Rock physics consideration of S-wave attenuation in methane hydrate bearing sediments at Nankai Trough, Japan: Possible attenuation mechanism of contact line friction

Understanding S-wave attenuation in methane hydrate-bearing sediments (MHBS) is essential for accurate geophysical characterization and risk assessment in hydrate exploitation. Existing Biot-based rock physics models significantly underestimate observed S-wave attenuation values across seismic and sonic frequencies in the MHBS at the Nankai Trough, Japan. To address this discrepancy, we propose a novel rock physics model that incorporates dynamic contact line friction as a key attenuation mechanism. The model uses a representative element volume (REV) comprising an elliptical pore partially saturated by a droplet of methane hydrate. We simulate the deformation of the REV under cyclic shear stress and estimate the energy dissipation due to dynamic friction at the three-phase contact line. The numerical results indicate that the S-wave attenuation is highly sensitive to the pore aspect ratio and contact angle hysteresis. Under certain geometric and saturation conditions, contact line slip can occur even at low seismic stress levels, leading to frequency-independent attenuation. Our model successfully bridges the gap between theoretical predictions and field observations, offering a physically plausible mechanism for S-wave energy loss. The results suggest that incorporating contact line dynamics into rock physics models can enhance the interpretation of S-wave attenuation data and contribute to improved hydrate reservoir characterization.