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The movement of low viscosity fluid through a porous medium containing extremely viscous fluid is emerging as an important phenomenon in several petroleum engineering applications. These include the recovery of heavy oil by solvent injection, the preferential reduction of water flow using polymer gels, and the enhancement of acid fracturing treatments. The displacement of one fluid from a porous medium by a second, immiscible fluid has been extensively studied in two cases: when capillary forces are dominant, and when viscous forces are comparable to capillary forces. This dissertation research examines a third case: when viscous forces are dominant. The viscosity of the fluid initially present in the porous medium is four or more orders of magnitude greater than the viscosity of the displacing fluid. Consequently, the displacement through an individual pore will be dictated by the hydrodynamic forces required to move the high viscosity fluid. However, very little is known about grain-scale behavior of such displacements. The research will develop a mathematical model of the viscosity-dominated displacement in a network of conduits. By neglecting pressure drop within the low viscosity fluid, the model will treat the displacement as a moving boundary problem. The high viscosity fluid will be assumed Newtonian and will move in response to the pressure gradient imposed via the low viscosity fluid. The movement can be treated as pseudo-steady state flow of the highviscosity fluid. The flow field will be updated whenever the low viscosity fluid advances into a pore previously occupied by high-viscosity fluid. Swept volume will be calculated in each run for comparison and further investigation. We will use classical methods for direct and iterative solutions of large, sparse linear systems to compute these steady states. Key practical insights to be obtained from the model are the nature of the displacement and effects of geometry and hydraulic conductivities on the sweep efficiency. The model will form the basis for examining additional physical processes, notably mass transfer between fluids, and the possibility that fingering of the low viscosity fluid occurs within individual pore throats.

The effect of water content and soil-water hysteresis on transport of unreactive water-tracers and volatile organic compounds (VOCs) in porous media is investigated under steady-state water-flow conditions. Specifically, this research addresses the effect on dispersive and mass transfer processes affecting the movement of NaC1 and trichloroethene (ICE) and how these processes influence the approach to Fickian flux conditions. Transport experiments were conducted in a 25-cm column packed with silica sand. Based on the results, it is concluded that water content (0), pore-water velocity, and flow history affect the average movement and spread of water-tracers and VOCs. It is suggested that non-volatile solutes in unsaturated media travel longer distances or times to achieve a Fickian state. Consequently, a greater number of averaged heterogeneities are encountered and solute flux is characterized by a greater dispersion coefficient (D). A power (n) law relationship (D(m) = η(v(m)/ θ(m))ⁿ), found between mobile dispersion coefficients (D(m_), pore-water velocity (v(m)), and water content (θ(m)) for different porous media, indicates that dispersivity (η) is not only a function of the media, but also of θ(w). TCE transport is controlled by advection processes for Ow greater than 50% saturation. Lower θ(w) result in greater TCE dispersion, retardation, mass-transfer resistance, vapor diffusion, and spreading. Consequently, VOCs reach the Fickian regime at shorter distances than unreactive solutes in water. Although VOC transport is influenced by multiple rate-limited mass transfer, the mechanisms controlling the overall mass-transfer resistance vary as a function of θ(w). The hysteretic behavior of solute transport parameters is attributed to a greater degree of irregular flow paths and entrapped air, higher air-water interfacial areas, and thicker water-films for wetting than draining scenarios. Consequently, wetting conditions result in slower mixing (up to 98% lower mass-transfer coefficients) of dissolved solutes. Since TCE transport at low water contents and wetting conditions is dominated by diffusion and dispersion mechanisms, the TCE velocity distribution in the liquid phase is normalized by velocity distributions in the gas-phase and becomes closer to Fickian conditions.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy