We systematically investigate the effects of low salinity, potential determining ions (Mg2+, SO42-) and oil composition on wettability alteration of Indiana limestone in a model system by spontaneous imbibition test at elevated temperature (90oC). The spontaneous imbibition test in the model system reveals the individual roles of asphaltene, naphthenic acid and divalent ions. Such study in a well-defined system for “smart water” induced wettability alteration is currently not available in the literature. In the spontaneous imbibition experiments, the cores are first saturated with initial high salt brines and then saturated with the model oil, following by oil aging in 120oC to restore the oil-wetness. Then the cores are exposed to high salt brine (5M NaCl) and low salt brines (I=0.164M NaCl, Na2SO4, MgSO4) step by step to investigate the individual effects of salinity and different potential determining ions. Model oil A (AN1.5 with naphthenic acid in dodecane/toluene mixture), model oil B (0.05% wt. asphaltene in dodecane/toluene mixture) and model oil C (0.05% wt. asphaltene in toluene) are tested to compare the responses of different surface active components (naphthenic acid, asphaltene) to the “smart water”. Initial brine A (5M NaCl) and initial brine B (I=5M formation brine) are tested to compare the effect of initial brine composition on wettability alteration. In the experiments, low salinity brine without any divalent ions is found to be effective in altering the carbonate wettability in the model system and the additions of SO42- and Mg2+ are found to further improve the oil recovery. Moreover, the “smart water” is found to have significantly different response to naphthenic acid and asphaltene.

Effects of low salinity, potential determining ions and oil composition on carbonate wettability alteration in a model system

256th National Meeting (2018)

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