Perforation strategy for multilayered gas reservoirs

The gas reservoirs in the Gulf of Thailand are generally hosted by fluviodeltaic sands, which are generally limited in extent and dissected by numerous faults. This depositional environment and trapping mechanism result in multilayered reservoirs with different reservoir characteristics. The drive mechanisms associated with the reservoirs are either depletion or water drive. This study was initiated to determine the optimum depletion scenario for the multilayered reservoirs with different drive mechanisms. The study includes computer modeling of the reservoirs as well as several simulation runs to determine the effect of drive mechanism to the recovery performance under various perforation strategies. The study reveals that when the multilayered reservoirs are under depletion drive mechanism, depletions from all reservoirs at the same time would provide optimal recovery performance in terms of production time and crossflow minimization between layers. When all reservoirs are under water drive mechanism, to produce from all layers and later on shut the layer with high water production off would provide optimal solution in terms of recovery efficiency, crossflow, and recovery time. For commingled production from both depletion drive and water drive reservoirs, separate production between different reservoir drive mechanisms, with early shutting-off the water producing reservoirs would provide optimal solution in terms of recovery efficiency, crossflow, and recovery time. It is also found that permeability plays important role in determination of recovery efficiency for each reservoir.