Petroleum migration and accumulation in the Bozhong sub-basin, Bohai Bay basin, China: Significance of preferential petroleum migration pathways (PPMP) for the formation of large oilfields in lacustrine fault basins

This paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in Bozhong sub-basin, Bohai Bay basin. Modeling of secondary petroleum migration pathways has been conducted using a simple three-dimensional model, which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces. The modeling results have accurately predicted the petroleum occurrences, and have been supported by petroleum geochemical studies. Most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways (PPMP) formed by focusing of numerous “small petroleum streams” close to the kitchens, and most large fields (petroleum reserves greater than 1×108 ton) have more than one preferential petroleum migration pathway to convey petroleum to the traps. The focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields. The strong porosity and permeability heterogeneities of the carrier beds, and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity, suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales.