Acidic resins naturally occurring in crude have been found to be responsible for a variety of interfacial phenomena in oil-aqueous systems. Those components which colloidally suspend high molecular weight asphaltene particles may also be used in enhanced recovery processes to inhibit asphaltene deposition in porous media. This paper presents results of laboratory core flooding tests using a microwave absorption technique to monitor in-situ oil/water saturations during enhanced recovery by alkaline flooding.
Resinous additives were found to significantly alter permeability reductions caused by asphaltene deposition and to affect the formation of a single and continuous oil bank during the laboratory core flood. Data were also obtained for the dynamic interfacial tension, electrophoretic mobility and emulsion stability for the whole crude/aqueous solution with and without the resinous additives.
These observations, combined with microwave analysis are used to suggest a possible mechanism for improved oil recovery through the prevention of asphaltene deposition and resulting permeability reductions.
High molecular weight components naturally occurring in crude oil have been identified as the major contributors to the interfacial activity of crude oil aqueous systems. Various methods have been used in the past to separate the crude residue into two or more fractions in an effort to structurally characterize these components. Generally, these techniques succeed in separating the alkane (i.e. normal pentane or heptane) insoluble asphaltene fraction from the more soluble resin/gas oil fraction.
Qualitative analysis of the petroleum asphaltene fraction by Yen and Speight and Moschopedis has led to the development of a hypothetical average structure for this particular component. This structure is characterized as a cluster of five to seven flat sheets of condensed aromatic rings that are linked by short chain alkanes as well as pi-pi attractions between the peri-condensed polynuclear aromatic systems. Yen et al. have also suggested the presence of gaps or holes within these particles that are capable of complexing vanadium or nickle ions present in most crudes. Early investigators have established that the high molecular weight asphaltene particles in crude are stabilized as colloids via peptization by the lower molecular weight resinous components. Speight and Moschopedis have suggested that the degree of aromaticity and presence of hetero atoms in the resinous fraction presence of hetero atoms in the resinous fraction are closely related to the peptization of the insoluble asphaltenes. This resin-asphaltene attraction has been attributed to hydrogen-bonding as the electron donor-acceptor attraction that occurs between the polar groups of these two species. The high molecular weight carboxylic acids present in the resinous fraction have been shown to result in ultra-low (less than 10(-2) dyne/cm) interfacial tensions when contacted with an aqueous alkaline phase. phase. These resinous components, in addition to naturally occurring metallo-porphyrins indigenous to all crudes, have been shown to exhibit film-forming characteristics at oil-aqueous interfaces. Such interfacial films have been characterized as either rigid or mobile, depending upon the pH of the aqueous phase, and are believed to affect wettability changes in silica surfaces.
Recently, we have investigated the individual and combined roles that the high molecular weight acidic resins and asphaltenes play in interfacial structure and activity for various crude-caustic systems. It was determined that the asphalt residue, when added to a lower boiling crude fraction, displayed highly viscous interfacial behavior coupled with increased interfacial activity. These oil-aqueous alkaline systems exhibited typical interfacial tensions (measured via spinning drop technique) on the order of 10(-3) dyne/cm.
