Enhanced Oil Recovery by Polymer Flooding: Optimizing Polymer Injectivity

Abstract

Abstract Polymer flooding has been widely applied through past decades to increase oil recovery after waterflood. Water-soluble polymers are used to increase the viscosity of injected water that is a requirement for better sweep efficiency, but accelerated production due to polymer flooding may be limited by reduced injectivity. The objective of this paper is to give guidelines for optimizing polymer injectivity as key parameter for polymer flooding design. Analysis of polymer injection data from field tests, and different analytical and simulation approaches from academic or commercial simulators will be discussed. Field realistic laboratory flooding in porous medium has been performed. Presented experiments study the influence of pre- injection treatment like pre-shearing or other methods on rheological properties in porous medium. Injectivity is discussed in relation to polymer molecular weight, polymer concentration, pre-treatment, and presence of oil. Field scale injectivity is reviewed from available literature data. Impact of fracturing has been analyzed in order to isolate the matrix impact on injectivity and compare to laboratory data. Investigations show that injection pressure build up in the near wellbore region, which is also referred to as polymer shear thickening behavior, limits the injectivity of polymer solutions. The effect is more significant when high molecular weight polymer is injected compared to high polymer concentration. Hence, pre-shearing the polymer solution prior injection weakens the elastic properties of polymer while maintaining its viscous properties. Also, better polymer injectivity observed when oil is present (two phase flow) in porous media compared to no oil present (one phase flow). This paper will discuss polymer injectivity and isolate key parameters for optimizing injectivity. The data from this study gives guidelines for optimizing polymer injectivity.