Quantitative characterization of shale oil in different occurrence states and its application

Crude oils in shale systems exist in different modes, where only free oil could be a potential contributor to shale oil production. However, there is a general lack of analytical methods for quantitative characterization of free and adsorbed oils in organic-rich shale, and little is known of the interrelationships among different states of oils and porous media in shale. A modified Rock-Eval and pyrolysis-gas chromatographic method was established to quantify different modes of shale oil occurrence in various geological samples. In combination with solvent extraction, this technique was applied to analyze continuous shale core samples collected from exploration wells in the Jiyang Depression, Bohai Bay Basin, East China. The results showed a positive correlation between adsorbed oil content and total organic carbon abundance, and a pronounced decrease in the kerogen miscible oil content with increasing thermal maturity. On the other hand, the free/adsorbed oil ratio decreases with increasing TOC in a shale system, suggesting that free oil is associated mainly with inorganic mineral matrix and/or fractures. The study provides a rapid technique for the characterization of shale oil occurrence and the quantitative evaluation of shale oil resources.