Organic Geochemistry and Petrology of Mudrocks from the Upper Carboniferous Batamayineishan Formation, Wulungu Area, Junggar Basin, China: Implications for Petroleum Exploration

摘要

The hydrocarbon generation potential of the Carboniferous Batamayineishan mudrocks has been overlooked for a long time. In this study, organic petrology and geochemistry were used to determine the sedimentary environments, organic matter (OM) type, and organic maturity of the Carboniferous Batamayineishan source rocks, collected from outcrops, Wulungu area, Junggar Basin, China. The maceral composition of the studied samples is dominated by vitrinite and inertinite, ranging from 40 vol % to 100 vol % and from 0 vol % to 60 vol % on a mineral matter free basis, respectively. Liptinite macerals, mainly as lamalginites, are only present in trace amounts in several sediments. Vitrinite reflectance values are 0.67% to 2.78%. TOC values are high in these samples, whereas the S-1, S-2, and HI are very low. Pr/Ph ratios, the plot of Pr-C-17 versus Ph-C-38, DBT/P versus Pr/Ph, and ternary of fluorene, dibenzothiophene, and dibenzofuran indicate that anoxic saline environments prevailed during deposition of the Batamayineishan Formation. This is consistent with the presence of beta-carotane and high abundances of gammacerane in the studied samples. The major biological source is from vascular plants, and the kerogen type is humic (type III) as indicated by the maceral composition and rock pyrolysis data. The samples from the No. 4 and No. 6 sections occur in the oil window, whereas the other samples are overmature in terms of hydrocarbon generation. The abundant organic richness, humic kerogen, and high thermal maturity demonstrate that these rocks are effective gas source rocks. The volcanics and mudrocks in the Carboniferous Batamayineishan Formation collectively constitute a self-generation and self-storage petroleum system, and represent a main exploration target for gas discovery for the Carboniferous in the Wulungu area.