Abstract

The Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (GOM JIP Leg II) began on 16-April-2009 with the mobilization of the semi-submersible drilling vessel Helix Q4000 at sea in the Gulf Mexico and drilling was conducted in the Walker Ridge, Green Canyon and the Alaminos Canyon lease blocks. The primary objective of the GOM JIP Leg II program was the collection of a comprehensive suite of logging-while-drilling (LWD) data within gas-hydrate-bearing sand reservoirs. The LWD sensors just above the drill bit provided important new information on the nature of the sediments and the occurrence of gas hydrate. The two holes drilled at Walker Ridge yielded evidence of a laterally continuous thick fracture-filling gas hydrate section, but more importantly both wells also encountered sand reservoirs, between 40- to 50-ft-thick, nearly saturated with gas hydrate. Gas-hydrate-bearing sands were also drilled in two of the Green Canyon wells, with one occurrence slightly more than 100-ft-thick. Initial interpretation of the Alaminos Canyon drilling results is that the sands appear to exhibit uniformly low gas hydrate saturation over a large area. Nevertheless, the discovery of thick hydrate-bearing sands at Walker Ridge and Green Canyon validates the integrated geological and geophysical approach used in the pre-drill site selection process in order to predict hydrate accumulations before drilling, and provides increased confidence in assessment of gas hydrate volumes in the Gulf of Mexico and other marine sedimentary basins.

Drilling operations within GOM JIP Leg II were marked by the constant challenge of optimizing data quality by maintaining borehole stability, which is difficult to achieve within shallow unconsolidated sediments. In addition, several of the targets were exceptionally deep: the two wells drilled in Walker Ridge 313 (at more than 3,000 feet below the seafloor) exceeded by more than 1,000 ft the previous record for the deepest gas hydrate research wells (NGHP Expedition-01, Site 17, Andaman Islands). The process of drilling the GOM JIP Leg II wells provided new insights into the optimal drilling strategies for marine " open-hole?? drilling programs without surface conductors or drilling mud returns. Most notably, original plans to drill these deep holes with minimal mud use were revised due to difficulties with borehole stability observed in the first well drilled (WR313-G). In fact, despite the large volumes of gas hydrate that the expedition encountered, it is apparent that many of the primary drilling hazards that needed to be managed during the drilling program were not gas hydrate related, but were instead the common problems that face all drilling programs: borehole stability, drill cutting removal, gas releases into the borehole, and water flows. Additional experience was also gained relative to the expected response of thick gas hydrate bearing units to drilling, providing further opportunities to improve future gas hydrate drilling protocols.

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