Geological controls over coal-bed methane well production in southern Qinshui basin

Southern Qinshui basin is the only area where coal-bed methane (CBM) in anthracitic reservoir is developed in large scale, making the research on development geology an urgent task. The results of tracking geological research on developing engineering of coal-bed methane show that 1) geological structure, tectonic stress field, and coal reservoir pressure control regional changes in productivity; 2) high productivity wells in research area distribute in the secondary anticline core synclinorium while low productivity wells mainly distribute in secondary anticline core of anticlinorium or normal fault zone; 3) primary reservoir pressure has a remarkable effect on coal-bed methane well production; and 4) tectonic stress fields determine development of folds and closure of fractures and control gas content and permeability of coal. The coal reservoir structure is the basic factor affecting productivity of coal-bed methane wells while gas content and permeability are direct geological factors controlling coal-bed methane well production. In addition, factors of desorption, diffusion, and seepage network related to reservoir structure determine the development difficulty.