Experimental Three-Phase Flow in Porous Media: Development of Saturated Structures Dominated by Viscous Flow, Gravity, and Capillarity

Abstract

Summary The motivation for this work is the need to understand the formation of oil banks during waterflooding operations as well counter-current gravity driven oil recovery mechanisms. The success of these operations depends on a combination of viscous, gravitational, and capillary forces. This paper focuses on the development of three-phase saturation structures driven by viscous flow, gravity, and capillarity. Three liquids: water, benzyl alcohol, and decane are flowed through glass bead packs. Dynamic water floods of cores saturated with mixtures of benzyl alcohol and decane are described. Saturation distributions in the core are determined using x-ray computer tomography (CT). The injection of water generates a benzyl alcohol bank that displaces most of the decane ahead of it. Benzyl alcohol and decane, driven by gravity, exchange places in the core. This gravity driven counter-current flow is rapid in the presence of low water saturation ahead of the benzyl alcohol bank and within the benzyl alcohol bank. The gravity exchange is slow in the presence of mobile water behind the benzyl alcohol bank. The water saturation structure is stable and is not significantly affected by the counter-current flow of benzyl alcohol and decane. The accumulation of decane at the top of the core triggers a backward migration of a decane tongue. The decane tongue disappears when water injection is resumed and the benzyl alcohol bank re-forms where the decane tongue existed. When mobile decane is not present, significant capillary driven longitudinal fluid transport is observed while the high gradient saturation structure in the transverse direction remains stable. Even high saturation gradients in the longitudinal direction are quite stable. Fluid flow patterns during the shut in periods and displacement mechanisms are proposed.