Economic Comparison of Hydrocarbon Recovery under Injection of Different Polymers

Abstract

Abstract Injection of water in waterflooding operations provides pressure support and displaces oil in the reservoir, thereby improving the recovery factor. A factor of significant importance in this process is mobility ratio; a higher mobility ratio allows for better displacement of oil by the injected water. For further increasing the volume of reservoir swept, gelling agents are used to improve the mobility ratio of injected water. It is imperative to identify the right type and amount of viscosity reducer to be used since shear stress and high temperatures cause polymer degradation, due to which polymer macromolecules may be forced into narrow channels. Performance of xanthan and synthetic polymers in a polymer injection process were compared. The model is assumption is that reduced gel kinetics forms a microgel without redox catalysis. For modeling purposes, a commercial reservoir simulator coupled with an optimization tool was used. The reservoir was modelled having 6 layers for injection, where first 4 layers have high horizontal permeabilities and the bottom 2 layers have a high permeability streak. For the first 450 days, injection water was continuously pumpedinto all layers andin the next 150 daysgel systems were injected only into the bottom 2 layers followed by which water was continuously injected for a period of 4 years. The optimization tool was used for sensitivity analysis investigation of variables to reduce variable uncertainty. Per modelling results, gel penetrated deep in reservoir but in bottom layers there was blocking. In terms of viscosity effects, the relative benefits of biopolymers and xanthan polymer were highlighted in the sensitivity analysis. Also, this investigation indicated merits of synthetic PAM in terms of resistance factor, insitu gelation treatments and their crossflow dependence. Retention of polymer-gel and their adsorption were shown to be dependent on permeability. In this study, for comparative purposes, different viscosity reduction treatments were modelled in the same model reservoir to highlight their relative advantages. Also, investigation of control variables through sensitivity analysis outlined the significance of each towards displacement efficiency. Keeping in mind the wide spectrum of areas around the globe where gel solutions can be applied, this study highlights factors that are critical to optimal reservoir management.