Quantifying Patterns of Brittle Damage in Fractured Rock

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Cracks control the flow of fluids in the Earth's crust - this is critical for producing hydrocarbons, for planning subsurface waste storage and for understanding earthquakes. The strength or weakness of fractured rock depends on the pressure of the fluid in the cracks and the pattern of those cracks. In the simplest case, in a rock with spherical fluid-filled pores, changes in pore fluid pressure are felt equally in all directions. This is known as isotropic poroelasticity. However, fractured rocks are known to contain arrays of narrow cracks, many of which are oriented in a similar direction. This suggests that changes in pore fluid pressure will *not* be felt equally in all directions, and this has been described by a theory of anisotropic poroelasticity. This project aims to test the hypothesis of anisotropic poroelasticity: chiefly, that changes in stress in a fluid saturated rock depend on the pattern of cracks in that rock. To date, there has been no systematic assessment of this theory based on measured data from deformed rocks. This project will collect quantitative data on crack patterns from fractured rocks and then predict changes in stress with changes in fluid pressure. These predictions will be compared to the commonly used isotropic case, and the discrepancy will be quantified. The research described in this proposal will significantly improve our mechanical models of fluid-saturated fractured rock, leading to more efficient management of subsurface resources and better assessment of seismic hazards and risks of waste facility failure.