A new strategy of using pH sensitive polymers for conformace control is proposed. the rheological properties of some plymers such as anionic derivatives of polyacrylic acid are shown to be very pH sensitive. For example, thier viscosity varies from 5cp at a pH of 2.5 to 20,000 cp at a pH above 6.0. This rheological behavior is reversable as the pH is cycled. Rheological data is presented at different polymer concentrations, temperatures and in solutions with different ionic strength. The effect of temperature on the rheological properties of the polymer is shown to be small. Compatibility tests showed that this polymer is compatible with most brines (NaCl, NH4Cl, and KCl).
Core flow experiments were conducted on Berea cores. The results showed that the polymer solution was easily propagated through 6 inch long cores due to its low initial viscosity ( 5cp). The polymer solution formed a rigid gel inside the pores after a shut-in period of 24 hours as the pH of the fluid increased above 6. The gelled polymer was found to be stable up to the maximum examined pressure gradients of 4000 psi/ft across the core. Experiments were conducted by using acid pre-flushes ahead of the polymer solution. These results indicate that the polymer can be place deep into a formation by using pre-flushes designed for a specific rock mineralogy.
The pH sensitive polymers studies here are excellent candidates for conformance control. It may also be possible to use them for temporary zonal isolation since they can be easily broken down with a mild acid wash and flowback.