Characteristics and densification mechanisms of shallow oil in Chengbei Terrace Area

ABSTRACTShallow oil is gaining more and more attentions worldwide due to its low cost. However, it is easy to form heavy oil in shallow layers. The wide varieties of oil make research on this subject difficult and oil densification mechanisms are usually controversial. Therefore, the geochemical characteristics of both heavy and light oil in shallow layers are compared and studied comprehensively. Research is conducted on the physical properties, group compositions, and diverse biomarkers. Most shallow oil samples exhibit high densities and low freezing points, which show low-sulfur biodegradation environment. With respect to group compositions, asphalts are more prevalent in the sag center. At different oil densification stages, tricyclic and tetracyclic terpanes are found to increase when viscosity is more than 1000 cp, and decrease when viscosity is less than 1000 cp. Pr/nC17 has similar characteristics. The changes in the contents of n-alkanes and tricyclic terpanes are found to be diametrically oppos...