Study on the Oil Displacement Mechanism of Different SP Binary Flooding Schemes for a Conglomerate Reservoir Based on a Microfluidic Model

The objective of this study is to elucidate the oil displacement mechanism of different surfactant- polymer (SP) binary flooding systems in conglomerate reservoirs and to determine the optimal scheme. On the basis of water flooding, the microfluidic model is used to reveal the oil–water flow law of different SP binary flooding systems and then determine the oil displacement mechanism. The experimental results show that the SP binary flooding solution can enhance oil recovery by enhancing the sweep volume; the oil displacement efficiency of the echelon viscosity reducing (EVR) scheme is better than that of the echelon viscosity increasing (EVI) scheme and the single constant viscosity (SCV) scheme. For the EVR scheme, the oil displacement system with a high molecular weight and high concentration preferentially enters the large-scale pore-throat of the reservoir. After a period of time, a high resistance area can be formed in the large-scale pore-throat along the main flow direction of water flooding so as to reduce the mobility of the displacement solution in the dominant seepage channel and decrease the frequency of water channeling and then improve the oil displacement efficiency in the large-scale pore-throat to enhance the oil recovery. When the molecular weight and viscosity of the SP binary solution are both reduced, the oil displacement solution with a low molecular weight and low concentration mainly produces low-permeability layers by adjusting the displacement path to enhance the sweep volume in the small-scale pore-throat. Through the reconstruction of a pressure field and the redistribution of seepage paths of chemical micelles with different sizes, the displacement mechanism of crude oil in pores and throats shows a changing trend from large-scale pore-throats to small-scale pore-throats. After the viscosity reduction of the SP solution, the lower production limit of the pore-throat radius is reduced to 1 μm and the sweep volume of the small-scale pore-throat is enhanced. The stepwise production of crude oil in pores and throats with different radii is realized so as to enhance the oil recovery of the conglomerate reservoir. Finally, a new model of SP binary flooding suitable for "echelon injection and stepwise production" of a conglomerate reservoir is established innovatively.