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doi:10.2204/iodp.pr.343343T.2012

Expedition 343 operations

Shimizu, Japan, port call

Loading for Expedition 343 began on 25 March 2012 at Shimizu, Japan. A “prespud” meeting was held aboard the Chikyu, with representatives from Center for Deep Earth Exploration (CDEX), Marine Works Japan, Mantle Quest Japan, and the Expedition 343 Science party on 31 March 2012. The Chikyu departed Shimizu at 1630 h on 1 April en route to Site C0019 (proposed Site JFAST-3).

Transit to Site C0019

During transit to Site C0019, the Chikyu engaged in a series of system integration tests with the dual elevator system (DES) and began building up drill pipe stands and casing running tools for the 20 inch wellhead. The Chikyu arrived on site at 0800 h on 3 April 2012. However, extreme winds (30 m/s, maximum gusts near 40 m/s) necessitated putting the vessel into auto heading mode and entering wait on weather (WOW) while weather conditions remained poor. The Chikyu continued to WOW until the morning of 5 April, when transponders were dropped and continued to make up dynamic positioning. The UWTV cable was rigged up in the moonpool for a free-fall test on 6 April and required troubleshooting the winch and software issues affecting deployment. While the UWTV was undergoing troubleshooting, the jetting and running bottom-hole assembly (BHA) for the MTL observatory was being rigged up and tested. Testing for the UWTV continued over several days, working to solve twisting and kinking issues. Eventually, the Chikyu needed to be moved to deeper water (7500 m) to fully unwind the weighted UWTV cable. Problem solving focused on eliminating unwanted rotation in the cable, which could result in wrapping and snapping the UWTV cable on the drill string while deployed near the seafloor. Finally, on 13 April, the Chikyu moved to the site location and prepared the guide horn and running tool for the 20 inch casing. All the holes surveyed and drilled at Site C0019 were along a transect running along strike at ~10 m intervals (Fig. F3).

Hole C0019A

Initial operations began with running the 20 inch casing with a 30 inch outside diameter guide funnel into the water at 1800 h, reaching 2415 m drilling depth below rig floor (DRF) at 2400 h. Once the BHA reached 4074 m DRF, the DES was installed and tested in preparation for running deeper. However, several problems with the DES operation were discovered, delaying jetting in Hole C0019A. Preparations for running the UWTV were made but then postponed because of 14 h of WOW (waves exceeding operational criteria). After WOW, the UWTV dove to the wellhead housing at 4677 m DRF. While running to the seafloor, the DES and UWTV continued to experience problems during operation. A seabed survey started on 17 April at 1945 h, taking advantage of the weather and close proximity of the coring hole and the LWD hole. Once the survey was completed, the Chikyu returned to the LWD hole position to spud in the 20 inch casing. After troubleshooting the DES again, jetting in Hole C0019A (37°56.3367′N, 143°54.8100′E) began on 18 April at 0745 h. The jetting was successful to 28.0 mbsf, but the running tool would not release. Many attempts were made to release the running tool, but all were unsuccessful. It was decided to recover the running tool dart with the wireline winch, which eventually succeeded by 2030 h. Investigation showed no apparent issues with the dart, so the running tool dart was rerun with a new shear pin. The tool still refused to part from the wellhead, so attempts were made to jar down nine times. Attempts at raising pressure and repeating dart landings were equally unsuccessful, while continuous observation via the UWTV showed no apparent mechanical irregularities that might account for the stuck casing. Upon retrieval, the X Barrel Retrieving Tool showed no pin shear. Ultimately, the decision was made on 19 April to pull the casing and running tool out of the hole and return them to the rig floor for inspection. On 20 April, the running tool and wellhead were laid down for careful inspection and testing of the running tool. During this time, the Chikyu moved to drop a new seafloor transponder to replace a malfunctioning one. Since the jet-in failed, it was decided to move on and begin LWD drilling at a new hole.

