Classification of lacustrine shale oil reservoirs in China and its significance

China has significant potential for the exploration of lacustrine shale oil, which serves as an important alternative resource for conventional oil and gas. However, the development and recovery of lacustrine shale oil face significant constraints due to the lack of fundamental research, unclear mechanisms of its formation and accumulation, and the absence of standardized criteria for evaluating “sweet spots”. To address these issues, the authors proposed a set of simplified standards for lacustrine shale oil classification, taking into account previous research and the practical conditions of exploration and development. Based on the storage space and type of reservoir rocks, shale oil reservoirs are commonly classified into three major types, namely interbedded sand-shale, fractured shale, and pure shale, with the last type being taken as the focus of discussion in this paper. The pure shale type can be classified into laminated, bedded and massive shale oil reservoirs based on the sedimentary structure. Although the grain size was not taken as one of the parameters for shale oil classification, we kept the traditional three terminal element category and mixed category of minerals, and removed further subdivided subcategories; the Rock-Eval S₁ was used instead of TOC and R_o to divide shale oil reservoirs into three types: low oil content, medium oil content and high oil content; the formation pressure coefficient less than 0. 8 is defined as abnormally low pressure, 0. 8 ~ 1. 2 is classified as normal pressure, and greater than 1. 2 is classified as abnormally high pressure; the crude oil viscosity is not involved in the classification of shale oil reservoir types. In addition, this study designated type Ⅰ, Ⅱ and Ⅲ sweet spots, and discussed the representative types of shale oil reservoirs in typical continental basins in China. This paper enhances our understanding of the assessment standards, the type of rocks and the distribution of “sweet spots” in shale oil reservoirs. As a result, this research contributes to the advancement of shale oil exploration and development, providing valuable insights for future endeavors in this field.