Reinjection of Produced (Sheared) Polymer in a Canadian Viscous Oil Reservoir: Considerations to Improve Economics and Reduce Carbon Footprint

Abstract

Summary Chemical enhanced oil recovery (EOR) flooding is one of the more attractive methods to improve oil recovery. However, during times of instability in the oil market, cost of specialized chemicals and necessary facilities for alkali-surfactant-polymer (ASP) or surfactant-polymer makes this technology very expensive and challenging to implement in the field. In the majority of cases, polymer flooding alone has proved to be the most cost-effective solution that has resulted in attractive and predictable return on investment. In recent times, a challenging economic environment has operators looking for added economic and sustainable savings. The possibility of reinjection of produced (sheared) polymer to offset injection concentration requirements can lead to reduced cost and longer sustainability of oil recovery, thus offering a subsequent reduction in produced water (PW) treatment and a reduced full-cycle carbon footprint. This innovative approach is subject to conditions experienced in the surface facilities, as well as in the reservoir. As part of this study, different polymer chemistries were investigated for their mobility control in porous media and comparative effect on oil recovery trends in the presence of produced fluid containing residual polymer. The initial fluid-fluid testing and laboratory characterization results were validated against a mature field EOR project for reduction in polymer requirement to achieve target viscosity. Monophasic flow behavior experiments were performed in Bentheimer and Berea outcrop cores, while oil recovery experiments were performed in Bentheimer outcrops with different polymer solutions—freshly made and combinations with residual produced polymer. Based on field observations and laboratory measurements, a 10 to 15% reduction in fresh polymer loading could be achieved through the reutilization of water containing residual polymer in these specific field conditions. Note, this case study involved produced polymer that was degraded through progressive cavity pumps (PCPs) resulting in only 15 to 20% of the injected viscosity in the produced fluids in addition to thermal and chemical degradations. The monophasic injectivity experiments in both outcrop cores resulted in similar resistance factors (RFs) for fresh polymer and blends with produced water reinjection containing residual polymer (PWcRP) solution, establishing the robustness of this blending system. Oil recovery experiments also resulted in similar oil displacement behavior [approximately 30 to 40% oil originally in place (OOIP) after 0.5 pore volumes (PV) waterflood] for fresh and blends with sheared polymer solutions, validating no loss in recovery potential, with the added benefit of 10 to 15% polymer loading reduction.