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doi:10.2204/iodp.proc.336.109.2012

Future plans

At the time of this writing, two future visits are scheduled at North Pond, in the spring of 2012 and fall of 2013, using the ROV Jason-II and a German research vessel (Maria S. Merian).

ROV dives

ROV dives are planned for North Pond in 2012 in order to service the wellheads in Holes U1382A and U1383C and to conduct operations in Holes 395A and U1383B. The following operations are planned for North Pond:

1. Pump fluids from each of the borehole observatory hydrological intervals in Holes U1382A (1 horizon) and U1383C (3 horizons).
2. Install two seafloor wellhead sleds (Cowen et al., 2012) in Holes U1382A and U1383C to sample one horizon each.
3. Inspect Hole 395A and possibly center or remove the ROV/​submersible platform.
4. Install a simplified “CORK-lite” CORK plug system (described in more detail below) in Hole U1383B with a downhole OsmoSampler package and pressure recorder.
5. Collect rocks and sediments for geochemical and microbiological analyses.
6. Make heat flow measurements at the perimeter of the sediment pond.
7. Map rock outcrops that flank the pond using multibeam seismic surveys.
8. Exchange wellhead OsmoSampler fluid and microbiological experiments.

CORK-lite

A major objective of the 2012 CORK servicing cruise will be the trial installation of a simplified CORK plug system into the abandoned cased basement borehole in Hole U1383B (Fig. F25). In brief, this simplified system termed CORK-lite is designed to connect a simplified wellhead sampling system and seafloor seal to the observatory reentry cone and casing existing in Hole U1383B, enabling this borehole to become a shallow basement observatory at Site U1383. If successful, the CORK-lite will enable monitoring of pressure in shallow basement and also the exchangeable deployment of a simplified downhole instrument string for sampling fluids and microbial material from upper basement. Furthermore, the CORK-lite may also be amenable to future adaptation of other legacy boreholes equipped with reentry cone and casing systems to become subseafloor observatories.

The CORK-lite consists of a 12 inch (ID) pipe with a gravity seal that will contact the 16 inch casing hanger. The 12 inch pipe extends ~2 m above the ROV platform and contains two ¼ inch OD stainless steel valves. These valves are intended to be connected to a pressure logger. The top of the CORK-lite has a removable cap with a rubber seal that is locked in place with a turnable latching mechanism. Also on the cap is a valve to vent borehole pressure to remove the cap should the borehole be under or over pressured. Inside the bottom of the cap is an eyebolt for attaching a shackle connected to Spectra line, a series of OsmoSampler packages, a lowered intake, and sinker bar.

For the CORK-lite deployment in Hole U1383B, a series of operations will be undertaken to install observatory components. Approximately 15 m of open hole extends below steel 10¾ inch casing in Hole U1383B, which is equipped with a reentry cone and ROV landing platform. The ROV platform may be slightly askew, based on VIT imaging during Expedition 336. Assuming that the landing platform skew can be corrected, the CORK-lite will be deployed from the support ship and maneuvered into place with the ROV Jason-II. Following installation of the CORK-lite, pressure loggers will be connected to the sampling valves, and an OsmoSampler instrument string will be latched into the cap. The OsmoSamplers will be designed to hang within open basement hole below casing, to be recovered during a subsequent ROV servicing cruise.

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