From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, March 26, 2010
The Discovery of Rich Gas Hydrate Accumulations in Sand Reservoirs in the Gulf of Mexico- Results from DOE-Chevron Joint Industry Project Drilling
Dan McConnell, AOA Geophysics; Ray Boswell, U.S. Department of Energy; Timothy S. Collett, U.S. Geological Survey; Matthew Frye and William Shedd, Minerals Management Service; Stefan Mrozewski, Gilles Guerin, and Ann Cook, Columbia University; Dianna Shelander and Jianchun Dai, Schlumberger; Paul Godfriaux and Rebecca Dufrene, Minerals Management Service; Emrys Jones and Rana Roy, Chevron
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, $11.5M 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. Over 17,000 ft of sedimentary section were logged using a state of the art bottom hole assembly. The three sites drilled were Walker Ridge (WR) 313, Green Canyon (GC) 955, and Alaminos Canyon (AC) 21. The expedition was completed on-time and under budget. The locations for JIP Leg II drilling were the result of an integrated geological and geophysical prospecting approach that considered direct geophysical evidence for gas hydrate-bearing strata in the context of evaluation of indicators for gas sourcing, gas migration pathways to the shallow section, and occurrence of sand reservoirs within the gas hydrate stability zone. High saturation gas hydrate deposits in sands were found, where predicted, at four of five holes at two sites, WR313 and GC 955. The third site, AC 21, indicated low to moderate gas hydrate saturation in extensive shallow sands. The full research-level LWD assembly deployed for Leg II collected gamma-ray, neutron and density porosity, neutron spectroscopy data, as well as full azimuthal resistivity and acoustic velocity, including both compressional and shear-wave measurements.
The expedition demonstrated the ability to reasonably predict gas hydrate occurrence through seismic data in the absence of pre-drill well data. At WR313, the model linking aligned phase reversals at multiple levels with gas-hydrate bearing sands at the base of gas hydrate stability (BGHS) was confirmed. Furthermore, initial results suggest that gas hydrate has the potential to fully saturate reservoirs well above the BGHS, with the primary control being occurrence of reservoir quality facies. In addition, unexpected findings, such as the complex nature of the gas hydrate occurrence at GC955, and the discovery of the extensive, strata-bound shallow hydrate occurrence at WR313, raise exciting new questions.
The DOE and the JIP are committed to making these data publically available as soon as possible to support a wide range of scientific studies. The initial reports will be published shortly at http://www.netl.doe.gov/MethaneHydrates/JIPLegII-IR/