Method of performing combined drilling, flushing, and cutting operations on coal seam having high gas content and prone to bursts to relieve pressure and increase permeability

A drilling-flushing-slotting coupled pressure relief and permeability increasing method for a high gas outburst coal seam comprising

• adjusting a water inlet pressure of a water flow at different stages according to
• different positions where a borehole construction is carried out, wherein
• when in drilling, the water flow is controlled to respectively perform a low pressure water flow drilling and a medium pressure water flow flushing;
• when a drill bit is withdrawn, a high pressure water flow slotting is performed;
• and
• the water inlet pressure is gradually released level by level according to the low pressure water flow, the medium pressure water flow and the high pressure water flow, thereby implementing the drilling-flushing-slotting coupled pressure relief and permeability increasing integrated method inside a crossing borehole (3);
• and
• the method comprising the following steps:
• a. arranging multiple crossing boreholes (3) to a pre-extraction area of a coal seam (2) from a floor rock roadway (1);
• b. constructing the multiple crossing boreholes (3) arranged in the pre-extraction area one by one by utilizing a pressure control integrated drill bit (7), wherein when the pressure control integrated drill bit (7) does not drill to reach the coal seam (2), a low-pressure water flow of 3 to 5 MPa is utilized to assist the drilling and the slagging, so that while the drilling speed is increased, a dust-fall effect is achieved;
• c. increasing the pressure of the water j-e flow to 8 to 12 MPa when the pressure control integrated drill bit (7) drills to reach a coal seam floor (5) and enters the coal seam (2), and flushing the borehole by utilizing a medium-pressure water flow at the coal seam (2), wherein since a front portion of the pressure control integrated drill bit (7) is pressed in the drilling process, a side spray nozzle of the pressure control integrated drill bit (7) is closed under the pressure, the water flow flushes the front coal only through a front spray nozzle, as the broken coal is discharged, a pressure relief hole (9) is formed in the coal seam (2), and the internal energy of the coal is primarily released;
• d. observing a coal output situation at a drilling opening,
• determining an occurrence condition of the coal seam (2), and
• stopping the drilling when the borehole (3) runs through the coal seam (2);
• e. withdrawing the drill bit, further
• increasing the water pressure of the water flow in the withdrawing process, and adopting a high-pressure water flow of 15 to 25 MPa to cut the coal, wherein since the front portion of the pressure control integrated drill bit (7) is not pressed, the front spray nozzle is closed, the side spray nozzle is opened, the water flow is sprayed out only from the side spray nozzle, and a plurality of hydraulic cutting slots (10) are formed in the coal seam (2) in the withdrawing process, so that the homogeneous pressure relief of the coal is realized;
• and
• f. forming a crossing extraction borehole (11) of a particular shape after the hydraulic slotting is completed in the coal seam (2), stopping conveying high-pressure water to the pressure control integrated drill bit (7), and withdrawing the pressure control integrated drill bit (7) and a drill stem (8) from the borehole (3) while maintaining rotation.