in the coal seams. In the process of coal mining, the residual gas will not only be released into the mining space, causing gas to exceed the limit, but may also induce gas outburst accidents, seriously threatening the safe production of mines. In addition, the gas released into the mining space will be discharged into the atmosphere with the mine wind flow, which will not only cause a greenhouse effect (the greenhouse effect of gas is about 22 to 28 times that of carbon dioxide), but also cause a huge waste of gas resources, with more than 20 billion cubic meters of gas discharged into the atmosphere each year.

[0003] The main components of high-temperature hot flue gas generated by gas power generation are N2, CO2, and H2O. If they are captured and injected into underground gas extraction boreholes or coalbed methane wells, on the one hand, they can displace and replace the gas in the coal seam; on the other hand, the thermal effect produced can promote the desorption and flow of gas in the pores and fissures of the coal body, thereby improving the efficiency of gas extraction. Studies have shown that the adsorption capacity of gas decreases with increasing temperature. In addition, the high temperature of hot flue gas can cause the coal body to expand and deform and induce secondary pores and fissures, which helps to form new channels for gas migration, providing a new method for reducing carbon emissions and gas extraction. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and to provide a method for increasing the production of coal seam gas by combining water jet cutting with hot flue gas displacement. The method is a method for extracting gas by combining hot flue gas produced by a gas power plant with water jet permeability enhancement. Specifically, hot flue gas is injected on the basis of hydraulic cutting to enhance the permeability and displacement of coal seam gas, modify the pore and fracture structure of the coal body, and promote gas desorption and flow, so as to improve the extraction efficiency of difficult-to-extract coal seam gas.

[0005] The present invention is achieved through the following technical solutions: A method for increasing coal seam gas production by coordinating water jet cutting and hot flue gas displacement comprises the following steps: A. Determine the low permeability coal seam, and then use conventional drilling methods to drill holes in the coal seam to be extracted. The top of the hole passes through the coal seam roof by 0.5-1m, and the interval between two adjacent holes is 5-10m. The holes are arranged in an alternating manner of slotted gas injection holes and extraction holes.

[0006] B. Use a water jet cutting system to cut seams in the slotting and gas injection drilling. Open the water flow electromagnetic shut-off valve and set the water pump pressure to 80-150MP to start the hydraulic cutting operation. Cut seams for 5-10 minutes at the same coal seam position. After completing one cutting operation, withdraw the drill 1-2m and then cut seams again. Repeat this step according to the actual coal seam thickness. Conventional sealing is performed on the extraction borehole and the extraction pipe extending out of the exposed end of the borehole is connected to the extraction pump in the extraction system.

[0007] C. After the slitting is completed, the drill is withdrawn to release the accumulated water and solid coal slag in the slit gas injection borehole, and a borehole sealing device is used to seal the hole between the coal seam and the rock layer to reduce subsequent gas leakage. The borehole sealing device reserves slit gas injection holes and primary extraction holes, and the gas injection pipe and the extraction pipe are extended from the reserved hole into the super-drilling hole sealing device by 30-40cm. The gas injection pipe is directly connected to the hot flue gas injection pump.

[0008] D. Open the first extraction throttle valve and the first gas extraction device to extract the free and partially desorbed gas in the coal seam after hydraulic cutting; use the gas-solid filter in the first gas extraction device to filter the extracted gas, and return it to the coal-fired power plant through the gas transportation pipeline for power generation. At the same time, start the hot flue gas injection pump to the high-pressure gas insulation tank, and turn off the hot flue gas injection pump when the gas tank volume is filled to 70%-80%.

[0009] E. When the gas extraction flow rate drops to 20%-45% of the normal range, close the first extraction throttle valve and the first gas extraction device, open the tank outlet valve, adjust the hot flue gas heating device to keep the output hot flue gas temperature at 400-500°C, turn on the hot flue gas booster pump and adjust the pump pressure range to 5-10MPa to inject hot flue gas into the slit gas injection borehole for displacement. The CO2 in the hot flue gas can drive and replace the gas that cannot be normally resolved in the coal seam. The high temperature causes the coal body to expand and deform and induce secondary pores and cracks.

