Sequence Stratigraphy and Geochemistry of Oil Shale Deposits in the Upper Cretaceous Qingshankou Formation of the Songliao Basin, NE China: Implications for the Geological Optimization of In Situ Oil Shale Conversion Processing

The Songliao Basin contains some of the largest volumes of oil shales in China; however, these energy sources are located in areas covered by arable land, meaning that the best way of exploiting them is likely to be environmentally friendly in situ conversion processing (ICP). Whether the oil shales of the Songliao Basin in the Qingshankou Formation are suitable for ICP remain controversial. In this paper, through sequence stratigraphic correlations, three main thick oil shale layers (N1, N2, and N3) of the Sequence1 (Sq1) unit in the first member of Qingshankou Formation (K2qn1) are confirmed as consistently present throughout the Southeastern Uplift region of the basin. The spectral trend attributes reflect that the lake reached a maximum flood surface of the K2qn1 in N2 oil shale layer, and the total organic carbon (TOC) and Fischer assay (FA) oil yield are significantly increasing. The N2 and N3 oil shale layers were deposited in a high lake level environment associated with ingressions of ocean water. The oil shale in these layers with the characteristics of high TOC (maximum of 23.9 wt %; average of 7.2 wt %), abundance of aquatic organic matter (OM) (maximum hydrogen index (HI) of 1080.2 mg/g; average of 889.9 mg/g) and carbonate contents (maximum of 29.5%; average of 15.4%). The N2 and N3 oil shale layers have higher brittleness index (BI) values (generally 40–50%), larger cumulative thicknesses (maximum of 13.3 m; average of 12.0 m), and much higher source potential index (SPI) values (0.92 and 0.88 tHC/m2, respectively) than the N1 oil shale layer within Sq1 transgressive system tracts (TST), indicating that the N2 and N3 layers are prospective targets for ICP. In addition, oil shales buried to depths of <1000 m have strong hydrocarbon generation capacities that make them suitable for ICP.