Quantitative characterization of extractable organic matter in lacustrine shale with different occurrences

The extractable organic matter (OM) in lacustrine shale can be classified into free, adsorbed or miscible states. The quantitative study of OM of these different occurrences has significance for oil/gas resource evaluation, shale oil mobility, hydrocarbon generation mechanism and oil/gas occurrence. Two lacustrine shale samples of different lithofacies from East China were successively extracted by solvents with different polarities. Three different occurrence states of soluble OM were obtained, including free, kerogen adsorptive-miscible and mineral surface adsorptive states, which were characterized using FT-IR spectra and GC-FID analyses. The kerogen adsorptive-miscible state accounts for a large proportion of the soluble OM, followed by the free OM. The free soluble OM was dominated by light compounds, and fracturing was conducive to the precipitation of light components. The kerogen adsorptive-miscible state OM mainly had heavier components, and also contained a lower portion of light fractions. The mineral surface adsorbed OM was mainly comprised of oxygen-containing compounds. Compared to the massive shale samples, the laminated shale samples had a higher proportion of soluble OM, and the hydrocarbon molecules were smaller.