Using Multiple Elimination to Image Geologic Structures beneath the

Gas Hydrate Stability Zone in the Northern Gulf of Mexico

ByErika J. Geresi,

Deborah R. Hutchinson, Patrick E. Hart, Thomas M. McGee

Erika Geresi

OverviewOverview

Geographic Distribution

Drilling Hazards

Cruise Instrumentation

Processing Flow

Results

Conclusions

Outline of the AreaOutline of the Area

Gas hydrates are well known for their capacity to change the Gas hydrates are well known for their capacity to change the physical properties of near-surface sediments and have been physical properties of near-surface sediments and have been linked to massive slope failures on continental margins. linked to massive slope failures on continental margins.

As drilling in the Gulf of Mexico has progressed from shallow-As drilling in the Gulf of Mexico has progressed from shallow-water shelf depths (<200m) to deep-water slope depths water shelf depths (<200m) to deep-water slope depths (>1000m), wells now penetrate the gas hydrate stability zone. (>1000m), wells now penetrate the gas hydrate stability zone. In order to understand the consequences of drilling through In order to understand the consequences of drilling through the hydrate zone, it is imperative to understand the geological the hydrate zone, it is imperative to understand the geological setting in which these hydrates exist and to be able to setting in which these hydrates exist and to be able to estimate the distribution and concentration of gas hydrate estimate the distribution and concentration of gas hydrate deposits especially in the subsurface. deposits especially in the subsurface.

Cruise OverviewCruise Overview

In May 2003, the USGS conducted a 14-day cruise aboard In May 2003, the USGS conducted a 14-day cruise aboard R/V Gyre to collect high-resolution multichannel seismic R/V Gyre to collect high-resolution multichannel seismic reflection data and develop the geologic framework around reflection data and develop the geologic framework around two deep-water sites (near lease blocks Atwater Valley 14 two deep-water sites (near lease blocks Atwater Valley 14 and Keathley Canyon 195). Both may be drilled by industry and Keathley Canyon 195). Both may be drilled by industry in spring, 2004, to study gas hydrates in the Gulf of Mexico.in spring, 2004, to study gas hydrates in the Gulf of Mexico.

The multichannel data from Atwater Valley, in 1300-m The multichannel data from Atwater Valley, in 1300-m water, show many shallow unconformities, deeper dipping water, show many shallow unconformities, deeper dipping reflections, numerous diffractions, and substantial amplitude reflections, numerous diffractions, and substantial amplitude variations. variations.

Geographic DistributionGeographic Distribution

Drilling HazardsDrilling Hazards

Cruise InstrumentationCruise Instrumentation

Primary navigation: Differential Global Positioning Primary navigation: Differential Global Positioning System, YoNav software;System, YoNav software;

Multichannel Seismic: 24-channel high-resolution Multichannel Seismic: 24-channel high-resolution seismic reflection profiling, 13/13 cu. inseismic reflection profiling, 13/13 cu. in³ G.I.Gun;³ G.I.Gun;

Bathymetry: Knudsen bathymetry system;Bathymetry: Knudsen bathymetry system;

Data Processing: Promax, Datatrend and Lookout 22 Data Processing: Promax, Datatrend and Lookout 22

Processing FlowProcessing Flow

Reformating, Reformating, Editing, amplitude balancing,Editing, amplitude balancing, Detrending,Detrending, Deep-water delay correction,Deep-water delay correction, FK Filtering, FK Filtering, Spiking Deconvolution,Spiking Deconvolution, NMO Correction,NMO Correction, Stacking,Stacking, Spherical Divergence Correction,Spherical Divergence Correction, Bandpass Filtering,Bandpass Filtering, Multiple Suppression.Multiple Suppression.

ConclusionsConclusions

The re-processing and the multiple elimination improved the strength The re-processing and the multiple elimination improved the strength and and continuity of the shallow and the deeper reflections.continuity of the shallow and the deeper reflections.

The multiple suppression helped to get rid of the multiple and gave a The multiple suppression helped to get rid of the multiple and gave a better interpretable image. better interpretable image.

Results from this reprocessing of selected profiles around one of the Results from this reprocessing of selected profiles around one of the vents/sea-floor mounds shows faulting and pathways that more clearly vents/sea-floor mounds shows faulting and pathways that more clearly

demonstrate the relations between the shallow and deeper structures.demonstrate the relations between the shallow and deeper structures.

Thanks toThanks to

Deborah Hutchinson, USGS, 384 Woods Hole Road, Woods Hole, Deborah Hutchinson, USGS, 384 Woods Hole Road, Woods Hole, MA 02543,MA 02543,

Patrick Hart, USGS, MS 999, 345 Middlefield Rd, Menlo Park, CA Patrick Hart, USGS, MS 999, 345 Middlefield Rd, Menlo Park, CA 94025,94025,

Tom McGee, MMRI/CMRET, University of Mississippi, 220 Old Tom McGee, MMRI/CMRET, University of Mississippi, 220 Old Chemistry Building, University, MS 38677,Chemistry Building, University, MS 38677,

Bob Woolsey, MMRI/CMRET, University of Mississippi, 220 Old Bob Woolsey, MMRI/CMRET, University of Mississippi, 220 Old Chemistry Building, University, MS 38677.Chemistry Building, University, MS 38677.