Abstract
This work systematically studied the significant geochemical heterogeneity of natural gases inside and outside the buried hills of the Xinglongtai area, West Sag, Liaohe Depression, Bohai Bay Basin. The gases inside the buried hills are thermogenic, whereas those outside the buried hills are dominated by secondary microbial gases, with a biodegraded thermogenic gas contribution. The humic-and sapropelic-type gases are primarily derived from the ES3 and ES4 source rocks, respectively. The gases inside the buried hills are primarily derived from the ES3 source rocks, and decreasing δ~(13)C1 and C1/C1.5 ratio towards the northeast are a result of the decreasing maturity of the adjacent ES3 source rocks. The different geochemical characteristics of the gases outside the buried hills results from the relative contribution of secondary microbial and thermogenic gases, the maturity and organic type of the thermogenic gas, and biodegradation. In the Xinglongtai area, secondary microbial gas is an important shallow Paleogene exploration target, and the natural gas inside the buried hills is primarily enriched near the ES3 source rocks. The findings and methods of this work are significant for studies on the origin and accumulation of natural gas inside and outside the buried hills in other petroliferous sags of the Bohai Bay Basin. Considering the geological and geochemical significance of the spatial geochemical heterogeneity of natural gas is essential for researching the origin and accumulation mechanism of gas and oil in complex exploration areas with multiple source rocks.
NSTL