Optimization of Polymer Flooding with a Tapered Concentration Slug

This paper provides hints and guidelines towards a better understanding of the correlation between the polymer injection schedule and the project profitability. In the optimization study, the polymer slug will be represented by three parameters: the slug length, which is the effective duration of polymer injection at maximal polymer concentration, the maximal injected polymer concentration itself and the tapering (in terms of slope of polymer concentration profile versus time). This last factor is often ignored due to the complex problems of parameterisation in numerical models. The polymer flood model and inverse problem formulation were adapted to be solved by CMG’s tools and a special method was introduced to account for the effect of varying the optimization parameters on the rheological properties of the water phase (combining viscosity dependence on shear-thinning and concentration) and on the polymer injectivity. The injectivity issue was treated by introducing an additional negative well skin factor which corrects the well inflow model for non-Newtonian polymer solutions. The Net Present Value was used as an objective function during the optimisation phase to estimate the economic benefit. The method was applied to a North-German mature oil field where a polymer project is at the stage of pilot testing.