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

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.