A computational method for determining oil expulsion efficiency based on the ideal effective oil expulsion mode

Abstract

The oil expulsion efficiency of hydrocarbon source rocks is a key parameter for predicting conventional oil and gas resources and is closely related to the source rock thickness. Pyrolysis experiments and oil expulsion models were used to establish an oil expulsion efficiency calculation formula and to then analyze the trend of the oil expulsion efficiency. We determine the theoretical maximum oil expulsion efficiency via pyrolysis experiments to investigate hydrocarbon generation and expulsion. Then, we establish three ideal and effective oil expulsion models based on the single-layer source rock thickness: full type, full and transition type, and full and transition and retention type. Finally, we derive a corresponding correction formula for the oil expulsion efficiency. Using a type II1 hydrocarbon source rock from the Dongying Sag as an example, we calculate the oil expulsion efficiencies. The oil expulsion efficiencies of single-layer source rocks of different thicknesses exhibit only small differences at a low-maturity stage but exhibit obvious differences at a high-maturity stage. The oil expulsion of thin hydrocarbon source rocks is high, even exceeding 70%, but the oil expulsion of super-thick hydrocarbon source rocks is only approximately 30%. Therefore, the thickness of a single-layer hydrocarbon source rock exerts an important influence on oil expulsion, particularly during the raw oil generation and peak discharge stages.