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doi:10.2204/iodp.sp.324.2009

Risk and contingency strategy

General contingency plan

Three principal factors could affect the implementation of the drilling plan:

1. Adverse hole conditions (e.g., an unstable section of the borehole wall that collapses into the hole or broken pieces of hardware lodged in the hole),

2. Weather conditions that limit the ability to continue coring (e.g., high seas) or to stay on station (e.g., approaching typhoon), and

3. Time delays (e.g., arising from equipment breakdowns, inclement weather, and measures taken to respond to hole conditions).

Hole conditions

In general, unusually adverse hole conditions are not expected during Shatsky Rise drilling. Prior drilling has shown that chert layers may cause drilling difficulties, but sites have also been chosen to minimize sediment cover where possible. Hole conditions in the igneous section depend on the type and consolidation of the igneous rocks. It is common to encounter fractured, friable zones while drilling lava flow sections, usually between flows. Occasionally rock pieces from the borehole wall cave into the hole after being knocked loose by the drill string. Loose rocks above the drill bit can cause the drill string to bind and may require clearing the hole. On rare occasions, such debris causes so much difficulty that the hole must be abandoned. Depending on time estimates and the importance of the site for archiving the overall objectives of this expedition, a new "B" hole could be drilled. To save valuable time, coring of the new "B" hole would not start before reaching the maximum penetration depth of the abandoned "A" hole.

Weather

Another potential issue that may shorten operations time is weather. Expedition 324 will take place in September and October, which are months in the middle of western Pacific typhoon season. Although many typhoons track to the south of Shatsky Rise on their way westward, they may turn around east of Japan and head to the east, thus threatening northern Shatsky Rise, even though it is at a northerly latitude. A drillship with thousands of meters of drill pipe hanging from the derrick is highly vulnerable to being overtaken and damaged by a cyclone, so the captain will be conservative and stay well away from projected storm paths. ODP Leg 191, which occurred in the same months (September–October 2000) lost 4.3 days while waiting out a typhoon. Leg 32 lost 2.1 days in similar fashion, and operations at Site 810 during Leg 132 were terminated early because of an approaching storm. The implication is that Expedition 324 could lose several operation days because of nearby typhoons. If a hole must be abandoned because of an approaching typhoon, we might deploy a FFF if return to the site and reentry is deemed worthwhile.

Timing

If significant time is consumed by responding to poor hole conditions, slow penetration rate, or weather-related delays, a decision would have to be made to drop a primary site from the schedule. We consider proposed Sites SRSH-3B and SRSH-8 (and their respective alternates) located on the summit and southern flank of Tamu Massif (and supposed to reflect the early stages of Shatsky Rise volcanism/possible plume head arrival) as our highest priority sites. Proposed Sites SRNH-2 and SRCH-5 on the northern and central massifs reflect the later stages of Shatsky Rise activity and are therefore of intermediate priority. Proposed Site SRSH-6 at the northern flank of Tamu Massif has the least priority.

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