[0010] F. After the displacement is completed, close the tank outlet valve and the hot flue gas booster pump, open the II extraction throttle valve and the II gas extraction device, and pass the extracted gas through the gas-solid filter in the II gas extraction device to remove impurities. The separated gas is returned to the coal-fired power plant through the gas transportation pipeline for power generation, and N2 and CO2 are collected in the gas tank of the II gas extraction device for gas injection displacement in other coal seams.

[0011] Finally, the above steps can achieve the effect of increasing gas production.

[0012] As a preferred technical solution, a N2 monitoring meter is provided on the drilling plugging device at the slit gas injection drilling site.

[0013] As a preferred technical solution, the hot flue gas injection method is cyclic injection, and each slit gas injection drilling adopts the "two days of injection and ten days of rest" cycle until the N2 monitoring meter on the drilling plugging device detects N2 and stops gas injection.

[0014] As a preferred technical solution, all underground equipment adopts intrinsically safe equipment.

[0015] As a preferred technical solution, the main components of the hot flue gas are N2, CO2 and high-temperature water vapor.

[0016] As a preferred technical solution, the high-pressure gas insulation tank is provided with a drain port to reduce the adverse effects of moisture on displacement.

[0017] As a preferred technical solution, a real-time gas concentration detection device is provided on the extraction pipe, which automatically closes the first extraction throttle valve when the gas concentration threshold is reached.

[0018] Compared with the traditional coal seam permeability enhancement technology, the present invention combines water jet cutting of coal seams with hot flue gas displacement and gas extraction, which has the following advantages: (1) First, hydraulic cutting is carried out to make full use of the water hammer pressure of the water jet to destroy the coal rock, which initially improves the permeability of the coal seam and forms a large number of initial cracks, providing a preliminary channel for gas migration and increasing more injection space and specific surface area in contact with coal for subsequent hot flue gas injection.

[0019] (2) Inject hot flue gas from a coal mine gas power plant into the borehole to heat the surrounding coal, activate the coal pores and promote gas desorption. Under the combined effects of pressure drive and multi-media competition, the hot flue gas and desorbed gas migrate to the activated pores, and the heat flow carried by the flue gas continues to conduct into the coal body, promoting the formation of new pores and driving the gas out, thereby improving the gas extraction efficiency of difficult-to-extract coal seams.

[0020] (3) The present invention seals a large amount of CO2 in the hot flue gas in the coal seam and proposes a new method of enhanced permeability to displace gas, which solves the multiple problems of efficient development of gas in deep coal seams with high gas content and difficult to extract, and reduction of greenhouse gases such as hot flue gas in coal mining areas, thus raising the construction of green mines to a new level. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 Flow chart of the method of the present invention.

[0023] Figure 2 The present invention is a system block diagram of the implementation process of the method.

[0024] Figure 3 Schematic diagram of the arrangement of the holes drilled in the method of the present invention.

[0025] In the figure: 1- thermal power plant, 2- hot flue gas injection pump, 3- high-pressure gas insulation tank, 4- gas transport pump, 5- hot flue gas heating device, 6- hot flue gas booster pump, 7- N2 monitoring meter, 8- injection throttle valve, 9- water tank, 10- water pump, 11- water flow electromagnetic stop valve, 12- drilling rig, 13- first gas extraction device, 14- gas storage tank, 15- second gas extraction device, 16- second extraction throttle valve, 17- first extraction throttle valve, 18- drill bit, 19- horizontal nozzle, 20- extraction pipe, 21- gas injection pipe, 22- coal seam, 23- extraction borehole, 24- slot gas injection borehole, 25- working face return air tunnel, 26- working face air inlet tunnel, 27- secondary extraction pipeline, 28- working face cut eye, 29- rock formation, 31-tank outlet valve, 32-drain port. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0027] This embodiment provides a method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement. The various systems involved in the implementation process of this method are as follows: Figure 2 As shown, it includes coal body system, water jet drilling system, hot flue gas system and gas extraction system.