Hole C0019B

Preparations began to assemble the LWD BHA to drill the logging hole while the casing and casing running tool were inspected. On 21 April, the LWD tools were made up and run in for a shallow-water test. Unfortunately, a first shallow communication and function test at the sea surface revealed that the proVISION tool was not functioning properly. After some unsuccessful attempts at repair, the tool was removed, and then the 8½ inch LWD BHA including geoVISION, arcVISION, and MWD (TeleScope) tools was run. Subsequent shallow tests of the MWD pulse telemetry were conducted at water depths of 1988.7, 3872.4, and 5985.0 m. Spud-in of Hole C0019B was achieved at 0011 h on 23 April, followed by jetting in with an initial surface pump rate of 150–500 gallons per minute (gpm). About 1 h later the spud-in pumping rate was increased and the MWD mud-pulse transmission was confirmed. At around 0916 h the bit passed 7049.5 meters below sea level (mbsl). This is the deepest total length from the sea level in the history of scientific ocean drilling. After continuous drilling and real-time monitoring to 576.0 mbsf, the drill string was pulled up due to WOW on 24 April. Drilling operation was resumed from 576.0 mbsf at 2400 h on 24 April. In the evening of 25 April, the largest changes in resistivity and NGR were observed at the interval of about 820–840 mbsf. The large changes in the logging parameters were interpreted that the LWD had reached hard chert layer, which was the designated target formation. At 2143 h on 25 April, the rate of penetration had dropped to nearly zero and the decision was made to stop drilling. The borehole reached a final depth of 850.5 mbsf (7740 mbsl). This extends the world record for total length of drill pipe below sea level, which was set 2 days earlier. Repeated measurements at three designated 50 m intervals were conducted while pulling out of the borehole. By the end of the day of 25 April the LWD assembly was out of the borehole, all LWD tools were recovered on the rig floor at 1200 h on 27 April, and all memory data were successfully downloaded.

Hole C0019C

Preparations for the wellhead installation in Hole C0019C began on 28 April with the make-up and running of the 20 inch casing and running tool BHA. The wellhead and running tool BHA were run into the water from 0215 h and had reached 4084 m DRF by 1415 h. To prevent problems with the inner lining of the drill pipe from fouling the running dart landing, the pipe was flushed with 1000 gpm of seawater at 1000, 2000, 3000, and 4000 m. The UWTV was installed and run in the hole from 2000 h and underwent a function check at 180 m. Communication checks failed to contact the minibeacon, and a phase of troubleshooting the issue began. The drill pipe continued to be run in, in conjunction with the UWTV, until the seafloor was tagged at 0815 h on 29 April. Jetting in the 20 inch casing began in Hole C0019C at 1500 h, confirming the seafloor depth at 6928.5 m DRF, stopping only when the casing had reached 29 mbsf. Upon starting to pick up the core barrel retrieving tool (CBRT), it was found that the core line winch counter was malfunctioning, so it was run with a calculated pay out. Circulation to clear out Hi-Vis mud began, and then the CBRT with dart was run to 6721 m DRF without pumping. Closing and pumping at 20, 40, and 60 strokes per minute (spm) began when the CBRT suddenly released the wellhead; recovery of the CBRT and dart showed that the dart broke in two within the drill pipe. The UWTV and drill pipe were pulled up to 4100 m DRF, checking the minibeacon signal on the UWTV every 1000 m with no response. The UWTV was recovered to the surface by 1415 h on 30 April, while the running tool BHA was recovered and laid down on 1 May.

The LWD assembly was made up in preparation for reentry into the wellhead of Hole C0019C on 1 May. Just as for Hole C0019B, the LWD tools included the geoVISION, arcVISION, and MWD (TeleScope). Following the standard procedure, the tools were assembled, and shallow communication and function tests were conducted on the surface and at water depths of 320, 2014, and 3917 m. On 2 May, due to bad weather, the drill string was brought up to ~3000 m and secured for riding out the rough seas. Following 2 days of WOW, operations resumed, running the LWD assembly with UWTV on 5 May. Adjusting vessel position, the attempt to reenter the wellhead was successful at 0000 h on 5 May. The LWD assembly was continuously run into Hole C0019C; however, there was an engineering problem at 1400 h on 6 May with a loss of the BHA at ~120 mbsf. The cause of the problem is being examined. Analysis of LWD data showed that the disconnection of the BHA was not a result of any abnormal conditions of the borehole or the response of the formations being drilled. Once the pipe was returned to the ship on 7 May, the engineering staff determined it was a mechanical failure of one section of the drill pipe. The loss of the BHA inside the wellhead necessitated abandoning this hole and starting preparation for jetting a new wellhead in Hole C0019D.

