Enhanced oil recovery (EOR) refers to a variety of techniques including hydraulic fracturing that are used to boost productivity of gas and oil reservoirs. A common EOR method is the introduction of surfactants into a reservoir. The interaction of these surfactants with mineral/water interfaces in the reservoir is an important chemical process that can determine the commercial viability and environmental impact of an EOR operation. For example, if surfactants irreversibly bind to mineral/water interfaces and cannot be recovered then the cost of an EOR project may be prohibitive. In addition, this scenario raises environmental concerns because large amounts of surfactant would remain underground after treatment of the reservoir. Given this environmental context, the interaction of an alkylammonium surfactant, namely dodecyltrimethylammonium chloride (DTAC), with silica/water interfaces was studied under pH and ionic strength conditions representative of aqueous solutions used in hydraulic fracturing. The pH is an important parameter in EOR treatments, and the pH of the aqueous phase in reservoirs can be modified as part of a treatment. Thus, surfactant adsorption is studied under acidic, neutral and basic conditions. In addition, high ionic strength conditions (100 mM NaCl) are studied as well, since high concentrations of such electrolytes are used in EOR. Silica/water interfaces were chosen for this study because sandstone reservoirs are common, and silica and aluminosilicate minerals are abundant in sandstone. Sum frequency generation (SFG), a surface-specific vibrational spectroscopy that is sensitive to interfacial symmetry, is utilized to characterize the molecular and macromolecular structure of DTAC at the silica/water interface. To complement the SFG experiments, total internal reflection Raman (TIR-Raman) experiments are carried out that provide further information regarding the amount of adsorbed surfactant at the interface. The influence of pH on surfactant structure and interface wettability will be discussed. In addition, evidence for surface charge neutralization as well as surface overcharging (e.g. the buildup of excess positive charge on the surface due to the adsorbed surfactant) under certain pH and ionic strength conditions will be presented.

Adsorption and self-assembly of alkylammonium surfactants at silica/water interfaces studied by interface-specific vibrational spectroscopy: Investigating pH and ionic strength conditions relevant to hydraulic fracturing

249th National Meeting (2015)

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