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doi:10.2204/iodp.sp.311add.2005

REVISED OPERATIONS PLAN

As originally planned (table T1 in Collett, Reidel, Malone, and the Expedition 311 Project Team, 2005), this expedition was scheduled to carry out logging-while-drilling (LWD) and measurement-while-drilling (MWD) operations (drilling in Hole A) prior to coring each site (pending Environmental Pollution and Safety Panel approval). After completing the LWD/MWD logging program, the expedition was scheduled to conduct conventional and pressure-controlled coring operations (drilling in Hole B) at each of the sites drilled during the LWD/MWD campaign. The main change in the Expedition 311 science plan to accommodate for the addition of 15 operational days is the inclusion of a third special core and tool deployment hole (drilling in Hole C) at each of the five sites to be drilled during the expedition. Under the new operational plan for Expedition 311 (Table T1), Hole A at each site will be dedicated to the LWD/MWD operations, Hole B will be dedicated to "continuous" advanced piston corer/extended core barrel (APC/XCB) coring, with additional temperature measurements using the APC temperature (APCT) and Davis-Villinger Temperature-Pressure Probe (DVTPP) tools as well as monitoring pressure/temperature conditions of each core by deploying the APC methane (APCM) tool. The new Hole C at each site will be a dedicated "special tools hole" with a focus on pressure core deployments, special spot core requirements, and wireline logging and vertical seismic profile (VSP) deployments (Table T1).

The drilling schedule for Expedition 311 will be updated during the cruise to accommodate any unforeseen changes in the schedule. However, the new Hole C is mainly dedicated to pressure coring, with a total of six alternating deployments of the pressure coring sampler (PCS), HYACINTH pressure corer (HPC) and Fugro percussion corer (FPC) systems. Previous gas hydrate drilling has often been characterized by incomplete core recovery; thus, the addition of Hole C will allow us to include additional conventional APC/XCB spot coring in the to sample missed or poorly sampled intervals in Hole B. At this stage the total amount of additional coring required to fill gaps in the Hole B coring program is unknown. Based on experience gained during Ocean Drilling Program (ODP) Leg 204 off Oregon, we plan for an additional generic 100 m coring at each site during Expedition 311. Hole C, which is likely to be in better condition than the continuously cored Hole B, will also be wireline logged after coring operations are completed. Within the new operational plan, Hole B will also include limited pressure coring with three deployments of the PCS. These three PCS cores, along with the PCS cores from Hole C will be used for degassing experiments. The ability to use a three-hole rather than a two-hole strategy at each site will allow a more complete and continuous coring strategy and more judicious deployment of pressure coring systems based on knowledge gained in Holes A and B.

A second change to the original operations plan includes revision of the VSP strategy. Originally, a single zero-offset VSP was planned at proposed Site CAS-01B. The geophone spacing will be changed from the original 25 m to a more closely spaced 5 m interval. This will yield higher-resolution seismic data to better image details in the gas hydrate–bearing sedimentary section at proposed Site CAS-01B. Changing the VSP spacing to 5 m will add ~7 h to the original plan. If less time is available, a 10 m geophone spacing may be used, which would add only ~3 h to the project plan. A lower-priority addition to the VSP program is a possible VSP at proposed Site CAS-06A with 5 m geophone spacing. This second VSP at Site CAS-06A will add an additional 13 h to the original operational plan.

The third change to the Expedition 311 operational plan includes the addition of shallow (~18 m deep) dedicated microbiological core holes at proposed Sites CAS-06A and CAS-01B. The addition of two dedicated shallow microbiological core holes will give us an improved understanding of the three-dimensional aspects of microbiological system associated with the active cold vent at proposed Site CAS-06A and a regular background site (proposed Site CAS-01B). Furthermore, we will use Hole C to core the upper ~18 m at each other site (proposed Sites CAS-03B, CAS-02C, and CAS-05D) for dedicated microbiological sampling.

At the time the Expedition 311 Scientific Prospectus was published, funding for the third-party HYACINTH pressure coring system (HPC/FPC) and infrared (IR) and computed tomography (CT) core imaging was pending. Supplemental funding from the U.S. Department of Energy for these activities has been approved. A detailed operational plan for the IR core imaging system is being currently developed by Peter Schultheiss (Geotek) and Phil Long (PNNL). The HYACINTH pressure coring and IR core imaging programs will most likely follow our experience from ODP Leg 204 with modifications based on new experiences gained during the JIP cruise in the Gulf of Mexico earlier this year.

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