Ion exchange plays an important role in transport of aqueous species in the porous media in a variety of processes such as nuclear waste disposal, ground water remediation and enhanced oil recovery (EOR). For example, the effectiveness of anionic surfactants to displace non aqueous phase liquids (NAPLs) for groundwater remediation or crude oil for enhanced oil recovery is highly dependent on the concentration of divalent cations. These cations are capable of exchanging with the porous media leading to an unfavorable surfactant phase behavior (Windsor type II) and an increase in the interfacial tension of surfactants with the NAPLs or oil. As a result, an increase in surfactant losses and a reduction in displacement efficiency are observed. In this research, we investigate the impact of ion exchange reactions on surfactant floods, and develop a methodology to make reliable predictions and design robust surfactant floods. In this research, single phase experiments are performed to study the transport of ions and a surfactant in outcrop sandstone cores by injecting surfactant solutions prepared in different brines. The effluent ions and surfactant concentrations are measured using ion chromatography and high performance liquid chromatography. An analytical solution is developed for simultaneous cations and anions exchange to make predictions on efficiency of surfactant floods using anionic surfactants. The solution is derived for a mobile aqueous phase and a stationary solid phase. The law of mass conservation is used to obtain a system of hyperbolic equations for cations (Na+, Ca2+, Mg2+) and anions (Cl-, Ab-) under the assumption of local equilibrium and no dispersion, where Ab- respresents the anionic surfactant that undergoes ion exchange. The adsorption of anionic surfactant is assumed to depend on the aqueous phase concentrations of the surfactant, divalent ions and total dissolved solids. This system of hyperbolic equations is solved using the multicomponent chromatography theory for constant initial and boundary conditions called the Riemann condition. The results from the analytical solution and insights from the experimental data are used to obtain the optimum injection conditions that result in a robust surfactant flood with minimal loss of surfactants and high oil recovery.

Analytical solution of multicomponent ion exchange during surfactant floods in porous media

251st National Meeting (2016)

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