The tight oil potential of the Lucaogou Formation from the southern Junggar Basin, China

The mudstones of the Lucaogou Formation are the most important and organic-rich sediments and tight oil exploration target in the northwestern China. The organic and stable isotope geochemistry, and organic petrology were used to evaluate their sedimentary environments and hydrocarbon generative potential. The Lucaogou mudstones contain abundant organic matter, S2, hydrogen index (HI) and extractable organic matter (EOM), whereas S1 values are low. The δ13C values of EOM are very light and display a negative correlation with HI. Rock pyrolysis data imply a low maturity (0.6-0.7 %Ro equivalent) of the Lucaogou Formation, consistent with aliphatic and aromatic hydrocarbon ratios. The biological sources are predominately algae and bacteria, with less contribution of higher plants in the Lucaogou Formation as indicated by δ13CEOM, biomarkers and maceral composition. The Lucaogou mudstones contain low ratios of C31R/C30 hopane, C29/C30 hopane and C22/C21 tricyclic terpane, and high C24/C23 tricyclic terpane value, which are consistent with their depositional environments (i.e., lacustrine). The abundant β-carotane, gammacerane and hop-17(21)-enes indicate a hypersaline and anoxic environment. The studied samples are predominantly oil-prone with a dominant type I and II1 kerogen. High contents of total organic carbon (TOC), S2, HI, EOM, saturated and aromatic hydrocarbons indicate that the Lucaogou Formation hold significant exploration potential of tight oil.