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doi:10.2204/iodp.sp.340T.2011

Risks and contingency strategy

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

1. Adverse hole conditions at Site U1309 (e.g., encountering collapsed intervals where basement rock has blocked the hole or extremely high borehole temperatures);

2. Weather conditions that limit the ability to conduct logging operations; and

3. Time delays arising from equipment breakdowns, measures taken to respond to hole conditions, or weather conditions.

Hole conditions

Narrow bridges indicated by the caliper log or high borehole temperatures (>175°C) indicated by the temperature log on the first logging run may be addressed by minor remediation. Minor remediation activities include rotation of the logging bit to clear bridges and circulation of seawater to cool the hole, both of which require lowering the pipe into the open hole to be effective. Prohibitively poor hole conditions would require a bit change to the rotary core barrel (RCB) system to remediate and would lead to a significant time penalty that would severely reduce the planned logging program. The advantages and disadvantages of this remediation strategy will have to be evaluated at sea should the need arise.

Weather conditions

Expedition 305 to Site U1309 experienced favorable weather conditions up until the last day of operations. Expedition 340T is scheduled in the same weather window as Expedition 305, so we expect weather-related risks to be minimal.

Timing

Any time gained during the transit from Lisbon to Site U1309 will be used to augment the 3 days allotted to Expedition 340T operations. Once on site, time spent on hole remediation, marine mammal observation activities, or weather-related delays will be considered part of the time allotted to operations and may result in reducing the logging program. Expedition 340T operations should be concluded in order to allow a timely departure for Antigua by midnight on 31 January 2012.

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