Abstract
Oiliness and mobility are key indicators to evaluate the sweet spots of shale oil. Due to the complex oil occurrence states and the lack of in-situ oiliness related experimental methods, the relationship between oiliness and mobility of shale oil is still unclear, which affects the evaluation of movable oil and the optimization of sweet spots. In this paper, the Upper Cretaceous Qingshankou Formation of lacustrine shale in the Changling Sag, the southern Songliao Basin is taken as the research object. Two-dimensional nuclear magnetic resonance (2D-NMR) experiments were performed on pressurized sealed cores before and after centrifugation to accurately characterize the effective porosity, oiliness, and oil mobility of shale reservoirs, these properties’ international relationships and controlling factors were discussed, and then a suitable model for evaluating the movable oil was proposed. Based on 2D-NMR and pressurized sealed samples, shale in-situ oiliness can be accurately revealed, with a free oil content 2.48 times that of pyrolysis free hydrocarbons (S1), which makes the previously used OSI (S1/TOC) calculated by pyrolysis S1 unable to assess shale oil mobility. The correlation between effective porosity, oiliness, and oil mobility was better in siltstone and limestone interlayers and worse in shale reservoirs. Microcracks can significantly promote the mobility of shale oil, while adsorbed oil has the binding effect on the move of free oil, resulting in that shale oil can move until free oil or OSI reaches a certain threshold. The movable thresholds were redefined through the relationship between movable oil and free oil content, we found that as TOC or the adsorbed oil content increases, the movable thresholds for free oil and OSI also gradually increase, shale oils within different lithologies correspond to different movable thresholds, and using a fixed movable threshold for mobility discrimination will misjudge the sweet spots of shale oil interval. Based on the movable threshold of free oil, a model related to the maximum mobility of shale oil has been developed in this study, which has better applicability and is more accurate than the existing OSI method. The results of the present study are very important for deepening the understanding of the mobile mechanism and guiding the selection of sweet spots for shale oil.
Paper Information：
Xiao Dianshi, Zheng Lehua, Wang Min, Wang Rui, Guan Xiaodie, 2024, The relationship between oiliness and mobility and their controlling factors for lacustrine shale oil: A case study of Qing1 Member in Changling Sag, Songliao Basin. Fuel, https://doi.org/10.1016/j.fuel.2024.132738
