Quantitative studies of distribution and phase of shale oils in nanoscale pore space for the Qingshankou Formation in Songliao Basin of China

Abstract

It is generally believed that shale oil mainly exists in free and adsorbed phases, with a small amount in dissolved state (Jarvie, 2012). According to recent practices for shale oil development, free shale oil is the main contributor to production. Compared with marine shale, the lacustrine shale is greatly affected by the sedimentary environment, including the limitation of lake development, environmental change, and source supply. Lacustrine shales are characterized with high clay contents and a development of both micro- and nano-pores, with a strong heterogeneity in both vertical and horizontal directions to the bedding planes. Previous studies of shale oil in different phases mainly focused on the quantitative characterization of shale oil content in each phase, but the relationship between shale oil in different phases and the pore space in which they fill is still not clear, especially in terms of the characterization of shale oil distribution pattern in nano-scale pore space. The Cretaceous lacustrine Qingshankou Formation (K2qn1) shale in Songliao Basin was selected in this study for its great development potential of shale oil resources. The contents of the shale oil in free and absorbed states were quantified by using sequential extraction, and shale pore structure in different extraction stages was analyzed by using low temperature nitrogen adsorption (LT-N2), Nuclear Magnetic Resonance (NMR) T1-T2 and T2 spectra. Finally, the quantitative characterization of the distribution of shale oil in nano-scale pore space at different phases was studied. The results show that free shale oil is rich in light hydrocarbon components and also enriched in large pore space with T2 cutoff >0.35 ms, while the adsorbed shale oil rich in heavy hydrocarbon components is mainly located in pore space less than 20 nm along with T2 cutoff > 0.2 ms. Note: This paper was accepted into the Technical Program but was not presented at IMAGE 2022 in Houston, Texas.