Improved Polymer Flooding in Harsh Environments by Free-Radical Polymerization and the Use of Nanomaterials

Abstract

High temperature and high salinity (HTHS) and extreme pH conditions can significantly affect the stability of polymers and deteriorate the performance of polymers in enhanced oil recovery (EOR). This work advances polymer flooding in harsh environments on two fronts: engineering polymers with improved temperature tolerance and dispersing suitable nanoparticles in the synthesized polymers to further improve their capabilities to withstand temperature, salinity, and different pH conditions. Different modified acrylamide copolymers (polymers synthesized from two different monomers) and terpolymers (polymers synthesized from three different monomers) are produced via free-radical polymerization, and multiwall carbon nanotubes (MWCNTs) were introduced to obtain aqueous polymer dispersions with unique properties. The conversion, molecular weight, and polydispersity of the co/terpolymers were evaluated by 1H-NMR and GPC analysis. The interfacial, rheological behavior and stability of the dispersions were investigated under HTHS conditions at various pH values to identify the suitable candidates for EOR applications. The oil recovery performance is examined in a core flooding setup at 85°C and American Petroleum Institute (API) brine conditions. The polyampholytic terpolymer and polyelectrolyte copolymer containing negative sulfonate groups showed improved viscosity and stability in the presence of MWCNTs in alkaline and saline conditions, respectively. Compared to the pure polymer dispersions, the addition of MWCNTs to polymers improves the oil recovery efficiency at high temperature (85 °C) in the presence of both alkaline pH and API brine conditions yet with a lower pressure drop. This shows great promise for future EOR applications.