Heavy oil carbonate reservoirs of the giant Wafra field located in the Kuwait - Saudi Arabia Divided Zone hold huge resource of heavy oil in 3 reservoirs, namely 1st Eocene, 2nd Eocene, and Maastrichtian. More than 50 years of primary production from these high porosity, moderate permeability carbonates has recovered less than 5% of this volume and the ultimate recovery is not expected to exceed 10%. Suitable EOR technology is needed to unlock these huge resources. In absence of any commercial analogs, application of EOR technology carries enormous risk in terms of technical viability, reserves recovery and resources commitment. Proper understanding of the reservoir and optimization of EOR technology are essential to mitigate these risks to a manageable level.
This paper will discuss the process used to mitigate the risks of EOR application in the 2nd Eocene reservoir. Production in this reservoir is from dolomitized carbonates associated with anhydrite. Ultimate recovery from primary production is estimated about 12%. Low primary recovery in this highly porous and moderate permeability reservoir is attributed to oil gravity, viscosity and drive mechanism. Detailed screening study to select suitable EOR processes suggested the suitability of both waterflood and steamflood for this reservoir. The study indicated the opportunity to recover up to 20% with waterflood and 40% with steamflood. Economic Modeling work indicates similar NPV for both processes but higher profitability in water flood case due to substantially lower capital requirement. Both projects have serious challenges due to reservoir nature, uncertainty in reservoir characterization, non-availability of fresh water, lack of proven technology for processing produced water for steam generation, disposal of excess produced water, fuel for steam generation, and safe environment for workers, public and wild life. These challenges make the EOR projects very high risk ventures in the areas of oil recovery, return on investment, and health, safety and environment (HSE). These risks are being managed through extensive G&G and simulation studies, exhaustive screening work and properly designed pilot projects. Two pilot projects, steamflood and waterflood, are under implementation to resolve the number of uncertainties and manage associated risks in the high reward EOR process for this reservoir.
This paper will share the work flow (reservoir to economic modeling) for planning, designing and evaluation of pilot projects and innovative technology being utilized to manage risks of EOR in carbonate reservoirs. Success in mitigation of such risks will help industry to enhance sustainable and economic energy resource for future.