Origin of the Ultra-Deep Hydrocarbons from the Shunbei No. 1 Fracture Zone in the North of Shuntuoguole Low Uplift, Tarim Basin, North-Western China

In order to have a deeper insight into the accumulation mechanism of ultra-deep hydrocarbons, in this paper, recently discovered Ordovician light oil and gas deposits (>7200 m) Shunbei No. 1 fracture zone are studied intensively, including maturity, source kitchens, extent secondary alterations, possible migration directions, based on an analysis molecular compositions stable carbon isotopes crude oils natural gases. The average equivalent vitrinite reflectance (Rc) these oils, estimated from hydrocarbons (H versus I), MDI, DNR, MDR, about 1.50%, 1.58%, 1.48%, 1.51%, respectively, which suggests that most late stages crossing window. two maturity grades (1.06–1.25% 1.36–1.67%) samples calculated aromatic compounds indicate presence at least hydrocarbon charge. addition, positive correlation plot DNR MDR (y = 3.59x − 12.84; R2 0.96) indicates southwestern region F1 (S1-11–S1-16) slightly more mature than northeastern well SL1, far main fault zone. study shows belong same kitchen reduced marine sedimentary environment with mixed organic matter comprising benthic planktonic algae, biomarker parameters, isotope compositions. oil–oil analyses suggest probably derived situ Lower Cambrian Yuertusi formation rocks. Various geochemical parameters consistently show limited significant alteration processes, indicating favorable preservation conditions area. integrated characteristics allow us infer they mainly migrate vertically rocks toward reservoirs, followed by certain degree lateral southwest northeast.