Organic bases in NAPLs and their impact on wettability

Abstract

Organic bases in crude oil have been linked to complex interfacial phenomena that could affect the multiphase flow of these fluids in subsurface systems. Little information is available, however, to correlate the strength and concentration of organic bases in nonaqueous phase liquids (NAPLs) to interfacial properties. The specific objectives of this paper were: (1) to evaluate and apply titration techniques employing nonaqueous solvents to quantify the acid neutralizing capacity and characterize the strength of the organic base constituents in complex NAPL mixtures; and, (2) to relate these characteristics to the wetting properties of quartz minerals exposed to environmentally significant NAPLs. The selection of a suitable organic solvent is critical for nonaqueous titration. Mixtures of known organic bases were used to verify the capability of three different solvent systems for quantifying the concentration and strength of organic bases. Methyl iso-butyl ketone was identified as the best solvent for the nonaqueous titration—providing both accurate measurement of the total concentration of bases as well as providing a means of differentiating between strong and weak base constituents. The NAPLs tested showed a wide range of base concentrations and were found to contain only weak organic bases. All of the NAPLs with a base number greater than two significantly altered the system wettability at pH=4.6. Only a few, however affected the wettability at pH=7.2. These observations confirm the characterization of the organic bases as weak bases. The titration techniques, however, cannot characterize the strength of the bases precisely enough to predict the aqueous phase pH at which a NAPL–water–quartz system would become oil wetting.