Characterization of oil generation and expulsion from coals and source rocks using diamond anvil cell pyrolysis

Abstract

A visual technique has been developed using a diamond anvil cell to characterize oil-prone vs. gas-prone coals and source rocks, and evaluate their oil expulsion efficiency. The experiments, conducted using 15 humic or shaly coals, two boghead coals, and eight source rock samples from Taiwan, Turkey, North America, and Australia, show that the technique has potential to distinguish oil-prone coals from gas-prone coals. The oil potential of humic coals was estimated from the amounts of total liquid generated during pyrolysis, which show correlations with the Hydrogen Index (HI) from Rock-Eval pyrolysis and the gas-to-oil ratio (GOR) determined by Py–GC analysis. The changes of visual area (or volume) of neoformed liquid as a function of temperature at four heating rates were used to calculate the extents of kerogen-to-oil transformation for determining the kinetic parameters. The results confirm the kinetic controls on the measured transformations but reveal unusually high apparent activation energies and frequency factors. The use of this technique as a quantitative tool to predict oil generation kinetics should be treated with caution until this discrepancy has been resolved. In addition, this study has demonstrated that the expulsion of oil-like liquid from coals is generally more efficient than from shales, possibly due to the much higher organic content in coal.