Operations summary

During Leg 146, two attempts were made to establish CORK hydrologic observatories, one at Site 889 and the other in a similar setting at ODP Site 892 off central Oregon (Westbrook, Carson, Musgrave, et al., 1994; Davis et al., 1995). These were equipped with sensors to monitor temperatures at multiple formation levels and pressure at the level of perforations in a liner extending below casing. The installation in Hole 892B was successful and operational for roughly 2 y before the instrumentation was removed to facilitate fluid sampling. Owing to unstable formation conditions and deteriorating weather, the installation in Hole 889C did not succeed. Instability of the formation caused sediment to be squeezed into the casing through the perforations, the open end of the liner, and/or the annulus between the liner and the casing. This prevented the thermistor cable from reaching its intended depth, which in turn precluded a pressure-tight seal of the pressure logging system at the top of the hole. The total hole depth was 385 mbsf; the bottom of the liner was at 323 mbsf. After two aborted attempts to deploy the thermistor cable, a sinker-bar run indicated fill had reached 253 mbsf. The failed third attempt with a cable shortened to 240 m suggested that sediment had progressively intruded the casing up to this depth. The CORK was never refurbished.

Expedition 328 began at 0836 h on 5 September 2010 when the first line was passed ashore at Ogden Point Pier A in Victoria, British Columbia (Canada). After completing port call public relations, logistical, and maintenance activities, we departed Victoria for Site U1364 (CAS-01CORK) when the last line was released at 1606 h on 9 September. After maneuvering away from the pier, the vessel began the 145 nmi transit to the site at 1700 h. The ship arrived on location (48°41.9962′N, 126°52.3291′W) at 0600 h on 10 September, concluding a transit that averaged 11.2 kt.

Our first objective was to perform a jet-in test to verify the water depth and establish the conductor casing length to be deployed with the reentry cone, followed by jetting the casing and reentry cone (Fig. F19). The vibration-isolated television (VIT) frame was deployed to observe the bit contacting the seafloor at 1329.0 meters below rig floor (mbrf), and the jet-in test was completed to 55 mbsf. Based on this result, the conductor casing was assembled consisting of three joints of 16 inch casing and a casing shoe joint for a total length of 53 m, which was latched into a standard reentry cone. Once the drilling BHA equipped with a 11 inch advanced piston corer (APC)/extended core barrel (XCB) bit was latched into the casing hanger, the reentry cone was deployed, and the jetting of the reentry cone and casing was initiated at 0600 h on 12 September while being monitored via the VIT. The 53 m assembly was jetted in and landed by 1435 h, and the drill string was tripped back to the rig floor.

The next operation was to drill a 14¾ inch hole to accommodate the 10¾ inch casing string (Fig. F19). A drilling BHA with a 14¾ drilling bit was made up and deployed, reentering Hole U1364A at 0905 h on 13 September. The VIT was recovered, and drilling advanced without incident to a final depth of 336.0 mbsf. Penetration rate and weight on bit were fairly constant throughout the history of drilling below the ~100 m thick unit of slope basin sediments, although a drop in weight on bit and a significant increase in penetration rate were observed over a ~20 m interval below the limit of gas hydrate stability (Fig. F20). High-viscosity mud sweeps (20 bbl each) were circulated at 164, 193, 222, 278, 307, and 336.0 mbsf. A large high-viscosity 50 bbl flush was pumped at the conclusion of drilling. The hole was then displaced with 250 bbl of 10.5 ppg barite-loaded mud. The drill string was recovered with the bit clearing the rotary table at 1435 h on 14 September.

The next step was to make up the ACORK assembly. The construction of the ACORK, which includes making connections to the hardware, strapping and taping the umbilical to the casing, and making the plumbing connections to the screens and ACORK, began at 1430 h on 14 September and continued to 1000 h on 15 September. The ACORK assembly included a custom ACORK head, a 10¾ inch casing hanger, 20 joints of 10¾ inch casing, two pup joints of 10¾ inch casing, a TAM Freecap 10 inch × 14 inch dual-element swellable packer, and four screen joints of 10¾ inch casing and one shoe joint. The length of the entire assembly was 329.1 m. Because 6.0 m of ACORK head extended above the hang-off point in the reentry cone, the effective depth of the assembly into the hole was 323.1 m. This left a 12.9 m rat hole between the bottom of the casing shoe and the bottom of the hole at 336.0 mbsf. The next phase of rigging up was to make up a reaming BHA, which included a 9⅞ inch tricone bit, a 9.5 inch HOC DTU950 underreamer, a 9.5 inch Ultra XL mud motor, and the cam-actuated drill-ahead (CADA) casing running tool. The total length of this BHA was 418.9 m. As the BHA was being assembled, it was lowered incrementally into the ACORK suspended in the moonpool until the CADA running tool landed into the ACORK at 1345 h on 15 September. The ACORK and reaming assembly were then lowered into the water with the ACORK head ~10 m beneath the surface for 5 min to purge any entrapped air. The four purge valves were then manually turned to the closed position, the ACORK and reaming BHA were deployed, and Hole U1364A was entered for the second time at 1930 h. The ACORK was gradually lowered into the open hole until it was successfully landed in the reentry cone at 0025 h on 16 September. The hole appeared to have remained open, possibly because of the presence of the 10.5 ppg mud that was pumped into the hole at the conclusion of the drilling process, so no circulation or underreaming was required. It is anticipated that the barite (specific gravity = 4.2; average grain size ~ 44 µm) contained in the mud probably settled out to fill the lower few tens of meters of the hole and annulus around the lower screen within days. The mud remaining in the remainder of the annulus would have had a density little different than seawater, and thus not impede hole collapse.

The ROV platform was tethered to the VIT frame and deployed at 0400 h on 16 September. The platform was successfully deployed when the mechanical release activated upon contacting the CADA top hat at 0515 h. The VIT frame was then recovered.

A Hammer Drilling System (HDS) cone, adapted to fit over the 16 inch casing hanger at the top of the ACORK to facilitate reentry, was made up and free-fall deployed at 0820 h on 16 September. However, the cone was dislodged while retrieving the drill string and fell to the seafloor. The drilling string was tripped back to the rig floor.

The final operation was the deployment of a hydraulic packer to seal the bottom of the 10¾ inch casing. The packer assembly was deployed, and Hole U1364A was reentered for the third time at 2320 h on 16 September. Although the 23¾ inch diameter throat of the ACORK presented a smaller target than the HDS cone, the reentry was made in <1 h. The packer was positioned at 319 mbsf or 4 m above the casing shoe with a circulating head in place. Prior to activating the packer, the inside of the casing was displaced with one volume of seawater while maintaining pressure below 200 psi to ensure that the packer would not inflate prematurely. At 0230 h, the activating steel ball was dropped into the pipe and seated inside the bridge plug. The pressure was gradually increased until the packer set at ~1300–1400 psi. The packer was released at 0335 h when ~2700 psi was applied. The driller pulled back in the hole, circulated seawater while waiting for the cement to be mixed, and then pumped ~4 bbl of 16 ppg cement, covering the packer with ~14 m of cement. The inside of the casing was then flushed with three volumes of seawater. At 0600 h, the driller began to recover the drill string, which was back onboard at 1400 h, ending operations at Site U1364.

The ship was secured for transit, the thrusters raised, and the ship departed for port. The JOIDES Resolution arrived at Esquimalt Graving Dock in Victoria at 0804 h on 18 September 2010, concluding Expedition 328.