Leg 204 was originally scheduled to begin in San Francisco, California, and end in San Diego, California. As a result of an impending West Coast dock strike, both port calls were ultimately moved to Victoria, British Columbia, Canada. Leg 204 officially began with the first line ashore, Westcan Terminal B at 0655 hr on 7 July 2002.
In many ways, the leg turned out to be extraordinary. Almost all science objectives were successfully achieved during the course of drilling/coring the seven primary sites and two alternate sites. In addition, a series of holes geared specifically toward the rapid recovery and preservation of hydrate samples was cored at the end of the leg at Site 1249 as part of a hydrate geriatric study funded by the Department of Energy.
Some significant statistics of Leg 204 are listed below, followed by a more descriptive discussion:
Special tool deployments and successes during the leg included the following:
Operations on the southern Hydrate Ridge also required coordination with several other oceanographic research vessels. The Sonne, a German research vessel, operated in the same area, deploying and recovering instrumented seafloor landers. The Ewing, from LDEO, worked in conjunction with the JOIDES Resolution conducting two-ship seismic operations and independent research, including the setting of ocean-bottom seismometer (OBS) packages on the seafloor. The Atlantis, from Woods Hole Oceanographic Institution, was on site for 4 days of Alvin diving at the ridge crest. And finally, the New Horizon, a Scripps Institution of Oceanography vessel, was on location briefly doing independent oceanographic research work.
The leg also included a two-ship seismic program conducted in conjunction with the Ewing to acquire vertical, constant-offset, and walk-away VSPs. A new Schlumberger tool called the Vertical Seismic Imager (VSI) was used for most of the VSP work, whereas the older Well Seismic Tool (WST) was used for the remaining holes. Deployment of the VSI tool was problematic because of its fragile construction and because the tool is not designed to have the electric line slacked off during the data acquisition period. Nonetheless, the tool worked well enough to achieve most of the seismic objectives.
Eight of the sites were drilled using LWD technology. A developmental LWC system, jointly developed by LDEO, Anadrill, and Texas A&M University (TAMU), was also successfully tested using a RAB-8 LWD tool. This marked the first time that core samples have been recovered simultaneously with LWD data.
Several other specialized tools developed all or in part by TAMU were successfully deployed during the leg. These include the PCS, MT, APCT shoe, DVTP, and DVTPP.
Two other developmental pressure coring systems developed by the European consortium (HYACINTH) were deployed. These tools were designed to allow transfer of a pressurized core sample from the downhole tools autoclave chamber to a pressurized logging chamber. The FPC and HRC were deployed 10 times and 8 times, respectively. Two runs with the FPC and four runs with the HRC successfully recovered core at or near in situ pressure. Functionally, the pressurized core transfer and logging chambers worked well, although some tolerance variations with the FPC made the transferring of the FPC cores more problematic.
Prior to the leg, TAMU worked with Fugro-McClelland on the adaptation of their piezoprobe tool to the ODP/TAMU bottom-hole assembly (BHA). This tool was deployed twice on the first site, with the second attempt fully successful. Data from this electric linedeployed tool will be compared to DVTPP data. The DVTPP tool is deployed in a much faster and simpler fashion by being free-fall deployed and then recovered using the standard ODP coring line.
LDEO deployed its DSA tool to gather downhole data in support of the HYACINTH tool deployments and also as part of an experimental study using the APC as an energy source. The APC impact energy was recorded using OBS stations placed on the seafloor earlier by the Ewing. Initial results indicated that this experiment was successful and that useful data were obtained.
The scientific and operational achievements were impressive; however, the leg was extremely demanding because of the confined operating area. All nine drill sites were located within 3.6 nmi of each other. As a result of the close proximity of the sites, all moves between sites were done using the ship's dynamic positioning system. Because of the commonality of the coring BHAs to be used, most of these moves were made with the pipe suspended below the ship. When a BHA change or bit replacement was required, the move was made simultaneously with the pipe trip to and from the surface. With no transit time, other than traveling to and from port and limited pipe trips between sites, the operating time available for drilling and coring was considerable. For the 57.1-day leg, 50.4 days, or 88.3%, of the available time was spent on site. The remaining 6.7 days was spent in port (4.14 days) and under way (2.54 days).
Leg 204 operations were confined to an area located ~50 nmi off the coast of Oregon. The close proximity of land meant that this leg was a candidate for numerous changes of personnel and equipment. An initial supply boat rendezvous was planned to allow removal of specialized and expensive VSP equipment along with an Anadrill VSP engineer. This soon grew to include numerous other personnel changes via helicopter, and another supply boat brought out special pressure vessels, dewars, and liquid nitrogen to support the add-on effort to recover and preserve the additional hydrate samples. Ultimately, there were a total of nine rendezvous completed with the JOIDES Resolution, including seven helicopters and two supply vessels.
Leg 204 officially ended at 0900 hr on 2 September 2002, with the first line ashore Westcan Terminal Pier B in Victoria.
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