Using flowback additives in slickwater fracturing fluids is a relatively recent innovation, and regained permeability testing using corefloods is the preferred performance evaluation method. The coreflood rig simulates the hydraulic fracturing process by injecting the fracturing fluid through a core under relevant pressure and temperature conditions, and measures the permeability and relative permeability changes during injection. Permeability measurements indicate whether the fracturing fluid damages the formation during hydraulic fracturing that in turn reduces oil productivity during flowback. While coreflooding is useful for comparing the performance of different flowback aids, it is unable to resolve the mechanisms associated with porescale transport. The goal of this study is to directly visualize and quantify the pore-scale dynamics of fracturing fluid injection and oil flowback using a microfluidic chip device and correlate these observations to the coreflood test results. Microfluidics-based measurements provide pore-scale visual evidence of the flowback dynamics, not achievable using conventional experimental methods such as the coreflood.
Large hydrophobe Carboxylate surfactants (MW above 1000) are a relatively new class of surfactants developed for surfactant flooding during chemical enhanced oil recovery (EOR) processes. The presence of carboxylate groups and alkoxylate groups in the molecules provides stability and salinity tolerance at high temperature and in high salinity environments. Many high temperature reservoirs have injection and reservoir brine containing high concentrations of divalent ions making them prime targets for using carboxylate surfactants. Much of the earlier literature showed successful carboxylate applications at high pH during alkali-enhanced flooding, as the high pH stabilizes the carboxylate groups. Such processes are not feasible in the presence of hardness at high temperatures. We present an approach where we use an alkali buffer wherein the pH is adjusted from highly basic to near neutral. Under such conditions we demonstrated low retention and high performance in terms of phase behavior and coreflood oil recovery.
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