Fractional composition and evolution of residual oil from coal of Early Permian Shanxi Formation (P1s), Ordos Basin (China)

Abstract

To explore the residual oil contents and its fractional compositions changes with thermal stress, experiment of a whole coal sample from lower Permian Shanxi formation (P1sh) of Ordos Basin (China) was conducted in the grain-based micro-scale sealed vessel to explore the residual oil contents, fractional compositions and evolution at different temperatures and maturities. The residual oil of Shanxi coal reach the maximum at Ro=0.92% which was only 47.87 mg/g TOC. In oil window, the residual oil of Shanxi coal is mainly composed of asphaltenes, aromatics and resins with less saturates, showing lower oil prospective. In wet and dry gas windows, the residual oil becomes lower due to oil expulsion and cracking into gases. The main fractional compositions of residual oil are mainly aromatics and resins, which are gas-prone and can be the source of coal-bed methane at higher maturity stages.