Factors Contributing to Petroleum Foaming. 2. Synthetic Crude Oil Systems

The influence of petroleum asphaltenes and resins on stabilizing model oil foams comprised of light mineral oil mixed with toluene (minerol) was investigated. Two factors contribute significantly to foam volume and stability: bulk viscosity and asphaltene state of aggregation. An increase in bulk viscosity was found to increase foam stability as gauged by the total time required for a foam to collapse. Asphaltene aggregation is governed primarily by the solvent aromaticity and resin/asphaltene (R/A) ratio. There is a threshold size in the state of asphaltene aggregation above which the ability of these aggregates to stabilize foams is markedly reduced. This appears to be closely related to asphaltene flocculation and precipitation at compositions beyond the solubility limit of the asphaltenes. Solvent systems generating the highest foam volume were found to reduce the air-oil surface tension to the greatest extent. Addition of an asphaltene dispersant increased the foamability of asphaltenes in minerol and seems to indicate that asphaltenes enhance foam stability when they are well dispersed or dissolved and in solvent mixtures in which they are highly surface active. By analogy to the role of asphaltenes in stabilizing emulsions, the highest foam stability was observed for asphaltenes near their solubility limit, the thermodynamic state at which asphaltenic aggregates are most surface-active. Addition of resins, similar to addition of dispersants, increased foam stability, presumably by decreasing the size of asphaltene aggregates.