Adsorption of Foam-forming Surfactants In Berea Sandstone

Abstract

Abstract Adsorption measurements carried out with representatives of four classes of surfactant suitable for foam flooding (alpha olefin sulphonate, internal olefin sulphonate, linear xylene sulphonate, and betaine) on Berea sandstone at different conditions of temperature and salinity are described. Adsorption of (he anionic surfactants from a low salinity brine is low, but increases substantially at moderate salinities. Limited solubility of the anionic surfactant in aqueous media tends to drive these surfactants to the solid/liquid interface and can also lead to increased surfactant loss through precipitation. The betaine is highly soluble, but adsorbs very strongly on sandstone. Adsorption of this surfactant can be reduced by mixing it with an anionic surfactant. Introduction EOR production in North America is dominated heavily by gas or vapor flooding. Out of total of 371 EOR projects, 294 involve injection of steam CO2 or hydrocarbon solvent(1). Became of the low density and viscosity of the injected fluid, gas and vapor flooding processes tend to suffer from poor sweep efficiency. This problem may be alleviated through the use of mobility control foams(2,3). While the mechanism of lamella generation and collapse is crucial to foam performance and propagation, the maximum distance that a foam will travel is dictated by surfactant loses in the reservoir, caused by adsorption at the solid/liquid interface, precipitation, chemical degradation, and partitioning into an immobile oil phase. This paper deals with the last and frequently most important of these mechanisms. Surfactant classes most commonly applied in laboratory studies of EOR-foams and in field applications include alkyl aromatic sulphonates and olefin sulphonates. Since much of the EOR-foam literature deals with steam foams, surfactant selection has often been determined by the requirement of chemical stability at steam flood temperatures. The following ranking has been assigned to several surfactant classe in terms of their thermal stability(4) alkyl aryl sulphonates > olefin sulphonates > petroleum sulphonates > ethoxylated alcohols and ethoxylated sulphates. The surfactants that have been found the most thermally stable are also the most likely to precipitate in the presence of inorganic electrolyte. Surfactant solubility has been found to decrease in the following order(4); ethoxylated alcohols or sulphates > olefin sulphonates > petroleum sulphonates = alkyl aryl sulphonates. A characteristic of the surfactants most commonly described in connection with EOR-foams is thus their limited solubility in brines. The high molecular weight surfactant homologues suitable for steam-foams have very limited solubility in aqueous media and are expected to have a higher affinity for the solid/liquid interface than lower molecular weight homologues. Steam flood temperatures will favour low adsorption levels and increased solubility. During steam flooding, a surfactant encounters salinity and temperature gradients and a knowledge of the dependence of surfactant behavior on both parameters is required. Surfactants suitable for the extreme conditions of salinity and hardness encountered in many Alberta reservoirs have been identified(5). Detailed measurements of the adsorption properties of these surfactants have been previously described(6–8). By contrast, reported adsorption data for surfactant classes commonly used for steam flood applications are rather limited(9–15).