Use of a novel pH-triggered polymer-gel system for optimal mobility-control applications

Abstract

AbstractThere are two challenges in using polymers for conformance control applications in the petroleum industry. The first difficulty is to maintain a good injectivity to overcome the large pressure drop caused by the high viscosity of the polymers. Secondly, large polymer volumes required to be injected to compensate for polymer retention in a reservoir. The main objective of this work is to study the viability of using a pH-sensitive polyelectrolyte to alleviate the above two challenges. The results showed that the pH of the swelling medium has great effect on the swelling behavior of poly(acrylic acid) hydrogels. At low pH regime, the viscosity increases gradually as pH increases until certain pH value, ‘critical pH’ is reached. In the second regime and once critical pH value is exceeded, the viscosity increases sharply with the pH. This is followed by independency of the viscosity on pH, in the third regime. It was found that this sensitivity to the pH varies with the change in crosslink density and shear rates. At pH=4 (before the gellation), the sample (Carbopol 981) which has the lowest crosslink density exhibits the highest viscosity among the three samples. After the gellation (PH=8), the rheological behavior is reversed for the highest crosslinked density polymer (EZ-4) and the lowest crosslinked density polymer (981) which contradicts with the well known swelling ratio-crosslink density relation. It is concluded that the examined polymers are good candidates for mobility control applications. They can also be used for temporary zonal isolation since they can be easily broken down with mild acid wash and flowback