AN APPROCH ON GEOLOGICAL CONDITIONS OF THERMOGENIC GAS IN THE DONGMING DEPRESSION AND IT’S GEOCHEMICAL MARKERS

This paper describes the geological distribution and the burial depth of Carboniferous and Permian coal beds in the Dongming depression and points out that the coalification has reached a higher degree so that the coal series have become an important source rock of thermo-genic gas. The analytical reasults of the geological conditions for gas accumulation and preservation shows that the Dongming depression is a favorable area for prospecting thermogenic gas. A gas deposit was discovered in Wen-Liu anticline in the north of the depression. The gas is produced from the fouth number of the Sha-hejie Formation.The data of stable carbon isotopic composition of the gas indicate that the type of organic matter in its source rock is humus. The gas was derived from the Carboniferous and Permian coal series. This example shows clearly that there exists thermogenic gas in the depression. Nitrogen occurring within sedimentary rocks in the depression seems to have something to do with the thermogenic gas. This paper also points out the favorable structures for prospecting thermogenic gas.