Risks and contingencies strategy

We hope that previous drilling experience at this site will allow risks to be anticipated and planned for. Difficulties arising from hole instability are considered unlikely, but if encountered they can be overcome with aggressive use of the underreamer. Difficulties were encountered with reaching target depths with ACORK installations in ODP Holes 808I and 1173B, but they appear to have been due in large part to failure of the undereamer bit used. Similar problems for Expedition 328 are not anticipated; a more robust bit will be used, and the casing completion depth is much less (300 mbsf at Site 889 versus 750 and 930 mbsf at Sites 808 and 1173, respectively). Integrity of the internal seal in the 10¾ inch casing is crucial for the success of the pressure monitoring experiment, and placement of the seal at the bottom of the casing string is of utmost importance for later experiments that require instruments to be installed deep inside the sealed casing. Correct choice of the hardware to achieve a tight seal at depth is critical.