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 Δ and the fracture development degree parameter ξ are suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin. Further, the control functions of ξ and Δ to CBM enrichment and high production are discussed. The results show that in present stage the area with high ξ value is located in Anze and Qinyuan, and then Zhengzhuang and Fangzhuang, where fracture development degree is high. The area with high Δ 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 ξ and Δ, 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.