Geochemical characteristics and origin of the ultra-deep hydrocarbons from the Shunbei Oilfield in the Tarim Basin, China: Insight from molecular biomarkers and carbon isotope geochemistry

To better evaluate the exploration prospects of ultra-deep hydrocarbon resources in the Tarim Basin, origin of the newly discovered ultra-deep hydrocarbons from the Shunbei Oilfield are investigated thoroughly concerning the maturity, secondary variations, and source kitchens based on molecular biomarkers and carbon isotope geochemistry. Given the physical and chemical properties of the studied oils and gases, they are classified into five families: A, B, C, D, and E. Newly proposed maturity parameters are employed for evaluating the maturity of the studied oils and gases as Family D > E > B > A, except for Family C hydrocarbons, which may be a mixture of relatively high-maturity natural gas with relatively low-maturity oil. Secondary alterations are concentrated in the southern part of the Shunbei region, primarily including oil cracking and TSR effects, both of which may occur in deeper strata than in situ. Furthermore, the simulated maturity evolution and variation of sedimentary facies of the Yuertusi Formation (is an element of(1)y) source rocks in the Shuntuoguole Low Uplift (STLU) area match well with the genesis of the studied hydrocarbons, which suggests that the studied hydrocarbons may be derived from the is an element of(1)y source rocks in the STLU area. Collectively, Family A hydrocarbons originate from the western is an element of(1)y source kitchen in the STLU region where the water column is shallow, rich in planktonic algae, and the maturity is relatively low; in contrast, Family E hydrocarbons are derived from the eastern is an element of(1)y source kitchen in the STLU region where the water column is deep, rich in benthic algae, and the maturity is relatively high; Families B and C hydrocarbons originate between them. This research also contributes to the establishment of a geochemical evaluation system for ultra-deep hydrocarbons.