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.
Highlights
Frequency-dependent attenuation of seismic waves (1/Q) should be considered in geophysical processing to improve exploration geophysics (e.g., De Siena et al, 2014)
Measurements have been conducted at confining pressure between 0 and 40 MPa, and frequency ranges 1–100 Hz, and 0.1–1 MHz
The dry sample and samples confined above 14 MPa exhibit negligible and frequency independent attenuation
Summary
Frequency-dependent attenuation of seismic waves (1/Q) should be considered in geophysical processing to improve exploration geophysics (e.g., De Siena et al, 2014). While dry rocks typically exhibit 1/Q < 0.02, saturated rocks may exhibit frequency-dependent attenuation as high as ∼0.1 (e.g., Winkler and Nur, 1982; Peselnick and Liu, 1987; Yin et al, 1992; Batzle et al, 2006; Barton, 2007; Adam et al, 2009; Tisato and Madonna, 2012; Madonna and Tisato, 2013; Tisato and Quintal, 2014; Pimienta et al, 2015a,b; Tisato et al, 2015; Chapman et al, 2016). Tisato and Madonna (2012) and Yin et al (1992) report that in dry and partially saturated Berea sandstone attenuation at ∼100 Hz is ∼0.01 and ∼0.04, respectively
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