The shale oil potential of Permian Lucaogou shales (Southeastern Junggar Basin) evaluated by a new quantitative index based on geochemometric methods

The decline of conventional petroleum resources has shifted attention to the exploration of shale oil resources. The shale oil potential of organic-rich shales is a critical focus, which is controlled by organic matter (OM) abundance, thermal maturity, kerogen type, and thickness. However, some commonly-used indicators to characterize the shale oil potential often yield inconsistent results. Hence, to precisely assess the shale oil potential, in this study, combined with the rock-eval pyrolysis, organic petrography, total organic carbon (TOC) content, organic elements, vitrinite reflectance (Ro, %), and gas chromatography-mass spectrometry (GC-MS), a new evaluation index for shale oil potential (SOPI) was proposed to evaluate the shales of Permian Lucaogou Formation in southeastern Junggar basin. Several geochemometric methods including principal component analysis (PCA), grey correlation analysis (GCA), hierarchical cluster analysis (HCA), and analytical hierarchy process (AHP) were used to calculate the SOPI. PCA serves to transform multiple shale oil evaluation metrics into a few integrated metrics (main principal component, PC) that reflect the practical geological significance (OM abundance, kerogen type, thermal maturity, and dark mudstone thickness). Then, the weights of these PC with practical geological significance were determined by GCA. Based on this, SOPI was obtained by which the quality of Permian Lucaogou shales in different areas was quantitatively determined. The SOPI values were examined by the HCA, which indicates a high coincidence rate of 89.4%. The AHP method also confirmed the credibility of the weights obtained from GCA with a good result of the consistency test. The results of shale oil potential evaluation based on the SOPI are consistent with the previous unilateral shale oil evaluation based on uni- and bivariate evaluation parameters, the distribution characteristics of shale oil resources volume, and the lithological distribution proposed by previous research. The comprehensive analysis suggests that, in the six areas of the southeastern Junggar Basin, the Qitai area exhibits the highest shale oil exploration potential, and its shale oil potential even exceeds that of the Jimusaer area, followed by the Miquan and Mulei areas. The shale oil potential in the Chaiwopu and Shiqiantan areas are the lowest.