Comparison of WAG and Water Over Injection for Carbon Storage and Oil Recovery in a Heavy Oil Field

Compositional reservoir simulation studies show that CO₂ enhanced oil recovery (CO₂EOR) combined with carbon storage using water over gas injection improves production performance and carbon storage compared to WAG injection. The fluid description is based on matching the PVT-derived viscosity, total and relative volume of a heavy oil sample (density 893 kg/m³ [17 degrees API]). The reservoir description is based on an unconsolidated deltaic, sandstone deposit in the Gulf of Paria, offshore Trinidad. Water over gas injection is an injection strategy proposed by Stone and Jenkins to increase gas sweep efficiency. In this injection design water is injected in the upper portion of the reservoir and gas is injected in the bottom portion of the reservoir using either vertical or horizontal injectors. Increasing the sweep efficiency improves both oil recovery and carbon storage. The counter current flow of injected fluids uses gravity effects to reduce gas override and water underride typical of WAG injection strategies and continuous single fluid injection. The results show that the water over gas injection design results in a larger mixing zone that extends further into the reservoir. Although oil recovery was essentially the same, with water over gas injection, there was greater than 50% increase in carbon storage, 20% reduction in water cut and 85% reduction in producing GOR compared to WAG.