Simulation of hydrocarbon generation of the Paleozoic coals in the Dongpu Sag, Bohai Bay Basin

The hydrocarbon generation and expulsion characteristics under different temperatures and pressures and the hydrocarbon potential of coals were studied based on the thermal simulation with water in a half-open system of coals using the geological conditions of the Carboniferous-Permian coals in the Dongpu Sag, Bohai Bay Basin. The results indicate that: (1) The Carboniferous-Permian coals in the Dongpu Sag show a very high hydrocarbon generation potential. The yield of hydrocarbon generated can reach 254 mg/g, among which the gaseous products account for 220 mL/g, and the liquid part about 145.8 mg/g. (2) The yield of thermal cracking oil from coal shows a single peak, which appears at 325 ℃ (R_o=1.08%). Almost 40% of the liquid hydrocarbon was expelled from coal. (3) The hydrocarbon generation of coal followed an increasing tendency in several stages. The intervals 325-400 ℃ and 500-550 ℃ are the stages when gaseous hydrocarbon shows a rapid increase. The former increase should be a result of thermal cracking of liquid hydrocarbon, while the latter maybe caused by the condensation of aromatic hydrocarbon. (4) The Carboniferous-Permian coals in the Dongpu Sag yielded both oil and gas, with an oil generation potential appro-ximately equal to that of the Jurassic coals in the Turpan-Harmi Basin, and a gas generation potential matching the Carboniferous-Permian coals in the Ordos Basin.