Incremental Recovery Using Dual-CompletedWells in Gas Reservoirs With Bottom WaterDrive: A Feasibility Study

摘要

Water drive reduces gas recovery though themechanism of water coning that results in liquid loadingand killing the wells. Installation at a Downhole GasWater Separator (DGWS) in the well may prevent theliquid loading. The paper presents another solution tothis problem - a dual-completed well with downholewater sink (DWS) drainage and injection installation.DWS wells are different from the DGWS wells byinclusion of a second bottom completion that controlswater outside the well and prevents commingled inflow ofgas and water to the top completion. The wells have beensuccessfully tested in oil reservoirs.The study qualifies DWS concept for gas wells bycomparing simulated performances of a conventionalwell, and a DWS well. The simulation runs were madeover a broad range of the initial reservoir pressure and permeability values for a gas reservoir with largeassociated aquifer. Also included is a comparisonbetween DGWS and DWS wells for selected conditions.The results show considerable advantage of dualcompletion over conventional wells in low-pressure(subnormal) tight (1 md) reservoirs – a 2.6 - foldrecovery increase before killing the well with water. Theadvantage, however, reduces to 10% for reservoir withnormal pore pressure gradient and permeability 10 md.When compared to DGWS wells, the final gas recovery ofDWS wells is the same, but DWS produces all the gas35% sooner than DGWS. The study also identified thebest DWS completion design where the top completion isused only for gas production, and the bottom completionfor inverse gas coning, gravity separation and waterinjection.