Previous   |   Next

doi:10.2204/iodp.sp.318.2008

Operations plan

The overall operations plan and time estimates are summarized in Table T1. After departing Wellington (New Zealand), we will transit for ~8 days to the Wilkes Land drilling area and prepare for drilling operations.

Our plan is to conduct operations at the near-shore shelf (proposed Sites WLSHE-09B and WLSHE-08A) and Adélie Drift (proposed Site ADEL-01B) sites followed by the deeper rise sites (proposed Sites WLRIS-02A and WLRIS-04A). However, the sequence of operations will depend on ice, weather, and formation conditions.

The operations plan and time estimates are based on formations and depths inferred from seismic and regional geological interpretations without benefit of prior drilling in this area. We have, however, based our plans on information from previous DSDP and ODP sites located on other portions of the Antarctic margin.

Shelf sites

Proposed Sites WLSHE-09B and WLSHE-08A

Prior to starting drilling operations at proposed Site WLSHE-09B, we will conduct a short seismic reflection survey to provide a cross-line and confirm the regional geometry of the sequences to be penetrated.

The first hole at both shelf sites (proposed Sites WLSHE-09B and WLSHE-08A) will be cored with the advanced piston corer (APC) to refusal. Given the potential for coarse glacial deposits, this may have very limited penetration.

The second hole at these sites will be drilled without coring to depth of the prior hole. Rotary core barrel (RCB) coring will extend from this depth to 200 (proposed Site WLSHE-09B) and 220 (proposed Site WLSHE-08A) meters below seafloor (mbsf).

After coring is completed, the hole will be conditioned and loaded with mud and the bit released in the hole. We will run a series of wireline logs including a check shot vertical seismic profile (VSP) in open hole. Once operations at the two shelf sites re finished, we will transit ~150 nmi to begin operations at proposed Site ADEL-01B.

Proposed Site ADEL-01B

Three holes will be cored with the APC to total depth at proposed Site ADEL-01B. We will attempt to recover a short core of the uppermost diamict with the extended core barrel (XCB) system at one of the three holes.

After coring is completed in the last hole, we will conduct two wireline logging runs. Following operations, we will transit ~145 nmi to begin operations at proposed Site WLRIS-02A.

Rise sites

Proposed Sites WLRIS-02A and WLRIS-04A

The first hole at each of the two rise sites (proposed Sites WLRIS-02A and WLRIS-04A) will be APC/XCB cored to ~500 mbsf. RCB coring will extend from this depth to 1050 (proposed Site WLRIS-02A) and 1000 (proposed Site WLRIS-04A) mbsf.

After coring is completed, the hole will be conditioned and loaded with mud and the bit released in the hole. We will run a series of wireline logs including a check shot VSP in open hole. After the operations are finished at proposed Site WLRIS-04A, the ship will start the ~8 day transit back to Wellington.

In addition to the logistical hurdles presented by operating in such a remote area, there are environmental threats unique to the region. Floating ice can be a hazard to the vessel and to coring operations. Free-fall funnels can be deployed at designated sites as a means to "bookmark" depth should a hole have to be temporarily abandoned because of the proximity of floating ice.

Although the expedition has been scheduled to take place during the optimum weather window, erratic and katabatic winds can disrupt operations and force land-locked ice over the site. In the Antarctic region, there are prominent cold katabatic winds that blow for most of the year. Our current plan includes participation of an onboard ice/weather specialist to assist in managing weather and ice threats.

Ice-rafted debris can negatively impact core recovery and rate of penetration and can destroy APC shoes and XCB cutting heads. Unconsolidated sediment can create unstable hole conditions and result in lost time because of stuck drill strings and/or core barrels. We anticipate that this may be especially problematic for the shelf sites. We will sail with sufficient bulk material to optimize the management of hole problems.

Top of page   |   Previous   |   Next