The Displacement of Viscous Oil by Associative Polymer Solutions

Abstract

Abstract About half of world oil production results from waterflooding. The remaining resources, however, are more viscous and less amenable to waterflood as conventional oil reserves are produced. In offshore and Arctic environments improved methods of cold production for viscous oil are needed because the introduction of heat to thin viscous oil appears to be unlikely. Unfavorable mobility ratio and sweep is modified by use of polymer solutions. Of the various EOR polymer formulations, newly developed associative polymers show special promise. We investigate pore and pore network scales because polymer solutions ultimately flow through the pore space of rock to displace oil. We conduct and monitor optically water/oil and polymer solution/oil displacements in a two-dimensional etched-silicon micromodel. The micromodel has the geometrical and topological characteristics of sandstone. Conventional hydrolyzed polyacrylamide solutions and newly developed associative polymer solutions with concentrations ranging from 500 ppm to 2500 ppm were tested. The crude oil had a viscosity of 210 cP at test conditions. Our results provide new insight regarding the ability of polymer to stabilize multiphase flow. At zero and low polymer concentrations, relatively long and wide fingers of injectant developed, leading to early water breakthrough and low recoveries. At increased polymer concentration, a much greater number of relatively fine fingers formed. The width to length ratio of these fingers was quite small and the absolute length of fingers decreased. At a larger scale of observation, the displacement front appears to be stabilized; hence, recovery efficiency improved remarkably. Above a concentration of 1500 ppm, plugging of the micromodel by polymer and lower oil recovery was observed for both polymer types. For tertiary polymer injection that begins at breakthrough of water, the severe fingers resulting from water injection are modified significantly. Fingers become wider and grow in the direction normal to flow as polymer solution replaces water. Apparently, improved sweep efficiency of viscous oils is possible (at this scale of investigation) even after water flooding. The associative and conventional polymer solutions improved oil recovery by about the same amount. The associative polymers, however, showed more stable fronts in comparison to conventional polymer solutions.