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doi:10.2204/iodp.pr.345.2014

Operations summary

Expedition 345 occupied 16 holes in water depths ranging from 4675 to 4853 m. Seven holes were cored by rotary core barrel (RCB), recovering 55.2 m of gabbroic rock. An additional 19.8 m of core was recovered during hole-cleaning operations (“ghost cores”) (Table T1).

Two RCB holes were cored to >100 mbsf (111.8 mbsf in Hole U1415J and 107.9 mbsf in Hole U1415P). The other five RCB holes were cored to total depths ranging between 12.9 and 37.0 mbsf. The remaining holes occupied during Expedition 345 consisted of six jet-in tests and three failed attempts to establish reentry capability.

Port call in Puntarenas, Costa Rica

Hess Deep IODP Expedition 345 officially began when the ship arrived in Puntarenas at 0500 h on 11 December 2012. All times reported in this operations section are in ship local time. Ship local time initially was Universal Time Coordinated (UTC) – 6 h. During the transit to Hess Deep, ship local time changed to UTC –7 at 1400 h on 20 December.

After the ship was secured to the dock, we started our port call activities, including customs and immigration, IODP-United States Implementing Organization (USIO) crew change and crossover, boarding of chief scientists, and loading of airfreight. Because of shared dock space with cruise ships for the first three days of port call, most port call activities were limited to evening hours.

Activities on 12 December included the ship’s crew change, offloading of temperature-controlled sample shipments and all departing sea freight and loading of three containers of freight for the ship’s crew and a hydraulic pump required to repair a crane.

Early in the morning of 13 December, we moved to anchorage because of the arrival of two cruise ships. Key USIO staff met with the chief scientists to plan initial Expedition 345 operations. Expedition 345 scientists boarded the ship by water taxi and underwent safety orientation. In the evening, the cruise ships had departed, so we returned to the dock and resumed normal port call activities, including loading of arriving shipments and preparing for loading of drilling mud on the following day.

Following the introductions of Hess Deep scientists and technical staff on 14 December, the Co-Chief Scientists presented an overview of the expedition science objectives. Scientists were given a tour of the laboratories and also underwent an orientation to shipboard computing and communications technology. Loading and storing of supplies continued, including drilling mud.

On 15 December, the Hess Deep scientists were given a presentation covering the expedition science expectations, procedures, deliverables, and obligations. Following this, the final tours of the laboratories and personal computer setup were conducted. Loading of the final drilling supplies and drilling mud were completed.

Port call operations continued on 16 December with dock cleanup after the bulk loading operation. One 40 ft container of refrigerated food was loaded along with another 20 ft container of frozen food. The drill crew also began spooling on the new aft core line.

On 17 December, the drill crew completed spooling the new drill line. This process took much longer than anticipated (>24 h) because of poor spooling of the line by the vender. The installation would not have been possible without the recent modifications to the spooling tensioner that included replacement of the drum brakes with significantly better disc brakes. The last 20 ft container of dry goods was loaded aboard along with a replacement shipment of local fresh food, as half of the original fresh food delivery was rejected due to poor quality.

Departure from Puntarenas, Costa Rica

The pilot boarded the ship at 1715 h on 17 December 2012 for the scheduled departure; however, after a captain and pilot conference, the pilot elected to delay departure until slack tide at 1800 h. In the interim, a second tug was also brought over from the nearby container port of Caldera. All lines were singled up in preparation for an imminent departure. A few minutes before departure the Schlumberger hazmat/tools airfreight shipment arrived dockside. The tools were quickly lifted aboard with the crane and the last line was cast off at 1818 h. The pilot disembarked at 1832 h, and we got underway at full speed for Site U1415 (proposed Site HD-01B). This was 0.6 days ahead of the originally scheduled 0800 h departure on 18 December.

