MODELING STUDY ON HYDROCARBON EXPULSION FROM JURASSIC COAL SOURCE ROCKS IN TAIBEI SAG OF TURPAN-HAMI BASIN

The theory of hydrocarbon expulsion threshold was applied in a numerical simulation of hydrocarbon expulsion from lower-Jurassic coal source rocks in Taibei Sag, Turpan-Hami Basin. The results show that methane and heavier hydrocarbon gases were expulsed first at burial depth of about 500m. This was followed by expulsion of liquid hydrocarbons at burial depth of about 2000m. The rate of hydrocarbon expulsion reached a maximum at burial depth of around 3500m. Currently, the amount of methane, heavier hydrocarbon gases and oil expelled from 1 m3 coal source rocks is 64.72 m3, 3.82 m3 and 34.97kg, respectively. Main mechanisms of hydrocarbon expulsion from the coal source rocks include dissolution in formation water, diffusion, dissolution in oil and free phase, with the last two being the most important. Expulsion efficiencies for methane, heavier hydrocarbon gases and liquid hydrocarbons are 73.5%, 66.1% and 69.9%, respectively. The process of hydrocarbon expulsion can be divided into three stages: (I) gas expulsion by dissolution in formation water and by diffusion; (II) gas expulsion in free phase, and (III) oil and gas expulsion in free phase.