Multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method

Abstract

A multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method is provided. A large amount of N.sub.2 or CO.sub.2 is injected into a drill hole by a heat injection and gas injection extracting pipe and by a high-pressure gas cylinder and a reducing valve, then a certain amount of methane and dry air are injected into a high-temperature and high-pressure combustion chamber by the high-pressure gas cylinder and the reducing valve, to be mixed and combusted to form high-temperature and high-pressure impact wave. High-temperature vapour is injected into the drill holes by the heat injection and gas injection extracting pipe to promote desorption of the coal masses.

Claims

1. A multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method, the method comprising following steps in sequence: step 1: constructing an impacting and heat injecting drill hole in a coal seam; step 2: placing a porous cylinder with a piston in the impacting and heat injecting drill hole, penetrating one end of a heat injection and gas injection extracting pipe through the piston to be put into the porous cylinder, extending the other end of the heat injection and gas injection extracting pipe out of the impacting and heat injecting drill hole, and connecting the other end of the heat injection and gas injection extracting pipe with a gas injection pipe and a heat injection pipe by a tee joint; putting one end of an impact wave ingress pipe into the porous cylinder, and connecting the other end of the impact wave ingress pipe to a combustion chamber outside the impacting and heat injecting drill hole, wherein the impact wave ingress pipe does not penetrate through the piston; step 3: sealing the impacting and heat injecting drill hole, closing the heat injection pipe, opening the gas injection pipe, injecting N.sub.2 or CO.sub.2 into the impacting and heat injecting drill hole by the heat injection and gas injection extracting pipe, and then closing the gas injection pipe; step 4: injecting combustible gas and auxiliary gas into the combustion chamber; step 5: igniting the combustible gas in the combustion chamber by a control system, wherein impact wave generated by combustion of the combustible gas is guided into the porous cylinder by the impact wave ingress pipe to impact the piston, and the piston slides along the heat injection and gas injection extracting pipe to extrude N.sub.2 or CO.sub.2 in the impacting and heat injecting drill hole, so that coal masses at a periphery of the impacting and heat injecting drill hole generate a large quantity of cracks; step 6: closing the gas injection pipe, opening the heat injection pipe to inject high-temperature vapour of 150 C.-250 C. into the impacting and heat injecting drill hole by the heat injection and gas injection extracting pipe, and closing the heat injection pipe after injection of the high-temperature vapour lasts for 2-3 hours; step 7: connecting the heat injection and gas injection extracting pipe into an extracting system to perform gas extraction after temperature in the impacting and heat injecting drill hole is reduced; step 8: when concentration of gas extracted by the extracting system is reduced to 25% or lower, withdrawing the heat injection and gas injection extracting pipe from the extracting system, opening the gas injection pipe, continuously injecting a large amount of N.sub.2 into the impacting and heat injecting drill hole by the heat injection and gas injection extracting pipe to extrude the piston so as to reset the piston, and then closing the gas injection pipe; and step 9: repeating the steps 4-8, and intensifying the gas extraction by synergistic effect of the multi-stage combustion impact wave coal mass cracking and heat injection alternating.

2. The multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method according to claim 1, wherein step 1 further comprises constructing the impacting and heat injecting drill hole and a common drill hole in the coal seam, wherein the common drill hole is located at the periphery of the impacting and heat injecting drill hole; and step 2 further comprises placing the porous cylinder with the piston in the impacting and heat injecting drill hole, penetrating the one end of the heat injection and gas injection extracting pipe through the piston to be put into the porous cylinder, extending the other end of the heat injection and gas injection extracting pipe out of the impacting and heat injecting drill hole, and connecting the other end of the heat injection and gas injection extracting pipe with the gas injection pipe and the heat injection pipe by the tee joint; putting one end of the impact wave ingress pipe into the porous cylinder, and connecting the other end of the impact wave ingress pipe to the combustion chamber outside the impacting and heat injecting drill hole, wherein the impact wave ingress pipe does not penetrate through the piston; putting one end of a common extracting pipe into the common drill hole and sealing the hole, and connecting the other end of the common extracting pipe to the extracting system.

3. The multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method according to claim 1, wherein a solenoid valve is further provided on the impact wave ingress pipe, and the solenoid valve is set and regulated by the control system.

4. The multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method according to claim 3, wherein an opening pressure value of the solenoid valve is 30 MPa.

5. The multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method according to claim 1, wherein the combustible gas is methane, and the auxiliary gas is dry air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an equipment structure used by a multi-stage combustion impact wave coal mass cracking and heat injection alternating intensified gas extracting method in embodiment 1 of the present invention and a mounting position thereof.

DESCRIPTION OF THE EMBODIMENTS

(2) Further descriptions of the present invention are made in the following by referring to the accompanying drawings.

Embodiment 1

(3) As shown in FIG. 1, coal mine underground multi-stage combustion impact wave coal mass cracking and intensified gas extracting equipment includes a porous cylinder 9 with a piston, a heat injection and gas injection extracting pipe 6, an impact wave ingress pipe 8, a combustion impacting device, a vapour generating device 12 and an extracting system 11.