[0028] The coal body system includes coal seams and rock strata, on which extraction boreholes 23 and slotted gas injection boreholes 24 are opened.

[0029] The water jet drilling system includes a drilling rig 12, a water tank 9, a water pump 10, a water flow electromagnetic shut-off valve 11 and a drill bit 18. The water tank 9 is connected to the water pump 10 through a pipeline, the water pump 10 is connected to the water flow electromagnetic shut-off valve 11 through a pipeline, the water flow electromagnetic shut-off valve 11 is connected to the drilling rig 12 through a pipeline, and the drill bit 18 is connected to the drilling rig 12. A plurality of lateral nozzles 19 are arranged on the drill bit 18.

[0030] The hot flue gas system includes a thermal power plant 1, which is connected to a hot flue gas injection pump 2 through a pipeline, and the hot flue gas injection pump 2 is connected to a high-pressure gas insulation tank 3 through a pipeline. The high-pressure gas insulation tank 3 is provided with an exhaust port and a drain port, and the exhaust port is provided with an outlet valve and is connected to a hot flue gas heating device 5 through a pipeline. The hot flue gas heating device 5 is connected to a hot flue gas booster pump 6 through a pipeline, and the hot flue gas booster pump 6 is connected to an injection pipe 21 through a pipeline with an injection throttle valve 8. The injection pipe 21 passes through a drilling plugging device and then extends to a slit gas injection borehole 24. An N2 monitoring meter is provided on the drilling plugging device at the slit gas injection borehole 24.

[0031] The gas extraction system includes a gas storage tank 14, a first gas extraction device 13, and a second gas extraction device 15. The gas storage tank 14 is connected to the first gas extraction device 13 and the second gas extraction device 15 through pipelines; the first gas extraction device 13 is connected to the extraction pipe 20 through a pipeline with a first extraction throttle valve, and the extraction pipe 20 passes through the borehole plugging device and extends to the slit gas injection borehole 24; the second gas extraction device 15 is connected to the secondary extraction pipeline 27 through a pipeline with a second extraction throttle valve 16, and the secondary extraction pipeline 27 extends to the extraction borehole 23; the second gas extraction device 15 is connected to the thermal power plant 1 through a pipeline with a gas transport pump 4.

[0032] The above-mentioned method of increasing coal seam gas production by combining water jet cutting with hot flue gas displacement is as follows: Figure 1 As shown, the specific steps include: A. Drilling construction: First determine the specific location of the deep low-permeability coal seam, such as Figure 3 As shown, a row of through-layer drill holes are constructed from the working face return air tunnel 25 and the working face air inlet tunnel 26 to the working face cut eye 28. The drill holes are alternately arranged as extraction drill holes 23 and slit gas injection drill holes 24. The distance between two adjacent drill holes is 5-10m (10m, 7m, 5m, etc. can be selected during specific implementation), and the top of the through-layer drill hole exceeds the roof coal seam by 0.5-1m (1m, 0.5m, 0.8m, etc. can be selected during specific implementation).

[0033] B. Hydraulic cutting: Use the drilling rig 12 to control the lateral nozzle 19 to open, open the water flow electromagnetic stop valve 11, set the pressure of the water pump 10 to 80-150MP (80MP, 125MP, 150MP, etc. can be selected during specific implementation), and the high-pressure water jet reaches the lateral nozzle through the water braid to start hydraulic cutting of the cutting and gas injection drilling holes, and cut the same coal seam position for 5-10min (8min, 5min, 10min, etc. can be selected during specific implementation); after completing one cutting, close the water pump 10 and the water flow electromagnetic stop valve 11, retreat 1-2m (2m, 1m, etc. can be selected during specific implementation) and then perform the above-mentioned cutting work; repeat 4 times according to the thickness of the coal seam, complete the cutting, close the water pump 10 and the water flow electromagnetic stop valve 11, and retreat.

