Dai, Jianchun1, Haibin Xu1, Fred Snyder1, Lecia Muller1,
Adam Koesoemadinata1, Diana Gillespie1, Gary Wool1, Nader
Dutta1
(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.