It can be challenging to forecast polymer flooding performance at the field, in large part because of the complex non-Newtonian fluid rheology of polymer solutions. In this paper, we apply a model, previously developed to study linear core flooding experiments, to investigate polymer behaviour in radial flow near a vertical injector. The polymer system studied here is very common, HPAM in seawater. One key result is that a grid resolution on the order of millimetres is needed near the wellbore to accurately capture the well pressure, and the amount of mechanical degradation. We also demonstrate that for typical injection rates and permeabilities, the apparent shear thickening and mechanical degradation flow regimes are only relevant to consider within a few metres from the well. For the purposes of full field simulations, a pure shear thinning model should therefore suffice to describe fluid flow outside of the well grid blocks. Approximate analytical expressions are derived to test the numerical model. The steady-state molecular weight far away from the well is shown to scale as Q-0.65k0.425, where Q is the injection flow rate, and k is permeability. This scaling makes it possible to collect simulated values onto a single curve and can be used to predict mechanical degradation under different conditions. The results are in broad agreement with observations made of polymer mechanical degradation at the Dalia field. For the case of linear flow, there is an additional length dependency of degradation. The model then predicts an approximate power-law scaling MwLL, with MwL being the model molecular weight at a distance L from the inlet, which is consistent with recent laboratory experiments.