Hole C0019D

Preparation for jetting a new wellhead in Hole C0019D began at 1700 h on 7 May once the remaining sections of the LWD BHA had been recovered and examined on the rig floor. On 8 May, the jetting BHA and running tool were made up and run into the water, reaching 5030 m DRF by 1000 h. The seafloor was reached by 0500 h on 9 May, and Hole C0019D was tagged at 0630 h at 6929.5 m DRF. Jetting in operations began at 0945 h, when the seabed was noted as being 6926 m DRF, a 3.5 m difference! The wellhead was jetted in to 27.5 mbsf by 1245 h, when operations to release the running tool began. Several issues were noted, particularly that the tool would not release, even after confirming landing of the dart several times. The drillers made multiple attempts over the next few hours, finally noting, by visual UWTV confirmation, that the tool had released at 2000 h. Preparations for drilling ahead began with the UWTV recovery, when the video feed from the UWTV was lost. Attempts to recover visual communications failed, so the UWTV was recovered on deck to examine it more closely. Finally, at 1000 h on 10 May, the UWTV was recovered on the working cart above the moonpool so that troubleshooting could begin. Meanwhile the jetting BHA was recovered on deck, laying down at 2130 h. The umbilical cable for the UWTV was found to have one more cut fiber-optic line and two short circuits in the power lines, all close to the spool connection. A quick consultation among the Co-Chief Scientists, Operations Superintendents (OSI), Offshore Installation Managers (OIM), and Expedition Project Managers (EPM) concluded that since the problem could not be fixed rapidly, coring operations would begin immediately.

Hole C0019E

The decision was made on 10 May to proceed with a blind spud of Hole C0019E with the coring BHA without use of the UWTV. The location was selected with two considerations in mind: (1) it was close to Hole C0019B (10 m south of Hole C0019B), where the LWD data could guide and identify coring key target intervals, and (2) it was far enough away to minimize the possibility that the holes would intersect at depth. The RCB coring BHA was made up and run in the hole on the morning of 11 May, reaching 4000 m DRF by 1845 h. Sea conditions necessitated WOW, which continued until 0600 h on 12 May. There were several more short WOW periods during 12 May, mainly due to maximum wave heights exceeding operational parameters. The seafloor was reached on 13 May, when the center bit was dropped for washing down and tagging the seafloor. The seafloor depth (6918 m DRF) was estimated from drilling parameters and the proximity of Hole C0019E to the LWD Hole C0019B. A test core was performed from 176.5–186 mbsf and recovered on deck on 14 May at 0752 h. It was decided to drill ahead before beginning the next series of coring operations, which began on 16 May at 648 mbsf. Cores 343-C0019E-2R and 3R were recovered, and then we drilled ahead to 680 mbsf. From this point, we cored continuously until reaching 729 mbsf on 19 May, when a consultation among the OSI, OIM, Co-Chief Scientists, and EPM decided that with the limited time left to the expedition, we would drill ahead to 770 mbsf before coring resumed. The drill ahead target was reached on 19 May, with the first core (343-C0019E-10R) of the second coring run on deck at 2359 h. It was decided to core ahead until the end of 22 May so that we would have the best chance of recovering the next identified presumed fault zone at 820 mbsf. Coring operations finished at 844.5 mbsf at 1640 h on 22 May, with the recovery of Core 343-C0019E-21R, a short chert section of 0.5 m, after a drilling advance of 8 m. A deplugger assembly containing three MTL sensors was dropped, and then pulling out of the hole operations commenced. The BHA was recovered on deck 0400 h on 24 May, and the ship began moving 30 nmi west of Site C0019 to reach the helicopter rendezvous point from 0445 h.

Expedition 343 end

Expedition 343 ended at sea on 24 May 2012, with the helicopter transfer (in three flights) of the science party to Sendai, Japan, from the Chikyu. In July 2012, the expedition continued as Expedition 343T in order to deploy the MTL observatory.

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