Polymer Stability After Successive Mechanical-Degradation Events

Abstract

Summary A key challenge in polymer-flood forecasting is the prediction of polymer stability far from the injector. Degradation may result from various mechanical-degradation events in surface facilities and at the wellbore interface, as well as possible oxidative degradation caused by the presence of oxygen and reduced transition metals. All these steps must be closely examined to minimize degradation and ensure propagation of a viscous polymer solution. In this paper, polymer solutions are pushed toward degradation rates that would be unacceptable for enhanced-oil-recovery applications to better understand the underlying physics. Multistep degradation events are induced in various geometries, such as capillaries, blenders, and porous media. For the geometries and range of polymer and salt concentrations investigated, degradation (as defined here) approaches an asymptotic value as the number of degrading events increases. An empirical normalization method is proposed, allowing superimposition of curves of viscosity loss vs. time across multiple possible geometries. The normalization procedure is applied to predict the extent of degradation during a field injection in which near-wellbore degradation occurs after degradation in surface facilities. We predict that degradation in the porous medium reaches a stable value after passing through approximately 6 mm of rock. Finally, degradation is proposed as a tool to probe the molecular-weight distribution and to narrow the polydispersity of polymers, which can be used for maximizing both viscosifying power and injectivity simultaneously.