Dai, Jianchun1, Haibin Xu1, Fred Snyder1, Lecia Muller1,
Adam Koesoemadinata1, Diana Gillespie1, Gary Wool1, Nader
(1) Schlumberger RS/DCS, Houston, TX
ABSTRACT: Physical Rock Properties of Gas Hydrate Bearing Sediments, Geophysical Modeling, Inversion and Quantitative Volumetric Estimation in the Deepwater Gulf of Mexico
Natural gas hydrates are formed when methane, or a mixture of methane and other gases, combine with water in the porous space of sediments at high pore pressure and low temperature. Gas hydrates occur extensively worldwide, such as in permafrost areas and deepwater regions of the ocean. Approximately 10,000 gigatonnes of natural gas are estimated to be trapped as naturally occurring gas hydrates worldwide (USGS, 1997) and have drawn international attention for their potential as an alternative energy resource. In addition to being an asset, hydrates can also act as shallow hazards, influence wellbore stability and possibly affect global climatic changes. Extensive hydrate drilling, as well as remote seismic exploration, indicates that elevated elastic properties, such as P-wave and S-wave, are key diagnostic features of shallow gas-hydrate-bearing sediments. As the level of hydrate saturation within the sediments increases, so do the elastic properties. Understanding the physical rock properties is therefore essential for realistic geophysical hydrate modeling and volumetric estimation. To derive and validate the physical rock model, gas hydrate wells with known hydrate saturation levels were used. Construction of realistic hydrate-bearing sediment models were achieved through the integration of shallow rock properties typical of the study area, and the hydrate physical rock model. Full waveform prestack elastic modeling was then performed to obtain the seismic signature, and AVO response and to investigate seismic detection capabilities. Through the combination of full waveform prestack and hybrid inversion, elastic property volumes were generated, including estimates of gas hydrate saturation.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.