Attenuation of Seismic Waves in Partially Saturated Berea Sandstone as a Function of Frequency and Confining Pressure

Abstract

Frequency-dependent attenuation (1/Q) should be used as a seismic attribute to improve the accuracy of seismic methods and imaging of the subsurface. In rocks, 1/Q is highly sensitive to the presence of saturating fluids. Thus, 1/Q could be crucial to monitor volcanic and hydrothermal domains and to explore hydrocarbon and water reservoirs. The experimental determination of seismic and teleseismic attenuation (i.e., for frequencies < 100 Hz) is challenging, and as a consequence, 1/Q is still uncertain for a broad range of lithologies and experimental conditions. Moreover, the physics of elastic energy absorption (i.e., 1/Q) is often poorly constrained and understood. Here, we provide a series of measurements of seismic wave attenuation and dynamic Young’s modulus for dry and partially saturated Berea sandstone in the 1–100 Hz bandwidth and for confining pressure ranging between 0 and 20 MPa. We present systematic relationships between the frequency-dependent 1/Q and the liquid saturation, and the confining pressure. Data in the seismic bandwidth are compared to phenomenological models, ultrasonic elastic properties and theoretical models for wave-induced-fluid-flow (i.e., squirt-flow and patchy-saturation). The analysis suggests that the observed frequency-dependent attenuation is caused by wave-induced-fluid-flow but also that the physics behind this attenuation mechanism is not yet fully determined. We also show, that as predicted by wave-induced-fluid-flow theories, attenuation is strongly dependent on confining pressure. Our results can help to interpret data for near-surface geophysics to improve the imaging of the subsurface.

Permeability and elastic properties of rocks from the northern Hikurangi margin: Implications for slow-slip events

“…When comparing seismic and ultrasonic velocities, we should note that they have been estimated at frequencies around 20 Hz and 800 kHz, respectively. Considering such a frequency range, a typical P-wave quality factor range of 30 to 150, and a nearly-constant Q model (Liu et al, 1976;Tisato et al, 2021), we should expect velocities to increase between 2.3 and 12%. Another difference between SHIRE and laboratory data is that the latter are measured on dry samples, whereas the accretionary prism must be saturated.…”

Seismic Wave Propagation in Partially Saturated Rocks With a Fractal Distribution of Fluid‐Patch Size

“…Many studies, especially experimental ones, show that the WILFF effect occurs at different scales (e.g., Agofack et al., 2018; Ba et al., 2019; Chapman et al., 2018; Li, Zhao, et al., 2020; Ma et al., 2018; Mikhaltsevitch et al., 2016; Murphy, 1982, 1984; Szewczyk et al., 2018; Tisato et al., 2021; Zhao et al., 2019). In particular, Adam et al.…”

“…Many studies, especially experimental ones, show that the WILFF effect occurs at different scales (e.g., Agofack et al, 2018;Ba et al, 2019;Chapman et al, 2018;Ma et al, 2018;Mikhaltsevitch et al, 2016;Murphy, 1982Murphy, , 1984Szewczyk et al, 2018;Tisato et al, 2021;Zhao et al, 2019). In particular, Adam et al (2009) measured the elastic properties and attenuation of carbonate samples with different porosity and permeability at seismic and ultrasonic frequencies.…”

On Frequency-Dependent Rock Experiments: A Comparative Review

“…Chapman et al [127] observed significant E and K but insignificant G dispersion and attenuation caused by fluid pressure diffusion (FPD) in partially saturated Berea specimens featuring CO 2 -exsolution by depressurisation. Tisato et al [128] measured dry and partially saturated Berea specimens as function of confining pressure in which the former are frequency-independent and the latter are frequency-dependent at pressures below 14 MPa. Tisato et al [128] also used KKR-consistent models to determine the mechanism WIFF but was unable to distinguish between "squirt-flow" and patchy-saturation as sub-mechanisms.…”

“…Tisato et al [128] measured dry and partially saturated Berea specimens as function of confining pressure in which the former are frequency-independent and the latter are frequency-dependent at pressures below 14 MPa. Tisato et al [128] also used KKR-consistent models to determine the mechanism WIFF but was unable to distinguish between "squirt-flow" and patchy-saturation as sub-mechanisms. Wei et al [173] assumed isotropy to converted K and Q −1 K from measured E and Q −1 E plus ν and Q −1 ν for two sandstones at different saturation states.…”