Interaction of n-pentane and n-heptane insoluble asphaltenes in brine with clay and sand

Abstract

Destabilized asphaltenes cause serious flow assurance problems such as asphaltenes precipitation. This study investigates the impact of clays and salinity on the stability of asphaltenes for five different crude oil samples. First, both n-pentane and n-heptane insoluble fractions of five crude oils were examined under microscope after the interaction with water, brine, and porous media. The porous media was prepared with clay, sand, or sand-clay mixture. A monovalent (NaCl) and a divalent (CaCl2) salts at 0.2% and 4% concentrations were used to prepare the brine solutions. Several systematic microscopic analyses were conducted on the asphaltenes-water and the asphaltenes-brine blends. We have observed that both n-pentane and n-heptane asphaltenes clusters are getting dispersed in water-phase in smaller pieces. This dispersion of asphaltenes clusters form lacework-like structures in the water-phase. The void spaces within these dispersed asphaltenes clusters trap water droplets. This interaction is due to the polar nature of both asphaltenes and water. Further in our systematic analysis, the general trend showed that the polar-polar attraction between water and asphaltenes clusters was disturbed in the presence of dissolved sodium and chlorine ions especially for some oil samples which already contain sodium in its asphaltenes fractions. This phenomenon is observed with the bridge-like formations in the asphaltenes-brine solutions. This indicates that asphaltenes have charged surfaces and the repulsion forces between the surface of the asphaltenes cluster and the dissolved ions in the brine solutions make the asphaltenes cluster align to form a line in the brine solution. The presence of clay in the porous medium reduced the water-asphaltenes or the brine-asphaltenes interaction and resulted in big chunks of asphaltenes-clay mixtures. Our study showed that asphaltenes interact with brine, water, and reservoir fines. Understanding these interactions may help us to mitigate many flow assurance issues such as asphaltenes precipitation and water-in-oil emulsion formation.