Simulation and Benefit Estimates of EOR in Wara and Burgan 3SU Reservoirs, Greater Burgan Field

Abstract

Abstract The Greater Burgan field in Kuwait is the largest sandstone oilfield in the world. Kuwait Oil Company (KOC) recognizes that enhanced oil recovery (EOR) is of strategic importance to maximize recovery and extend field life. We studied several EOR options using reservoir simulation to evaluate the benefits of using low salinity waterflood (LSW), low salinity polymer (LSP) injection and high salinity polymer (HSP) injection applications in Wara and Burgan upper (3SU) reservoirs. Full-field reservoir-simulation with adequate resolution for EOR assessment of giant fields (e.g., Greater Burgan) is computationally expensive, if even possible. To overcome this, we ran high-resolution sector-models, representing different areas, with inputs from laboratory and single-well-chemical-tracer-tests and generated type-curve profiles (e.g. oil recovery vs. cumulative pore-volume injection). A scaling-up tool was developed that considers infrastructure-facility constraints (e.g., high- and low-salinity capacities and injection priority of field areas), combines type-curve profiles, and outputs field-level profiles. At sector-level, we optimized all EOR slug sizes. For cases with polymer, polymer concentration was optimized on basis of polymer amount required per incremental oil barrel. The following five development scenarios were studied: 1) HSP everywhere across Wara and Burgan (3SU) reservoirs 2) LSW everywhere across the reservoirs 3) LSP everywhere across the reservoirs 4) secondary LSW for certain areas of the reservoirs and HSP for remaining areas 5) secondary LSP for certain areas of the reservoirs and HSP for remaining areas. The scenario #3 shows the highest incremental oil as it adds the benefits of both LSW and polymer injection. However, using low salinity-polymer in conjunction with high salinity-polymer (i.e., scenario #5) gives the highest incremental oil peak rate. In general, polymer flooding reduces the amount of water production. Use of low salinity without polymer resulted in higher water production. Significantly less volumes of polymer are associated with low-salinity water injection as compared with high-salinity water injection. Optimal polymer concentration was found to be well above that which gave unit mobility ratio. Although, the EOR incremental benefits and their corresponding screening-level economics look reasonable for the EOR schemes investigated, the schemes vary significantly in feasibility, capital costs and operating costs. A long-term injectivity pilot of high-salinity polymer is planned. Our approach combines the understanding of recovery efficiency that comes from detailed type pattern modelling with understanding of realistic facility constraints to rapidly generate realistic field-wide projections. We evaluated several facilities options corresponding to the five EOR development scenarios and generated cost profiles that were used in economic modelling.