(4) One end of the heat injection and gas injection extracting pipe 6 penetrates through the piston in the porous cylinder 9 and extends into the porous cylinder 9, and the piston slides on the heat injection and gas injection extracting pipe 6. The other end of the heat injection and gas injection extracting pipe 6 extends out of the porous cylinder 9 and is connected with a gas injection pipe and a heat injection pipe by a tee joint. A first valve 7 is mounted on the gas injection pipe, a second valve 13 is mounted on the heat injection pipe, the gas injection pipe is connected with an N.sub.2 cylinder, and the heat injection pipe is connected with the vapour generating device 12. One end of the impact wave ingress pipe 8 is connected with the combustion impacting device, and the other end of the impact wave ingress pipe extends into the porous cylinder and does not penetrate through the piston. A common extracting pipe 10 is connected with the extracting system 11.

(5) The combustion impacting device includes a high-temperature and high-pressure combustion chamber 1, a first gas injection pipe, a second gas injection pipe and a control system 4. One end of the first gas injection pipe and one end of the second gas injection pipe are respectively connected with the high-temperature and high-pressure combustion chamber 1, and the other end of the first gas injection pipe and the other end of the second gas injection pipe are respectively connected with a methane cylinder 3 and a dry air cylinder 2. An ignition device of the control system 4 extends into the combustion chamber, the first gas injection pipe is used for injecting methane into the high-temperature and high-pressure combustion chamber 1, the second gas injection pipe is used for injecting dry air into the high-temperature and high-pressure combustion chamber 1, and the control system 4 is used for igniting methane in the high-temperature and high-pressure combustion chamber 1. The solenoid valve 5 is mounted on the impact wave ingress pipe 8, and is controlled by the control system 4.

Embodiment 2

(6) The coal mine underground multi-stage combustion impact wave coal mass cracking and intensified gas extracting method 1 is performed by using the equipment in embodiment 1, wherein the method specifically includes following steps.

(7) a. A common drill hole and an impacting and heat injecting drill hole are alternately constructed in a coal seam, wherein the common drill hole is located at a periphery of the impacting and heat injecting drill hole.

(8) b. After construction is completed, a porous cylinder 9 with a piston is put in the impacting and heat injecting drill hole, wherein the cylinder wall of the porous cylinder 9 is tightly adhered to the impacting and heat injecting drill hole.

(9) c. A heat injection and gas injection extracting pipe 6 is put in the porous cylinder 9, then the heat injection and gas injection extracting pipe 6 and the porous cylinder 9 are placed in the impacting and heat injecting drill hole together, an impact wave ingress pipe 8 is tightly connected with the piston, and then hole sealing operation is performed; after the hole sealing operation is completed, a common extracting pipe 10 is connected to an extracting system 11 to extract gas; and then an opening pressure value of a solenoid valve 5 is set as 30 MPa by the control system 4.

(10) d. A second valve 13 is closed, a first valve 7 is opened, a large amount of N.sub.2 or CO.sub.2 is injected into the impacting and heat injecting drill hole via the heat injection and gas injection extracting pipe 6 by a gas injection pipe by using a high pressure gas cylinder and a reducing valve, and then the first valve 7 is closed.

(11) e. A certain amount of dry air and methane is injected into the high-temperature and high-pressure combustion chamber 1 by a methane cylinder 3, a dry air cylinder 2 and the reducing valve, and the mixed gas is ignited by the control system 4.

(12) f. After the pressure in the high-temperature and high-pressure combustion chamber 1 reaches 30 MPa, the high-temperature and high-pressure impact wave is instantly released by the automatic start of the solenoid valve 5, and the piston is impacted by the impact wave ingress pipe 8, wherein the piston slides along the heat injection and gas injection extracting pipe 6 to extrude N.sub.2 or CO.sub.2, and further a large quantity of cracks are generated at the periphery of the impacting and heat injecting drill hole, and the connectivity of the crack network is intensified.

(13) g. A vapour generating device 12 is started, the second valve 13 is opened, high-temperature vapour of 150 C.-250 C. is injected into the impacting and heat injecting drill hole via the heat injection and gas injection extracting pipe 6 by the heat injection pipe to promote the desorption of gas in the coal mass, and the second valve 13 is closed after heat injection lasts for 2-3 hours.

(14) h. After temperature in the impacting and heat injecting drill hole is reduced, the gas injection pipe is connected into the extracting system 11, and the first valve 7 is opened to perform gas extraction.

(15) i. When the concentration of the gas extracted by the extracting system 11 is reduced to 25% or lower, the first valve 7 is closed, and the gas injection pipe is withdrawn from the extracting system 11; then the first valve 7 is opened, a large amount of N.sub.2 or CO.sub.2 is continuously injected into the impacting and heat injecting drill hole via the heat injection and gas injection extracting pipe 6 by the gas injection pipe to extrude the piston, to reset the piston, and then the first valve 7 is closed.

(16) j. Steps e-i are repeated, and drill hole gas extraction is intensified by the synergistic effect of combustion impact wave coal mass cracking and heat injection alternating.