Hydrocarbon potential of Pennsylvanian coal in Bohai Gulf Basin, eastern China, as revealed by hydrous pyrolysis

A hydrous-pyrolysis experiment was performed using Pennsylvanian brown coal with a vitrinite reflectance (VR ₀) of 0.56% from a coal mine at the southwest corner of the Bohai Gulf Basin, eastern China, to evaluate the hydrocarbon potential of the coal. The coal sample is vitrinite-rich (74.5%) and inertinite-poor (16.7%) with liptinite content of 8.8%. Much of the vitrinite in the sample consists of hydrogen-rich vitrinite (collodetrinite). Hydrous pyrolysis was performed at 200 °C, 230 °C, 260 °C, 290 °C, 320 °C, and 350 °C for 72 h separately. Yields of both total liquid pyrolysates and expelled oil increased with temperature before reaching their maximum production of 17.27 kg/t coal and 14.57 kg/t coal at the same temperature of 320 °C (VR ₀ = 1.18%), and decreased afterwards. Gaseous products increased sharply at 320 °C and tended to increase even at the highest experimental temperature (350 °C; VR ₀ = 1.53%). Results show that the coal has not only a certain oil-generation potential but also a large capacity for gas production and a high expulsion efficiency. Oil potential of the coal is attributed to its depositional environment, which was transitional from shallow marine to coastal plain or swamp during middle to Late Pennsylvanian. The coal was protected from oxidation under water after deposition. Experimental results indicate that this Pennsylvanian coal could have contributed to oil/gas accumulation in the Bohai Gulf Basin.