Synthesis and evaluation of the potential of nonionic surfactants/mesoporous silica systems as nanocarriers for surfactant controlled release in enhanced oil recovery

One of the most efficient enhanced oil recovery processes involves surfactant flooding to increase the oil displacement efficiency by lowering the oil/water interfacial tension, in an attempt to produce at least part of the large amount of oil that remains in place after conventional methods have been employed. However, this process presents the disadvantage of a great loss of surfactant that occurs due to its adsorption on the reservoirs rocks surface, lowering the efficiency of the process or turning it economically unattractive. The purpose of this study was to synthesize and evaluate the potential of nonionic surfactants/mesoporous silica systems as nanocarriers for surfactant controlled release, to be employed in enhanced oil recovery, in order to avoid the surfactant losses during the process. The employed surfactants were fatty diethanolamides (DEA) obtained from the waste of vegetable oils (coconut, castor and soybean oil) production. The synthesized silica, SBA-15, was characterized by FTIR, Si-29 NMR, BET, X-ray diffraction, SAXS and TEM, while the DEAs were characterized by FTIR and H-1 NMR. By spinning drop measurements it was possible to observe that the synthesized surfactants reach ultra-low IFT (4.9 x 10(-3) mN/m for DEA soybean). Adsorption data of DEA on SBA-15 were analyzed through the fitting to Langmuir and Freundlich isotherms models. The results did show that the adsorption processes with castor amides and soybean amides fit better to the Freundlich model, while the one with coconut amides adjusts to the Langmuir model. The SBA-15-DEA systems were washed with water and characterized by FTIR, TGA and TEM, showing that the surfactant remained adsorbed on the silica surface. Tensiometry results showed that no surfactant release occurred in water medium even after 7 h of contact, but when the SBA-15-DEA systems dispersed in water, were in contact with oil, rapid desorption to the oil/water interface did occur. The interfacial tension was reduced to values lower than 1 mN/m after 6 h of analysis, showing that the loss of surfactants by adsorption on reservoir rocks surface could be avoided by using SBA-15-DEA systems as surfactant nanocarriers for controlled release in EOR processes