Experimental Investigation of Factors Influencing Remaining Oil Distribution under Water Flooding in a 2-D Visualized Cross-Section Model.

About 70% of the remaining oil remains underground after water flooding, and there is a need to better understand the formation and distribution of this remaining macroscopic oil to enhance oil recovery. In this study, three types of visual plate models were devised with different packing sequences: homogeneous (J), high-permeability layer on top (F), and low-permeability layer on top (Z). Based on these models, several visual flooding experiments were conducted to study the water flooding physics and the remaining oil distribution pattern of an offshore thick heavy oil reservoir under the impact of formation heterogeneity, packing sequence, model length, and permeability contrast during water flooding. These displacements were monitored photographically, and the effluent production profiles were recorded. The results showed that layer permeability and gravitational segregation play an important role during the water flooding process in layered porous media. Experimental results based on the model with different lengths show that the breakthrough oil recovery decreases with the increase of well spacing. Finally, a correction was made to the gravity number by introducing a scaling factor that characterized the formation heterogeneity and packing sequence in thick formation, compared to a known gravity number; the modified gravity number showed a better correlation with breakthrough oil recovery of water and polymer flooding. The research results provide effective guidance for the remaining oil distribution and injection and production parameter optimization in actual reservoirs.