Numerical simulation study on reservoir damage caused by adsorption and capture retention in polymer injection

Polymer flooding is a key technology for improving oil recovery in reservoirs with heavy to medium crude oil. However, the adsorption and retention of polymers in reservoir pores can cause reservoir damage. This study investigates the dynamic changes at the wellhead pressure and reservoir damage induced during polymer injection due to adsorption and retention. By integrating continuity equations, polymer flow equilibrium equations, and pore permeability damage equations, a mathematical model is proposed to calculate polymer damage. The model is discretely solved using the finite difference method, effectively simulating the reduction in reservoir porosity and permeability caused by polymer adsorption and retention, as well as the changes in wellhead pressure caused by permeability variations of reservoir and viscosity variations of polymer solutions. Numerical simulation under different injection conditions reveals that the viscosity of polymer solutions is primarily influenced by polymer concentration and Darcy velocity, showing a trend of initial increase followed by decrease radially. The extent of reservoir damage and the rate of increase in wellhead pressure of the injection well correlate positively with polymer concentration and injection volume, with significant reservoir damage concentrated within approximately 2m around the wellbore. Considering interlayer heterogeneity, inflow is identified as the main factor causing uneven damage distribution. This research enriches the study of damage caused by injection wells and provides a new mathematical model for diagnosing such damage.