To investigate the enhanced oil recovery (EOR) technology by chemical flooding in an edge water reservoir, a 3D physical simulation experimental device for the edge water reservoir was developed, and polymer/surfactant binary flooding experiments were carried out under different edge water energies. In addition, the effect and mechanism of binary flooding on EOR under different edge water energies were comprehensively analyzed. Experimental results show that edge water intrusion considerably affects EOR by binary flooding. The stronger the edge water energy, the worse the effect of EOR by binary flooding. Edge water possibly diluted the concentration of the chemical agent medium that is injected into the reservoir, and the degree of dilution varied in different regions. The dilution region was mainly distributed between the injection wells and edge water. The stronger the edge water energy, the higher the dilution multiple of chemical agent and the greater the recovery loss rate by binary flooding.

Strong edge water reservoirs have sufficient natural energy. After long-term natural water flooding development, it is in the stage of ultrahigh water cut. There is an urgent need to change the development mode and improve the development effect. Taking Jidong Oilfield as an example, the mechanism model of strong edge water reservoirs is established by using the method of numerical simulation. Then, the factors and rules affecting the effects of gel-assisted polymer and surfactant binary combination flooding are studied. The screening criteria of gel-assisted polymer and surfactant binary combination flooding in strong edge water reservoirs are obtained. The results show that the existence of edge water is not conducive to binary combination flooding. Smaller water volumetric multiples and larger oil-bearing areas are more suitable for binary combination flooding. Compared with closed reservoirs, binary combination flooding in strong edge water reservoirs is more difficult to establish a displacement pressure gradient. The reservoir with high crude oil viscosity is not suitable for binary combination flooding. Gel-assisted polymer and surfactant binary combination flooding can be adopted for reservoirs with an oil-bearing area greater than 0.2 km2, a water volumetric multiple less than 200, and oil viscosity less than 100 mPa·s. The research results are of guiding significance for the reservoir selection of gel-assisted polymer and surfactant binary combination flooding after natural water flooding.

A three-dimensional (3D) experimental model considering the influence of water energy is established to innovatively analyze oil−gas interface stability, and it is found that a stable gas cap with sufficient driving energy can be formed only under a stable oil and gas interface. So, the bidirectional displacement through the gas cap and edge water can be realized during the late development stage in the strong edge-water drive reservoirs. Results show that the recovery of bidirectional displacement can reach 60%, while the recovery of an unstable interface is basically below 50%. The recovery degree under a stable oil−gas interface is more than 25.63% than that of the unstable interface. Based on the Navier−Stokes equation, a "steady flow velocity u s " formula that considers the influence of multiple factors is defined, and the ratio of the flow velocity at the oil−gas interface to the gas injection rate is controlled between 0.6 and 0.85 to determine the criteria for the stable oil−gas interface. At the same time, the differentiationhindered quasi-number (Gr) is defined to clarify the influence mechanism of various mechanical factors on gravity differentiation and the difficulty of oil and gas replacement. When Gr is equal to 1, the oil−gas interface reaches stable migration conditions. Larger formation dip angle, higher permeability, smaller oil viscosity, and lower gas injection rate are the favorable conditions for forming stable flow. The findings are recommended to be used in reservoirs with relatively homogeneous reservoirs, certain dip angles, and moderate or low oil viscosity.