Investigation of the enhanced oil recovery mechanism of CO2 synergistically with nanofluid in tight glutenite

Abstract

Huff-n-puff methods using nanofluid and/or CO2 are most promising methods for enhancing oil recovery in the Mahu Oilfield, Xinjiang, China. Six tight glutenite reservoir samples were conducted the huff-n-puff experiment using different displacement fluids (i.e. D2O, supercritical CO2 and nanofluid) following saturation with oil. The results of T2 NMR spectra of the samples show that D2O can readily enter the larger pores stripping the oil with smaller pores remaining relatively untouched. Furthermore, the oil recovery was initially fast before quickly tapering with the final average oil recovery over samples using D2O huff-n-puff alone being only 14.89%. However, CO2 could effectively enter both small and large pores with the oil recovery efficiency from small pores being greater than 20% and from the large pores being even higher with the final average recovery over two samples using CO2 huff-n-puff alone being 40.44%. Relative to D2O alone, the nanofluid improved the oil recovery in small pores by more than 10%. There appears to be a synergistic effect combining CO2 and nanofluid huff-n-puff; both CO2 followed by nanofluid huff-n-puff or nanofluid followed by CO2 huff-n-puff achieved similar final recoveries close to 50% of the overall oil.