Coring in Holes 1179A to 1179D
The transit from Yokosuka, Japan, to Site 1179 began at 0800 hr on 22 July 2000 (Universal Time Coordinated [UTC] + 9 hr) and was completed on 25 July at an average speed of 12.5 kt. At 1545 hr on 26 July, the initial advanced piston coring (APC) core recovered 10.0 m of siliceous ooze but the full core did not accurately establish the mudline. This core was curated as the first and only of Hole 1179A, to provide extra material for sampling near the seafloor. Hole 1179B was spudded at 1700 hr on 26 July. This time a 7.6-m mudline core was recovered, establishing a seafloor depth of 5563.9 meters below sea level (mbsl). APC coring proceeded through Core 191-1179B-6H to a depth of 55.1 meters below seafloor (mbsf). The Lamont Doherty Earth Observatory (LDEO) drill string accelerometer (DSA) tool was deployed on top of the Core 191-1179B-7H core barrel, and a rubber centering ring on the tool caused the core barrel to become stuck in the drill string at a depth of about 650 meters below rig floor (mbrf). Recovering the stuck core barrel required lifting the drill string clear of the seafloor, ending Hole 1179B at 0400 hr on 27 July.
Hole 1179C was spudded at 1400 hr on 27 July 2000. Recovery from the first core established a seafloor depth of 5563.9 mbsl. The hole was washed to a depth of 48.8 mbsf, where continuous APC coring was resumed at 6.3 m above the total depth (TD) of Hole 1179B. APC coring continued to a depth of 266.8 mbsf (Core 191-1179C-24H), where an incomplete stroke necessitated the end of piston coring. The DSA tool was deployed successfully on Cores 191-1179C-4H and 7H without the rubber centering ring installed. Of the 223.8-m cored interval, the APC recovered 230.42 m of core (103.0% recovery). Extended core barrel (XCB) coring began with Core 191-1179C-25X and continued through Core 27X to a depth of 292.9 mbsf, where chert stringers caused the destruction of a hard formation shoe. The APC/XCB drilling assembly was pulled clear of the mudline at 1310 hr on 29 July. Hole 1179C was cored to a TD of 292.9 mbsf. The maximum drill string deployed was 5869.6 mbrf. A total of 246.89 m of core was recovered for an overall average recovery of 98.8%. Of the 26.1 m penetrated with the XCB, 16.47 m, or 63.1%, of core was recovered.
Tensor core orientation data were taken for Cores 191-1179B-4H through 6H and for Cores 191-1179C-3H through TD. Adara temperature measurements were taken from Cores 191-1179C-3H (67.8 mbsf; 5.492°C), 6H (96.3 mbsf; 7.670°C), 9H (124.8 mbsf; 8.2°-8.8°C), and 12H (153.3 mbsf; 11.2°-11.7°C). Perfluorocarbon tracer (PFT) was pumped into the drilling fluid for microbiological studies of drilling fluid contamination during deployment of Cores 191-1179B-5H and 191-1179C-5H, 21H, and 27X.
Hole 1179D was spudded at 0300 hr on 31 July. Drilling continued with a rotary core barrel (RCB) center bit in place to a depth of 281 mbsf. An RCB core barrel was then pumped to bottom to initiate RCB coring approximately one core above the TD of Hole 1179C. Coring was difficult in this interval because of chert layers. A total of nine cores were recovered through the chert zone. Of the 86.5 m penetrated, <6 m of core was recovered (6.7% recovery). The basement contact was cored in Core 191-1179D-10R at an estimated depth of 377 mbsf. Coring continued 98 m into basaltic basement through Core 191-1179D-22R to a TD of 475 mbsf. Of the 98 m of basalt cored, 44.4% was recovered.
