Experimental investigation of zwitterionic surfactant-based silica nanofluid spontaneous imbibition at high salinity and elevated temperature conditions

High-efficiency development of low permeability reservoirs is significant to maintaining a balance between energy supply and social needs. Surfactant-based nanofluids with an excellent interfacial activity that can penetrate the small throats and narrow pores are considered promising EOR agents. However, the applications of nanofluids in harsh reservoir conditions remain to be challenging due to high stability requirements. In this work, a highly stable active nanofluid that could withstand high salinity (API brine) and elevated temperatures was prepared by mixing zwitterionic hydroxypropyl sulfobetaine surfactant with low-molecular-weight ligand modified silica nanoparticles. At a surfactant/nanoparticle concentration ratio of 0.5, the spontaneous imbibition recovery factor of dodecyl hydroxypropyl sulfobetaine-based nanofluid was 2.61 times higher than API brine, 1.29 times higher than API brine-based nanofluid and 0.37 times higher than surfactant alone. Meanwhile, the impacts of surfactant carbon chain length, permeability as well as hydrochloric acid were included. Experimental results indicated that surfactants with longer carbon chain length would destabilize the nanofluids due to increasing hydrophobic interactions, and nanoparticle aggregation/precipitation would impose adverse impacts on spontaneous imbibition because of pore/throat plugging. Though increasing permeability could partially ease the negative plugging effects, the potential risks should never be overlooked. Properly using hydrochloric acid could greatly enhance the stability of nanoparticles by forming an “H+” protection layer and extend their applications to over 80 °C, but the presence of acid also disturbed the adsorption behaviors of surfactants, therefore, different phenomena were noticed when the nanofluid formula changed. A good spontaneous imbibition system should possess both IFT reduction and wettability alteration capabilities, and nanoparticles’ ability to adsorb and disperse polar compounds such as asphaltene should be fully fulfilled. This study provides new guidance for nanofluid formulation to support the effective development of low-permeability oil reservoirs.