Abstract

The Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) Leg II conducted logging-while-drilling (LWD) operations in seven wells at three deepwater sites in the Gulf of Mexico during April and May of 2009. The LWD logging program, optimized based on the results of earlier gas hydrate expeditions, featured a research-level dataset that included gamma ray, laterolog and propagation resistivity, resistivity imaging, acoustic velocity, density, neutron porosity, spectroscopy and sigma. The program also provided an opportunity to evaluate new LWD tools that had not previously been available to gas hydrate drilling programs: a quadrupole acoustic tool and an azimuthal propagation resistivity tool.

JIP Leg II was successful in determining the occurrence of gas hydrate within sand reservoirs in the Gulf of Mexico, assessing current approaches for interpreting gas hydrate occurrence from geologic and geophysical data, and determining suitable sites for additional drilling and coring in future phases of the JIP program. Basic formation evaluation determined varying gas hydrate saturations in sand reservoirs at each site, and characterized laterally-continuous sections of gas hydrate-filled fractures in clays.

The collection of a comprehensive LWD dataset through expected hydrate-bearing reservoirs validated both the site selection process and the logging program, providing new information on the nature of sediments and the occurrence of gas hydrate in the Gulf of Mexico. Lessons from JIP Leg II will help to refine future LWD logging programs in gas hydrate research.

Introduction

The Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) is a cooperative research program between the U.S. Department of Energy, the U.S. Minerals Management Service, and an industry consortium led by Chevron. Since 2001, the JIP has been committed to achieving a better understanding of the safety hazards involved in drilling through hydrate-bearing sediments. Following a drilling, logging and coring expedition in 2005 (JIP Leg I) that centered on evaluating the fine-grained, clay-dominated sediments that typify the shallow sub-seafloor in the deepwater Gulf of Mexico, the JIP focused a second drilling expedition on the occurrence of gas hydrates in sand-dominated reservoirs in order to assess geohazards as well as investigate gas hydrate resource potential (Boswell et al., 2009).

Using a petroleum systems approach, the JIP identified three Leg II sites with the potential for gas hydrate-saturated sand reservoirs (Hutchinson et al., 2008). A logging-only strategy was taken in order to assess the greatest number of sites and test the effectiveness of the program's geological/geophysical site selection approach. The results of JIP Leg II would then be used to plan subsequent JIP field programs that would collect conventional and pressure-core samples from the most promising sites.

This report describes the design of the logging program aboard the semi-submersible Helix Q4000, documents the acquisition of data and its initial processing, and discusses preliminary formation evaluation results in the Walker Ridge 313 (WR313), Green Canyon 955 (GC955), and Alaminos Canyon 21 (AC21) lease blocks.

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