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doi:10.14379/iodp.pr.350.2014

Operations

Site U1436

The transit from Keelung, Taiwan, started on 4 April 2014 and ended at 1142 h on 8 April, marking the beginning of operations at Site U1436. All times reported here are ship local time, which was UTC + 9. See Table T5 for coring summary.

Hole U1436A (32°23.883′N, 140°21.928′E; 1775 m water depth)

An APC/XCB BHA was built and deployed to a depth of 1781 meters below rig floor (mbrf). The subsea camera was lowered to the bottom and a seafloor survey was conducted to determine if any subsea communications cables could be found in the drilling area. None were found. After visually confirming that the drill pipe tagged the seafloor, the camera was retrieved. Coring in Hole U1436A commenced at 0705 h on 9 April. Cores 350-U1436A-1H through 9H (0–59.7 m) cored with the APC system yielded 59.4 m of core (99% recovery). Cores 10F through 12F (59.7–65.0 m) drilled with the HLAPC system retrieved a total of 5.22 m of core (98% recovery). The rate of penetration with the HLAPC decreased exponentially, and we switched to the XCB system. Cores 13X through 21X (65.0–150.0 m; total depth) recovered only 7.1 m of core (8% recovery). The drill string was recovered and the bit cleared the rotary table at 1245 h, ending operations in Hole U1436A. Hole U1436A was completed with a total of 21 cores for a total of 150 m cored and 71.6 m recovered (average recovery = 48%). The rig was secured for transit to Site U1437 (proposed Site IBM-3C).

Return to Site U1436

After operations were prematurely terminated at Site U1437, the science party decided to use the remaining time to attempt to recover undisturbed sections containing conspicuous black ash layers found 7 weeks earlier at ~50 mbsf in Hole U1436A that was severely disturbed by coring. This would better constrain the thickness to assist in determining the explosivity of the eruption that generated them. The short transit to Site U1436 took from 0930–1700 h on 25 May 2014.

Hole U1436B (32°23.896′N, 140°21.929′E; 1774 m water depth

An APC/XCB BHA was made up and deployed to the seafloor. Hole U1436B was positioned 20 m north of Hole U1436A, and coring was initiated at 0015 h on 25 May. Cores 350-U1436B-1H through 14H (0–61.8 mbsf) obtained 61.79 m (100% recovery). After the target depth of ~62 mbsf was reached, the bit was raised and cleared the seafloor at 1425 h.

Hole U1436C (32°23.873′N, 140°21.930′E; 1774.5 m water depth)

The ship moved 20 m south of Hole U1436A, where Hole U1436C was initiated at 1545 h on 25 May. Cores 350-U1436C-1H through 18F (0–70.4 mbsf) obtained 70.38 m (100% recovery). The sequence recovered in Hole U1436C had less coring disturbance than sequences obtained in Holes U1436A and U1436B, particularly over the target interval near 50 mbsf, presumably owing to the more extensive use of the HLAPC. Operations in Hole U1436C ended when the bit cleared the seafloor at 1255 h on 27 May.

Hole U1436D (32°23.885′N, 140°21.942′E; 1774.5 m water depth)

We decided to make a last attempt to recover the black mafic ash layer undisturbed in the shortest amount of time possible. The ship moved 20 m east of Hole U1436A, where Hole U1436D was initiated at 1355 h on 27 May, using a center bit to wash down to 40 mbsf. Cores 350-U1436D-2F through 9F (40–62.0 mbsf) obtained 22.07 m (100% recovery). Although several cores in Hole U1436D were plagued by a large proportion of impenetrable tephra that fell into the hole from further up in the formation, presumably due to washing down to 40 mbsf, we did eventually, after a discussion of the circumstances with the Tool Pusher on shift, recover excellent cores containing the targeted tephra layers. The last core of Expedition 350, Core 9F, arrived on deck at 0210 h on 28 May.

The ship remained on station at Site U1436 until departure for Yokohama, Japan, at 0930 h on 29 May. The transit took 24 h to the pilot station, and the ship was dockside at 1100 h on 30 May, ending Expedition 350.

