Impact of viscous fingering and permeability heterogeneity on fluid mixing in porous media

Christos Nicolaides1, Birendra Jha2, Luis Cueto-Felgueroso1 and Ruben Juanes3, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)University of Southern California, Mork Family Department of Chemical Engineering and Materials Science, Los Angeles, United States, (3)Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering and Earth Resources Laboratory, Dept. of Earth, Atmospheric and Planetary Sciences, Cambridge, MA, United States
Abstract:
Fluid mixing plays a fundamental role in many natural and engineered processes, including groundwater flows in porous media, enhanced oil recovery, and microfluidic lab-on-a-chip systems[1]. Recent developments have explored the effect of viscosity contrast on mixing, suggesting that the unstable displacement of fluids with different viscosities, or viscous fingering, provides a powerful mechanism to increase fluid--fluid interfacial area and enhance mixing[2]. In this paper, we revisit the problem of subsurface contaminant transport through a heterogeneous aquifer in a quarter five-spot geometry[3] and we focus on the impact of two principal sources of disorder in the flow field: viscosity contrast between the fluids and heterogeneity in the permeability field. We consider a wide range of viscosity ratios of the contaminant and the water, from a less viscous to a more viscous contaminant, flowing through a range of permeability fields, from almost homogeneous to strongly heterogeneous. We ask the following practical question: how does the interplay between viscosity contrast and permeability heterogeneity determine the evolution of macroscopic quantities that characterize the spatial structure and temporal evolution of a contaminant plume? We answer this question by conducting high resolution simulations of contaminant flow and transport in an aquifer, and by analyzing both point measurements of contaminant breakthrough and clean-up times as well as global degree of mixing and dilution of the contaminant plume.

[1] M. Dentz, T. Le Borgne, A. Englert, and B. Bijeljic, Mixing, spreading and reaction in heterogeneous media: A brief review, J. Contam. Hydrol. 120, 1-17 (2011).

[2] B. Jha, L. Cueto-Felgueroso, and R. Juanes, Fluid mixing from viscous fingering. Phys. Rev. Lett. 106, 194502 (2011)

[3] J. Luo, M. Dentz, O. A. Cirpka, and P. K. Kitanidis, Breakthrough curve tailing in a dipole flow field, Water Resour. Res. 43(9), W09403 (2007).

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