Complex Flow: Patterns and Predictions in the Subsurface
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Recovery of subsurface fluids, whether oil and gas, or contaminants, requires understanding the ways fluid(s) flow within porous and fractured rocks and soil. This is particularly complicated when there are multiple fluids (oil-methane-water; water-CO2; water-NAPL). New experiments, combined with theoretical and computational modeling, have tracked the flow of two phases in fractured and porous media and shown how both phases move in competition. Each phase separately responds to the aperture field and its own and the others' capillary, gravity and viscous forces. The relative mobility of a phase is a function of the surface tension of the phase boundaries, and one phase may act as a barrier to the other. Flow paths are significantly longer than under single-phase conditions and transport is very sensitive to differences in phase structure, even at relatively similar values of phase saturation and relative permeability of the two phases. Interphase mass-transfer (dissolution of non-aqueous phase, dissolution/growth of bubbles, dissolution/ deposition on minerals) also strongly influences phase structure. This can result in differential dissolution and creation of preferred flow channels through the entrapped phase and the loss of stability between phases.