Site U1437

Hole U1437A (31°47.390′N, 139°01.580′E; 2115.8 m water depth)

The 77 nm transit from Site U1436 to Site U1437 was completed in 7.5 h. All times reported here are ship local time, which was UTC + 9. A beacon was dropped at 2304 h on 10 April 2014, marking the beginning of operations at Hole U1437A.

An APC/XCB BHA was made up and deployed to a depth of 2110 mbrf. The subsea camera system was lowered to depth, and a seafloor survey was conducted to confirm that no subsea cables were present at the site. The seafloor was tagged at 2127 mbrf with visual confirmation through the camera. After the camera was recovered, Hole U1437A was initiated at 0915 h on 11 April for a jet-in test to ~25 mbsf. Upon completion of the jet-in test, the ship was repositioned 10 m north of Hole U1436A to begin coring in Hole U1437B.

Hole U1437B (31°47.391′N, 139°01.579′E; 2116.1 m water depth)

Coring in Hole U1437B commenced at 1035 h on 11 April. Cores 350-U1437B-1H through 10H (0–89.2 mbsf), drilled with the full-length APC system, recovered 89.2 m of core (100% recovery). Pulling the core barrels from the formation became increasingly harder at the bottom of that interval, and we therefore switched to the HLAPC system. Cores 11F through 24F (89.2–145.7 mbsf) recovered 56.5 m of core (100% recovery). When the rate of penetration decreased to a critical point, we changed to the XCB system. Coring in Hole U1437B was completed with Cores 25X through 55X (145.7–439.1 mbsf), recovering 96.9 m of core for the 293.4 m interval drilled (33% recovery). The last core from Hole U1437B arrived on deck at 0000 h on 14 April. We cored 439.1 m and recovered 242.6 m in Hole U1437B (55% recovery). The drill string was recovered and the bit cleared the rig floor at 0645 h on 14 April, ending the hole.

Hole U1437C (31°47.381′N, 139°01.579′E; 2116.0 m water depth)

A RCB BHA was made up with three stands of drill collars, and a core barrel with a center bit was installed. Our plan was to drill without coring to 425 mbsf, several meters above the total depth cored in Hole U1437B, and then start RCB coring. The ship moved 20 m south of Hole U1437B, and the bit was lowered to the seafloor. Drilling in Hole U1437C began at 1530 h on 14 April. At 232 mbsf, the center bit was pulled for inspection and then deployed again. Circulation and rotation was lost at 309.7 mbsf. The stuck pipe was worked for several hours without success. The ship was offset 140 m to allow the rig crew to pull the center bit and run the rotary shifting tool to drop the bit. A single joint of drill pipe was laid out at this time as well. With the bit dropped, the ship moved back to the Hole U1437C coordinates and the pipe was worked for another 2 h. The drill pipe was finally worked free at 0910 h on 15 April. The bit was raised to 183.7 mbsf using the top drive. After the top drive was set back, the drill string was retrieved, clearing the seafloor at 1055 h and the rig floor at 1305 h on 15 April, and ending operations in Hole U1437C.

Hole U1437D (31°47.387′N, 139°01.573′E; 2116.0 m water depth)

A new mechanical bit release (MBR) and RCB bit were made up, and the drill string was run into the hole while the vessel was repositioned 10 m west of Hole U1437A.

Drilling without coring in Hole U1437D began at 2250 h on 15 April and extended from the seafloor to 427.2 mbsf. The center bit was retrieved and a RCB core barrel was deployed. The first core (350-U1437D-2R) arrived on deck at 2045 h on 16 April. RCB coring continued until 21 April with Cores 2R through 59R (427.2–980.4 m) recovering 434.56 m (79% recovery). At this time, the bit had been rotating for 51.5 h and required changing, so we decided to stop coring and collect wireline log data.

A free-fall funnel (FFF) was deployed, and the drill string was pulled out of the hole to drop the bit in preparation for logging. When we attempted to reenter Hole U1437D without the bit, the top connection of the MBR, which has razor sharp edges, was unable to slide into the FFF and the reentry was aborted. The drill string was retrieved, with the end of the pipe clearing the rotary table at 0430 h on 22 April. The MBR top connection was removed, and a logging bit was made up to the BHA. The drill string was then lowered and Hole U1437D was reentered at 1207 h on 22 April. The logging bit was set at 92.4 mbsf.

