EFFECT OF COAL METAMORPHISM ON METHANE CONTENT AND PERMEABILITY OF COAL IN NORTH CHINA

The contrast in geological conditions for the coalbed methane between North China and United States indicates that the telemagmatic thermal metamorphism is favorable for the increase of the coalbed methane volume and permeability characteristic of coal metamorphism in North China. Additionally, the mechanism of the telemagmatic thermal metamorphism is discussed in this paper. The majority of coals in North China were ranked in the low level before the intrusion of Yanshanian magma. Therefore, at the high temperature caused by the rapid increase of the temperature, the coalbed methane occurred the second time. That is to say the coalbed was of great potential to the "superimposed hydrocarbon generation" or "superimposed coalbed-methane generation". The porosity and fissure system turned more developed. Moreover, the late generation of the coalbed methane derived from the telemagmatic thermal metamorphism favored the reservation of the coalbed methane. The coal-rank zonings superimposed by the telemagmatic thermal metamorphism, including high-rank and middle-rank coals, increase distinctively the methane content and the permeability. Therefore, special attention should be paid to the location of the coalbed-methane prospecting target in the telemagmatic thermal metamorphic coals.