Abstract
The performance of chemicals used in chemical enhanced oil recovery (EOR) is sensitive to the local ionic environment. Divalent ions are in particular known to reduce polymer solution viscosity and methate the adsorption of surfactants and polymers to the rock surface. Here, we study whether the addition of divalent ion-complexing agents can mitigate these interactions and thus improve the performance of EOR chemicals. The addition of sodium polyacrylate (NaPA) is found to be highly effective in reducing surfactant adsorption and increasing polymer viscosity. The reduction in surfactant adsorption is attributed to a combination of divalent ion complexation and the adsorption of polyacrylate to the rock surface. The increase in polymer viscosity is also attributed to complexation of divalent ions that would otherwise interact with the polymer. Polymer flooding experiments in a limestone core show that the addition of NaPA also significantly enhances solution injectivity and propagation, thus providing a host of benefits to chemical EOR performance.
NSTL