Once coring was suspended, the hole was prepared for logging first by circulating and making a wiper trip up to 150 mbsf and back to TD. The bit was released and the end of the drill string was positioned at ~150 mbsf (slightly deeper than normal because of the exceptionally soft sediments in the upper sediment column). The triple combo tool string (phasor dual-induction tool [DIT], hostile-environment lithodensity sonde, acceleration porosity sonde [APS], and hostile-environment natural gamma sonde) with the LDEO temperature/acceleration/ pressure tool and a high-resolution multisensor gamma-ray tool (MGT) was run in the hole, making this one the longest wireline tool strings (>130 ft) ever deployed by ODP. The logging run consisted of two planned passes plus some short repeat runs for data quality verification. A first pass in the logged depth interval was required for recording Schlumberger triple combo data and the second for running the LDEO MGT. The tool string was lowered to 300 mbsf, and the run was reversed, moving up ~100 m. When the tool was once again lowered it was not able to pass 253 mbsf. After repeated efforts to pass this depth were unsuccessful, the remaining hole was logged up to the mudline. After logging concluded, the drill string was lowered to a depth of 377 mbsf and a cement plug was set to ensure that there would be no communication of seawater downhole and through fractures to the instrument installation in Hole 1179E. The end of the drill string reached the rig floor at 1150 hr on 6 August, ending Hole 1179D.
Drilling Operations for Borehole Instrumentation Deployment: Hole 1179E
At 1145 hr on 6 August, Hole 1179E was spudded using a bottom-hole assembly (BHA) with a reentry cone and a 16-in casing hanger assembly at a seafloor depth of 5566.0 mbsl. Within 2 hr, the casing was jetted in and the Dril-Quip (DQ) running tool was released from the reentry cone/casing assembly. The drill string was assembled with a tricone bit, and at 0715 hr, Hole 1179E was reentered and the drill pipe was run in the hole to just above the 16-in casing shoe located at ~64 mbsf. Drilling of Hole 1179E was initiated and basement was ultimately contacted at ~371.0 mbsf. Drilling continued into the basement to a depth of 399.0 mbsf (~28.0 m into basement). The drill string was recovered back to the ship, and preparations began for making up and deploying the 10.75-in casing string. At 0230 hr, Hole 1179E was reentered for the second time and the 10.75-in casing string was run to bottom without incident. The casing hanger landed out with the shoe placed at a depth of 393.4 mbsf. A cement slurry was pumped into the hole to firmly attach the casing into the host rock. The DQ running tool was released within an hour, and at 0900 hr, the cementing swivel and top drive were laid out and the pipe trip out of the hole was begun. All tools were clear of the rotary table by 0300 hr on 14 August; however, further drilling operations were halted because a tropical storm was headed toward the drilling location.
By 0800 on 14 August, all of the drill collars had been safely stored in the racks and the ship was secured for transit in possible heavy weather. The ship then entered a waiting-on-weather mode. When the tropical storm intensified into Typhoon Ewiniar, it was necessary to abandon the site. Eventually, the storm weakened and Site 1179 was reoccupied. With the storm downgraded to a tropical depression and no longer a threat to drilling at Site 1179, the thrusters were dropped at 0930 hr on 18 August and work on site was resumed. Including the time to lay out and pick up the 8.25-in drill collars, the avoidance of Typhoon Ewiniar cost a total of 104 hr (4.3 days) of operating time. A total of 909 nmi was transited during this period at an average speed of 10.1 kt.
The drilling assembly was made up and run in the hole. Hole 1179E was reentered for the third time at 2230 hr on 18 August. Reentry time was 45 min. The bit was advanced, and by 0615 hr on 19 August basement drilling began. Drilling proceeded until a TD of 475.0 mbsf was achieved at 0115 on 21 August. Drilling was consistent throughout the basement interval, averaging 2.0 m/hr. Based on drilling data, the hole appeared to be in excellent condition for installation of the two Guralp three-component broadband seismometers. The bit reached the rotary table at 1445 hr on 21 August 2000, ending the reentry cone, casing, and drilling preparations for Hole 1179E.
Installation of the Seismic Observatory
The primary objective of Site 1179 was to establish a seismic borehole observatory in the upper igneous crust on abyssal Pacific lithosphere in order to record high-quality seismic data for monitoring earthquake waves from around the globe. The plan was to install two Guralp CMG-1T three-component broadband seismometers within the upper 100 m of igneous basement because studies have shown that igneous basement is an especially quiet environment at seismic frequencies. After studying the igneous section drilled in Hole 1179D, it was decided to place the seismometers at a depth of about 90 m (461 mbsf) into the igneous rock. From measurements of physical properties, average densities and velocities in the basalt section were 2.754 g/cm3 and 5002 m/s, respectively.
