ANALYSIS OF THE SEEPAGE OIL AND OIL SOURCE IN CHENGKOU AREA OF THE SOUTHERN MARGIN OF DABASHAN

The oil seepages were occurred along a series of thrust faults in the front of Dabashan.Based on comparative analysis of the source rocks in the southern margin of Qinling mountain and its surroundings and the seepage oil in Chengkou area,it showes that carbon isotope of the seepage oil is close to that of the extract of the Lower Paleozoic source rocks,but different with that of the extract of the Permian source rocks.The results show intimate relationship between the seepage oil and the Lower Paleozoic source rocks.However,the biomarker parameters by GS-MS indicate that the seepage oil is more similar to the Permian source rocks.According to analysis of tectono-depositional history and hydrocarbon generation history of the source rocks,the seepage oil came from the Permian source rocks.During hydrocarbon migration and entrapment,some organic geochemical information of the Lower Paleozoic source rocks was mixed.