Fabrication, optimization and characterization of preformed-particle-gel containing nanogel particles for conformance control in oil reservoirs

The present study introduces a new method of preformed particle gel (PPG) synthesizing that leads to manufacturing gel particles containing nanogel particles inside them with optimized properties at high temperature and high salinity. Acrylamide-based nanogels cross-linked with N,N′-methylenebis(acrylamide) were prepared by inverse microemulsion polymerization and using sorbitan monooleate and polyoxyethylene sorbitan monooleate as emulsifiers and cyclohexane as oleic phase. The cross-linker-to-monomer weight ratio, emulsifier composition and oleic phase-to-emulsifier weight ratio were optimized using gel purification tests, conductivity tests and phase separation tests. Image analysis of nanogel particles showed that their shape is spherical with about 86 nm in diameter. In the next step, bulk gel containing nanogel particles was manufactured by bulk polymerization method and nanogel content in bulk gel was optimized. Finally, swelling test of gel particles in brine with the salinity of 180,000 ppm and the temperature of 80 °C for three days showed that the new PPG has higher water absorbance capacity compared to the ordinary PPG. In addition, dynamic swelling of both samples followed Voigt’s equation and showed that the new PPG has higher swelling rate at initial stages than the ordinary PPG. Rheology tests at this condition indicated that the amount of elastic modulus of the new hydrogel is lower than that of the ordinary hydrogel. These properties make the new synthesized gel a good candidate for deep reservoir conformance control at harsh conditions of high salinity and high temperature.