Research on directional drilling technology for superimposed “three zones” passing through goaf

Guizhou has a large amount of coal resources, which have been mined for a long period of time, resulting in the formation of a large area of goaf. There is a large amount of coalbed methane resources in the goaf, but the exploitation and utilization rate are low, mainly because of  the complex ground conditions, the large longitudinal span of coal measure strata, and the thin development of coal seam in Guizhou. When extracting pressure relief gas from overlying coal seam and coalbed methane from goaf using drilling wells passed through goaf, it is difficult to form wells using conventional drilling technology and is prone to complex underground accidents, which leads to less exploitation and utilization of gob coalbed methane resources in Guizhou. In order to extract pressure relief gas from the overlying coal seam and make full use of the goaf coalbed methane resources, it is particularly important to explore the longitudinal development characteristics of the superimposed “three zones” of overlying coal strata and the stress variation law of the bottom bulge coal strata after multi-seam mining. Taking Shanjiaoshu Mine, Panjiang mining area, Guizhou as an example, a directional test well passing through goaf with multiple coal seams was carried out. The results shown that the implementation of directional well to extract pressure relief gas from overlying coal seam and underlying goaf coalbed methane under special geological conditions in Guizhou had great economics. Meanwhile, through the successful implementation of the well, the longitudinal development characteristics of the superimposed “three zones” in Panjiang mining area after multi-seam mining were firstly verified. Secondly, the key geological and engineering technical parameters of coalbed methane extraction from the underlying coal seam in the coal mining goaf were also successfully obtained, and the utilization of coalbed methane resources in the goaf had been maximized. The project provided valuable engineering experience and technical support for the subsequent development of extracting pressure relief gas in gob and coalbed methane from underlying coal seam in Panjiang mining area and even in the whole Guizhou region.