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 at 0655 hr on 7 July 2002 with the first line ashore at Westcan Terminal B.
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 gas hydrate geriatric study funded by the Department of Energy (DOE).
Some significant statistics of Leg 204 are listed below (see also Tables T2, T3, T4), followed by a more descriptive discussion:
- Water depths ranged from 788.5 to 1228.0 meters below rig floor.
- Eight of nine sites were drilled using LWD technology.
- Overall, a total of 45 holes were drilled/cored at nine separate drill sites.
- Eleven holes were drilled with a tricone bit for LWD/resistivity-at-the-bit (RAB)-8 or wireline logging.
- Thirty-three holes were cored with the advanced piston corer (APC) and/or extended core barrel (XCB) coring systems, and one hole was rotary core barrel (RCB) cored.
- A total of 3674.5 m was cored with 3068.3 m (83.5%) recovered.
- Of a 57.1-day leg, 50.4 days (88.3% of the time) was spent on site operating and 6.7 days in port/transit.
- Twenty-nine nautical miles (43.8 hr) were covered during 23 moves between sites, using dynamic positioning.
- Seven helicopter and two supply boat rendezvous were conducted, resulting in 42 personnel exchanges.
- Visitors included two journalists (Dallas Morning News and American Geophysical Union/Eos), two engineering observers (DOE and Chevron/Texaco), and a two-man German film crew (Context TV).
- Whirl-Pak latex microbeads and perfluorocarbon tracer were used on 85 cores that were sampled for microbiology.
- Fifty meters of hydrate-bearing core were recovered and stored under pressure in a methane environment; 35 m of additional samples was recovered and stored in six liquid nitrogen dewars.
Special tool deployments and successes during the leg included the following:
- Sixteen of sixteen operationally successful runs with the Davis-Villinger Temperature-Pressure Probe (DVTPP);
- Eight of eight operationally successful runs with the Davis-Villinger Temperature Probe (DVTP);
- Sixty-one of sixty-one successful runs with the APC temperature (APCT) tool;
- One hundred and seven of one hundred and ten successful runs with the APC-methane tool (APCM);
- One of two successful deployments of the Fugro-McClelland piezoprobe;
- Thirty of thirty-nine successful runs with PCS;
- Two of ten cores successfully recovered under pressure using the Fugro Pressure Corer (FPC);
- Five of eight cores successfully recovered under pressure using the HYACE Rotary Corer (HRC);
- Twenty-eight runs with the Lamont-Doherty Earth Observatory (LDEO) drill string acceleration (DSA) tool; seventeen were all or partially successful; and
- Eight of eight cores successfully recovered using the RAB-8 logging-while-coring (LWC) technology.
Operations on southern Hydrate Ridge also required coordination with 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 OBS packages on the seafloor. The Atlantis, from Woods Hole Oceanographic Institution, was on site for 4 days of Alvin diving at the southern summit. And finally, the New Horizon, a Scripps Institution of Oceanography vessel, was on location briefly doing independent oceanographic research work.
The leg included a two-ship seismic program conducted in conjunction with the Ewing to acquire vertical, constant-offset, and walkaway VSPs. A new Schlumberger tool called the Vertical Seismic Imager (VSI) was used for most of the VSP experiments, whereas the older Well Seismic Tool (WST) was used for the remaining seismic work. 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, APCM, APCT tool, DVTP, and DVTPP.
Two new pressure coring systems developed by a European Union-funded consortium (deployment of HYACE tools in new tests on hydrates [HYACINTH]) were deployed. These systems were designed to allow transfer of a pressurized core from the downhole tools autoclave chamber to a pressurized logging or storage 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. Pressurized core transfer to the logging and storage chambers worked well, despite some tolerance variations with the FPC.
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 at the first site, with the second attempt fully successful. Data from this electric line-deployed tool will be compared to DVTPP data. The DVTPP tool is much faster to deploy because it is deployed and 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 a seismic 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 partially successful and that useful data were obtained.
The scientific and operational achievements were impressive; however, the leg was extremely demanding because 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 used, most of these moves were made with the pipe suspended below the ship. When a BHA changed 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 (88.3% of available time) were spent on site. The remaining 6.7 days were 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 allowed for numerous changes of personnel and equipment. An initial supply boat rendezvous was planned to allow exchange of specialized and expensive LWD equipment and personnel for the VSP equipment. There were also numerous personnel changes via helicopter, and another supply boat brought out special pressure vessels and dewars of liquid nitrogen to support an add-on effort to recover and preserve the hydrate samples collected with additional funding from the DOE. 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 at Westcan Terminal Pier B in Victoria.