[0034] C. Sealing operation: After completing the hydraulic seam cutting, the accumulated water and solid coal slag in the seam gas injection borehole 24 are discharged, and then the gas injection pipe 21 and the extraction pipe 20 are simultaneously extended into the seam gas injection borehole 24. The gas injection pipeline is sequentially provided with an injection throttle valve 8, a hot flue gas booster pump 6, a hot flue gas heating device 5 and a high-pressure gas insulation tank 3. At the same time, the secondary extraction pipeline 27 is extended into the extraction borehole 23; in the rock stratum 29 and the coal seam in the extraction borehole 23 and the seam gas injection borehole 24, the gas injection pipe 21 and the extraction pipe 20 are simultaneously extended into the seam gas injection borehole 24. A secondary sealing method is used between 22 to carry out the sealing operation to reduce the amount of gas leakage during subsequent gas injection. When sealing, a hole is reserved for the extraction pipe to be inserted into. The extraction pipe 20 is inserted into the reserved hole 30-40cm beyond the upper part of the drilling plugging device (40cm, 30cm, 35cm, etc. can be selected during specific implementation). An electronic gas flowmeter is installed on the first extraction throttle valve 17, and an N2 monitoring meter 7 is installed on the drilling plugging device of the slit gas injection borehole 24.

[0035] D. Initial gas extraction: Open the first extraction throttle valve 17 and the first gas extraction device 13 to extract the free and partially desorbed gas in the coal seam after hydraulic fracturing; filter the gas using the gas-solid filtration device in the first gas extraction device 13 and store it in the gas storage tank 14; a real-time gas concentration detection device is provided on the extraction pipe 20, which automatically closes the first extraction throttle valve 17 when the gas concentration threshold is reached; at the same time, open the hot flue gas injection pump 2 to the high-pressure gas insulation storage tank 3, and close the hot flue gas injection pump 2 when the volume of the gas tank 3 is 70%-80%. After a period of rest, open the drain port 32 to discharge the cooling water to reduce the adverse effects of moisture on displacement.

[0036] E. Inject hot flue gas for displacement: According to the real-time results of the electronic gas flowmeter, when the gas flow drops to 20%-45% of the initial flow, the first extraction throttle valve 17 is automatically closed, and the first gas extraction device 13 is closed at this time; the hot flue gas injection throttle valve 8, the hot flue gas heating device 5 and the tank outlet valve 31 are opened, and the hot flue gas booster pump 6 is set to adjust the pump pressure to 5-10MPa (7MPa, 5MPa, 10MPa, etc. can be selected during specific implementation), and the hot flue gas is transported to the slit gas injection borehole 24 through a high-temperature resistant pipeline to inject hot flue gas into the coal seam for displacement. The main components of the hot flue gas are N2, CO2 and high-temperature water vapor; the slit gas injection borehole 24 adopts the method of "inject for 2 days and stop for 10 days" for gas injection, and the gas injection is stopped when the N2 monitoring meter 7 detects N2.

[0037] F. Secondary extraction: After the displacement is completed, close the hot flue gas injection throttle valve 8, the storage tank outlet valve 31, the hot flue gas booster pump 6 and the hot flue gas heating device 5, and open the second extraction throttle valve 16, the second gas extraction device 15 and the gas transport pump 4. The gas-solid filter in the second gas extraction device 15 removes impurities and irrelevant gases from the extracted gas, and the separated N2 and CO2 are collected in the gas storage tank of the second gas extraction device 15 for gas injection displacement in other coal seams. The separated gas is returned to the thermal power plant 1 through the gas transport pipeline and the gas transport pump 4 for power generation.

