Distribution and burying characteristics of the Permo-Carboniferous system and the coal-formed gas source rock in Jiyang depression

Several tectonic movements took place in Shandong area, which caused severe destruction to the coal-bearing measures, as a result, the preservation of the strata is of great difference here and there. The Permo-Carboniferous system is deeply buried in Jiyang depression where the structural condition is complicated and the coal-bearing measures is generally preserved in the secondary sags. The Permo-Carboniferous is generally buried at the depth of 3 000~5 000 m, with big difference in different secondary sags, 10,000 m being the maximum, while 1 000 m or so the minimum. The source rocks of the coal-formed gas are mainly coal seams and dark mudstone, and the maximum thickness of the former is 40.5 m(in Chezhen sag) while that of the latter 555.5 m(in Huimin sag). The thickness of the mudstone and coal seams varies with the remnant thickness of the Permo-Carboniferous system. The coal is a good kind of source rock while mudstone generally bad to medium and locally relatively well.