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doi:10.2204/iodp.sp.342.2011

Risks and contingencies

Three principal factors could affect implementation of the drilling plan:

1. Adverse hole conditions at the principal sites because of dropstones and chert and adverse formation conditions (e.g., if we were to encounter sediments that do not allow generation of high-quality composite sections suited to modern paleoceanographic analysis).

2. Weather conditions that could limit the ability to drill, particularly hurricanes early in the hurricane season.

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

Hole conditions

Poor hole conditions at all sites will be dealt with in the first instance by using frequent high-viscosity mud sweeps and or heavy mud to condition the holes. The only possible remedial action if hole conditions prove to be insurmountable is to plug and abandon the hole and move to an alternate hole/site. In the event that we encounter formations that do not allow us to build high-quality composite sections suited to modern paleoceanographic analysis, a primary site may be shortened or dropped from the schedule. Such a decision will only be made following consultation with the science party.

Weather conditions

Hurricane season at the operation area is between August and November; thus, Expedition 342 is scheduled (mid-June to mid-August) to be largely outside this window. However, we had to abandon the site survey for 3 days to run south into the North Atlantic Gyre due to Hurricane Alex in mid-August 2004.

Timing

If significant time is spent responding to poor hole conditions, slower-than-expected penetration rates, or weather-related delays, a primary site may be shortened or dropped from the schedule. Such a decision will only be made following consultation with the science party.

Alternate sites

Alternate sites may be cored and logged if poor hole conditions or other operational difficulties are encountered at the respective primary sites and if better conditions are expected at the alternate sites. Seismic profiles of all proposed alternate sites (as well as of all primary sites discussed above) are included in “Site summaries.” The operations plans for the alternate sites can be found in Tables T1 and T3.

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