Study Of Amphiphilic Janus Graphene Oxide As Nano-Flooding Material

Nanofluid displacement technology plays an increasingly important role in tertiary oil recovery.In recent years,some researchers have reported the excellent EOR performance of asymmetrically modified amphiphilic Janus graphene oxide(JGO)nanosheets as nanomaterials for oil displacement.The nanofluid can significantly improve EOR efficiency at very low concentrations,and exhibit unique EOR mechanism.This work aims prepare JGO with different modification degrees,and exploring the influence of modification degree on its colloidal stability through experimental and theoretical methods.Then the influence of modification degree on the displacement efficiency of JGO nanofluid is assessed,and the EOR mechanism of JGO is further clarified.In addition,JGO was mixed with surfactant to construct compound flooding system with high performance.A series of JGO with different modification degrees was prepared by controlling the conjunction ratio of dodecylamine on one side of GO.The influence of modification degree on the colloidal stability of JGO in aqueous solution with or without additional electrolyte was studied by experimental measurement(TSI index and UV absorption)and theoretical calculation(classical and extended DLVO theory).The applicability of theoretical calculation model(sheet-sheet model or sphere-sphere model)in different conditions was also given.Furthermore,the influence of modification degree on the interfacial properties of JGO at the oil-water interface and the solid-liquid interface(interfacial activity,wettability alteration,adsorption)was investigated,based on which the oil displacement efficiency and EOR mechanism of JGO with different modification degrees were verified via core-flooding tests.Finally,the synergistic effects between JGO and various types of surfactant,including cationic surfactant dodecyl trimethyl ammonium bromide(DTAB),anionic surfactant sodium dodecyl sulfate(SDS),and nonionic surfactant Triton X-100(TX-100),was studied to construct highperformance compound EOR systems for ordinary heavy oil.The results show that the JGO with higher modification degree presents less colloidal stability in aqueous solution and the stronger amphiphilicity.When the conjunction ratio of dodecylamine reached 41.07%,the stability of JGO decreased significantly.In addition,JGO would curl from a two-dimensional sheet structure to a three-dimensional spherical structure in the presence of electrolyte.The formation of interfacial film and climbing film are affected by the modification degree of JGO and the hydrodynamic strength,and JGO could be effective in wettability alteration via its amphiphilic Janus structure.When the injection rate keeps constantly,the increase of modification degree caused higher EOR efficiency of JGO.The main EOR mechanism of JGO is to reduce interfacial tension and induce wettability alteration,and the interface film and climbing film could push the crude oil slug.Increasing the injection rate could improve the EOR efficiency of JGO with a lower modification degree.The strong interaction between JGO and asphaltene significantly increases the interfacial activity of JGO at the heavy oil/water interface.JGO-5 has a great synergistic effect with DTAB in heavy oil/water system.Meanwhile,a certain concentration of DTAB can improve the salt tolerance of JGO-5.In the core-flooding test,the oil recovery of the JGO-5/DTAB system is much higher than that of the single system,which is mainly due to the low interfacial tension of the compound system,emulsification ability and its capacity in wettability alteration.