Experimental constraints on the evolution of organic matter in oil shales during heating: Implications for enhanced in situ oil recovery from oil shales

In situ oil shale conversion experiments have revealed that to efficiently obtain shale oil, factors such as heating temperature, products, and matter thermal evolution of organic matter during heating need to be optimized. In this study, oil shales from China were subjected to retorting experiments involving eight heating steps. During steps I-II (≤300 °C), the expelled product is mainly water, the hydrocarbon generation potential (PP) of the samples was extremely high, and the organic matter was in the immature to low-mature stage. The oil shale produced a large amount of oil in steps III–VI (300–475 °C), and the TOC contents and S2 of the shale showed the greatest decreases during these steps. The analysis data suggest that the organic matter entered the mature stage during these steps. After heating to 400 °C and expelling a large amount of oil and gas, the PP decreased gradually. From 475 to 520 °C (steps VII–VIII), only a small amount of gas was produced and the organic matter had almost no PP in the high- and over-mature stages. Based on our experimental results, in situ conversion of oil shale the final heating temperature should be ~440 °C. These constraints require further field testing to be properly optimized.