ARTICLE pubs.acs.org/IECR
Polymer-Functionalized Nanoparticles for Improving Waterflood Sweep Efficiency: Characterization and Transport Properties R. Ponnapati,† O. Karazincir,†,‡ E. Dao,†,§ R. Ng,‡ K. K. Mohanty,†,§ and R. Krishnamoorti*,† †
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States Chevron Energy Technology Company, 1500 Louisiana Street, Houston, Texas 77002, United States § Department of Petroleum & Geosystems Engineering, University of Texas at Austin, Austin, Texas 78712, United States ‡
ABSTRACT: Water-dispersible polymersilica nanocomposite particles, SiO2ethylene oxide-based polymer nanoparticles hybrids, were synthesized using a “grafting-from” method, where polymer brushes were grown on silica nanoparticles using living radical polymerization. Water-soluble polymer chains were grown from initiator-tethered 15-nm silica nanoparticles with ∼600 chains grafted per nanoparticle, resulting in a surface grafting of ∼1 chain per square nanometer. The single-phase and multiphase transport properties of low concentration brine dispersions of these polymer nanoparticles hybrids through a Berea sandstone core were measured. Experiments show that, while the viscosity increase is modest for dispersions with concentrations of 0.52 wt % of the nanoparticle hybrid, the dispersions were able to transport without hindrance through the porous media and, furthermore, were found to be effective at mobilizing waterflood residual oil.
’ INTRODUCTION Polymers have been used for many decades to improve oil recovery by polymer flooding,1 alkaline-surfactant-polymer flooding,2 and profile control.3,4 Partially hydrolyzed polyacrylamides and xanthan are two groups of polymers commonly used for polymer flooding. Polymers increase the viscosity of injected water and can improve sweep efficiency in heterogeneous and viscous oil reservoirs.5 While a tertiary polymer flood cannot mobilize the waterflood residual oil, it has been shown recently that a secondary polymer flood can reduce the residual oil saturation to values below that of a waterflood.6 The higher oil recovery from secondary polymer floods is presumed to result because of both improved sweep and residual oil saturation reduction and the breakage of the oil column into oil ganglia is delayed by the elasticity of the polymeric solution. The critical difficulties in using polymers in reservoirs to improve oil and gas recovery are chemical degradation of the polymer at high hardness and temperature, and low permeability.7 Polyacrylamides hydrolyze at high temperatures and can precipitate with divalent ions. If the divalent ion concentration is
