Operations plan/drilling strategy

The coring and drilling program for Expedition 359 targets seven primary and two alternate sites located in waters of the Republic of the Maldives. The planned sequence of drill sites, coring/downhole measurements, and time estimates is provided in Table T2. The final operations plan and number of sites to be cored is contingent upon changes to the R/V JOIDES Resolution operations schedule, operational risks, and the outcome of a request for permission to occupy these sites. The current planned operations schedule also includes two half-day moorings for required ship clearance and immigration formalities, one at the arrival to and one at the exit from the Maldives.

For operational efficiency, the proposed sites will be occupied in the following sequence: MAL-07A, MAL-06B, MAL-05A, MAL-01A, MAL-02A, MAL-03A, and MAL-09A. The coring strategy will consist of triple advanced piston corer (APC) coring using nonmagnetic core barrels to ~200 mbsf or APC refusal at proposed Sites MAL-07A, MAL-06B, and MAL-03A. Coring using the extended core barrel (XCB) system will be used to advance the holes to total depths at proposed Sites MAL-07A (642 mbsf), MAL-06B (604 mbsf), MAL-03A (435 mbsf), MAL-02A (325 mbsf), and MAL-09A (554 mbsf). Coring with the rotary core barrel (RCB) system will be used to advance to total depth at proposed Sites MAL-05A (420 mbsf), MAL-01A (1060 mbsf), and MAL-02A (1010 mbsf). Multiple holes at selected sites will allow us to build a composite section at each site.

Coring operations at proposed Sites MAL-08A and MAL-09A and the extended penetration depth at proposed Site MAL-02A are pending EPSP approval.

All APC sections will be cored using nonmagnetic core barrels. Only cores in Hole A at each site will be oriented. The half-length (4.7 m) APC coring system will be employed to maximize APC penetration where desirable. For planning purposes, the APC refusal depth for most sites is estimated at 200 mbsf, although we anticipate that this may be exceeded at some of the more carbonate mud–rich sites, especially when using the half-length APC system.

All sites will be wireline logged using standard logging tool strings: triple combination (triple combo) and Formation MicroScanner (FMS)-sonic. Three proposed sites (MAL-07A, MAL-01A, and MAL-09A) also will be logged with the Versatile Seismic Imager (VSI).