Bio-precursor characterization and hydrocarbon generation potential of shale in Eocene Huadian Formation, Huadian Basin

A set of high-quality oil shales developed in the Eocene Huadian Formation in the Huadian Basin, Jinlin Province. Twenty-two rock samples were collected from the Guanglangtou district for bio-precursor and hydrocarbon generation potential analyses. Two samples containing different types of algae were chosen for thermal simulation. The Huadian shale has a high TOC content (10.6%-39.6%) and a high Rock-Eval hydrogen index (HI) value (887 mg/g), suggesting a good hydrocarbon generation potential. Detailed bio-precursor analyses demonstrated that the organic matter was dominated by phytoplankton, such as lamalginite and telalginite (including botryococcus and diatom), and fragments from benthic macroalgal rhodophyte were found in some thin layers. Higher plants mainly include detrital vitrinoids, fungi and detrital plastids, and sporophytes. The sample HD-20 with more benthic algae produced the maximum amount of hydrocarbon (427 mg/g) at 400℃ (R_o=1.02%), while the sample HD-21 dominated by planktonic algae produced the maximum amount of hydrocarbon (909 mg/g) at 425℃ (R_o=1.18%). Thermal simulation experiments showed that the sample HD-21 had a much higher hydrocarbon generation potential than the sample HD-20, even though the TOC content of HD-20 was much higher, indicating that the benthic macroalgal macerals have a much lower capacity to generate oil when thermally mature.