The transit to Site U1415 was uneventful and operations and drilling personnel and Co-Chief Scientists used the time to have multiple meetings discussing the specifics of the planned Hess Deep operations. The drill crew began testing the readiness of all drilling equipment. The 1117 nmi distance from Puntarenas to Site U1415 was covered in 4.2 days at an average speed of 11.0 nmi/h.

Arrival at Hess Deep and initial near-bottom survey

We arrived on location at Site U1415 at 2350 h on 21 December 2012 and began the process of switching from the bridge “cruise” mode to dynamic positioning control. By 0040 h, all thrusters were deployed and dynamic positioning was in full control of the ship. The drill crew spent the remainder of the day picking up drill collars and assembling the drill string. This required removing collars from the forward main deck rack and making them up into stands as well as drifting and strapping (measuring) all tubulars. After deploying 130 stands of 5 inch drill pipe, the tripping operation was suspended at 1130 h to raise the upper guide horn (UGH) and deploy the subsea camera system. We deployed the camera system, to which we had attached a seafloor positioning beacon, so that it could be released in a precise position from just above the seafloor. A 3.5 kHz subbottom pinger, for surveying the thickness of sediments, was also attached to the camera system but was not turned on. Our highest priority was to deploy the seafloor positioning beacon, and we wanted to minimize the chances another sound source (e.g., 3.5 kHz pinger) might cause problems with this.

Our initial operations were designed to verify our position relative to the site survey microbathymetric data. After arriving at Site U1415, we tripped the drill pipe to the seafloor and offset the ship 300 m south of the site coordinates. This allowed the drill string to be extended to a depth of 4886 m below rig floor (mbrf), or 20 m below the estimated seafloor depth of the first proposed drill site located on the bench. Once the vibration-isolated television (VIT) subsea camera system was in position just above the seafloor, we moved the ship to the north, upslope of the site coordinates. From there the ship was moved an additional 35 m north where the depth began to decrease, consistent with the site survey bathymetry. By monitoring the changes in water depth we were able to confirm that the drill site was indeed located in the area of interest on the target bench. The ship was then moved back to the site coordinates and from there west 100 m, where a seafloor positioning beacon attached to the subsea camera was released without difficulty. Once again the ship returned to the site coordinates, where a drill string seafloor depth of 4850.5 mbrf was visually observed. The subsea camera was then recovered to turn on the previously mounted 3.5 kHz subbottom profiling system (pinger).

Hole U1415A

Our objective in this hole was to get an initial idea of sediment thickness in preparation for surveying. The camera system was redeployed to the seafloor with the ship positioned over the Hole U1415A coordinates (Fig. F8) and the hole was spudded at 0255 h on 23 December 2012. We conducted a jet-in test by lowering the drill string and circulating, but not rotating. This test penetrated 10.3 m into the seafloor (4848.5–4858.8 mbrf). After the test was completed, we continued the 3.5 kHz pinger and camera survey to determine sediment distribution and thickness continued along the length of the bench as per the arranged Co-Chief survey plan.

Holes U1415B and U1415C

The locations of these holes were selected to test sediment thickness and subseafloor drilling conditions, with the aim of finding a suitable site for establishing a deep hole.

Near-bottom 3.5 kHz pinger and camera survey

After pulling out of the seafloor in Hole U1415A, we continued a near-bottom survey of the bench with the 3.5 kHz pinger and camera system. At 0830 h on 23 December, we stopped the survey to conduct operations in Holes U1415B and U1415C.

Hole U1415B operations

The drill string was spaced out for a jet-in test and Hole U1415B was spudded at 0905 h on 23 December (Fig. F8). This test penetrated 11.7 m into the seafloor (4856.3–4868.0 mbrf) before the driller had to make a drill string connection to add another drilling knobby. After making the connection, the driller was unable to get back to bottom, indicating something had fallen into the hole preventing further advancement. The drill string was pulled clear of the seafloor, ending Hole U1415B.

