Estimates of Coal as a Source of Oil and Gas: Genetic Potential and Reaction Kinetics from Hydrous Pyrolysis Experiments

Peigui Yin, Ronald C. Surdam, Steve W. Boese

Coal samples from North and South America, Australia, and Asia, most associated with giant hydrocarbon accumulations, were analyzed by hydrous pyrolysis to assess hydrocarbon genetic potential and generation kinetics. For each coal type, a coal-water mixture was heated within a sealed vessel. Pyrolysates were measured and liquid hydrocarbons were characterized. Raw coals and experimental residues underwent anhydrous pyrolysis, elemental analysis, nuclear magnetic resonance (NMR), and organic petrography.

Both oil and gas were generated during hydrous pyrolysis of all coal samples, but genetic potential varied among coals. Samples with higher hydrogen index (HI) and liptinite content showed greater genetic potential for both oil and gas. The oil to gas ratio increased with increasing HI and liptinite content. Significant genetic potential remained at vitrinite reflectance values up to 1.7%, even after liptinite macerals disappeared.

Characteristics of oil derived from hydrous pyrolysis experiments are similar to naturally produced oil spatially associated with the coals. Carbon dioxide and organic acid anions were also generated during hydrous pyrolysis and are similar to those present in formation waters associated with the coals. Based on the hydrous pyrolysis experiments, the typical calculated activation energy for oil generation is about 30 kcal/mole and > 20 kcal/mole for generation of water-soluble organic acid anions, indicating that organic acid generation generally precedes hydrocarbon generation from coaly source rocks. It is concluded that coal from around the world is not only a source of gas, but also a significant source of liquid hydrocarbons.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995