Development of oil rim reservoirs is challenging and could lead to low oil recovery, if multiple determining factors are not well understood, that influences successful field development concept. It requires detailed analysis and development of specific procedures to optimize the oil production from a thin oil rim underlaying gas cap. Few IOR/EOR applications for oil rim development have been reported in the literature so far. This study presents a concept for the optimization of oil production from an oil rim reservoir by numerical simulation.
As a starting point, a representative sector of the field was selected for the initial analysis. It was decided to perform IOR/EOR methods including water/gas flooding/injection and surfactant flooding using inverted five-spot horizontal well pattern, for the application in the selected sector. Upon execution of the detailed sensitivity analysis, the pattern was optimized by its characteristic geometric variables including the length of the vertical/horizontal section of the well, the location of the wells, lateral well distances and the orientation of the pattern. The optimization was performed by setting an objective function to improve recovery factor and reduce water/gas cut by using the differential evolution algorithm. The latter was run until converging, and the optimal solution was used to perform further IOR/EOR studies.
Finally, after selection of a base-case scenario and best well pattern, IOR/EOR options were evaluated, and the comparative results were reported. The generated results show that the application of 5-spot horizontal well pattern in the oil rim reservoir could increase the oil recovery by water flooding, but with low sweep efficiency. The losses of injected water into the underlaying aquifer and up laying gas gap are large. Immiscible gas injection into the gas cap can support the pressure but massively increases the gas cut. In addition, displacement efficiency by gas flooding is poor.
Simulation results of the surfactant flooding case shows better displacement efficiency compared to water flooding. Also, the possibility of reducing residual oil saturation could increase the ultimate oil recovery but at very late time.