Abstract:

The Middle Carboniferous-Late Permian strata in North China are char-acterized by complete development,widespread distribution,common exist-ence of coal,and more stable petrography and thinkness.Coal rank rangesfrom gas coal to anthracite,predominantly the medium-high level metamorphiccoal.The predicted reserves,above 1,000m,is estimated at 1,300 billionton.Based on a genetic rate of coal-formed gas of 250 M³/T,the predictedgenetic potential of coal-formed gas amounts to 325,000 billion cu.m.Becauseof the intense tectonic activity in this area,an accumulation factor of 1percent is used for calculating.As a result,coal-formed gas can be stillaccumulated at 3,250 billion cu.m.The traps,formed during the lndosinian and the Early Yenshanian movements in North China,are favorable to the accumulation and preservationof coal-formed gas.So far the following preservative forms of coal-formedgas have been recongnized in this area.1)the accumulation in the Permian and Triassic red beds overlying coalmeasures.2)the accumulation in coal measures.3)the accumulation in ancient weathering crust.4)the accumulation in the Meso-Cenozoic sandstone.5)the accumulation in the solution in water layer.The prospecting and exploration for coal-formed gas,first of all,shouldbe in areas where Triassic system developes better and structural traps ex-ists and where the burial depths of the top of coal measures are at 1,000-4,000 m,for example,Qinshui Basin,Jiyuan Depression and Baodin-Shijia-zhuang-Xingtai-Handang-Anyang areas,etc.coal-formed gas means the gas associated with a coal source.