Geochemistry and possible origin of petroleum in Palaeozoic reservoirs from Halahatang Depression

•Investigates the geochemical characteristics of the Halahatang oil.•Conduct oil/oil/source correlation to delineate the origin for Halahatang oil.•Halahatang oil correlates well with O2+3 source rock.•Halahatang oil is similar to Tahe oil in main geochemical features.•Source facies are different between Halahatang and Tahe oils.

The Halahatang Depression in the Tabei Uplift of the Tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields. Geochemical analysis indicates that Halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions. The maturities for Halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring Tahe oils. The Halahatang oils feature low Pr/Ph, C21/C23 tricyclic terpane and, C28/C29 sterane ratios, high C29/C30 hopane and C35/C34 hopane ratios, a “V” shape in the distribution of C27–C28–C29 steranes and light carbon isotope ratios, similar to the Tahe oils and correlate well with the Middle-Upper Ordovician source rock. However, some source-related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the Tahe oils.