--> The Discovery of High-Saturation Gas Hydrate Sands in the Gulf of Mexico — Results from Leg II Joint Industry Project Drilling, McConnell, Daniel R.; Boswell, Ray; Jones, Emrys; Collett, Timothy; Frye, Matt; Shedd, William; Hutchinson, Deborah; Mrozewski, Stephan; Guerin, Gilles; Cook, Ann; Dufrene, Rebecca; Godfriaux, Paul, #90100 (2009)

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The Discovery of High-Saturation Gas Hydrate Sands in the Gulf of Mexico — Results from Leg II Joint Industry Project Drilling

McConnell, Daniel R.1
 Boswell, Ray2
 Jones, Emrys3
 Collett, Timothy4
 Frye, Matt6
 Shedd, William5
 Hutchinson, Deborah7
 Mrozewski, Stephan8
 Guerin, Gilles8
 Cook, Ann8
 Dufrene, Rebecca5
 Godfriaux, Paul5

1AOA Geophysics, Houston, TX.
2
US Dept of Energy, NETL,
Morgantown, WV.
3
Chevron Energy Technology Co., San Ramon, CA.
4
US Geological Survey, Denver, CO.
5
Minerals Management Service, New Orleans, LA.
6
Minerals Management Service,
Herndon, VA.
7
US Geological Survey, Woods Hole, MA.
8
Lamont Doherty Earth Observatory,
New York, NY.

In April and May of 2009 the Gulf of Mexico Gas Hydrate Joint Industry Project realized its second field program (Leg II) with the semi-submersible Helix Q4000 drillship. The three week expedition drilled seven logging-while-drilling (LWD) holes at three sites that tested a variety of geologic/geophysical models for the occurrence of gas hydrate in sand reservoirs in the deepwater Gulf of Mexico.

High saturation gas hydrate deposits in sands were found, where predicted, at four of five holes at two sites. No high saturation gas hydrate sands were detected at a third site. Three of the five sites were selected for the final drill plan, WR 313, GC955, and the AC21, AC 65, EB992 area.
 

The full research-level LWD assembly deployed for Leg II collected data on formation lithology and porosity, and included quadrapole sonic tool and 3-D high-resolution resistivity tools. Two wells were drilled in WR 313. Both holes revealed a shallow unit with 350-500 ft of fracture fill gas hydrate beginning approximately 600 ft below the sea floor. The main gas hydrate targets were approximately 2,700 ft below the seafloor. Both wells encountered high-saturation of gas hydrate, where predicted, in separate 40 ft thick and 50 ft thick sands near the base of gas hydrate stability.Three holes were drilled in GC955, where a wide and thick late Pleistocene channel complex has been fractured and uplifted by a detached salt pillow. A four-way closure with numerous amplitude anomalies at the base of gas hydrate stability is near-to but west of the channel axis. The first was drilled very close to the channel axis in a location with muted geophysical indications of gas hydrate. More than 300 ft of porous sands as predicted; however the sands contained primarily water - with only modest indications of gas hydrate. The next holes targeted the sand at the four-way closure.Fracture fill gas hydrate was detected, and, at the target, 100 ft of sand fully saturated with gas hydrate with little to no gas beneath. A third well also encountered 80 ft of fully saturated gas hydrate sand at the target, but drilling was aborted because of a gas hydrate dissociation event and subsequent gas flow. The JIP's discovery of thick gas hydrate-bearing sands validates the integrated geological and geophysical approach used in the pre-drill site selection and provides increased confidence in assessment of gas hydrate volumes in the
Gulf of Mexico.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil