Methyltrimethyltridecylchromans in Mature Oils from Saline Lacustrine Settings in the Dongpu Depression, Bohai Bay Basin, East China.

The measured composition and distribution of methyltrimethyltridecylchroman (MTTC) compounds in the crude oils from Wenliu (salt-rich zone) and Machang (salt-free zone) areas of the Dongpu Depression were correlated with redox conditions and paleosalinity. The oil samples derived from the mesosaline environment were found with all alkylated MTTC series present. In addition, the dimethyl MTTCs developed more favorably in the oils derived from a relatively reducing and hypersaline environment (Wenliu) compared to those from the fresh lacustrine settings (Machang), while the trimethyl MTTCs developed more favorably in the fresh water environment (Machang). Determination of the oil maturity in the "oil window" by a series of aromatic maturity indicators suggests that MTTC compounds are not only present in immature or low-mature oils but also distributed in mature oils. Therefore, the "low-mature" oil found with abundant MTTC compounds, especially derived from the saline lacustrine settings, should be assessed with caution.