Gelation of Emulsified Polyacrylamide/Polyethylenimine under High-Temperature, High-Salinity Conditions: Rheological Investigation

Abstract

Emulsified gels are proposed as a method of water shut-off in oil and gas reservoirs and are designed to separate into a water phase and an oil phase under reservoir conditions. A first of its kind rheological study on the gelation kinetics and strength of organically cross-linked polyacrylamide (PAM) with polyethylenimine (PEI) emulsified into a diesel phase is presented. A lower rate of cross-linking is achieved when emulsified PAM/PEI systems are compared with nonemulsified PAM/PEI systems. For the stable emulsified PAM/PEI formulation (with no separation), the elastic modulus decreased by ∼54% at 120 °C in comparison with the nonemulsified system. It is suggested that the emulsification acts as an insulator, hence heat transfer to the gelant is slow. The elastic (i.e., storage) modulus of the emulsified PAM/PEI increased by about 29% when the temperature was raised from 120 to 150 °C. The elastic modulus decreased in the presence of salts, leading to low gel strength and longer gelation time. Ammonium chloride proved to be more efficient than NaCl in the retardation of emulsified gels. The gelation kinetics of the emulsified PAM/PEI is analyzed using the Avrami-based model. The activation energy for emulsified gels was found to be ∼10 times higher than for nonemulsified gels.