Department of Geology and Geological Engineering
Van Tuyl Lecture Series- Fall 2015
4:00-5:00 p.m. in Berthoud Hall Room 241
Thursday, October 1, 2015
Russell Detwiler
Department of Civil and Environmental Engineering
University of California, Irvine
“Reactive Alteration of Fractured Rock: Can a Fractured Caprock Self-heal?”
Abstract: The ability of geologic seals to prevent leakage of fluids injected into
the deep subsurface is critical for mitigating risks associated with greenhouse-gas
sequestration, waste disposal, and natural-gas production. Fractures and faults
caused by tectonic or injection-induced stresses create potential leakage
pathways. Fluids migrating through leakage pathways react with the host rock
leading to mineral dissolution or precipitation, which may mitigate or exacerbate
migration of injected fluids to shallow aquifers and the atmosphere; predicting
which requires improved understanding of the coupled hydrologic, geochemical,
and geomechanical processes that control the alteration of fracture permeability.
I present results from laboratory experiments aimed at quantifying these
coupled processes in a fractured dolomitic anhydrite caprock. During these
experiments, preferential dissolution of anhydrite left a compacted layer of
dolomite in the fractures. At lower flow rate, rock-fluid reactions proceeded to
near equilibrium within the fracture causing preferential flow paths to develop
over the 6-month duration of the experiment and a negligible change in
permeability. At higher flow rate, the compacted layer of dolomite sealed the
fracture resulting in a two-order-of-magnitude permeability decrease. This
laboratory-scale observation of significant permeability reduction demonstrates
a potential sealing mechanism for fractured porous caprocks composed of
minerals with differing solubilities and reaction kinetics. However, scaling
arguments suggest that at larger length scales the self-sealing process may be
offset by the formation of distinct channels as observed at lower flow rate.