Three logging strings were deployed in Hole U1437D. The first tool string deployed consisted of the triple combo with the MSS. The triple combo/MSS tool string reached ~960 mbsf, indicating ~20 m of fill had accumulated at the bottom of the hole. The data recorded from this first run show that the hole was in excellent condition, with a diameter barely exceeding the bit size for most of the hole. The second tool string deployed (FMS-sonic) was able to record high-quality velocity data and electrical images to a maximum depth of 950 mbsf. The final logging run was a VSP that obtained data at 14 depths spaced every 50 m from the maximum depth of 875 mbsf. All logging operations were completed within 24 h and the equipment was rigged down by 1330 h on 23 April.

The subsea camera system was lowered to observe the drill string exiting the FFF; however, a fishing line was observed tangled on the drill pipe ~300 m below the ship, so the camera system was brought back up. The drill string was then pulled out of the hole, the drill string recovered, and the logging bit cleared the rig floor at the 2235 h on 23 April.

A new RCB bit was made up to the BHA and Hole U1437D was reentered at 0630 h on 24 April. The drill string was lowered without circulation or rotation to 950 mbsf. The hole was then washed to the bottom of the hole (980.4 mbsf) and coring resumed. Hole U1437D was deepened to 1104.6 mbsf by the morning of 26 April. Cores 350-U1437D-60R through 73R (980.4–1104.6 mbsf) recovered 69.29 m (56%). At that time, hole-cleaning time was exceeding coring time because of crushed rock in the borehole that was difficult to remove, requiring a large number of mud sweeps. Also, packing of mud around the bottom of the core barrel indicated a malfunction. The drill string was recovered and the bit cleared the rig floor at 2040 h on 26 April, ending Hole U1437D. The total cored interval in Hole U1437D was 677.4 m, with 503.8 m recovered (74%).

At this point, we decided to drill and case a new hole to the total depth of Hole U1437D and then core and log it as deep as time permitted. This decision was prompted by (1) the increasing risk with penetration depth of not being able to clean a hole, particularly a deep noncased hole, and (2) the fact that the ship was carrying ~1100 m of 11.75 inch casing, just enough to cover the interval cored to date, which made this the optimal time to install the casing.

Hole U1437E (31°47.390′N, 139°01.591′E; 2115.8 m water depth)

The ship moved ~20 m northeast to begin installation of casing in Hole U1437E. The reentry cone, equipped with 20.7 m of 20 inch casing, was run to the seafloor. The subsea camera system was deployed to observe the jetting in of the casing and landing of the reentry cone on the seafloor. Deployment was complete at 1905 h on 27 April when the bit cleared the reentry cone. The drill string was retrieved back on the rig floor at 0030 h on 28 April.

A drilling assembly consisting of an 18.5 inch tricone bit and an underreamer was made up to drill the hole for the 264 m long, 16 inch casing. The underreamer was set to enlarge the hole to 22 inches and tested to confirm that the arms opened at a mud pump rate of 25 strokes/min. The drill string was deployed to the seafloor, followed by deployment of the subsea camera to guide the reentry into Hole U1437E at 1105 h. After successful reentry, the camera system was retrieved and Hole U1437E was drilled to the target depth of 271.7 mbsf by 0400 h on 29 April. The hole was swept with 60 bbl of high-viscosity mud to remove drill cuttings. The drill string was then raised to 12.7 mbsf and lowered back down to total depth (271.7 mbsf) while circulating seawater to ensure the borehole was clear. No obstruction or fill at the bottom of the hole was detected. Another 60 bbl high-viscosity mud sweep was circulated. The drill string was pulled out of the hole with the bit clearing the seafloor at 0910 h and arriving at the rig floor at 1300 h on 29 April.

The 264 m long 16 inch casing was assembled in an 8 h effort. The casing running tool was installed, and the casing string was lowered to the seafloor by 0145 h on 30 April. The camera system was deployed to guide the reentry into Hole U1437E, which was completed at 0350 h. The casing was lowered into the hole, and the top of the casing was latched into the casing hanger in the reentry cone at 0600 h. The latch was verified with 10,000 lb of pull from the rig.

