Abstract
Despite the importance of determining the maximum recovery and optimum production strategy for gas-condensate reservoirs under aquifer support, a rigorous systematic methodology is not available in the literature. Instead, most existing studies relied on running reservoir simulations with fine grids or LGR constrained by simulation runtime, producing great uncertainty in the reliability of the results. In this study, a comprehensive and systematic study of gas-condensate reservoirs under aquifer support was conducted instead.
This study focused on first benchmarking radial simulation models to available analytical solutions to within 1% of pore pressure prediction. Next, Cartesian grids were benchmarked against the calibrated radial model before applying to full field reservoir model. The full field reservoir model was then history-matched for all wells before various production regimes were simulated to determine optimum production strategy. Sensitivity analysis of water-breakthrough and total produced water volume were investigated under various aquifer sizes, formation reservoir properties, and production regimes. Optimum production strategy was selected to maximize the hydrocarbon recovery while reducing the water treatment costs.
The approach focused on the construction of benchmarked models to describe the water breakthrough phenomena and to investigate the impact of aquifer on deliverability and ultimate recovery of a gas-condensate reservoir. Factors that could affect recovery such as withdrawal rate, aquifer size, formation permeability, and vertical-to-horizontal permeability were examined. Different production schemes were then simulated on a history-matched full field model to determine optimum strategy.
It was found that for better reservoir quality (permeability greater than 100 mD), withdrawal rates do not have significant impact on ultimate gas recovery. On the other hand, with increasing withdrawal rate cumulative condensate recovery decreases and total water production increases. Aquifer size has large impacts on recovery factor, water breakthrough time, and total water production. For medium and strong aquifers, it was found that the field water handling capacity could impose a significant constraint on ultimate recovery and upgrading water handling capacity later in the field life may be instrumental in improving recovery.
