Abstract: The hydrocarbon expulsion efficiency of source rock is an important parameter in petroleum resources assessment. The study of hydrocarbon expulsion efficiency can not only guide the resource evaluation, but also be an important scientific means to verify the reliability of the resource evaluation results. To remedy the defects of current hydrocarbon generation potential method, an improved hydrocarbon generation potential method is proposed, and the hydrocarbon expulsion efficiency of shale in the Jurassic Da$'$anzhai Member of central Sichuan Basin was obtained by using this method. The results show that under the current geological conditions, the hydrocarbon expulsion efficiency of the shale in the Da$'$anzhai Member is distributed between 0${\sim}$62.6{\percent}. With the increase of organic matter maturity, the hydrocarbon expulsion efficiency gradually increases, and the oil saturation index increases first and then decreases. When $R_{\rm o}$ is in the range of 0.95%${\sim}$1.72%, oil saturation index is greater than 100 mg/g, and the movable hydrocarbon content of shale strata is higher. The lithofacies combination has a significant effect on the hydrocarbon expulsion efficiency. In the longitudinal direction, there is a tendency for shale to expel hydrocarbon from shell limestone, the development of interlayer fractures in interbedded combinations is conducive to shale oil flow and production. It is concluded that the interbedded assemblage in the lower part of the first submember in the area with $R_{\rm o}$>1.25% is the key exploration target for shale oil in the Da$'$anzhai Member. The results can provide theoretical guidance for the exploration and development of shale oil in the Jurassic Da$'$anzhai Member of central Sichuan Basin.

Key words: Sichuan Basin, Da′anzhai Member, shale oil, expulsion efficiency, hydrocarbon generation potential method