Hole U1415C operations

Hole U1415C was spudded at 0945 h on 23 December in the same location as Hole U1415B, only this time the driller made a connection before penetrating the seafloor. The third jet-in test extended from seafloor (4856.3 mbrf) to 76.4 mbsf (4932.7 mbrf). As it turned out, this penetration was only perceived. In reality, the BHA was most likely lying slack on the seafloor. This was discovered when the camera system was recovered and the driller found that the drill string could not be rotated. Damage to the BHA, including the bending of several collars and the tapered drill collar, were determined on recovery. This damage was attributed to the difficulty in starting a hole in unstable, rubbly basement with an unknown but likely very thin sediment cover. Drilling was further complicated by the use of drilling knobbies at the top of the drill string and significant ship heave, which led to large weight fluctuations (± 50,000 lb) on the driller’s weight indicator and masked the weight change when the bit encountered hard rubble to the extent that it was not detected at the driller’s console. The seafloor was cleared at 1445 h on 23 December, all 30 ft drilling knobbies in the string were laid out, and the remaining drill string was recovered. At the surface, the BHA was inspected, resulting in one joint of 5½ inch transition drill pipe, one tapered drill collar, and five control-length drill collars all being taken out of service because they were either obviously bent or suspect.

Holes U1415D and U1415E

The locations of these holes were selected to test sediment thickness and subseafloor drilling conditions, with the aim of finding a suitable site for establishing a deep hole.

Near-bottom 3.5 kHz pinger and camera survey

At the end of operations in Hole U1415C and while still at that location, we assembled a new BHA and lowered the bit to just above the seafloor. We lowered the camera system with the 3.5 kHz pinger attached and initiated a new survey of the seafloor and near-subbottom. The 3.5 kHz pinger ceased transmitting ~100 m into the survey, and we shortened the survey, which was completed using only visual observations of the seafloor.

Hole U1415D operations

A new location to drill was selected and the ship moved into position for Hole U1415D (Fig. F8). Following a routine slip and cut of the drill line, we observed the bit tag seafloor at 4850.8 mbrf. Hole U1415D was spudded at 2355 h 24 December 2012. We conducted a jet-in test that advanced 4.2 m into the seafloor. The bit was pulled clear of the seafloor at 0026 h on 25 December, ending Hole U1415D.

Hole U1415E operations

After the camera system was recovered, we installed a fresh core barrel and spudded Hole U1415E at 0330 h on 25 December. This hole was rotary cored from seafloor (4850.8 mbrf) to 22.2 mbsf (4873.0 mbrf). Cores 345-U1415E-1R and 2R were recovered (0–15.3 mbsf) with 5% recovery. Very difficult hole conditions were encountered throughout the interval, with high pump pressure, high drilling torque, and hole collapse occurring every time the bit was picked up off bottom. While cutting Core 3R (15.3–22.2 mbsf), the pump pressure dropped from 800 to 350 psi at 70 strokes/min, top drive torque dropped off significantly, and the driller noticed a string weight loss of ~10,000 lb, indicating a likely BHA failure. The drill string was recovered, and the fourth drill collar pin (first collar above the outer core barrel [OCB] stand) had broken off. Besides the inner core barrel assembly, three drill collars and the entire OCB assembly were lost in the hole. In addition, two other drill collars were bent. Only the uppermost stand was in working condition.

Holes U1415F and U1415G

The locations for these holes were selected to test sediment thickness and subseafloor drilling conditions, with the aim of finding a suitable site for establishing a deep hole.

Near-bottom 3.5 kHz pinger and camera survey

At the end of operations in Hole U1415E and while still at that location, we assembled a new BHA and lowered the bit to just above the seafloor. The previous problem with the 3.5 kHz pinger was traced to dead batteries, so the batteries were charged and the pinger was operational once again. We lowered the camera system with the 3.5 kHz pinger attached and conducted a new survey of the seafloor and near-subbottom in an attempt to locate an area on the bench with thin sediment and little or no rubble in evidence. This survey lasted from 1615 to 2000 h on 26 December 2012.

