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Geological Society, London, Special Publications; 1998; v. 137; p. 129-132;
DOI: 10.1144/GSL.SP.1998.137.01.09
© 1998 Geological Society of London

Exploration Strategy and Reservoir Evaluation Methodology

Detection of gas hydrates using downhole logs

D. Goldberg & S. Saito

Borehole Research Group, Lamont-Doherty Earth Observatory, RT 9W, Palasides, NY 10964, USA

Downhole logs have proven to be critical in quantifying natural gas hydrates found in marine sediments and the seismic signature associated with free gas below. In recent drilling on the Blake Ridge, the Ocean Drilling Program recorded in situ velocity and resistivity logs that reveal an increasing amount of hydrate with depth in the pressure-temperature stability window. The associated increase in shear rigidity (decrease in Vp/Vs ratio) and decrease in acoustic amplitude over this interval is attributed to the cementation of sediment grains by hydrate, which may also explain the prevalent seismic blanking across the Blake Ridge. In future drilling campaigns, the use of ‘logging-while-drilling’ (LWD) sensors placed just above the drill bit will improve the in situ estimation of porosity, lateral variability and hydrocarbon reservoir potential of natural gas hydrates.