Special Session - Gas Hydrates: Gulf of Mexico Gas Hydrates Joint Industry Project: Overview of Leg II LWD Results

The Gulf of Mexico gas hydrates Joint Industry Project (the JIP) is a cooperative research program between the US Department of Energy, collaborating federal agencies including the U.S. Geological Survey and Minerals Management Service, and an international industrial consortium under the leadership of Chevron. The JIP conducted its " Leg II?? loggingwhile-drilling (LWD) operations at three deepwater sites in the Gulf of Mexico in April and May of 2009. Leg II was intended to expand upon previous JIP work that had focused primarily on geohazards related to drilling through fine-grained gas hydrate bearing systems by investigating the occurrence and nature of pore-filling gas hydrate in sand reservoirs in the Gulf of Mexico. 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. The expedition experienced minimal operational issues with the advanced LWD tool string, and successfully managed a number of non-gas-hydrate-related shallow drilling hazards. Two wells drilled in Walker Ridge block 313 (WR313) confirmed pre-drill models by discovering gas hydrates at high saturations (>50%) in multiple sand horizons. In addition, operations at WR313 discovered an unanticipated, 500 foot-thick, shallow, stratal-bound occurrence of graindisplacing gas hydrate within fine-grained sediments. Two of three wells drilled in Green Canyon block 955 (GC955) closely matched the pre-drill prediction of extensive sand occurrence with gas hydrate fill along the crest of a structure with indications of active gas source and migration. The third well, drilled off the structure but more proximal to the interpreted sand source, encountered thick, water-bearing sands. Most notably, well GC955-H discovered ~100 ft of gas hydrate in sand at high saturations (>50%) within a complex fault-bounded occurrence. This accumulation is overlain, underlain, and most surprisingly, interbedded with, gas-hydrate-free, water-bearing sands. Two wells drilled in Alaminos Canyon block 21 (AC21) confirmed the pre-drill prediction of potential extensive occurrence of gas hydrates in shallow sand reservoirs at relatively low (<40%) saturations. However, further sample collection and analyses at AC-21 are needed to confirm the existence and quantity of gas hydrate. JIP Leg II operations fully met its scientific objectives; the abundant high-quality data collected from gas hydrate bearing sands in the Gulf of Mexico will enable further validation of geophysical detection/characterization methods, and will provide valuable locations for future JIP drilling, logging and coring operations.