S-Wave Attenuation Caused by Wave-Induced Fluid Flow

We study seismic wave attenuation (1/Q) caused by the physical mechanism of wave-induced fluid flow. Relaxation experiments are numerically performed to solve Biot’s equations of consolidation. The experiments yield stress-strain relations used in a post-processing step to calculate the complex moduli of 2D poroelastic media with mesoscopic-scale heterogeneities. Attenuation is then determined from the complex moduli. In our model, the rock is represented by a medium containing circular heterogeneities of much lower porosity and permeability than the homogeneous background. The background contains 80% of the total pore space in the medium and is fully saturated with oil, gas, or water, while the heterogeneities are always fully saturated with water. We<br>observe that the S-wave attenuation in the medium with 80% of oil is much higher than in the one with 80% of gas, and at low seismic frequencies (lower than around 10 Hz), the S-wave attenuation in the medium with 80% of oil is also much higher than in the one with 100% of water. This occurs because the maximum value of the S-wave attenuation is shifted to lower frequencies with increasing fluid viscosity. Additionally, we observe that S-wave attenuation can be high (e.g., Q = 15.8) when the porous and permeable background has also a much more compliant solid frame than the low-porosity, lowpermeability heterogeneities.