Method for gas extraction alternating oscillating pulse high energy gas extraction with thermal injection

Abstract

A gas extraction method in which high energy gas fracturing technology is used to form a fracture network in a thermal injection borehole. Then high-pressure, cyclically temperature-changing steam is injected into the borehole using a spinning oscillating-pulse jet nozzle to form oscillating superheated steam, alternatingly impacting and heating the coal body. The high energy gas forms a fracture network that provides channels for passage of the superheated steam, while oscillating changes in steam temperature and pressure also promote crack propagation and perforation of the coal body; the combined effect of alternation of the two enhances gas desorption and extraction efficiency.

Claims

1. A method for gas extraction by alternating oscillation pulsed high-energy gas fracturing and heat injection, comprising: first, arranging sites of extraction boreholes in a grid manner towards a direction of a coal seam, and then drilling the extraction boreholes, sealing the extraction boreholes, and connecting the extraction boreholes to a gas extraction pipe network for gas extraction, sequentially; wherein, the method further comprises the following steps: a. arranging fracturing and heat injection borehole at the intersections centers of extraction boreholes in the grid manner which has finished construction, drilling at each of the sites of fracturing and heat injection boreholes with a drilling machine till a drill bit of the drilling machine passes through the roof of the coal seam, and then withdrawing a drill stem of the drilling machine; b. inserting a steel pipe with a spinning oscillation pulsed jet nozzle mounted on a pipe head of the steel pipe into the fracturing and heat injection borehole till the pipe head reaches a spaced distance from the roof of the coal seam, pre-sealing the borehole for the steel pipe, and connecting the fracturing and heat injection borehole to the gas extraction pipe network through an extraction pipeline mounted with an extraction pipeline valve; c. connecting the exposed end of the steel pipe to a high-pressure gas station and a steam generator via a tee joint, closing the valve on the extraction pipeline and a valve on a hot steam transmission pipeline of the steam generator first, and then opening a valve on a high-energy gas pipeline of the high-pressure gas station, so that the high-pressure gas in the high-pressure gas station enters into the steel pipe via the tee joint, is jetted from the spinning oscillation pulsed jet nozzle and forms a high-energy oscillation pulsed jet stream to impact and fracture the coal mass in the fracturing and heat injection borehole; d. then, closing the valve on the high-energy gas pipeline, opening the valve on the extraction pipeline, and carrying out gas extraction from the fracturing and heat injection borehole; e. closing the valve on the extraction pipeline and opening the valve on the hot steam transmission pipeline when the gas concentration in the fracturing and heat injection borehole is below a predetermined percentage; starting the steam generator and injecting hot steam into the fracturing and heat injection borehole, and then shutting down the steam generator and closing the valve on the hot steam transmission pipeline to stop the heat injection; f. opening the valve on the extraction pipeline, and carrying out gas extraction from the fracturing and heat injection borehole again; g. repeating the steps c, d, e, and f when the gas concentration in the fracturing and heat injection borehole is again below the predetermined percentage, till the gas concentration in the fracturing and heat injection borehole is always lower than said predetermined percentage; then, withdrawing the steel pipe so that the spinning oscillation pulsed jet nozzle is moved in a direction towards the borehole orifice; h. repeating the steps c, d, e, f, and g, till the spinning oscillation pulsed jet nozzle is returned to a spaced distance from the floor of the coal seam; then, terminating the high-energy gas fracturing and heat injection in the fracturing and heat injection borehole.

2. The method according to claim 1, wherein, the spinning oscillation pulsed jet nozzle comprises a nozzle inlet, an oscillation cavity, and a nozzle outlet, the nozzle inlet has two stages of hole wall inclination transition from outside to inside, and the nozzle outlet has three stages of hole wall inclination transition from inside to outside.

3. The method according to claim 1, wherein, the spinning oscillation pulsed jet nozzle is connected with the steel pipe via a bearing, with a waterproof seal ring mounted between them.

4. The method according to claim 1, wherein, the hot steam temperature injected into the fracturing and heat extraction borehole is at 100 to 500 C.

5. The method according to claim 1, wherein, the outer wall of the steel pipe is cladded with a glass wool insulation layer.

6. The method according to claim 1, wherein said spaced distance from the roof is about 1 m.

7. The method according to claim 1, wherein said predetermined percentage is lower than 30%.

8. The method according to claim 1, wherein said spinning oscillation pulsed jet nozzle is moved in the direction towards the borehole orifice by 2 to 2.5 m.

9. The method according to claim 1, wherein said spaced distance from the floor is about 1 m.

10. The method according to claim 1, wherein in step e, the hot steam is injected into the fracturing and heat injection borehole for 1 to 2 h.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the implementation method according to the present invention;

(2) FIG. 2 is a schematic structural diagram of the spinning oscillation pulsed jet nozzle;

(3) FIG. 3 is a sectional view in A-A direction of the structure shown in FIG. 2;

(4) FIG. 4 is a schematic diagram of the nozzle inlet of the spinning oscillation pulsed jet nozzle;

(5) FIG. 5 is a schematic diagram of the nozzle outlet of the spinning oscillation pulsed jet nozzle.

