Method for synergistic permeability enhancement and extraction of coal mine gas

A method for synergistic permeability enhancement and extraction of coal mine gas, comprising the following steps:

• S1:
• drilling a plurality of vertical wells and a plurality of horizontal wells in a coal seam area to form a three-dimensional well network, thereby forming primary fractures;
• S2:
• composite electric field fracturing by applying a high-voltage pulsed electric field for transient impact, and then introducing low-frequency electromagnetic waves for sustained action to form secondary fractures;
• S3:
• extracting geothermal water from an underground abandoned mine by using a high-pressure pump;
• heating the geothermal water to a set temperature using a heat pump, then mixing the geothermal water with high-pressure nitrogen, and introducing the mixed geothermal water and high-pressure nitrogen into a wellhead of the three-dimensional well network in a pulsed manner;
• after a set period of time, extracting and returning the geothermal water to the underground abandoned mine, thereby forming tertiary fractures;
• and
• S4:
• extracting gas from the wellhead by using negative pressure adsorption equipment.