Smith, Michael A.1, William W. Shedd1
(1) Minerals Management Service, New Orleans, LA
ABSTRACT: Effects of Gas Hydrate on Seafloor and Borehole Stability in the Deepwater Gulf of Mexico – Seismic Prediction and Drilling Results
A prevalent assumption in the worldwide quest to develop potential huge gas hydrate resources is that dissociation in shallow hydrate-bearing sediment may result in geohazards, such as submarine landslides or seafloor instability, with unacceptable safety and environmental consequences for subsea facilities. Hundreds of exploratory and development wells have already been safely drilled through the zone of stability for hydrate deposits within in the deepwater Gulf of Mexico. At some of these locations hydrates form when a gas plume intersects the base of subsea equipment, suggesting that dissociation is caused by the heat from drilling fluids or production. Conventional 3D exploration seismic parameters and survey design are not designed to delineate naturally occurring gas hydrates in shallow sediments so, except for a few locations where an apparent bottom-simulating reflector indicates the base of the hydrate stability zone, there is no seismic confirmation of the existence of hydrates at these drillsites.
The Department of Energy Gulf of Mexico Gas Hydrates Joint Industry Project (JIP) has developed protocols and laboratory tests for the acquisition, processing, and interpretation of seismic data in order to image gas hydrate zones better. The JIP has selected locations near sampled seafloor hydrate mounds in the Atwater and Keathley Canyon areas of the Gulf of Mexico for drilling, logging, and coring deep stratigraphic test wells through the hydrate deposits this spring. These wells will allow calibration of geophysical data for characterizing buried gas hydrates and provide critical data on the impact of hydrate drilling and production on seafloor stability.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.