HYDROGEOLOGIC FEATURES OF CARBONIFEROUS-PERMIAN COAL BED GAS-ENRICHED AREAS IN NORTH CHINA

The hydrogeologic environment of coal bed gas fields in North China is divided by the authors into six types:contribution,strong alternation,weak alternation,detention,stagnation and drainage zone.It is considered that the hydrogeologic environment of Dacheng area is a weak alternation-detention zone with not obvious confined conditions,that of Jincheng area is an open and weak alternation zone,and that of Liulin area is a detention zone with good confined conditions.By analyzing on the hydrogeologic conditions of coal bed gas-enriched areas in the San Juan Basin and the Black Brave Basin of the United States,it is suggested that the areas nearby contribution zones,the gentle areas with sharp water potential surface,the areas with higher degree of NaHCO₃/H₂O-type mineralization and the areas with good inherited palaeohydrogeologic conditions are favorable for the enrichment of coal bed gases.The Guanbao River Valley,the northerm part of Sanhuzhuang,the western side of Shilou and the eastern side of Guxian County are elected preliminary as four favorable exploration blocks.