Convection, Dispersion, and Adsorption of Surfactants in Porous Media

Abstract

Abstract Using the theory of volume averaging, we have shown that molecular diffusion, mass tortuosity, and mechanical mixing contribute to the mass-dispersion coefficient. A series of experiments were conducted on the system Triton X-100(TM) surfactant, n-decane oil, and water to determine the contribution of each mechanism to the total-dispersion matrix for flow through fired Berea sandstone. The dynamics of adsorption and the effect of dead-space volume are considered for the single-phase transport of surfactant through fired Berea. A new dynamic asdorption model is developed which considers both mass transfer to the fluid/solid surface and a kinetic surface-adsorption mechanism. Both kinetic adsorption and mass-transfer rate mechanisms are shown to be important over a wide range of injection rates. Introduction It recently has been proposed to inject surfactants into oil-bearing reservoirs to improve the efficiency of the oil recovery process. To understand the effects that surfactants have on the recovery of oil, both the physical and chemical behavior of the oil/surfactant/water interface must be understood in terms of interfacial properties as well as the mass-transport properties of surfactants in porous media. This work presents a systematic study of the physical processes affecting the transport of a surfactant through a porous medium.First, experiments are presented for the determination of the diffusion, tortuosity, and mechanical mixing effects of the dispersion coefficient for both single-phase and two-phase flow in porous media. Finally, adsorption and dead-space volume effects are considered for the single-phase transport of surfactant through fired Berea.The system chosen for study is described as follows. Water Phase. Deionized distilled water was used since its purity ensured constant chemical properties. Oil Phase. Commercial grade n-decane was chosen because it has a low viscosity to ensure a favorable mobility ratio. Solid Phase. The porous medium used in this work was Berea sandstone. The rock was kiln-fired before use to dehydrate and deactivate the clay material. Water Soluble Solutes. Sucrose. It was necessary in some experiments to have tracer solutions with a nonadsorbing solute. Aqueous sucrose solutions were used since they do not interact with either the solid or oil phase. Analysis for concentration was by refractive index. Triton X-100. This commercial nonionic detergent manufactured by Rohm and Haas offered several desirable properties. It is very water-soluble and virtually insoluble in alkane hydrocarbons. In addition, aqueous solutions have been shown to have very little effect on the contact angle on sandstone. Also, the analysis of surfactant concentration can be done conveniently and accurately by ultraviolet spectroscopy. Mass Dispersion Coefficient Using the theory of volume averaging, it has been shown that molecular diffusion D, mass tortuositym, and mechanical mixing F contribute to the mass-dispersion coefficient. K=D(1+ m) + F(v).........................(1) SPEJ P. 430^