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doi:10.2204/iodp.proc.340.104.2013

Operations

Transit to Site U1394

After a 5.3 nmi transit from Site U1393 in dynamic positioning (DP) mode, the vessel arrived at Site U1394. The vessel stabilized over Site U1394 at 1230 h on 8 March 2012. All times reported in this volume are given in ship local time, which was Universal Time Coordinated (UTC) – 4 h. The position reference was a combination of GPS signals and a single acoustic beacon. The positioning beacon was deployed at 1750 h on 8 March. It was recovered at 2315 h on 12 March at the conclusion of operations at Site U1394.

Site U1394

Two holes were cored at Site U1394 (Table T1). The original plan called for two holes drilled to ~244 meters below seafloor (mbsf). Because drilling conditions were challenging, coring took longer than anticipated, and because the section below ~180 mbsf was deemed to be less scientifically interesting, the second hole was shortened to ~180 mbsf. Hole U1394B was successfully logged with both the Formation MicroScanner (FMS)-sonic and triple combination (triple combo) logging strings, but an attempt to perform a vertical seismic profile (VSP) experiment was canceled when all efforts to deploy the Versatile Seismic Imager (VSI) tool string through the bottom-hole assembly (BHA) failed. After trying unsuccessfully to lower the tools into the formation, 48 cores were recovered at this site. The extended core barrel (XCB) was deployed 28 times, and the advanced piston corer (APC) was deployed 20 times. The interval cored with the XCB was 265.8 m with a recovery of only 36.93 m of core (14%). The interval cored with the APC was 160.10 m with a recovery of 161.59 m of core (101%). Overall recovery for Site U1394 was 47%.

Hole U1394A

The vessel arrived at Site U1394 and was in position at 1230 h on 8 March 2012. After an uneventful pipe trip, the vibration-isolated television (VIT) frame was installed and run to bottom for a required camera survey. Because a subsea communications cable had been run in the general area of operations, a camera survey was performed and recorded to make certain that our operations would not impact the cable. At 1630 h the bottom survey began at the preliminary site coordinates. A 40 m × 40 m survey was conducted without signs of a subsea cable. The seafloor was tagged twice during the survey to establish the depth from the drill floor to the seafloor. Tagged depth at both locations was 1126.6 meters below rig floor (mbrf). After the survey was completed, the VIT frame was removed, the top drive was picked up, and the bit was spaced out to spud Hole U1394A. The hole was spudded at 1945 h on 8 March. The seafloor depth was calculated from the length of the first core: 1126.3 mbrf (1114.9 mbsl). APC refusal in Hole U1394A came on the fourth piston core at 23.9 mbsf. The XCB was then deployed, and coring continued through Core 340-U1394A-27X without problems but with generally poor recovery. Four piston cores were taken over a 23.9 m interval with a total recovery of 24.17 m. Twenty-three XCB cores were cut over a 220.6 m interval with a recovery of 33.20 m. Overall core recovery for Hole U1394A was 57.37 m for the 244.50 m interval (24%).

Just after midnight on 10 March, while retrieving Core 28X, the wireline overshot detached from the XCB barrel. The winch operator noted the immediate weight loss on the wireline weight indicator and informed the driller of the situation. The sinker bar assembly was pulled to the surface, the drill string connection was opened, and the wireline sinker bar assembly was inspected to determine where the overshot assembly parted. Upon investigation, we determined that the male thread on the overshot core unscrewed from the lower crossover on the sinker bar assembly. This connection is coated with Bakerlok and utilizes a split pin penetrating through the crossover adaptor sub female, preventing the upper mandrel on the overshot core from backing off.

A male two-lug quick release attached to a rotary core barrel (RCB) core catcher sub loaded with standard RCB hard formation catchers was deployed on the wireline in an attempt to catch the upper threaded mandrel on the overshot core assembly. The first deployment was unable to catch the overshot core mandrel, so a second attempt was made. When the mud pumps were engaged after tightening the pipe connection, the drill string was packed off and then bled off. Shortly thereafter drill string rotation was lost, and the Toolpusher and Driller phoned the Offshore Installation Manager (OIM) to assist with freeing the stuck pipe. Attempts were made to regain rotation and circulation for ~3.5 h, and the decision was made to call out the Schlumberger Wireline Engineer to begin preparations to sever the drill string just below the upper connection on the tapered drill collar (TDC).

