Several Chemical EOR processes were investigated to increase oil production in a mature giant on-shore field in North Africa, characterized by viscous oil and developed through sea water injection. Chemical selection was challenging due to high salinity and high hardness brine conditions. Polymer injection was finally identified for a test pilot to improve the mobility ratio during water flooding.
Polymer selection and characterization in sea water was performed in lab considering all factors potentially altering polymer performance such as high reservoir temperature, high brine salinity and hardness, mechanical degradation and adsorption. Tertiary corefloods on reservoir porous media were performed, showing a significant additional oil recovery up to 8%.
The experimental data were reproduced to derive input simulation parameters to describe the chemical EOR process: the benefits of polymer in comparison to a peripheral water injection and a dispersed water flood scenarios were predicted at sector scale. The pilot area was represented by a high resolution sector model, calibrated on production data and the chemical EOR forecast scenarios were built in a dispersed injection pattern. Very good results were achieved, showing additional oil recovery in the range 4-6% with polymer injection in the monitoring area. Based on the encouraging results of lab analyses and simulation, the polymer injection is currently under design in a cost-effective polymer inter-well pilot.
