H060-0013
Gravity-driven instability in fracture flows with miscible fluids

Wednesday, 9 December 2020
Poster
Hongfan Cao1, Seonkyoo Yoon1, Zhenyu Xu2, Laura J Pyrak-Nolte3 and Peter K. Kang4, (1)University of Minnesota Twin Cities, Department of Earth and Environmental Sciences, Minneapolis, MN, United States, (2)Purdue University, Department of Physics and Astronomy, West Lafayette, IN, United States, (3)Purdue University, Department of Physics and Astronomy; Department of Earth, Atomospheric and Planetary Sciences; Lyles School of Civil Engineering, West Lafayette, IN, United States, (4)University of Minnesota, Department of Earth and Environmental Sciences, Minneapolis, MN, United States
Abstract:
Variable-density flows in geologic fractures control important subsurface applications such as nuclear waste disposal, geologic carbon sequestration, and enhanced geothermal system. Understanding the role of variable-density flow on mass transport and geochemical reactions is essential for the prediction, design, and operation of the subsurface applications. While a few previous studies have investigated the effects of density contrasts on solute transport in horizontal fractures, variable-density flow effects in vertical or inclined fractures have rarely been studied. In reality, vertical fractures are common, and flow and transport in vertical or inclined fractures will determine the integrity of caprocks.

In this study, we combine visual laboratory experiments with direct three-dimensional (3D) numerical simulations to study the effects of fracture inclination angle (orientation relative to gravity), flow inertia, and density contrasts between fluids on the spatiotemporal distribution of miscible fluids in a fracture. Two miscible fluids with different densities are injected through two inlets at the bottom of the fracture and flowed out from the outlet at the top of the fracture. The density contrast between two injection fluids results in the lighter fluid being confined to a narrow path, which we term “runlet”, and the instability of this runlet is observed in both lab experiments and numerical simulations (Fig. 1). Numerically computed streamlines show that the runlet instabilities are controlled by 3D vortices (Fig. 1C). We investigate the underlying mechanism triggering gravity-driven instability in fracture flows by systematically conducting numerical simulations for various combinations of flow rates, density contrasts, fracture apertures, and fracture inclination angles.

FIG. 1 Comparison of experiment and simulation results. Aperture is 4 mm, and injecting rate is 1.68 ml/min for both fluids. A. Digital images from non-reactive miscible fluid mixing experiments. B. Concentration distribution of mixed fluids from 3D simulation. C. Streamlines of mixed fluids from 3D simulation (2D projection of 3D streamlines).

The experimental work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-AC02-05CH112.

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