To ensure the casing would act as the circulation conduit during future coring in Hole U1437E, the bottom of the casing had to be cemented firmly to the formation. With the casing running tool forming a seal at the top of the 16 inch casing, 20 bbl of 14.5 lb/gal cement was mixed and pumped from the rig floor through the drill string and through the 60 m stinger extending from the casing running tool down into the hole. The cement emplacement was followed with 295.8 bbl of seawater, a volume calculated to displace the cement to the bottom of the casing such that half the cement volume would extend upward between the formation and the base of the casing and the other half would remain inside the bottom of the casing to be drilled out later. The cement was in place at 0720 h on 30 April. The casing running tool was released, and the drill string and standpipe manifold were flushed clean with seawater. The camera was retrieved, the top drive was disengaged, and the drill string was tripped to the surface, with the running tool clearing the rig floor at 1220 h on 30 April.

The next operation was to drill out the cement and then a 14.75 inch hole to 1104 mbsf (the total depth of Hole U1437D) for the 10.75 inch casing. After breaking down the running tool and the underreamer assembly, a BHA with a 14.75 inch tricone drill bit was installed and the drill string was tripped back to the seafloor. The camera was deployed to guide the reentry into Hole U1437E, which was completed at 2245 h on 30 April, and was then retrieved back to the rig floor. At 0030 h on 1 May, the top drive was picked up and the bit was lowered to the bottom of Hole U1437E. At 0330 h, the bit tagged the top of the cement plug at 264.7 mbsf, 1 m below the 16 inch casing shoe. Cement should have been contacted ~10 m above the shoe. This indicated that the cement had been displaced several meters too far down the 16 inch casing and that the casing likely had not been cemented to the formation as planned, thereby requiring a second cementing round trip.

The drill string was pulled back to 230.7 mbsf, the top drive was disengaged, and the drill string was tripped to the surface, clearing the seafloor at 0440 h and arriving at the rig floor at 1030 h on 1 May. The casing running tool and logging bit were made up once more, the drill string was lowered to the seafloor, and the subsea camera was deployed to guide reentry into Hole U1437E, which was completed at 1740 h on 1 May. After tripping into the hole to 55.7 mbsf using the top drive, weight was applied through the drill string to ensure the casing running tool sealed the top of the casing in preparation for cement delivery. When circulation was attempted by pumping seawater into the hole and around the bottom of the 16 inch casing, a pressure increase was observed, indicating that the bottom of the casing was actually sealed off, either by the first cementing job or by the formation sealing off around the casing since. The second cementing job was therefore aborted at 1830 h. The drill string was raised to 18.1 mbsf, the top drive disengaged, the camera system retrieved, and the drill string tripped to the surface, clearing the drill floor at 2350 h on 1 May.

The 14.75 inch tricone bit was installed again, lowered to the seafloor, and Hole U1437E was reentered for the seventh time at 0605 h on 2 May. The bit was lowered to 230.7 mbsf, the camera used to guide reentry was retrieved, and the top drive was engaged to wash the hole down to 266.7 mbsf, where the cement plug was encountered. The cement plug, which extended to 271.7 mbsf, was drilled out and the hole was flushed with high-viscosity mud. Hole U1437E was drilled (without coring) to the target depth of 1104 mbsf (the total depth of RCB coring in Hole U1437D) at 1745 h on 5 May. The hole was cleaned with a 41 bbl mud sweep before the bit was raised to 988 mbsf and the top drive was disengaged. The bit was then further raised to 18.0 mbsf and lowered again to 260.1 mbsf, just above the bottom of the 16 inch casing string. The drill string remained in that position while the rig crew was slipping and cutting the drilling line.

A wiper trip was conducted to ensure the hole was clear. The bit was lowered into the hole without the top drive from 259.7 to 1016.7 mbsf. The top drive was then picked up to wash and ream to 1104 mbsf; fill was encountered at 1022.7 mbsf. High torque occurred at 1063.7 mbsf, and after raising the bit to 1035.7 mbsf, the hole was finally washed and reamed to total depth (1104 mbsf) at 0545 h on 6 May. The hole was swept with 40 bbl of high-viscosity mud, and the bit was raised to 1035.7 mbsf, where another 60 bbl high-viscosity mud sweep was circulated to ensure the hole was clean. The bit was then raised to 1016.7 mbsf, where the top drive was disengaged. The drill string was tripped out of the hole, clearing the seafloor at 1115 h and the rig floor at 1500 h on 5 May.

