Advances in Earth Science
1, Moldowan J M
2, Liu Zhaoqian
Chen Zhonghong, Moldowan J M, Liu Zhaoqian. Selective Alteration of Steranes in Heavy Biodegraded Oils from Dongying Sag[J]. Advances in Earth Science, DOI: 10.11867/j.issn.1001-8166.2012.10.1108.
The alkane and aromatic fraction of eleven biodegraded oils and five non-biodegraded oils from the Dongying Depression, Bohai Bay Basin, Eastern China were analyzed by GC-MS to investigate the effects of biodegradation and thermal maturation on the distributions of steranes. The results indicate that the biodegradation and depletion of steranes emerged in the heavily biodegraded oils (scale≥6). The oil samples show an increase in the C29sterane C2920S/(20S+20R) and C29ββ/(ββ+αα) thermal maturity parameters in the heavily biodegraded oils, indicating this level of biodegradation(scale≥6) can alter the two maturity parameters. The selective depletion of C27-C29steranes follows the order ααα 20R>αββ 20R>αββ 20S≥ααα 20S and C27>C29>C28, and the diasteranes and C20-C21steranes were much more resistant to biodegradation than regular C27-C29 steranes.