The geochemical characteristics of the Fengcheng Formation source rocks from the Halaalate area, Junggar Basin, China

The organic-rich sediments of the Fengcheng Formation in the Halaalate area, Junggar Basin, China are important source rocks and significant tight oil exploration targets. However, their geochemical characteristics have not been well documented. The hydrocarbon generation potential, genetic type of kerogen, organic matter (OM) sources, depositional conditions, and thermal maturity have been investigated based on a sample set of 11 mudstones. These source rock samples represent good to very good hydrocarbon generation potential, and primarily contain type I to II kerogen. The major organic input sources to the Fengcheng Formation from algae and bacteria were identified using stable carbon isotopes and biomarkers. Limited higher plant input can be inferred from trace amount of terrigenous OM biomarkers and minor contents of vitrinites and inertinites. The Fengcheng sediments were deposited under hypersaline and anoxic environments. Paleoclimate was arid during the deposition of the Fengcheng Formation. The presence of evaporites, mineral-bituminous gmundmasses (MBG), alginites and microbial mats also supports these conclusions about depositional environments and biological source. The OM enrichment in the studied samples are attributed to the reducing environments, the booming of algae and the important bacterial contribution. Vitrinite reflectance and T max suggest a low thermal maturity of the studied Fengcheng sediments, in agreement with maturity-related hopane and sterane ratios and detection of hop-17(21)-enes. In a consideration of the quantity, quality and maturity of OM and their large thickness, the Fengcheng sediments have a good petroleum exploration potential.