Use of Polymer Flooding to Enhance Oil Recovery from the Largest Oil-Bearing Clastic Reservoir in the South of the Sultanate of Oman

For more than 85 years, Petroleum Development Oman (PDO) has gained significant experience in oil production from different types of reservoirs, of which Gharif is the largest clastic formation in terms of oil reserves. The formation bears mainly medium to heavy oil, making primary and secondary (waterflooding) oil recovery less efficient due to the unfavorable oil-water mobility ratio. This paper demonstrates that polymer flooding is the best technology to improve sweep efficiency and achieve higher oil recovery at acceptable costs and risks. The technology is not new to PDO and has been implemented in the Al-Khlata formation in the Marmul oil field since 2010 (Svec et al., 2021). Gharif reservoir properties are more complex than those of Al-Khlata; therefore, additional laboratory studies were performed. The paper aims to present the results of such studies complemented by the production forecast results obtained from fit-for-purpose modeling approach. The approach was then used to accelerate phased project development in the Rahab field with multiple Gharif reservoirs, each characterized by a different oil viscosity. The Rahab polymer project aims to develop heavy oil in the Gharif formation through vertical polymer injection patterns. The success of this project will pave the way for future developments in the fields with similar reservoir (Gharif) characteristics. In order to reduce technical risks for Rahab polymer flooding, the project development was phased with Phase 1 as a trial and Phase 2 as a commercial-scale project. This paper is focused on the technical work done to design a polymer injection project for Phase 1. The objectives of Phasel are to: Expedite polymer injection in this field to monetize the opportunity while collecting more data and building a more robust understanding of Gharif polymer performance.Evaluate the surface facility modular approach against the standalone facility per single field (standard PDO approach). This could minimize the surface facility Capex and provide more operational flexibility.