A case study of gas-condensate reservoir performance under bottom water drive mechanism

This case study investigated the effects of formation reservoir properties, aquifer influx, and production scheme on ultimate recovery and production behaviors of a gas-condensate sandstone reservoir Sand20 offshore Vietnam. Optimum production strategy was then formulated to maximize the hydrocarbon recovery while reducing the water treatment cost. The approach focused on the construction of benchmarked radial numerical models to describe the water coning and breakthrough phenomenon and to better understand the impacts of aquifer on deliverability and ultimate recovery of a gas-condensate reservoir. In this study, all factors that have potential impacts on gas and oil ultimate recoveries such as gas production rate, completion length, aquifer size, reservoir horizontal permeability, and permeability anisotropy were investigated. The numerical results showed that for permeability greater than 100 mD, withdrawal rates do not have significant impacts on reservoir gas recovery, while the oil recovery decreases with increasing withdrawal rates. To maximize the ultimate oil recovery, minimize total water production, delay water breakthrough time, and prolong field production life, the wells are recommended to produce at a reasonable low gas flow rate. On the other hand, a minimum gas production rate is required to recover all the reserves to meet the field's production strategy. Aquifer size was found to have no impact on water breakthrough time for this gas-condensate reservoir, but it can have big impact on the recovery factor and the total water production. This study also suggested that perforation interval should be sufficiently long to maximize recovery. Finally, it was found that water-gas ratio does not increase rapidly until approximately 90% of perforation interval is flooded with water.