Optimization Study of the Remaining Oil Potential Exploitation Method in the Late Stage of Chemical Flooding with High Moisture Content

This paper focuses on the block of S II 1–4 + S II 7–12 oil layers in the late water cut rising period of chemical flooding. The development ratio of Class II B+ and Class III oil layers in this block reaches up to 84.5% at the highest. The stage recovery factor is 27.70%, and the comprehensive water cut is 95.75%. The remaining oil is distributed in the diversion line in the plane, and is concentrated in the thin and poor oil layers vertically. In terms of the distribution characteristics of remaining oil, there are dominant seepage layers, and the water cut of some layers exceeds 95%. Through numerical simulation, the remaining oil in different sand bodies, units and well groups is analyzed. The remaining oil in thick oil layers is located in the diversion line and non-dominant seepage thick layers, while that in thin and poor layers is in oil layers with poor injection capacity. Regarding the potential tapping methods, for thick oil layers with a high recovery degree, the adjustment of reducing the well pattern density to control the water cut is carried out. The third mode, which is to shut down three adjacent injection wells, is determined to tap the remaining oil in the diversion line. For thick oil layers with a low recovery degree, a high-concentration sealing slug is injected before converting to water flooding to control the water cut. For thin and thick interbedded layers with a low recovery degree, 1 IFEDC-202519253 the conversion to water flooding is optimized and subdivided to control the water cut. For thin and thick interbedded layers and thin layers with a high recovery degree, the adjustment of structural water cut is emphasized. In terms of the applicability of different technologies, there are certain conditions for injecting a high concentration and then converting to subsequent water flooding. The method of subdividing and converting to water flooding to control the water cut is effective for wells with a permeability contrast greater than 4. Although the third mode of reducing the well pattern density to control the water cut is slow to take effect, it can tap the remaining oil in the diversion line. In conclusion, by clarifying the characteristics of the remaining oil and making targeted adjustments, the rising speed of the water cut and the decline rate of daily oil production in the block have been effectively controlled.