Hole U1415F operations

A new location was selected, the top drive picked up, and a jet-in test was started at 2100 h on 26 December (Fig. F8). The seafloor depth for this hole was established as 4857.0 mbrf. The bit was jetted into the formation only 1.5 m before the test was terminated. The bit was pulled clear of the seafloor and the camera system was recovered.

Hole U1415G operations

The drill string was spaced out and Hole U1415G was spudded at 2355 h on 26 December without offsetting the ship from the location of Hole U1415F. RCB coring continued to 4869.9.4 mbrf (12.9 mbsf) before being terminated. Core 345-U1415G-1R covered this depth interval, with 2% recovery. Hole conditions were the same as in earlier holes, making it highly risky to attempt making connections with the bit in the hole. The bit was pulled clear of the seafloor at 0445 h on 27 December, ending Hole U1415G.

Hole U1415H

The location of this hole was selected to test sediment thickness and subseafloor drilling conditions, with the aim of finding a suitable site for establishing a deep hole.

Near-bottom 3.5 kHz pinger and camera survey

At the end of operations in Hole U1415G and while still at that location, we lowered the camera system with the 3.5 kHz pinger attached and conducted a new survey of the seafloor and near-subbottom en route to Hole U1415H, located 20 m west and 15 m south of Hole U1415G.

Hole U1415H operations

After arriving at the coordinates for Hole U1415H (Fig. F8), we visually observed the drill bit tag the seafloor at 4857.6 mbrf. The camera system was recovered, and Hole U1415H was spudded at 1040 h on 27 December 2012. Rotation began after penetrating ~1.0 m of soft material, and RCB coring continued to 12.9 mbsf. Core 345-U1415H-1R covered this depth interval, with 3% recovery. Drilling conditions in this hole were vastly different than in previous holes. All drilling parameters were much smoother and less erratic; however, when preparing to make a connection, the driller raised the bit off bottom. When the driller attempted to lower the bit back to bottom, immediate formation resistance was encountered. Drilling torque became elevated and erratic, indicating the hole had once again fallen in. Because it was considered unsafe to attempt making a connection under these circumstances, the decision was made to terminate the hole before possible loss or damage to another BHA. The bit was pulled clear of the seafloor at 0410 h on 28 December, ending Hole U1415H.

Hole U1415I

The location for this RCB-cored pilot hole was selected using 3.5 kHz data that indicated a thin sediment cover and bottom images that showed a flat-lying sedimented seafloor free of rock fragments.

Near-bottom camera survey

At the end of operations in Hole U1415H and while still at that location, we deployed the camera system, without the 3.5 kHz pinger, and moved the ship ~50 m northwest to the next potential site for a pilot hole. Once on location, a brief visual survey was conducted with the subsea camera confined to a ~5 m radius around the target coordinates. The area appeared to be relatively free of boulders or any indications of rubble.

Hole U1415I operations

After the camera system was recovered, we started Hole U1415I at 1110 h on 28 December 2012. Drilling proceeded much the same as in Hole U1415H, albeit with a slower rate of penetration (ROP). After penetrating ~6 m, drilling was halted, the drill string was picked up a few meters off bottom, and the circulating pumps were reduced. This initial test indicated that the hole was remaining stable. The test was repeated the following morning at ~9 mbsf with the same result, although once back on bottom, the drilling torque temporarily increased slightly as if something was being ground up below the bit. Associated with this increase in torque was an increase in ROP from 0.4 to 0.8 m/h. Slow penetration rates were to be expected given that we were applying a very light weight on bit (5 klb), as the majority of the BHA was still unsupported above seafloor. By mid-morning on 29 December, enough penetration had been achieved to allow the core barrel to be recovered and a drill pipe connection to be attempted. We deployed the sinker bars and Core 1R was recovered at 0945 h on 29 December. The core contained 0.16 m of gabbroic rocks from 0 to 11.7 mbsf. A drill pipe connection was made, the bit was run back to bottom, and coring resumed after circulating ~3.0 m of fill out of the bottom of the hole.

