Spectral changes of seismic wave energy in a partially saturated rock: contact angle hysteresis phenomena
Title: Spectral changes of seismic wave energy in a partially saturated rock: contact angle hysteresis phenomena
Low-frequency shadows are frequently interpreted as attenuation phenomena due to partial saturation with free gas. However, several researchers have argued that shadows are not necessarily a simple attenuation phenomenon because low-frequency energy must have been added or amplified by some physical or numerical process. Attenuation alone should simply attenuate higher frequencies, not boost lower frequencies. The physical or numerical effects explaining this phenomenon are still debatable in literature. To better understand the elastic wave energy's spectral changes in the partially saturated rock, we consider the hysteresis of contact angles phenomena inside the pore. We demonstrate that contact angles' hysteresis leads to the nonlinear energy exchange between frequencies, explaining wave energy boost at lower frequencies. Additionally, we show that at seismic frequencies, the attenuation 1/Q-factor due to friction of the contact line can be much larger than the attenuation due to viscous fluid flow inside the partially saturated rock. Our model depends on the wave amplitude and weakly depends on the wave frequency. The suggested model can help to interpret the low-frequency shadows, bright spots, microtremor, and attenuation anomalies frequently observed around hydrocarbon fields.
Alexander Rozhko received B.Sc. in Physics (2000) and an M.Sc. in Geophysics (2002) from Novosibirsk State University, a Ph.D. in Physics (2007) from the University of Oslo, and Dr.Sc. in Earth, Universe and Environmental Sciences (2007) from Joseph Fourier University (dual degree). Currently, he works for Equinor ASA in Stavanger, Norway, at the Rock Mechanics department. From 2015 to 2020, he also worked as the Adjunct Professor in Reservoir Geomechanics at the University of Stavanger. His research interest includes rock physics/rock mechanics, multiphase fluid flow modeling, interfacial science, and IOR methods.
About this Series:
The Friday Informal Seminar Hour [FISH, Earth Resources Laboratory] is a postdoc-run weekly seminar series within the ERL (Earth Resources Laboratory). Topics include research relating to geophysics, and in particular seismology, with applications in Earth resources exploration such as e.g. seismics exploration, microseismicity, earthquake physics, and Earth imaging techniques.