Novel method for determining the oil moveable threshold and an innovative model for evaluating the oil content in shales

In unconventional resource exploitation, an accurate evaluation of the oil content in shale is essential for locating favorable exploration zones. However, the substantial heterogeneity in shales has caused significant uncertainty in exploration. The commonly applied oil content evaluation model uses a single oil movable threshold (OMT) as a constraint. However, the OMT value is not unique in shale evolution. In this research, the parameter T-max representing the thermal maturity of the source rock is introduced as a variable to construct an innovative three-dimensional model for oil content evaluation. The source rock of the Paleogene Shahejie Formation in the Bohai Bay Basin was selected as an example to demonstrate the application. With an initial value of 84.1 mg HC/g TOC, the OMT decreased with increasing T-max, eventually reaching 51.2 mg HC/g TOC. The proportions of enriched, moderately enriched, less efficient, and invalid resources were 31.6%, 6.6%, 47.4%, and 14.5%, respectively. Our new model is advantageous because it evaluates the shale oil quality in terms of geochemistry and oil movability within the context of thermal maturity. Our research can offer a more accurate model and workflow for shale oil evaluation to can reduce the potential exploration risk. (C) 2021 Elsevier Ltd. All rights reserved.