Oil Storage Capacity in Organic-Rich Chang 7 Shale, Ordos Basin: Comparing Evaluation Methods and Controlling Factors

This study examines the oil storage capacity and controlling factors of organic-rich Chang 7 shale in the Ordos Basin, using multistep Rock-Eval pyrolysis (MREP) and liquid hydrocarbon vapour adsorption (LHVA) techniques. The research evaluates the effectiveness of these techniques in determining oil content and identifies key geological and geochemical factors impacting free and adsorbed oil. Analyses of geochemical, mineralogical, and pore structure characteristics reveal that Chang 7 shale, with high total organic carbon (TOC) content and oil-prone kerogen, along with moderate thermal maturity, is a high-quality hydrocarbon source rock. A strong linear correlation between MREP and LHVA results demonstrate the reliability of both methods for assessing adsorbed oil content, though discrepancies emphasise the impact of hydrocarbon loss during sample preparation. Statistical analysis indicates TOC content (> 2%, with > 4% especially favourable) and thermal maturity (R _o = 0.7%–1.0%) as the critical factors for shale oil accumulation and key indicators for identifying sweet spots. These findings improve the understanding of oil occurrence processes in shale and offer practical insights for optimising shale oil exploration and development.