Influence of dissolution on long-term frictional properties of carbonate fault gouge
Velocity stepping experiments have been performed on a simulated calcite gouge using an annular shear apparatus to investigate the effect of dissolution on the frictional properties of a carbonate fault. The tested material was put in contact with hydrochloric acid at different concentration in order to provoke grains dissolution prior to the experiments. Particle size analysis shows that the small grains tend to disappear due to the chemical reaction, whereas the distribution of large grains is not much affected. The dissolution process induces a decrease of the fractal number of the grain size distribution and an increase of the roughness of the particles. The study of the rate-and-state parameter of the materials, which is commonly used to characterize the ability of the fault to generate earthquakes, shows a decrease towards more negative values with dissolution for dry specimens and an increase for wet samples. Moreover, a decrease of the steady state friction coefficient is observed with dissolution for wet samples. This decrease of the friction would promote the triggering of slip along an existing fault after the injection of an acid fluid like in the cases of CO2 storage or acid gas disposal projects in a carbonate reservoir, but the increase of the rate and state parameter (a–b) of saturated specimens implies that the seismogenic potential of faults could potentially be reduced.
Rattez, H; Disidoro, F; Sulem, J; Veveakis, M
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