Downhole coal seam pulse detonation wave directional fracturing permeability-increasing method

摘要

A downhole coal seam pulse detonation wave directional fracturing permeability-increasing method, for regional gas control in a low permeability seam having a high gas content. The method comprises: firstly, respectively drilling a pulse detonation wave drill hole (8) and a pulse detonation guided drill hole (11) from a coal lane to a coal layer (12); pushing a positive electrode (7) connected to a positive output end (4) of a blast-resistant high voltage electropulse generator (3) to the bottom of the pulse detonation wave drill hole (8), and pushing a negative electrode (10) connected to a negative output end (5) of the blast-resistant high voltage electropulse generator (3) to the bottom of the pulse detonation guided drilling hole (11); executing an electropulse detonation to fracture a coal seam, then connecting the pulse detonation wave drill hole (8) and the pulse detonation guided drill hole (11) to an extraction pipeline to extract gas. The method utilizes an electropulse detonation wave to provide instantaneous high-energy fracturing of coal, and forms a network of fractures within the coal between a pulse detonation wave drill hole and a pulse detonation guided drill hole. In the present invention, a coal permeability coefficient can be increased by 200-400 times, an effective range for gas extraction for a single drill hole can be increased by 3-4 times, and a drill hole gas extraction volume can be increased by 3-8 times, thus effectively shortening a pre-extraction time of a coal gas.