Gas extraction of coal seam roof fractured zone in China: A review

Coalbed methane (CBM) is both a low-carbon and clean energy source, which can effectively alleviate the current shortage of natural gas supply and demand. Moreover, it is also a flammable and explosive dangerous gas, which seriously threatens the safe production of mines. With the influence of mining, numerous fractures in the overlying strata of coal seams are developed, forming "three zones" and an "O-shape" circle in the vertical and horizontal directions, respectively. The pressure-relief gas continuously surges into the goaf through the fracture channel and gathers in the fractured zone. By understanding the development of roof fractures and the principles of gas migration, extraction facilities are strategically placed in areas with high gas concentration to accurately extract fractured gas. According to the different extraction positions and conditions, the current gas extraction methods in the roof fractured zone mainly include the roadway method, borehole drilling method, and surface drilling method. This paper presents an analysis of the distribution of roof fractures and the law of gas migration, along with an overview of the main extraction methods currently in use. It provides a scientific reference for roof fractured gas extraction technology.