Organic geochemistry and significance of oil seepages in the Quse Formation in the Qiangtang Basin

In this paper, samples from Quse Formation mudstone, oil shale and liquid oil seedlings obtained from well QK-3 have been analyzed and their organic geochemical characteristics and the relationship between source rocks and liquid oil seedlings have been discussed. The results show that the mudstone and oil shale of QK-3 hole have reached the standard of medium to good source rocks, most of which are Ⅰtype or Ⅱ₁ type and are in the mature stage. The comparison of biomarkers shows that both the oil shale and oil seepages samples are with similar formation environment and maturity characteristics. The oil seepages found in Quse Formation have a good genetic relationship with the source rock, indicating that the oil seepages are derived from the oil shale of Quse Formation. Based on the organic geochemical characteristics of the source rocks, the distribution range, and the sedimentary thickness of Quse Formation, it is considered that the argillaceous source rocks of the lower Jurassic Quse Formation are of good hydrocarbon generation capacity. It is the most important source rock with the potential to form natural gas hydrate in study area.