[0038] The present invention utilizes the water hammer pressure of the water jet to destroy the coal rock through hydraulic cutting to initially improve the permeability of the coal seam, form a large number of initial cracks, and initially provide channels for gas migration, so as to increase more injection space and specific surface area in contact with coal through subsequent injection of hot flue gas, and then utilizes the high-pressure, high-temperature, multi-component and multi-phase characteristics of the hot flue gas to promote the generation of pores to form a more complex fracture network, so as to fully resolve the gas and improve the extraction efficiency.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement, characterized in that: The following steps are involved: A. Determine the low permeability coal seam, and then use conventional drilling methods to drill holes in the coal seam to be extracted. The top of the hole passes through the coal seam roof by 0.5-1m, and the interval between two adjacent holes is 5-10m. The holes are arranged in an alternating manner of slotted gas injection holes and extraction holes; B. Use a water jet cutting system to cut seams in the slotting and gas injection drilling. Open the water flow electromagnetic shut-off valve and set the water pump pressure to 80-150MP to start the hydraulic cutting operation. Cut seams for 5-10 minutes at the same coal seam position. After completing one cutting operation, withdraw the drill 1-2m and then cut seams again. Repeat this step according to the actual coal seam thickness. Perform conventional sealing on the extraction borehole and connect the extraction pipe extending out of the exposed end of the borehole to the extraction pump in the extraction system; C. After the slitting is completed, the drilling operation is carried out to release the accumulated water and solid coal slag in the slitting gas injection borehole, and the borehole plugging device is used to seal the hole between the coal seam and the rock layer to reduce subsequent gas leakage. The slitting gas injection hole and the primary extraction hole are reserved in the borehole plugging device, and the gas injection pipe and the extraction pipe are extended from the reserved hole into the super-drilling plugging device by 30-40cm, and the gas injection pipe is directly connected to the hot flue gas injection pump; D. Open the first extraction throttle valve and the first gas extraction device to extract the free and partially desorbed gas in the coal seam after hydraulic cutting; use the gas-solid filter in the first gas extraction device to filter the extracted gas, and return it to the coal-fired power plant through the gas transportation pipeline for power generation. At the same time, start the hot flue gas injection pump to the high-pressure gas insulation tank, and turn off the hot flue gas injection pump when the gas tank volume is 70%-80%; E. When the gas extraction flow rate drops to 20%-45% of the normal range, close the first extraction throttle valve and the first gas extraction device, open the tank outlet valve, adjust the hot flue gas heating device to keep the output hot flue gas temperature at 400-500°C, turn on the hot flue gas booster pump and adjust the pump pressure range to 5-10MPa to inject hot flue gas into the slotted gas injection borehole for displacement. The CO2 in the hot flue gas can drive and replace the gas that cannot be normally resolved in the coal seam. Its high temperature causes the coal body to expand and deform and induce secondary pores and fissures; F. After the displacement is completed, close the tank outlet valve and the hot flue gas booster pump, open the second extraction throttle valve and the second gas extraction device, and remove impurities from the extracted gas through the gas-solid filter in the second gas extraction device. The separated gas is returned to the coal-fired power plant through the gas transportation pipeline for power generation, and N2 and CO2 are collected in the gas storage tank of the second gas extraction device for gas injection displacement in other coal seams; Finally, the above steps can achieve the effect of increasing gas production.

2. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 1 is characterized in that: A N2 monitoring meter is provided on the drilling plugging device at the slotted gas injection drilling site.

3. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 2 is characterized in that: The hot flue gas injection method is cyclic injection, and each slit gas injection drilling adopts the "inject for two days and stop for ten days" method until the N2 monitoring meter on the drilling plugging device detects N2 and stops gas injection.

4. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 1 is characterized in that: All underground equipment is intrinsically safe.

5. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 1 is characterized in that: The main components of hot flue gas are N2, CO2 and high-temperature water vapor.

6. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 1 is characterized in that: The high-pressure gas insulation tank is equipped with a drain port to reduce the adverse effects of moisture on displacement.

7. The method for increasing coal seam gas production by combining water jet cutting with hot flue gas displacement according to claim 1 is characterized in that: A real-time gas concentration detection device is installed on the extraction pipe, which automatically closes the first extraction throttle valve when the gas concentration threshold is reached.

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