At 1445 hr on 21 August, we began to install the seismic borehole observatory in Hole 1179E. The borehole instrument assembly was made up to a joint of 4.50-in casing, and the stinger pipe was then lowered down to the moonpool level using the 4.50-in casing elevators. Each of the two instrument cables were fed off of their respective reels over sheaves hung below the rotary table and connected to the Guralp seismometers. After testing the seismometers through the instrument cables, the 4.50-in casing and cable deployment operation began in earnest at 1830 hr on 21 August. Each joint of 4.50-in casing was run with two electrical cables strapped to the outside and secured with tie wraps and duct tape. Approximately every 1.5 m, a 4.50-in casing centralizer (measuring ~9 in outer diameter) was attached. Nineteen joints (221.3 m) of casing were run at ~5 joints/hr, and then a circulating sub (0.34 m) was installed. Another 19 joints (221.8 m) of casing followed before it was time to pick up the riser/hanger assembly. The riser/hanger was made up to the J-slot running tool and the last joint (11.65 m) of 4.50-in casing. The assembly was lowered through the rotary table, and the slips were set on a 10-ft drill collar pup joint attached to the J-tool. The instrument cable was cut to length, and the long and tedious cable terminating process began at 0500 hr on 22 August in the subsea shop. It was completed with associated electrical tests later that same day at 2200 hr.
With the cable terminating process completed, the cables were then strapped onto the last two joints of 4.50-in casing and the MEG-191 was installed into the multi-access expandable gateway frame on the riser/hanger (Fig. 7). By 0130 hr on 23 August, the instrument string assembly and final electrical integrity checks were completed. The remainder of the BHA was
assembled, the drill string was lowered, and Hole 1179E was reentered for the fourth and final time at 1115 hr on 23 August. The instrument package was lowered into the hole without incident, and at 1500 hr on the same day, the riser/hanger landed out at just the right depth. A 50-bbl slurry of cement was mixed and displaced downhole, cementing the instruments in place with the end of the stinger located at a depth of 467.2 mbsf (96.2 m into basaltic basement). Using theoretical hole volumes and displacements, the top of the cement slurry should have reached a level of ~112 m above the 10.75-in casing shoe.
Once the drill string was adequately flushed, the vibration-isolated television (VIT)/subsea television (TV) system was recovered. Preparations then began for deploying the power supply access terminal (PAT; the frame for the seawater batteries) and continued through 0215 hr on 24 August. These included tack welding the frame structure and rigging the deployment bridle and the three glass balls for cable retraction, redundant acoustic release package, and the wire cables for transferring the weight of the platform to the logging line. After standing by for 1.25 hr waiting for enough daylight to see below the water line in the moonpool, the final rig-up of the logging line was completed and the PAT was lowered through the moonpool at 0415 hr 24 August (Fig. 8). The 4.75-hr trip ended at 0900 hr, when the PAT landed in the reentry cone. The PAT was released from the bridle by an acoustic command. After rigging down the platform deployment bridle assembly, the VIT/subsea TV system was deployed to survey the platform installation and observe the J-tool release from the riser/hanger (Fig. 9). By 1445 hr on 24 August, the camera was down, proper platform installation was verified, and the J-tool was released. The installation of the seismic borehole observatory in Hole 1179E was complete (Fig. 10).
Transit to Site 1180
At ~0800 hr on 25 August, with the nondestructive testing of the drill collars still in progress, it was necessary to halt operations because of a medical emergency that required evacuating a crew member to Japan. The remainder of the BHA inspection was canceled. The remaining drill collars were laid out and the rig was secured for transit as quickly as possible. At 0845 hr on 25 August, the Resolution got under way at full speed for Kushiro, Japan, a port city on the island of Hokkaido.
At 1345 hr on 26 August, a helicopter from the Japanese Coast Guard ship Soya landed on the helideck to take the doctor and patient the rest of the way to Japan. Because the Resolution could not resume work until the doctor returned, the ship continued to steam toward Kushiro. At 0720 hr on 28 August, a transport helicopter returned the doctor to the ship. In the meantime, a routine inspection of the brake bands on the drawworks winch found a crack that could not be repaired because there was no spare on board. Plans to go to Shatsky Rise were scrapped. Instead, the ship turned toward Guam, the final destination of Leg 191, in hopes that spare parts could be flown to Guam ahead of the ship. The next 7 days were spent in transit.
