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Dr. Rie Kamei Nakata, Visiting Scientist at MIT Earth Resources Laboratory / Dept. of Earth, Atmospheric and Planetary Sciences, presents “Monitoring of fluid injection by control-source time-lapse seismic full waveform inversion.”
“Seismic monitoring of Earth provides valuable information regarding the time-varying changes in subsurface physical properties that are caused by anthropogenic processes. However, the resulting changes in subsurface properties are often small both in terms of magnitude and spatial extent, leading to seismic data differences that are difficult to detect at typical non-repeatable noise levels. In order to better extract information from the time-lapse data, exploiting the full seismic waveform information can be critical, since detected amplitude or traveltime changes may be minimal. Full waveform inversion is one of such methods that estimate an optimal model of time-varying elastic parameters at the wavelength scale to fit the observed time-lapse seismic data with modelled waveforms based on numerical solutions of the wave equation. We study controlled-source seismic cross-well monitoring of microbubble water into shallow unconsolidated Quaternary sediments in the Kanto basin of Japan. Microbubble water is comprised of water infused with air bubbles of a diameter less than 0.1mm, and may be useful to improve resistance to ground liquefaction during major earthquakes. Repeated monitoring surveys (>10) reveal transient behaviors in waveforms during microbubble injection. Time-lapse waveform inversion detects changes in P-wave velocity of less than 1 percent, initially as velocity increases and subsequently as velocity decreases. The velocity changes are mainly imaged within a thin (1 m) layer between the injection and the receiver well, inferring the fluid-flow influence of the fluvial sediment depositional environment.”
Dr. Nakata is a Visiting Scientist in ERL/EAPS. She obtained a PhD at University of Western Ontario on the topic of seismic full waveform inversion. After a half-year post-doctoral position at University of Western Ontario, she was a research fellow at University of Western Australia in 2013-2018. She is interested in imaging, inversion and monitoring of Earth’s seismic properties in various scales ranging from rock samples to crustal scales. She works on scientific investigation of seismogenic zones (such as subduction zones), seismic monitoring of Carbon Capture and Storage programs, oil/gas exploration, and near-surface engineering problems.