The 1085.6 m long 10.75 inch casing string was assembled with a total of 85 joints, with the couplings of the bottom 7 joints welded in 4 places and the rest of the couplings tack-welded in 2 places. The casing hanger was installed, the running tool was engaged, and the complete assembly was hung from the moonpool doors while the casing stinger was assembled. A mud motor and underreamer were made up and tested. When the underreamer arms failed to open, a backup unit was installed, which performed as expected with the arms opening at a circulation rate of 35 strokes/min. The stinger BHA and the running tool were made up and run and latched into the casing by 1945 h on 7 May. The casing was tripped to the seafloor, the camera was deployed, and Hole U1437E was reentered with the 10.75 inch casing at 2115 h. When the bit had passed below the 16 inch casing shoe (264.1 mbsf; 2200 h), the camera system was raised above the running tool at the top of the casing string, to be lowered together with the casing string. Tripping of the casing continued to 1000.7 mbsf, where the top drive was engaged. After further lowering the casing string to 1034.7 mbsf (0145 h on 8 May), fill was encountered in the hole. The pumps were engaged and the casing was washed down to 1086.7 mbsf. At that point, the 10.75 inch casing hanger latched into the 16 inch casing hanger at the reentry cone. The latch was verified with 20,000 lb of pull from the rig floor. The casing was released and the stinger assembly was raised to 1057.7 mbsf. The top drive was disengaged and the trip to the surface continued, with a stop at 796.7 mbsf to retrieve the camera, and the bit cleared the seafloor at 0610 h and arrived at the rig floor at 1100 h on 8 May.

The underreamer and mud motor were removed, and a cementing BHA was made up consisting of a bullnose, two stands of drill collars, the casing running tool, and one stand of drill collars above. The cementing assembly was lowered to the seafloor, and after the camera was deployed, reentered Hole U1437E at 1700 h on 8 May. The running tool was landed in the reentry cone with the bit at 55.8 mbsf. Attempts to establish circulation failed, indicating that the bottom of the casing was sealed, and the cement job was aborted. The cementing string was raised and cleared the seafloor at 1830 h, and after recovering the camera, was tripped to the surface clearing the rig floor at 2235 h on 8 May. This ended the deepest casing deployment in the history of the JOIDES Resolution.

After several hours of routine rig maintenance, we were ready to resume RCB coring. An RCB coring bit was assembled and lowered to the seafloor, which was followed by the deployment of the camera to guide reentry of the bit into Hole U1437E at 0930 h on 9 May. The bit was lowered to 1048 mbsf, where the top drive was engaged, and the bit reached the bottom of the hole (1104 mbsf) at 1345 h. The hole was swept with 20 bbl of mud, and coring in Hole U1437E began at 1500 h on 9 May. The first core arrived on deck at 1815 h.

The rotation rate (and thus the coring rate) was kept low while the 95 m long BHA was still within the 10.75 inch casing that extended to 1086 mbsf. Drill collars in the BHA have a larger diameter than the regular drill pipe above and may compromise the casing and/or deviate the hole from vertical if not advanced into the formation below the (uncemented) casing shoe with care.

Cores 350-U1437E-4R though 24R (1104.0–1290.8 mbsf) obtained 140.43 m (75% recovery). Although recovery was generally good to excellent (two cores with >100% recovery), we also had two barrels with (near) zero recovery, presumably as a result of losing a perfectly cut core because it could not be broken off the formation (evidence found in one core), or, upon retrieval, could not be kept in the barrel by the core catchers.

On 13 May, the expected bit life cycle (~50 h of rotation with weight on bit) expired and a new bit needed to be installed. The bit was pulled from the bottom of the hole to 1077 mbsf with the top drive engaged. High torque, temporary loss of circulation, and the up to 40,000 lb overpull required to raise the drill string indicated that the hole was packing off at 1281–1242 mbsf. After circulation was reestablished and torque and pull returned to normal levels, the top drive was removed with the bit at 1077 mbsf, and the drill string was retrieved with the bit clearing the seafloor at 1025 h and the rig floor at 1400 h on 13 May.

