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 M

3

/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 re

d 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.