Chunming Zhang

Biomarkers and C and S Isotopes of the Permian to Triassic Solid Bitumen and Its Potential Source Rocks in NE Sichuan Basin

The potential parent source rocks except from Upper Permian Dalong Formation (P3d) for Upper Permian and Lower Triassic solid bitumen show high maturity to overmaturity with equivalent vitrinite reflectance () from 1.7% to 3.1% but have extractable organic matter likely not contaminated by younger source rocks. P3d source rocks were deposited under euxinic environments as indicated by the pyrite 34S values as light as and distribution of aryl isoprenoids, which were also detected from the Lower Silurian (S1l) source rock and the solid bitumen in the gas fields in the west not in the east. All the solid bitumen not altered by thermochemical sulfate reduction (TSR) has 13C and 34S values similar to part of the P3l kerogens and within the S1l kerogens. Thus, the eastern solid bitumen may have been derived from the P3l kerogens, and the western solid bitumen was likely to have precracking oils from P3l kerogens mixed with the S1l or P3d kerogens. This case-study tentatively shows that 13C and 34S values along with biomarkers have the potential to be used for the purpose of solid bitumen and source rock correlation in a rapidly buried basin, although further work should be done to confirm it.

A comparison of the distributions of carbazoles and dibenzothiophenes in western Qaidam Basin, Northwest China

Variations in the distributions of carbazoles and dibenzothiophenes were investigated in a set of source rocks, which differ mainly in their maturity levels during immature-mature stages. A comparison of the distributions of carbazoles and dibenzothiophenes has revealed the main results as follows: variations in the relative amounts ① of C0-, C1-, C2-dibenzothiophenes show a low correlation with that of the corresponding carbazoles, with the former’s being much higher than the latter’s; variations in the relative amounts of methyldibe ② nzothiophene isomers also display a low correlation with that of the corresponding methylcarbazoles, with 4-/4- +1-methyldibenzothiophene ratio ranging from 0.52 to 0.96, while the corresponding carbazole ratio of 1-/1- +4-methylcarbazole only being 0.71±0.05; the mat ③ urity parameter for 4,6-/4,6- +1,4-dimethyldibenzothiohene, ranging from 0.34 to 0.75, shows a remarkable linear correlation with the corresponding ratio of 1,8-/1,8- +1,4-dimethylcarbazole (R2>0.84). The un-correlation may indicate some different geological-geochemical fates for some isomers of dibenzothiophenes and carbazoles. The high correlation may reveal a strong maturation dependence on the dimethylcarbazole distributions, indicating that attention should be paid when 1,8-/1,8- +1,4-dimethylcarbazole is used as a petroleum migration indicator.