The oil recovery factor from oil reservoirs must be increased significantly to meet the ever-increasing demand for energy. Majority of oil reserves worldwide (estimated as 60%) are held in carbonate reservoirs. It is believed that most carbonate reservoirs are mixed-wet to oil wet with high variation in wettability within the reservoir rock. Water-Alternating-Gas (WAG) injection is one of the most applicable EOR techniques known to increase oil recovery factor by 8-20% on top of waterflood alone. To maximize recovery from carbonate reservoirs, numerical simulation is the best available tool to aid with such objective. In this paper, we are presenting a new approach to simulate near-miscible water- alternating-gas injection for mixed-wet reservoirs.

The coreflood experiment used in this study was performed on a 65mD mixed-wet sandstone core sample at 38°C (100°F) and 12.69 MPa (1840 psia) where calculated Interfacial tension (IFT) between gas and oil at these conditions is 0.04 mN/m.

As recorded in the literature, the current simulation capabilities to model WAG injection behaviour is questionable. Some authors suggested that Land’s gas trapping parameter [C] should be variable during the WAG injection process. In this study, we investigated the best way to match the results of WAG injection experiments performed on a mixed-wet core. Matching the full experimental results were not possible without varying gas trapping parameter [C]. However, by updating the gas trapping parameter, based on our suggested procedure, the match between the simulation results and experimental data improved significantly.

This paper highlights the shortcomings of the commercial simulators in modelling WAG injection process. The current WAG hysteresis model can be improved based on the information published in this paper for better WAG injection simulation.

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