Attenuation in Dry Sandstones: Role of Strain Amplitude, Frequency and Temperature

Attenuation of P- and S-waves is a powerful tool that, when combined to P- and S-waves velocities, allows increasing the certainty on inferring rock type, fluids and P-T conditions at depths. Increasing certainty is even more critical for geothermal energy as developing costs should be minimised. While decades of works in the laboratory and theoretical insights advanced our understanding on its intricacies (e.g. Winkler & Murphy, 1995 ), most works at the field scale focus on waves velocities and their ratio Vp/Vs but seldom use the informations contained in the retrieved attenuations.

A missing link might exist between the different attenuation mechanisms acknowledged at depths: (i) At low P-T conditions, fluid flow mechanisms dominate (e.g. Mueller et al., 2010 ); (ii) At elevated P-T, visco-plastic mechanisms dominate. Additional mechanisms might however exist, e.g. at intermediate temperatures representative to geothermal settings, and add up to that two large groups. Among those, dissipations from frictional loss could occur from large strain amplitudes (e.g. Winkler et al., 1979 ).

We will present investigations of this attenuation mechanism in a newly calibrated apparatus for large strain amplitudes over a broad frequency range, and will its applicability to standard approaches fitting to the mechanisms currently acknowledged.