Abstract
The Changling Sag in the petroliferous Songliao Basin has produced large amounts of conventional petroleum, but studies on unconventional resources are rare. A suite of core samples from the CY-1 well, drilled in the eastern Changling Sag, was analysed employing a series of micropetrographic, geochemical, and pyrolysis techniques to reveal the shale oil potential of the lower (K2qn1) and middle (K2qn2) Qingshankou Formation in this area for the first time. From the lower K2qn1 upwards the sampled section, the ratio of K/Al delineates an increasing palaeo-temperature trend but still within a warm climate. Based on element ratios Al2O3/TOC and TiO2/TOC, the highest terrestrial matter and nutrient supply on average occurred in the lower K2qn1 triggering bioproductivity. TOC/TS and Fe/Mn show that bottom water anoxia prevailed in the upper K2qn1 and lower K2qn2, providing excellent conditions for organic matter (OM) preservation, as compared to the lower K2qn1. High maturity of the studied layers is implied by e.g. vitrinite reflectance (VRr) of 1.03–1.09%, Tmax values over 445 °C and molecular organic-geochemical indices which correlate very well with VRr. Kinetic data on petroleum generation from open-system pyrolysis were implemented in a numerical 1D basin and petroleum system model. The K2qn1 has generated and expelled large amounts of petroleum (78% and 36% transformation of kerogen to petroleum) based on kinetics of the low mature Qingshankou shale. OM consisted originally of type I-II kerogen, but has lost more than half of its original hydrocarbon generation potential upon maturation. Oil saturation index (OSI) and ΔS1 suggest that the studied layers show fair shale oil potential but are regarded as good conventional petroleum source rocks. A newly proposed shale oil potential index (SOPI) takes also thickness into account. Application to the Qingshankou Formation implies that the lower K2qn2 holds the highest shale oil potential.
Published Version
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