Petroleum in the Jurassic Reservoirs within the Eastern Fukang Sub-depression, Junggar Basin, NW China: Correlation and Source Rock

The origin and source of the petroleum in the Jurassic reservoirs within the eastern Fukang sub-depression were geochemically investigated. They show thermal maturities matching the peak generation stage, while the condensates are at the early stage of intense cracking. Oils and condensates may have experienced mild evaporative fractionation, while mixing of severely biodegraded with non-biodegraded oils has occurred. Using biomarkers and isotopes, petroleums were classified into Group I, II and III genetic groups, with Group III further divided into IIIa and IIIb subgroups. Group I petroleum displays heavy carbon isotopes, a strong predominance of pristine over phytane, high C-19 and C-20 tricyclic and C-24 tetracyclic terpanes, low gammacerane, and dominant C-29 steranes, while Group II shows light carbon isotopes, a predominance of phytane over pristine, high C-21 and C-23 tricyclic with low C-24 tetracyclic terpanes, high gammacerane and dominant C-27 steranes. Group IIIa petroleum shows mixing compositions of Group I and II, while Group IIIb displays similar compositions to Group I, but with significantly higher Ts, C29Ts and C-30 diahopane proportions. Oil-source rock correlation suggests Group I and II petroleums originate from Jurassic and Permian source rocks, respectively, while Group IIIa are mixtures sourced from these rocks and IIIb are mixtures from Jurassic and Triassic source rocks.