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Capillary fracturing in granular media

Ruben Juanes (MIT), Michael Szulczewski (MIT), Mathias Trojer (MIT), Ran Holtzman (Hebrew University)

Engineering Mechanics and Materials in the Oilfield

Wed 9:00 - 10:30

CIT 227

The invasion of gas into liquid-saturated, deformable porous media occurs in many processes including gas venting, hydrocarbon recovery, geologic CO$_2$ sequestration, and soil wetting and drying. While fracturing during gas invasion has been observed in several experiments and simulations, the underlying mechanisms and macroscopic patterns remain poorly understood. Here, we study the invasion of air into a thin bed of water-saturated glass beads, and record the evolution of the invasion pattern. The control parameters are the injection rate, the bead size, and the vertical confining stress applied to the top of the bed. We identify three invasion regimes: capillary fingering, viscous fingering, and``capillary fracturing'', where capillary forces overcome frictional resistance and induce the opening of fracture-like conduits. We show that the transitions between the regimes are governed by two dimensionless numbers: a modified capillary number and a fracturing number. We then extend the experiments and analysis to investigate an additional control parameter---the wettability---and test the hypothesis that the regime transitions can be predicted by incorporating the contact angle into the capillary number and fracturing number. The experiments and analysis predict the emergence of fracturing in fine-grained media under low confining stress, a phenomenon that likely plays a fundamental role in fracking oil and gas shale.