Effective migration system of coalbed methane reservoirs in the southern Qinshui Basin

Effective migration system of coalbed methane (CBM) reservoir, which was controlled by development degree and opening-closing degree of fractures, determines the permeability of coal reservoir and can be characterized by the pore-fracture system in the extrinsic form. In this paper, based on coal matrix elastic self-regulating effect theory and coal reservoir combined elastic energy theory, the fracture opening-closing degree parameter Delta and the fracture development degree parameter xi are suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin. Further, the control functions of xi and Delta to CBM enrichment and high production are discussed. The results show that in present stage the area with high xi value is located in Anze and Qinyuan, and then Zhengzhuang and Fangzhuang, where fracture development degree is high. The area with high Delta value is located in Zhengzhuang and Fanzhuang, and then Anze and Qinyuan, indicating where coal matrix elastic self-regulating positive effect dominates and fractures tend to be open. Through the comprehensive analysis on xi and Delta, it can be found that their best match area is located in Zhengzhuang and Fanzhuang, with high values for fracture development degree and opening-closing degree probably bringing about high fluid pressure and good permeability of reservoirs, which are advantageous to an abundant CBM production.