RCB coring continued in Hole U1415I to 35.2 mbsf under challenging conditions. Cores 1R through 4R extended from 0 to 35.2 mbsf, with 7.12 m of recovered core. The overall recovery includes three sections of coarse sand–sized gabbro particles (Sections 345-U1415I-3R-1, 3R-2, and 3R-3). One interpretation of the presence of these particles is that were simply cuttings. Later examination showed them to be more highly altered and fractured gabbroic material than the recovered core, suggesting that a zone of cataclasis was being drilled. We spent many hours attempting to stabilize the hole so that we could hang the drill pipe off at the rig floor to deploy a FFF, but we were unable to get the bit below 8 mbsf. We eventually abandoned the effort to deploy a FFF because of the excessive risk to the BHA. We pulled the bit out of the seafloor and retrieved a core barrel (Core 5G) that contained 0.21 m of gabbroic rocks inferred to have come from no deeper than ~5 mbsf. The RCB coring assembly was changed out for a 14.75 inch tri-cone drilling assembly and deployed back to the seafloor. When the camera system reached bottom, we easily found the mound of cuttings around Hole U1415I; however, the hole appeared to be collapsed, precluding a bare-hole reentry. We decided to abandon Hole U1415I and drill a new hole nearby instead.

Hole U1415J

Hole U1415J was sited in close proximity to Hole U1415I because of the nature of the significant layered gabbroic series recovered at the bottom of Hole U1415I. From the beginning, Hole U1415J was established as a reentry hole, in a nested FFF configuration with casing.

Hole U1415J operations

After our last operation in Hole U1415I, a failed attempt to reenter the hole with a 14.75 inch tri-cone bit, we offset the ship 10 m to the north, verified that the seafloor was free of any boulders, and observed the bit tag the seafloor at 4850.0 mbrf. After we recovered the camera system, Hole U1415J was spudded at 1855 h on 31 December 2012 using a 14.75 inch tri-cone bit. Drilling proceeded at ~1.2 m/h from 0 to 7 mbsf and then slowed to ~0.6 m/h until total depth of 4865 mbrf (15 mbsf).

After three wiper trips to clean the hole, we assembled a FFF around the drill string in the moonpool. The base of the FFF has an opening of 16 inches, and we did not attach a casing stinger below the FFF. We dropped the FFF and the drill string began taking weight soon after the FFF was deployed. We then spent 11.25 h washing and reaming the bottom 10 m of the hole. After one last wiper trip, the drill string and the 14.75 inch bit were recovered to the rig floor at 1400 h on 2 January 2013.

A 15 m string of 10.75 inch casing was made up and hung off the moonpool doors for free-fall deployment. A new 9.875 inch RCB BHA was made up and lowered through the casing to the seafloor for reentry. The 16 inch FFF was found buried upright in the cuttings pile of Hole U1415J; only the upper part of the rim and deployment shackles were visible. The FFF was reentered at 0420 h on 3 January and the camera system was retrieved. The drill string began taking weight at 9 mbsf and was easily washed down one more meter to 10 mbsf. The cone of a FFF was assembled around the drill string in the moonpool and connected to the cut-off joint of the 10.75 inch casing that had been previously hung off in the moonpool. The total length of the casing was 15.0 m from the cone base to the end of the casing shoe. The assembly was free-fall deployed at 0730 h on 3 January.

