Chemical Transport in Partially Saturated Porous Media

The transport of chemicals in multiphase flows finds applications in many engineering problems, many of which occur in natural environments, including the geological storage of CO2 or enhanced oil recovery. In the latter case, oil and water coexist in the pore space, and their spatial distribution is controlled by the average displacement velocity and the viscosity contrasts between the two fluids. During production by waterflooding, capillary action leads to the formation of a disconnected oil phase that remains trapped into the pore space, as a so- called residual phase in the reservoir. Surfactant-polymer (SP) flooding can increase oil recovery by lowering both the water-oil interfacial tension and mobility ratio. However, field application is limited due to surfactant costs and process complexity. The residual phase acts as a highly effective disperser by increasing the tortuosity of the flow paths and controlling the velocity field in the brine phase, thereby affecting the ability of the brine-surfactant formulation to get in contact with the oil. This situation is further complicated by the manifestation of other processes: (i) retention of the surfactant, as a result of adsorption onto solid surfaces; (ii) emulsification of the oil phase, the formation of which under flow may greatly differ from an equilibrium situation. Understanding the mixing process between both phases is critical in the design of improved chemical EOR techniques, but at present the key mechanisms that control mixing and the subsequent mobilization of the oil are not fully understood.

The aim of this project is to quantify and describe the impact of saturation (water content) on solute dispersion and mixing, and its effect on oil recovery. We will deploy laboratory core-flooding experiments augmented by in-situ imagery to provide direct observations of the dynamics of solute dispersal in partially saturated rocks, including various SP formulations with and without polymer. A unique aspect of the proposed approach is the combined use of X-ray Computed Tomography (XCT) and Positron Emission Tomography (PET) to enable the acquisition of a suite of benchmark experiments showing rock/mineral heterogeneity, fluid distribution and chemical transport in both sandstone and carbonate rocks. One- and three- dimensional numerical models will be used to support laboratory observations and to obtain useful parameters that describe the mixing process in partially saturated porous media.