Gas hydrate quantification using full-waveform inversion of sparse ocean bottom seismic data: A case study from Green Canyon Block 955, Gulf of Mexico

We present a case study of gas hydrate quantification using dense short-offset multichannel seismic (MCS) and sparse long-offset ocean bottom seismometer (OBS) data in lease block Green Canyon 955 (GC955), Gulf of Mexico, where the presence of gas hydrate was interpreted using logging-while-drilling (LWD) acquired by the Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) Leg II expedition. We use frequency-domain full-waveform inversion (FWI) of seven OBS gathers to invert for a P-wave velocity (VP) model of a ~7-km long MCS profile connecting two LWD sites, GC955-H and GC955-Q. We build the starting model for FWI using traveltime inversion (TI) of both MCS and OBS data. In addition, we use the TI model for depth migrating the MCS stack. At the LWD sites, we constrain the hydrate saturation (Sgh) using both sonic and resistivity logs. Unfortunately, and typical of seismic quantification problems, the FWI model resolution is not sufficient to extrapolate the LWD-based Sgh. We apply Backus averaging to...