The hole was washed and reamed to total depth (15 mbsf) and circulated clean with two 25 bbl mud sweeps. Ghost Core 2G, containing 0.2 m of rock fragments and two buckets full of coarse sand, interpreted to be drill cuttings, was recovered from the cleaned interval at 1045 h. We resumed RCB coring and Cores 3R through 5R were retrieved. Hole problems required washing and reaming at ~32 and 35 mbsf, during which ghost Cores 6G and 7G were recovered by 0100 h on 5 January. Another fresh core barrel was dropped, and on this attempt the bit made it easily to total depth (34.9 mbsf) and RCB coring resumed. The hole drilled smoothly and Core 8R was recovered from 34.9 to 45.2 mbsf at 0805 h. During retrieval, the area between 4878 and 4882 mbrf (28 and 32 mbsf) remained problematic and was once again reamed and conditioned multiple times. RCB coring resumed at 0900 h, and Core 9R was cut from 45.2 to 55.3 mbsf and arrived on deck at 1200 h on 5 January.

Coring continued through Core 13R, which extended the hole to 79.4 mbsf. A wiper trip was conducted, and the bit was raised to 6.5 mbsf without encountering any problems. The bit was then lowered back into the hole and took weight at ~37 mbsf. The driller was able to wash and ream to 45 mbsf. The bit was lowered and encountered weight again at 57 mbsf. The driller washed and reamed the hole to total depth at 79.4 mbsf. The bit was raised off the bottom of the hole and became stuck at 72 mbsf with high circulation pressure, no rotation, and no ability to move the bit up or down. The pipe was worked for 2.5 h before it was pulled free with 100 klb overpull. The bit was pulled up to 6 mbsf inside the 10.75 inch casing. The core barrel that was in place during this wiper trip was recovered (Core 14G), and a new core barrel was dropped.

We decided to use cement to help stabilize the hole. However, we had not yet observed the nested FFFs and therefore did not know how far the 15 m of casing attached to the FFF extended into the borehole. We raised the bit back up into the 10.75 inch casing and deployed the camera system to constrain the height of the FFF above seafloor. The top of the second, “upper” funnel appeared to be ~2 m above the rim of the first, leaving the casing shoe at ~13 mbsf. After retrieving the camera system, we wanted to get the bit as deep as possible before cementing. After passing a tight spot at 38 mbsf, we were able to wash and ream to 57 mbsf. However, we could not get past this depth and stopped trying at 0800 h on 7 January. At this time, the core barrel that was in place during this washing and reaming was retrieved (Core 15G). We deployed a new core barrel, washed and reamed back down to 57 mbsf, and pumped 25 bbl of cement that contained 0.25 lb/sack of lost-circulation material. After the cement was in place, we raised the bit up to 15 mbsf and the 10.75 inch casing was flushed to remove any cement from this area. The bit was then pulled out of the hole, and the drill string was flushed to clear out any remaining cement residue. We slipped and cut 115 ft of drill line and then retrieved the drill string. The bit was back on the rig floor at 2315 h on 7 January.

We then assembled a new BHA with a 9.875 inch tri-cone bit for drilling out the cement. This bit does not recover core but has a more robust cutting structure for reaming and clearing operations. The drill string was lowered to the seafloor and we reentered Hole U1415J at 1130 h on 8 January. After recovering the camera system, the bit was run to 57 mbsf before encountering fill, without any evidence of cement. The hole was reamed once again to 77 mbsf and swept with high-viscosity mud. The bit was pulled up to 14 mbsf for a wiper trip and then lowered back down to 76 mbsf. The bit was then positioned at 63 mbsf, and a second remedial cement job was performed using 35 bbl of cement. During the cement job, the bit was lowered to 71 mbsf. After the cement was pumped, the bit was raised up to the casing shoe, and the 10.75 inch casing was flushed to ensure that no cement remained in this interval. The bit was pulled clear of the seafloor, and the drill string was circulated to flush any remaining cement from the pipe.

