Simulation of Hydrocarbon Source Rock Maturation by Hydrous Pyrolysis

Abstract Hydrous pyrolysis experiments were performed on samples of immature brown coal from the Gippsland Basin (southeastern Australia) for 72 hours at temperatures ranging from 270 to 350°C. The produced liquid pyrolysate ("oil"), gases, and aqueous organic acid anions were determined, and the geochemical properties of the "oil" were determined. The solid residue from the experiments was studied using conventional pyrolysis, elemental analysis, vitrinite reflectance microscopy, and nuclear magnetic resonance. The maturation stages of the solid residue with increasing experimental temperature can be correlated with the maturation trend of the natural brown coal samples in the Gippsland Basin from near the surface to a depth of 9,000 ft. The "oil" derived from hydrous pyrolysis is less rich in saturates and richer in aromatics and NSO compounds than the natural oil produced from the Gippsland Basin. The major carboxylic acid anions (acetate and propionate) generated during hydrous pyrolysis are present in the produced waters in the Gippsland Basin. The experimental results demonstrate that hydrous pyrolysis experiments simulate well the natural maturation of these hydrocarbon source rocks. The activation energies for hydrocarbon and carboxylic acid generation and decarboxylation, calculated from the hydrous-pyrolysis derived data, are useful in modeling source rock maturation.