While the Schlumberger Wireline Engineer made the necessary checks of the severing tool case and casing-collar locator (CCL) tool, a Bowen wireline fishing overshot was deployed twice in an attempt to grab the overshot outer body. These attempts failed, and the fishing overshot was laid out. The severing tool string less the detonator and explosive housing was laid out on the rig floor in preparation for severing operations. The 30 ft drill knobby was laid out from the drill string to lower the block height for installing the severing tool string. Items that required de-energizing in preparation for severing operations included the ship’s radars, radio room radio frequency transmitters, and Wi-Fi circuits.

After securing all of the high-energy radio frequency sources, the explosive charge was assembled in the Core Tech shop, brought to the drill floor, and installed on the Schlumberger electric logging line. The explosive charge assembly and CCL tool were installed into the top of the drill string and down through the traveling blocks and TDS-3. After deploying the severing assembly ~100 m below the drill floor inside the pipe, ground tabs were clamped to the drill string and piperacker stabber assembly and ground straps were attached in preparation for severing the pipe.

The severing tool string was lowered via the electric logging line to the top of the BHA, the severing point was located and verified with the CCL, and the drill sting was severed at 1420 h on 10 March at ~1240 mbrf, just below the upper connection of the TDC. All BHA components below the 5½ inch transition pipe were left in the hole along with the XCB core barrel and Core 28X.

Schlumberger severing equipment was rigged down, and the wireline was pulled back to the surface. The drill string was then pulled back with the top drive still installed to 1201 mbrf, and the 20 ft knobby and top drive were set back. The remainder of the drill string was tripped to the surface, and the severed end of the TDC cleared the rotary table at 1845 h on 10 March, officially ending Hole U1394A.

The flared end of the tapered collar was torched off, and the remains of the TDC were removed from the 5½ inch transition drill pipe.

Hole U1394B

A new bit and BHA were picked up, drifted, measured, and run into the hole for Hole U1394B. The trip to bottom was uneventful. The vessel was offset 20 m north from Hole U1394A and spudded at 0255 h on 11 March 2012. Seafloor depth was calculated from the mudline recovery: 1125.6 mbrf (1114.2 mbsl). For Core 340-U1394B-2H, the APC recovered only 6.4 m of core, and the XCB was deployed for the next five cores. After Core 7X, the APC was again picked up and used to complete the hole to 181.4 mbsf with Core 21H. The entire section was difficult to piston core with frequent partial strokes, and overpull was noted on all cores but one after Core 8H. Seven of the cores had to be drilled over to release them from the formation. Sixteen piston cores were taken over a 136.2 m interval with a total recovery of 137.42 m of core. Five XCB cores were cut over a 45.2 m interval with a recovery of 3.73 m of core. Overall core recovery for Hole U1394B was 141.15 m for the 181.4 m interval (78%). At the conclusion of coring, Hole U1394B was conditioned with a 30 bbl high-viscosity mud sweep and displaced with 71 bbl of 10.5 ppg mud for logging. The drill string was then pulled back, the top drive was set back, the bit was set at 82.69 mbsf, and the pipe was hung from the blocks. Schlumberger was then rigged up for logging, and the triple combo was deployed without the nuclear source. Two successful passes were made to 179.4 mbsf, and the triple combo string was rigged down. After a meeting with the logging staff and science party management, the VSI tool was rigged up and run down the drill string. Simultaneously the protective species watch began. After observing all seismic operating procedures, the seismic guns were ramped up in preparation for the VSP experiment. Unfortunately, the VSI tools were unable to pass through the BHA, and after 3 h of trying various means of getting the tools to pass the BHA, the VSI tool string was brought back to the surface and the VSP experiment was cancelled. The VSI tool string was rigged down, and the FMS-sonic tool string was picked up. A small delay was incurred when the tool string failed to test before deployment. After successfully troubleshooting the electrical issue, the tool was run to 180.4 mbsf and two passes were made over the length of the open hole. The tools were then pulled back to the surface and rigged down. The knobbies were laid out, and the drill string was pulled from the hole. The bit cleared the rotary table at 0140 h, and the drill floor was secured at 0145 h, ending Site U1394 and Hole U1394B. The vessel then proceeded underway to Site U1395.

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