pH-Insensitive Polymeric Particles for Enhanced Oil Recovery in Reservoirs With Fractures

Abstract

Summary Many carbonate reservoirs have natural fractures that reduce the sweep efficiency of displacement processes. The goal of this study is to improve oil recovery by reducing fluid bypassing caused by fractures, especially in carbon dioxide (CO2) floods. The pH-insensitive polymeric particles (PIPPs) synthesized in this study can plug fractures in reservoir rocks and divert fluid flow into the rock matrix. PIPPs swell in brine similar to polymeric particle gels (PPGs) published in literature; the swelling is a function of brine salinity. A PIPP expands many times (≈35 times) in deionized (DI) water, but swells only approximately 3 times in very-high-salinity (20 wt% NaCl) brine. The swelling of the particles is independent of pH in the range of 2 to 12. The swelling process is reversible with salinity. In water without divalent cations, these particles are stable at 80°C for at least a month. Coreflood results show that these small particles can be transported through fractures during high-salinity-brine injection and reduce the flow capacity of the fractures during low-salinity-brine injection. Subsequently, the injection fluid (brine, toluene, or CO2) is diverted into the matrix, and recovers oil from previously unswept matrix. PIPP injection increases waterflood recovery in cores with full fractures and half fractures connected to the inlet. PIPP placement also increases oil recovery for tertiary miscible/CO2 floods.