Polymer injection is an efficient EOR technology for viscous oil fields, aimed at improving mobility ratio between oil and displacing fluid hence optimizing the macroscopic sweep efficiency. This paper presents a polymer pilot project on onshore field in North Africa characterized by strong areal horizontal heterogeneities and bearing a medium-viscous oil.
Laboratory analyses were performed as first step aimed at assessing efficiency of polymer displacement: an initial screening was conducted to select the optimal polymer, focusing on viscosity-concentration and thermal stability. Then, core floodings were performed to evaluate effectiveness of polymer injection at reservoir conditions. Moreover, polymer rheology in porous media was investigated to better evaluate well injectivity during polymer flooding. Core flooding results were showing recovery factor up to 48%.
Based on laboratory analyses promising results, 3D simulations were conducted. Full field model was initially tuned to reproduce core results. Then, simulation were used to optimize injection strategy and development scenario, considering also full field project extension. Model results are showing that polymer injection, compared to water flooding case, leads to improvements up to 10.4% on cumulative oil at the end of reservoir life.
Field application started at the beginning of 2014. A dedicated plant to treat injection water for iron removal was installed. Indeed high concentration of iron ions, coupled with oxygen, is detrimental for polymeric solution effectiveness.
Preliminary results obtained during the start-up and the current monitoring phase are showing good injectivity of polymer and a delayed breakthrough time, if compared to the results obtained during tracer campaign.
The current prospective is to keep focusing on well monitoring to confirm effectiveness of polymer injection and to extend EOR application to full field.
