Use of seismic data in estimating the amount of in-situ gas hydrates in deep marine sediment

Journal Article · Fri Jan 01 04:00:00 EST 1993 · United States Geological Survey, Professional Paper; (United States)

OSTI ID:7052142

Lee, M W; Miller, J J; Agena, W F ^[1]; Hutchinson, D R; Dillon, W P; Swift, B A ^[2]

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1. Geological Survey, Denver, CO (United States)
2. Geological Survey, Woods Hole, MA (United States)

The bulk volume of gas hydrates in marine sediment can be estimated by measuring interval velocities and reflection amplitudes of hydrated zones from true-amplitude-processed multichannel seismic-reflection data. In general, neither velocity nor amplitude information alone is adequate to estimate hydrate concentration. We propose a method that uses reduction in amplitude (amplitude blanking) calibrated by interval-velocity data to quantify hydrate concentrations in the Blake Ridge area of the US Atlantic continental margin. Once calibration has been performed throughout the region, only reflection amplitudes are needed for estimating bulk-hydrate concentrations. This method is especially beneficial when applied to local areas where only single-channel seismic surveys are available (no interval velocities), but where at least one multichannel seismic line is available for initial calibration. The model, which gives the best estimates for the Blake Ridge, is based on the observation in this region that amplitude blanking is associated with relatively low interval velocities. In the model, there is a replacement of normal sediment with [open quotes]representative hydrated sediment.[close quotes] Representative hydrated sediment is a sediment of defined matrix density and porosity with pore space filled by a mixture of water and hydrate. The proportion of water to hydrate in the representative sediment is one of the variables in the model; it can be calculated using an equation in which velocity is estimated from the seismic data and known properties of pure hydrate, and in which porosity inferred from a velocity/porosity relationship. Once these calculations have been performed, the model is calibrated, and the porosity and hydrate proportions of the representative sediment are fixed. These parameters can then be combined with reflection amplitudes (blanking) to determine bulk-hydrate concentrations. 39 refs., 10 figs., 2 tabs.

• OSTI ID: 7052142
• Journal Information: United States Geological Survey, Professional Paper; (United States), Journal Name: United States Geological Survey, Professional Paper; (United States) Vol. 1570; ISSN XGPPA9
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CONTINENTAL MARGIN
FORECASTING
GAS HYDRATES
GEOLOGIC DEPOSITS
GEOLOGY
GEOPHYSICAL SURVEYS
HYDRATES
NATURAL GAS HYDRATE DEPOSITS
RESERVES
RESOURCE ASSESSMENT
RESOURCES
SEDIMENTS
SEISMIC SURVEYS
SURVEYS