Adsorptions of nonionic and anionic surfactants onto sandstone and carbonate surfaces were measured. Nonionic surfactants studied were polyethoxylated octyl phenols and polyethoxylated linear alcohols. Anionic surfactants were petroleum sulfonates and sodium ethoxysulfate. For nonionic surfactants we found that adsorption on sandstone was (1) high and dependent upon extent of ethoxylation, (2) relatively insensitive to solution salinity and (3) not selective on the basis of extent of ethoxylation of individual molecules. Adsorption on calcium carbonate, aragonite, was lower than on sandstone. For the anionic surfactants, we found that adsorption isotherms of Shell NEODOL 25-3S on sandstone were Langmiurian in shape at all solution salinities. Isotherms of mixtures of NEODOL 25-3S and petroleum sulfonates were Langmiurian at low salinities but contained maxima at higher salinities. Multivalent cations were found to increase adsorption of anionic surfactants, and salts of large anions, detergent builders, were found to reduce adsorption of anionic surfactants. Petroleum sulfonate-NEODOL 25-3S mixtures were Petroleum sulfonate-NEODOL 25-3S mixtures were adsorbed less on CaCO3 than was petroleum sulfonate alone. Within experimental error, selective adsorption onto sandstone of either petroleum sulfonate or Shell NEODOL 25-3S was not detectable.
Surfactant-enhanced waterflooding usually amounts to injecting a fractional pore volume slug of active surfactant solution, often thickened with polymer, followed by a viscous drive of polymer in polymer, followed by a viscous drive of polymer in water. For reasons of economy, minimum surfactant adsorption is vital to the success of such a project. However, low total surfactant loss does not guarantee a successful process. Key slug components must not adsorb preferentially and, to maintain favorable mobility, surfactant and polymer fronts must not separate from one another.
The goal of work presented here was to determine levels of adsorption on rock of a selected group of surfactants, to determine which molecular species are preferentially adsorbed, and to study some of the factors affecting adsorption, e.g., ionic makeup of the adsorbate and rock type. Surfactants chosen for study were polyethoxylated octyl phenols, polyethoxylated linear alcohols, a sodium ethoxysulfate of linear alcohol, and petroleum sulfonates. The nonionic surfactants are not, petroleum sulfonates. The nonionic surfactants are not, at present, considered to be practical oil recovery surfactants, although they may be useful as cosurfactants. Petroleum sulfonates and ethoxysulfates, on the other hand, are highly favored for formulating water continuous oil recovery slugs.
Adsorption on Sandstone of Polyethoxylated Octyl Phenols Phenols These were chosen as model nonionic surfactants for the following reasons:
They are available as reasonably pure products with a wide range of EO content - see products with a wide range of EO content - see appendix.
Properly formulated, they can serve as oil recovery agents.
Most important, their solution concentration can be determined by UV spectroscopy (absorption band at 277 my).
Unlike typical aqueous oil recovery systems, saline aqueous solutions of ethoxy octyl phenols (EOP) are optically clear and not appreciably more viscous than water. Solubility, salt tolerance and cloud point increase with increasing extent of ethoxylation. All of these materials display a broad distribution of EO content. Quoted EO content is the average of individual mixtures.