Monitoring and imaging water saturation

We develop a new method to monitor and locate seismic velocity changes in the subsurface using seismic noise interferometry. We use the ballistic Rayleigh waves computed from 30 days records on a dense nodal array located above the Groningen gas field (the Netherlands). We infer the daily relative phase velocity dispersion changes as a function of frequency and propagation distance with a cross-wavelet transform processing. Assuming a one-dimensional velocity change within the medium, the induced ballistic Rayleigh wave phase shift exhibits a linear trend as a function of the propagation distance. Measuring this trend for the fundamental mode and the first overtone of the Rayleigh waves for frequencies between 0.5 and 1 Hz enables us to invert for shear-wave daily velocity changes in the first 1.5 km of the subsurface. Most of the changes are observed in a carbonate layer below 800 m depth. Combined with P-wave velocity variations observations using a similar methodology, we interpret the changes as caused by slight water saturation variations induced by deep fluid flows.

About the Series

MIT Earth Resource Laboratory's Friday Informal Seminar Hour (FISH) takes place most Fridays while classes are in session, 12-1pm in 54-209. Most talks are also livestreamed on ERL's Youtube channel. Topics include seismology/inversion, rock physics, geomechanics, and machine learning for geophysics, and speakers range from PhD students to senior professors and industry leaders. Speaker and topic will be posted here once they are confirmed.