TAS

Dear ASEG Tasmania members and potential members,

Come and hear about Anton Rada’s work at the forefront of the development and implementation of drones for magnetic surveys.  Noon in the CODES Conference Room (UTas Sandy Bay campus), Wednesday 16th October.   Please let branch president Mark Duffett or branch secretary Matt Cracknell know if you’d like to join the speaker and Mark Duffett for lunch at the Uni Staff Club after the talk.

2019 Pacific South Honorary Lecturer Tour

Seismic attenuation, dispersion, and anisotropy in porous rocks: Mechanisms and Models
Boris Gurevich, Curtin University and CSIRO, Perth, Australia

Understanding and modeling of attenuation of elastic waves in fluid-saturated rocks is important for a range of geophysical technologies that utilize seismic, acoustic, or ultrasonic amplitudes. A major cause of elastic wave attenuation is viscous dissipation due to the flow of the pore fluid induced by the passing wave. Wave-induced fluid flow occurs as a passing wave creates local pressure gradients within the fluid phase and the resulting fluid flow is accompanied with internal friction until the pore pressure is equilibrated. The fluid flow can take place on various length scales: for example, from compliant fractures into the equant pores (so-called squirt flow), or between mesoscopic heterogeneities like fluid patches in partially saturated rocks. A common feature of these mechanisms is heterogeneity of the pore space, such as fractures, compliant grain contacts, or fluid patches. Using theoretical calculations and experimental data, we will explore how this heterogeneity affects attenuation, dispersion, and anisotropy of porous rocks. I will outline a consistent theoretical approach that quantifies these phenomena and discuss rigorous bounds for attenuation and dispersion.

Time table

Biography

Boris Gurevich has an MSc in geophysics from Moscow State University (1976) and a PhD from Institute of Geosystems, Moscow, Russia (1988), where he began his research career (1981–1994). In 1995–2000 he was a research scientist at the Geophysical Institute of Israel, where he focused mainly on diffraction imaging problems. Since 2001, he has been a professor of geophysics at Curtin University and advisor to CSIRO (Perth, Western Australia). At Curtin he has served as Head of Department of Exploration Geophysics (2010–2015) and since 2004 as director of the Curtin Reservoir Geophysics Consortium. He has served on editorial boards of Geophysics, Journal of Seismic Exploration, and Wave Motion. He is a Fellow of the Institute of Physics and has more than 100 journal publications in the areas of rock physics, poroelasticity, seismic theory, modeling, imaging, and monitoring of CO₂ geosequestration. His research achievements include development of advanced theoretical models of seismic attenuation and dispersion in heterogeneous porous rocks.

Sponsors

Platinum sponsors
Gold sponsor

Seismic Full Waveform Inversion for Fundamental Scientific and Industrial Problems.

Seismic waveform inversion is a powerful method used to quantify the elastic property of the subsurface. Although the development of seismic waveform inversion started in the early 1980s and was applied to solve scientific problems, it became popular in industry only about 15 years ago. One of the key elements in the success of seismic waveform inversion has been the increase of the acquisition of long offset seismic data from 3 km in the early 1990s to more than 15 km today. Not only did long offset data provide refraction arrivals, but it also allowed recording of wide-angle reflections, including critical angles, providing unique information about the subsurface geology.

In this talk, I will elaborate on the early development of the seismic full waveform inversion (FWI) and its application to solve fundamental scientific problems. The first big success of FWI was its application to gas hydrate reflections, also known as bottom simulating reflection (BSR), which showed that the
BSRs are mainly due the presence of a small amount of free methane gas, not a large amount of hydrates stored above the BSR, and hence the total amount of methane stored in marine sediments should be much less than previously estimated. A second major success of FWI was its application to quantify the characteristics of the axial melt lens observed beneath ocean spreading centers. The seismic full waveform inversion results show that one can distinguish between pure melt and partially molten mush within a 50 m thick melt lens, allowing to link the melt delivery from the mantle with the hydrothermal circulation on the seafloor. The application of full waveform inversion to spreading center problems has become an important area of research.

Unlike in sedimentary environment, the seafloor in general scientific environment could be very rough and water depth could be deep, making it very difficult to use the conventional method of background velocity estimation. To address this issue, the surface seismic data could be downward continued to the seafloor, as if both streamer and sources were placed on the seafloor, similar to land geometry. This method allows to bring the refraction starting from zero offset to far offset, which is extremely useful for full waveform inversion of first arrivals. The downward continuation also allows to reduce the seafloor diffraction, increase the moveout of reflection arrivals, and enhance wide-angle reflections, all important for seismic full waveform inversion. The application of a combination of downward continuation and FWI has allowed to quantify gas anomalies in sedimentary basins and fluids at subduction fronts. The waveform inversion also has been used to monitor CO 2 sequestration.

I will explain the intricacy of FWI, based on the physics of waves, specifically the role of amplitudes and converted waves in addressing fundamental scientific problems. The presentation should interest professionals working in the oil and gas sectors, or crustal studies and global seismology.

More details and biography.