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 C19and C20tricyclic and C24tetracyclic terpanes, low gammacerane, and dominant C29steranes, while Group Ⅱ shows light carbon isotopes, a predominance of phytane over pristine, high C21and C23tricyclic with low C24tetracyclic terpanes, high gammacerane and dominant C27steranes. 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 C30diahopane 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.