Abstract: Based on the recent study results of hydrocarbon expulsion and recent advances made in coal study, it is suggested that the main mechanism for oil and gas migration in coal is hydrocartbon expulsion as an independent phase along the microfracture driven by the elevated pressure resulting from hydrocarbon generation. Hydrocarbon saturation and fracturing pressure are the main controls on hydrocarbon expulsion. The model of hydrocarbon expulsion along the microfracture in coal is then developed, which proved to be reliable and valid while it was applied in the study of hydrocarbon expulsion in Taoyuan - Rongxingtun area, Liaohe basin.

Key words: Liaohe depression, Coal, Microfracture, Hydrocarbon expulsion, Simulation