Improving polymer flooding efficiency in Oman oil fields

Considering a depressed environment with low oil prices, optimizing the costs linked to polymer injection becomes important. In this paper, the efficiency of two polymers dedicated to Omani southern fields' conditions have been evaluated: A standard copolymer currently injected in the Marmul field and another polymer optimized in terms of chemistry and polymerization process. The purpose is to ensure that changing the polymer will not impact the project efficiency. Consequently, the rheological properties, long term stability and injectivity have been compared for both polymers. The standard polymer (P1) is a high molecular weight polymer widely used worldwide. The new polymer (P2) is a higher molecular product with better salinity and temperature resistances. In terms of rheological properties, P2 displays a higher viscosity in the field brine and also displays better viscoelastic properties with, in the end, a significant decrease of polymer dosage. Filterability of the polymer P2 is slightly poorer than for the P1, which is likely due to a higher molecular weight. P1 and P2 injectivity properties were assessed in two different cores: 100 mD Berea cores and 1500 mD Bentheimer cores. Both polymers propagate quite well in both core types showing no injectivity issues after injection of 4 to 5 pore volumes. In the Berea core, adsorption was approximately 42 μg/g for the P1 and 25 μg/g for the P2. Permeability reduction was nevertheless quite significant in such low permeability cores, and some face plugging was observed. In 1500 mD cores, adsorption valuewas determined around 12 μg/g and 10 μg/g for the P1 and the P2, respectively. Thermal stability for both polymers was performed in fully anaerobic or with specific amounts of O₂ and H2S. The efficiency of two protective packages against H2S induced degradation was evaluated. The results after the incubation for 4 months highlight the need to avoid oxygen ingress in the system in presence of H₂S. However, it is still possible to keep an acceptable level of viscosity by fine-Tuning the protective additives. This study demonstrates the viability of a cost-effective alternative to what is already used in the Marmul field. This new polymer can be an appropriate candidate to keep chemical EOR in Omani southern fields economically viable.