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Speaker: Ariel Lellouch, Tel Aviv University
 
Host: Duncan Young
 
Title: Seismic applications of downhole DAS

Abstract: Distributed Acoustic Sensing (DAS) is an emerging technology that leverages optical fibers to record the seismic wavefield with an unprecedented spatial resolution. In this talk, I will describe various seismic-band applications utilizing optical fibers deployed in boreholes. We first illustrate how records from a vertical DAS array can be simply and effectively processed to construct velocity models, detect microseismic events and earthquakes, locate them, and estimate their magnitude. Then, we show how a horizontal DAS array deployed in an unconventional shale reservoir records guided waves propagating for hundreds of meters with frequencies as high as 700 Hz. Thanks to the high resolution of DAS measurements, guided waves are recorded unaliased despite their very short (< 10 m) wavelength. We compare the field observations with semi-analytical and wave-equation modeling approaches. Guided waves are also strongly affected by open fractures induced by hydraulic stimulation. We use a horizontal cross-well acquisition of perforation shots recorded by a DAS array in a simple, geometrical analysis of horizontal fracture growth. We also analyze guided waves generated by microseismic events and can locate the events despite the unidirectional nature of the DAS measurements.

*** Due to the 14 hour time difference between Austin and Hong Kong, this seminar has been scheduled to start at 9:00am CT ***


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Speaker: Lin Liu, Chinese University of Hong Kong
 
Host: Xiaohua Xu
 
Title: Geophysical investigations of thawing permafrost 

Abstract: Accumulating observational evidence shows widespread thawing and degradation of perennially-frozen ground known as permafrost. Thawing permafrost has profound effects on terrestrial ecosystems, hydrologic and landscape processes, and infrastructure. However, it is challenging to study and monitor permafrost mainly because it is purely defined by the subsurface thermal condition. Through a few local to regional-scale studies, I will show how integrative measurements using geophysical methods, such as Ground Penetrating Radar, space-borne Radar Interferometry, and Surface Nuclear Magnetic Resonance, offer quantitative understandings on surface and subsurface processes associated with thawing ice-rich permafrost.