After a few hours of rig maintenance, including installation of the upper guide horn, a new RCB bit was installed and lowered to the seafloor. The camera was lowered to the seafloor to guide reentry into Hole U1437E with the new RCB bit at 0010 h on 14 May. When the bit could not easily pass 1176 mbsf, it was raised to 1164 mbsf and the top drive was engaged. The hole was washed to 1206 mbsf, where another obstruction and high torque were encountered. After raising the bit back to 1174 mbsf, where normal torque was reestablished, the bit was washed down to 1290 mbsf and no fill was detected in the bottom of the hole. The hole was swept with 40 bbl of high-viscosity mud, and RCB coring resumed at 0915 h on 14 May.

Cores 350-U1437E-25R through 31R penetrated from 1290.8 to 1359.0 mbsf and obtained 44.66 m of core (65% recovery). After Core 31R was recovered, a wiper trip was conducted from 1291 to 1359 mbsf (0930–1630 h on 15 May) to clear the hole of drill cuttings. The procedure included two sweeps with 30 and 40 bbl of high-viscosity mud, respectively.

RCB coring in Hole U1437E continued until the expected safe bit life (50 h of rotation with weight on bit) had expired again after Core 350-U1437E-54R (1573.0–1582.7 mbsf) arrived on deck at 0005 h on 19 May. Cores 32R through 54R (1359.0–1582.7 mbsf) recovered 94.81 m (42% recovery). The hole was swept with high-viscosity mud before the bit was raised with the top drive from 1583 to 1485 mbsf. The top drive was disengaged for the remainder of the trip, and the bit cleared the seafloor at 0515 h on 19 May. The drilling line was slipped and cut on the rig floor as part of general rig maintenance before the drill string was retrieved; the bit arrived back at the rig floor at 1100 h on 19 May.

A new bit was installed and lowered to the seafloor. The camera was deployed, and Hole U1437E was reentered at 1710 h on 19 May. The camera was retrieved, and the bit was lowered to 1489 mbsf, where resistance was encountered. The bit was pulled back to 1475 mbsf to engage the top drive and washed to the bottom (1582.7 mbsf) by 0215 h on 20 May. RCB coring resumed and continued until 0800 h on 24 May, except for 6 h on 22 May when rough seas forced us to suspend coring.

Cores 350-U1437E-55R through 79R penetrated from 1582.7 to 1806.5 mbsf and recovered 107.55 m of core (48% recovery). At 0800 h on 24 May, the expected safe bit life (50 h) had expired again. The hole was swept with 30 bbl of high-viscosity mud before the bit was raised to 1708.7 mbsf with the top drive. The top drive was disengaged for the remainder of the trip, with the bit clearing the seafloor at 1320 h and the rig floor at 1645 h on 24 May.

After installing the new bit, the drill string was lowered to the seafloor (1800–2200 h). At that time the camera transmission test, carried out routinely before the camera is lowered to the seafloor to guide reentry into the hole, failed to transmit a signal, indicating that the last of three fiber optic cables had broken. Measurements confirmed that the fiber was damaged at ~4000 m from the camera end of the cable—an interval that was never unspooled during Expedition 350. The other two fiber optic strands had been broken before our expedition, and a replacement cable was scheduled for installation during the next port call in Yokohama, Japan. We lowered the camera to the seafloor to see if decompression from the spool might bring back the connectivity, without success. This prematurely ended our expedition’s operations in Hole U1437E. Hole U1437E is currently in excellent condition for logging and/or further coring operations, preferably attempted soon, before the hole deteriorates.

Cores 350-U1437E-4R through 79R (1104.0–1806.5 mbsf) recovered 387.45 m (55% recovery). The drill string was recovered with the bit clearing the drill floor at 0730 h. The rig was secured for transit, ending Hole U1437E and Site U1437 at 0800 h on 24 May. Total time in Hole U1437E was 683.25 h or 28.5 days.

At 0930 h, the ship was under way for contingency operations at Site U1436.

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