Dynamic covalent carbon dot-based emulsifiers: A novel strategy for smart Pickering emulsions and enhanced heavy oil recovery in ultra-low permeability reservoirs

Abstract

Carbon dots (CDs), a class of fluorescent nanomaterials distinguished by their unique properties such as tunable surface chemistry and nanoscale dimensions, have garnered significant attention. In this study, we synthesize CDs-based emulsifiers through a combination of hydrothermal synthesis and hydrophobic modification utilizing dynamic covalent imine bonds, imparting them with amphiphilicity and pH-responsiveness. These carbon dot-based emulsifiers stabilize the oil–water interface to form Pickering emulsions and enable the reversible regulation of amphiphilicity through pH-induced cleavage and reformation of imine bonds, thereby facilitating transitions between emulsification and demulsification. Furthermore, the amphiphilic CDs effectively reduce oil–water interfacial tension and exhibit potential application in mobilizing heavy oil in ultra-low permeability reservoirs. Consequently, we observed a 28.78 % decrease in injection pressure and an 18.65 % increase in recovery rates. Experimental and theoretical results reveal that the CDs adsorb onto both solid and oil phase surfaces, modulating the interfacial properties and enabling the oil film attached to the rock wall to be more easily stripped off during water flushing. Additionally, the small size of the CDs allowed them to enter finer pore throats and effectively displace the residual oil film. This unique characteristic holds significant promise for future advancements in the fields of smart-response Pickering emulsions and enhanced oil recovery in ultra-low permeability reservoirs.