Brine to Enhance the Transport of Encapsulated Petroleum Sulfonates Nanosurfactants Deeper into the High Temperature Carbonate Reservoirs

Abstract

Development of NanoSurfactants (NSs), encapsulated petroleum sulfonates, is in progress for use as one of the most cost efficient surfactants in chemical enhanced oil recovery (CEOR) applications under extreme conditions. This work provides a better understanding of NS transport though porous carbonate rocks and demonstrates how hot and salty brines can facilitate NS transport when compared to deionized (DI) water. Transport of NSs at 90 °C in 57,000 ppm total dissolved solids (TDS) brine as well as NS components, petroleum sulfonate and zwitterionic co-surfactant, in 90 °C DI water through limestone core plugs was studied using a core flood apparatus. Effluent samples were measured for the total surfactant concentration using a total organic carbon (TOC) analyzer, and the dynamic retention values were calculated and compared. Structural integrity of NS assemblies before and after transport through the porous rock structure were studied using 1H Nuclear Magnetic Resonance (NMR) spectroscopy. Petroleum sulfonate surfactants are unstable in hot brines with high concentrations of divalent ions, and therefore cannot be transported through porous rock structures. Transforming such unstable sulfonates into NS formulations can overcome these challenges. Dynamic retention results in water-wet limestone demonstrate that NSs can be successfully transported through 150 - 200 millidarcy (mD) reservoir rocks with retention values < 0.4 mg/g of rock. These values are 30-50% lower than the retention of NS components alone, which is < 0.7 mg/g, if measured at the same conditions using DI water. Much lower retention for NSs was observed in brines, when compared to its surfactant components in DI water. This can be attributed to the NSs nanostructure which is designed to encapsulate sulfonates closer to the core while efficiently dispersing in the brines by co-surfactants with zwitterionic heads located at the surface. High salinity brine also helps to screen surface charges present on the rock surface. NMR spectroscopy results confirm that the nano-assembled NS structure does not exhibit noticeable changes after core flood experiments and confirms that the formulation has great potential for CEOR applications. Results presented in this work demonstrate that NS formulations made of assembled and dispersed nanocapsules enable the application of one of the lowest cost industrial surfactants for CEOR in hot and salty brines. This formulation in brines significantly reduces the loss of surfactants to the carbonate rock when compared to the same surfactant components in fresh water.