Full Field Polymer Flooding Development Concept in Nimr Oil Fields with Horizontal Injectors and Strong Bottom Aquifer

Abstract

The Nimr fields comprise a group of medium size mature oil fields in the Southern part of Oman. This study focuses on Nimr-A and Nimr-E fields. The fields have similar reservoir properties and have been in commercial production since 1980 through the depletion. The strong regional bottom aquifer provides pressure support in these fields. The combination of a strong aquifer and relatively high viscosity of Nimr crude (~250-700 cP at reservoir conditions) resulted in the rapid development of water conning, limiting the oil recovery efficiency. Therefore, polymer flooding was selected as the technology to improve recovery. During 2013-2019, a polymer injection trial was executed in the Nimr-E field, whereby three horizontal injectors were used to evaluate the performance of polymer flooding under the reservoir conditions. As a result, the incremental recovery factor due to polymer has reached ~7% of STOIIP. Furthermore, due to the strong bottom aquifer, incremental oil production was observed even during the extended periods of injection shut-in through the "water cone recharging" mechanism. This has led to the proposal of a new polymer flooding concept for oil reservoirs with strong bottom aquifers called Nothing-Alternating-Polymer (NAP). In 2020, a new field trial was started in the Nimr-E field to investigate the performance of the concept under controlled field conditions and identify the optimal NAP design. This publication presents the conceptual design of an integrated polymer flooding project in two mature Nimr oil fields. Both surface and subsurface considerations were taken into account and discussed here. Despite moving at different project development paces at the earlier stages, the projects were synchronized, and their value drivers were reviewed in line with modern-day requirements. Considerable attention was paid to reducing carbon intensity and water source sustainability. Polymer flooding was selected due to incremental and accelerated oil recovery at reduced carbon intensity. The selection of a sustainable water source was also important, given the high value of water resources in Oman. Commercial-scale polymer flooding in Nimr A and Nimr E is PDO's most recent polymer flooding project, with value drivers focused on reduced CO2 intensity, water sustainability, and commercial robustness. The proposed multi-field, phased polymer development concept uses ~80 horizontal injectors above the oil-water contact to benefit from the aquifer support. Nimr is a flagship project for polymer flooding, with its results defining the development of polymer flooding in Oman for years to come.