During the transit, the co-chiefs and staff scientist began trying to find a site suitable for HRRS testing near Guam with the idea of getting the new brake band, installing it at sea, and setting up an abbreviated HRRS test. A site with an igneous outcrop was desired, with a water depth between 1000 and 2000 m. A colleague on shore suggested a volcano in the Mariana arc located about 37 km west of the island of Rota, less than a half-day cruise from Guam. Clearances to drill were rapidly obtained.
Sites 1180-1181: HRRS Tests
After obtaining replacement parts in a rendezvous off of Rota Island with the supply boat Shamrock at 1415 hr (UTC + 10 hr) on 3 September, repairs were quickly made and the drawworks put back in order. A short survey was conducted of the target seamount using the 3.5- and 12-kHz echo sounders and magnetometer. The echo sounders showed that the slopes of the seamount were relatively steep for the HRRS test, typically about 14 on most flanks. A spot on the middle flank at a depth of about 2160 m was chosen because the slope angle seemed slightly less at this location. The VIT/subsea TV camera was run to the seafloor to examine the seafloor. The ocean floor appeared firm but sedimented despite the steep slopes. Because there was no evidence of a sediment veneer on the 3.5-kHz echo sounder profiles, it was decided that drilling should be attempted. A BHA with the hammer drill was rigged, tested, and sent to the seafloor. At 1315 hr on 4 September, Hole 1180A was spudded at 1418.52'N, 14444.75'E. The drill string quickly sank into the soft, sandy sediments, which are interpreted as volcanic ash. The hammer was unable to come to full pressure because fluid circulation flushed the sediments away, allowing the BHA to jet in. After 30 min and 5 m of penetration, the collapsing hole walls dictated pulling the BHA free. Twice more the hammer was tried at different locations with the same results. The largest penetration among Holes 1180A-1180C was 8 m.
The drill string was recovered and the ship moved 3 nmi upslope to the rim of a large crater on the west side of the seamount at a depth of ~956 m. The hammer was rigged again and run to the bottom. Hole 1181A was commenced at 0115 on 5 September in what appeared on the VIT/subsea TV camera to be coarse rubble (1419.26'N, 14448.00'E). As at Site 1180, the drill quickly penetrated the bottom by flushing away the volcanic ash and debris until circulation was lost and the hole collapsed on the BHA. Three holes were tried at Site 1181, all with similar results. The maximum penetration of the drill string at Site 1181 was 3 m. After surveying the seafloor with the VIT/subsea TV camera across the top of the crater rim and into the crater, we decided that this flank of the seamount was primarily composed of nonindurated ash and debris. The drill string was tripped to the rig floor, and preparations were made to survey the other side of the seamount.
Before the pipe trip was finished, weather reports indicated that a tropical low located east of Guam was intensifying and would turn into a typhoon (named Saomai), and Rota was in its path. The Resolution quit the site and headed southwest ahead of the storm. In disgust, the name Inutil, which is Spanish for "worthless," was bestowed on the unnamed seamount.
After a short transit past Guam, the Resolution conducted a brief survey over a seamount on the backarc spreading center of the Mariana Trough. The seamount was found to have a relatively flat summit at a depth of ~2880 m, which seemed suitable for drilling. The hammer was rerigged and sent to the bottom with the VIT/subsea TV system. The camera showed the rough, pillowed surface of a submarine lava flow. Hole 1182A was spudded at 0845 hr on 5 September at 12°57.00'N, 143°36.66'E. For the next 57 hr, spud tests with both types of drill bits and the vibration-dampner sub were conducted successfully at Holes 1182A-1182F. By 1800 hr on 7 September, spud tests were finished but insufficient time remained for making up a casing assembly and testing that part of the HRRS system. Consequently, the drill string was tripped back to the rig for the last time, clearing the rotary table at 0800 hr on 8 September. Having accomplished its missions for Leg 191, the Resolution sailed to Guam, arriving at 1400 hr on 8 September.
Site 1179 Scientific Results | Table of Contents