New data relating to the adsorption of asphaltenes on rock pore surfaces are reported. The data were obtained from the measurements of the electrokinetic potential of several different sandstone core samples with asphaltenic oils. The adsorption of asphaltene is accompanied by a numerical reduction in the (negative) surface potential of the pore walls, eventually stabilizing at a small positive potential, attributed to the asphaltene itself.

After increasing to around 30% of the pore radius, the asphaltene adsorbed layer thickness stopped growing either with time or with concentration of asphaltene in the flowing liquid. This behaviour is attributed to the effect on the disjoining pressure across the adsorbed layer described by Derjaguin and Churaev1 .

Alternative hypotheses involving asphaltene adsorption isotherm have been investigated. A theoretical treatment advanced describing particle adsorption in the same terms as molecular adsorption and the Langmuir isotherm, with the free energy of asphaltene adsorption on the rock surface (modeled on silica), calculated on the basis of van der Waals attraction. Acceptable agreement was obtained with the electrokinetic measurements.

Keywords:
pore surface, conductivity, rock core, asphaltene adsorption, upstream oil & gas, adsorption, thickness, permeability, hydrate remediation, asphaltene concentration
Subjects:
Drilling Operations, Production Chemistry, Metallurgy and Biology, Flow Assurance, Reservoir Characterization, Formation Evaluation & Management, Coring, fishing, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene, Precipitates (paraffin, asphaltenes, etc.)
Copyright 2005, Society of Petroleum Engineers
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