Effect of fluid rheology on enhanced oil recovery in a microfluidic sandstone device

As global energy usage increases, maximizing oil recovery from known reserves becomes crucial to meet the rising demand. In this work, we present the development of a microfluidic sandstone platform capable of quickly and inexpensively testing the performance of fluids with different rheological properties on the recovery of oil. Specifically, in this study we utilized these microfluidic devices to examine how shear-thinning, shear-thickening, and viscoelastic fluids affect oil recovery. Initial baseline experiments were performed by displacing oil with both water and a water-surfactant solution over a wide range of flow rates. The surfactant was found to reduce the interfacial tension of the water by a factor of ten and increased oil recovery by approximately 15% when compared to oil displaced by water at the same flow rates. Flopaam, a commercially available fluid thickener that is shear-thinning and viscoelastic was also studied. It was found to displace more oil then either the water or the surfactant solution and increase oil recovery at all flow rates studied. Finally, a shear-thickening nanoparticle solution was studied which was designed to thicken at a shear rate of approximately 10 s(-1). The shear rate corresponds to typical shear rates in the oil reservoirs, and values easily attainable in our microfluidic sandstone device. These shear-thickening fluids were found to be particularly effective at oil recovery. This was especially true for flowrates that closely matched the shear rates associated with the shear-thickening regime. When the appropriate choice of shear rate dependent viscosity was used to the capillary number, the oil recovery obtained from both the Newtonian and non-Newtonian was found to collapse quite well onto a single master curve. Additionally, it was shown that a two-stage recovery process that starts with an initial water flood followed by a flood with a secondary fluid can recover as much oil as a single stage recovery with that secondary fluid alone. These results clearly demonstrate that the microfluidic sandstone devices presented in this paper both reduce the time and cost required to investigate the effectiveness of enhanced oil recovery fluids using traditional methods, and can serve to quickly focus searches for customized oil recovery fluid selection. (C) 2013 Elsevier B.V. All rights reserved.