Research method of pressure relief and permeability enhancement in low permeability coal seam: A review

Abstract

Gas drainage can prevent accidents such as coal and gas outbursts and gas explosions, which is of great significance for coal mine safety production. The level of permeability directly determines the effect of gas drainage. Therefore, experts and scholars in related fields have conducted extensive research with regard to adopting different measures to increase the permeability of coal and thereby improve the efficiency of gas drainage. However, in analyzing, comparing, and summarizing the advantages, disadvantages, and adaptability of various methods, there are few review studies in the literature. First, this Review investigates the principles, processes, and effects of different methods and finds that each method has its own specific application conditions and limitations. Simultaneously, it classifies different stimulation methods according to the principle of stimulation, which are mainly divided into physical stimulation methods, chemical stimulation methods, microbial stimulation methods, and thermal stimulation methods. Then, for better field applications, this Review investigates emphatically these methods that are currently popular but still in the laboratory stage, such as acidification stimulation and freeze–thaw stimulation, and analyzes the experimental methods, principles, experimental effects, influencing factors, etc. Permeability represents the flow capacity of gas in porous media and thereby affects the efficiency of gas extraction. Therefore, this Review summarizes the influencing factor of permeability. Finally, this Review discusses the aspect that needs to be perfected and improved for different methods and points out the problems and possible development directions in the future.