Contingency plans

Contingency operations for Expedition 319 riserless drilling is based on the current state of knowledge at the time of writing this Scientific Prospectus and may be modified both before and during Expedition 319 based on continuing NT-PMT discussions.

Site C0002

Riserless drilling at Site C0002 is the primary contingency plan for Expedition 319 (Fig. F15). The scientific and operational objectives at Site C0002, which was previously drilled during Expeditions 314 (LWD) and 315 (coring), are to drill with LWD to 1000 mbsf and install 9⅝ inch casing using a similar configuration to that planned at proposed Site NT2-01J. The location for casing screens at this site will be selected on the basis of previous data from Expeditions 314 and 315 and from LWD data collected on this expedition. The casing will be cemented and a bridge plug with a pore pressure and temperature instrument package like that planned for proposed Site NT2-01J will be emplaced to monitor formation conditions at the screened interval. This will achieve the goal of drilling and preparing for a riserless observatory in the seaward portion of the Kumano Basin as part of a spatially distributed observatory network for NanTroSEIZE, should operational scheduling permit drilling at this alternate site. These operations at Site C0002 will also serve as contingency should operations prove not possible at proposed Sites NT2-01J or NT2-01K.

Proposed Site NT1-01A

Should operations at the riser and/or riserless observatory sites become impossible, or if time permits additional drilling operations during Expedition 319, proposed Site NT1-01A is an additional contingency site (Fig. F16). This site is located in the Shikoku Basin seaward of the trench above a basement high and provides a paired site for proposed Site NT1-07A, which constitutes the primary target for Expedition 322 from August 2009 to September 2009. The primary scientific objectives at this site are to characterize the material and state of the sediments atop the incoming (subducting) oceanic plate, with specific emphasis on the subducted strata. This will be achieved by analysis of core and through shore-based geotechnical studies of recovered core material. As noted above, if this contingency plan is invoked, the shipboard science parties for Expeditions 319 and 322 will be merged, the sample and data requests will be evaluated by a joint SAC, and a common moratorium period may be assigned.