Simulation of Hydrocarbon Generation and Expulsion by Miniature Oil Shale Core Cylinders Retaining Source Rock Minerals and Fabrics

In conventional pyrolysis experiments to simulate the hydrocarbon generation, carbonates and silicates are removed by acids to avoid interference in measurement. During the acid treatment, some hydrocarbons that are already present could also be removed. In addition, the information on the mineral effect and intrinsic water on hydrocarbon expulsion is also lost. Hence, the experimental results cannot truly represent hydrocarbon generation and expulsion in the nature. To explore hydrocarbon generation and expulsion under more realistic subsurface conditions, several miniature core cylinders (4.5 mm × 20 mm) retaining intrinsic minerals and fabrics in a source rock of Triassic Chang-7 oil shale were drilled for use in confined gold-tube temperature-programmed pyrolysis under high pressure. The experimental results reveal that (1) the minerals (carbonate and pyrite) and residual bitumen in oil shale have obvious effects on hydrocarbon generation; (2) hydrocarbon generation undergoes five stages: early oil generation (R o < 0.73%), fast oil generation (R o = 0.73–1.08%), early oil cracking (R o = 1.08–1.36%), late oil cracking/wet gas formation (R o = 1.36–2.09%), and wet gas cracking (R o > 2.09%), similar to that of kerogen pyrolysis. (3) Oil expulsion efficiency (OEE) is dominantly in the range of 65–70% during the stage of late oil cracking/wet gas formation. Oil expulsion (142–295.5 mg/g TOC) mainly occurs in the stages of early oil cracking and late oil cracking/wet gas formation, with OEE ranging from 38 to 68%. These are well reflected in the reconstructed comprehensive hydrocarbon generation and expulsion model based on the amounts of hydrocarbon generated and expelled. (4) Great potential of unconventional shale-oil resources for Chang-7 oil shale is in the EasyR o range of 0.9–1.7% calculated from the oil saturation index.