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GEOREF RECORD

High concentration methane hydrate in a silt reservoir from the deep-water Gulf of Mexico

Stephen C. Phillips, Peter B. Flemings, Melanie E. Holland, Peter J. Schultheiss, William F. Waite, Junbong Jang, Ethan G. Petrou and Helen Hammon
High concentration methane hydrate in a silt reservoir from the deep-water Gulf of Mexico (in Gas hydrates in Green Canyon Block 955, deep-water Gulf of Mexico; Part 1, Anonymous)
AAPG Bulletin (September 2020) 104 (9): 1971-1995

Abstract

We present results from 30 quantitative degassing experiments of pressure core sections collected during The University of Texas-Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition at Green Canyon Block 955 in the deep-water Gulf of Mexico as part of The University of Texas at Austin-US Department of Energy Deepwater Methane Hydrate Characterization and Scientific Assessment. The hydrate saturation (Sh), the volume fraction of the pore space occupied by hydrate, is 79% to 93% within sandy silt beds (centimeters to meters in thickness) between 413 and 442 m below seafloor in 2032 m water depth. Sandy silt intervals are characterized by high compressional wave velocity (Vp) (2515-3012 m s-1) and are interbedded with clayey silt sections that have lower Sh (2%-35%) and lower Vp (1684-2023 m s-1). Clayey silt intervals are composed of thin laminae of silts with high Sh within clay-rich intervals containing little to no hydrate. Degassing of single-lithofacies sections reveals higher-resolution variation in Sh than is possible to observe in well logs; however, the average Sh of 64% through the reservoir is similar to well log estimates. Gas recovered from the hydrates during these experiments is composed almost entirely of methane (99.99% CH4, <100 ppm C2H6 on average), with an isotopic composition (delta 13C: -60.4 ppm and -63.6 ppm Vienna Peedee belemnite and delta 2H: -178.2 ppm and -179.0 ppm Vienna standard mean ocean water) that suggests the methane is primarily from a microbial source. A subset of six degassing experiments performed using very small pressure decrements indicates that the salinity within these samples is close to the average seawater concentration, suggesting that hydrate either formed slowly or formed during a rapid event at least tens of thousands of years before present.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 104
Serial Issue: 9
Title: High concentration methane hydrate in a silt reservoir from the deep-water Gulf of Mexico
Title: Gas hydrates in Green Canyon Block 955, deep-water Gulf of Mexico; Part 1
Affiliation: University of Texas at Austin, Institute for Geophysics, Austin, TX, United States
Pages: 1971-1995
Published: 20200915
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Accession Number: 2020-077274
Categories: Oceanography
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N18°00'00" - N30°04'00", W98°00'00" - W80°30'00"
Secondary Affiliation: Geotek, GBR, United KingdomU. S. Geological Survey, USA, United StatesIntegrated Statistics, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 2020
Program Name: USGSOPNon-USGS publications with USGS authors
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