Evaluation of Double Displacement Process via Water and Gas Dumpflood

Abstract

Double Displacement Process (DDP) is an improved oil recovery method which is very effective in dipping reservoirs. However, this process requires large investment on water and gas injection facilities as well as high operating cost. For a certain reservoir system, water and gas injection can be eliminated by allowing water to cross flow from the nearby aquifer into the reservoir during the waterflooding phase and neighbouring gas reservoir to cross flow during the gas flooding phase of DDP. To determine how much more oil recovery can be obtained using DDP via water and gas dumpflood for an offshore oil field in the Gulf of Thailand, a simplified numerical reservoir model was constructed. The model was used to investigate effects of gas reservoir volume and aquifer size due to uncertainty in the determination of the two parameters and effects of production schedule in order to maximize oil recovery. Simulation results indicate that oil recovered by the proposed DDP can be much higher than that from natural depletion, depending on gas reservoir volume and aquifer size. Regarding production schedule, it was found that alternating oil production period with shut-in period during gas dumpflood yields up to 14% increment in oil recovery factor when compared with continuous production. The increment level depends on the duration of no-production period which helps stabilize gas flood front through gravity segregation, avoiding early gas breakthrough at downdip wells and leading to higher oil recovery.