(6) Among the figures: 1coal seam; 2roof of coal seam; 3fracturing and heat injection borehole; 4ordinary extraction borehole; 5steel pipe; 6spinning oscillation pulsed jet nozzle; 6-1nozzle inlet; 6-2oscillation cavity; 6-3nozzle outlet; 7valve on extraction pipeline; 8valve on high-energy gas pipeline; 9valve on hot steam transmission pipeline; 10high-pressure gas station; 11tee joint; 12steam generator; 13bearing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) Hereunder the present invention will be detailed in an embodiment with reference to the accompanying drawings.

(8) The method for gas extraction by alternating oscillation pulsed high-energy gas fracturing and heat injection provided in the present invention comprises the following steps: a. first, arranging sites of extraction boreholes 4 in a grid manner towards the direction of the coal seam 1, and then drilling the extraction boreholes 4, sealing the extraction boreholes 4, and connecting the extraction boreholes 4 to a gas extraction pipe network for gas extraction, sequentially; b. arranging fracturing and heat injection borehole 3 at the intersections centers of extraction boreholes 4 in the grid manner which has finished construction, drilling at each of the sites of fracturing and heat injection boreholes 3 with a drilling machine till the drill bit passes through the roof of the coal seam 2, and then withdrawing the drill stem; c. inserting a steel pipe 5 with a spinning oscillation pulsed jet nozzle 6 mounted on the pipe head into the fracturing and heat injection borehole 3 till the pipe head reaches to a position at 1 m distance to the roof of the coal seam 2, pre-sealing the borehole for the steel pipe 5, and connecting the fracturing and the heat injection borehole 3 to the gas extraction pipe network through an extraction pipeline mounted with an extraction pipeline valve 7; the outer wall of the steel pipe 5 is cladded with a glass wool insulation layer. d. connecting the exposed end of the steel pipe 5 to a high-pressure gas station 10 and a steam generator 12 via a tee joint 11, closing the valve 7 on the extraction pipeline and a valve 9 on a hot steam transmission pipeline of the steam generator 12 first, and then opening a valve 8 on a high-energy gas pipeline of the high-pressure gas station 10, so that the high-pressure gas in the high-pressure gas station 10 enters into the steel pipe 5 via the tee joint 11, is jetted from the spinning oscillation pulsed jet nozzle 6 and forms a high-energy oscillation pulsed jet stream to impact and fracture the coal mass in the fracturing and heat injection borehole 3; wherein, the spinning oscillation pulsed jet nozzle 6 is connected with the steel pipe 5 via a bearing 13, the spinning oscillation pulsed jet nozzle 6 comprises a nozzle inlet 6-1, an oscillation cavity 6-2, and a nozzle outlet 6-3, wherein, the nozzle inlet 6-1 has two stages of hole wall inclination transition from outside to inside, and the nozzle outlet 6-3 has three stages of hole wall inclination transition from inside to outside, the air stream jetted from the nozzle outlet 6-3 generates a counterforce against the spinning oscillation pulsed jet nozzle 6, and the tangential component of the counterforce drives the spinning oscillation pulsed jet nozzle 6 to spin automatically after the jetting; the spinning oscillation pulsed jet nozzle 6 is connected with the steel pipe 5 via the bearing 13, with a waterproof seal ring mounted between them; e. then, closing the valve 8 on the high-energy gas pipeline, opening the valve 7 on the extraction pipeline, and carrying out gas extraction from the fracturing and heat injection borehole 3; f. closing the valve 7 on the extraction pipeline and opening the valve 9 on the hot steam transmission pipeline when the gas concentration in the fracturing and heat injection borehole 3 is lower than 30%; starting the steam generator 12 and injecting 100 to 500 C. super-heated steam into the fracturing and heat injection borehole 3 for 1 to 2 h, and then shutting down the steam generator 12 and closing the valve 9 on the hot steam transmission pipeline to stop the heat injection; g. opening the valve 7 on the extraction pipeline, and carrying out gas extraction from the fracturing and heat injection borehole 3 again; h. repeating the steps d, e, f, and g when the gas concentration in the fracturing and heat injection borehole 3 is lower than 30% again, till the gas concentration in the fracturing and heat injection borehole 3 is always lower than 30%; then, withdrawing the steel pipe 5 so that the spinning oscillation pulsed jet nozzle 6 is moved towards the borehole orifice direction by 2 to 2.5 m; i. repeating the steps d, e, f, g, and h, till the spinning oscillation pulsed jet nozzle 6 is returned to a position at 1 m distance to the floor of the coal seam; then, terminating the high-energy gas fracturing and heat injection in the fracturing and heat injection borehole 3.