Because we wanted to drill out the cement with the same bit, we had to wait for the cement to harden. While waiting for this to happen, we conducted a near-bottom camera and 3.5 kHz pinger survey of two other potential drill sites. At the completion of the survey, we reentered Hole U1415J at 2215 h on 9 January. We felt that the cement still needed a little more time to harden, so we kept the bit in the 10.75 inch casing until 0630 h. On lowering the bit into the hole, we encountered the same obstruction at ~35 mbsf, but it was easily passed. This time, the bit encountered cement at 63 mbsf, which we drilled out to 73 mbsf. Several hours were required to drill back down to the total depth of the hole (79.4 mbsf). Little advancement could be made until we significantly reduced the pump strokes to ~30 strokes/min, which allowed the bit to advance to the bottom of the hole. Each time a mud sweep was pumped, clear pump pressure changes were observed suggesting that the cuttings might now be getting circulated out of the hole. We then drilled 5 m of new hole (to 84.4 mbsf) without coring in an unsuccessful attempt to reach a more competent formation. At this point, we decided to retrieve the drill string to switch back to a RCB coring BHA. The bit was back on the rig floor at 0600 h on 11 January.

We assembled a new BHA with a 9.875 inch RCB coring bit, lowered it to the seafloor, and reentered Hole U1415J at 1700 h on 11 January. The bit began to take weight at the normal 35 mbsf but was able to pass through quickly. The hole was then washed and reamed, reaching the bottom of the hole (84.4 mbsf) at 0130 h on 12 January. The core barrel used during this reaming (Core 17G) was recovered and on deck at 0230 h on 12 January. We dropped a new core barrel and resumed RCB coring. Core 18R advanced from 84.4 to 89.1 mbsf. All drilling parameters appeared stable and good. Initial indications were that the two remedial cement jobs were successful and that the cuttings were now being expelled from the hole. New fill on bottom between cores appears to be from the immediate formation being drilled into and not from uphole. Core 19R was advanced from 89.1 to 94.1 mbsf. Coring parameters remained reasonably constant and the penetration rate was initially 2.5 m/h but jumped to 5.0 m/h midway through cutting Core 19R.

After recovering Core 19R, we encountered challenges getting back to the bottom of the hole. Once we did, however, Cores 20R and 21R were cut from 94.1 to 101.8 mbsf and recovered 1.58 m (21%) of rocks. The hole conditions continued to be problematic, and we conducted a wiper trip up to 74 mbsf that encountered tight spots at 82 and 86 mbsf. Core 22G was recovered from this reamed interval. After eventually getting back to bottom, Core 23R extended 2 m into new formation (101.8–103.8 mbsf). Once again, we had challenges washing and reaming back to the bottom of the hole (103.8 mbsf). In the end, we were unable to get completely back to bottom and our pump pressures remained abnormally high, leading us to suspect that one or more bit nozzles were plugged. We decided to attempt cementing the lower 20 m of the hole (our third cement job in this hole) and then retrieve the drill string to replace the bit while the cement hardened. Before pumping the cement, we retrieved Core 24G. After positioning the bit at 96 mbsf, we pumped 12.5 bbl of cement. The bit was raised up to 76 mbsf while pumping the cement. The bit was then pulled to 15 mbsf so that any cement remaining in the casing/FFF could be circulated out. We pulled the bit out of the hole at 1605 h on 13 January. The drill string was then flushed of any remaining cement, and the bit was back on the rig floor at 0135 h on 14 January.

A new RCB (C-7) bit with a mechanical bit release (MBR) was assembled to the bottom of the BHA. We also added a fourth stand of drill collars to the BHA. After tripping to the seafloor, operations were put on hold while a slip and cut of the drill line was completed. We reentered Hole U1415J at 1542 h on 14 January. Once the camera system was back on board, the driller commenced lowering the pipe into the hole. The drill string took weight at 36 mbsf but was able to pass this interval relatively easily. The bit encountered cement at 78 mbsf and was drilled out to 99 mbsf (3 m below the bit depth when cementing). We washed and reamed the rest of the way back down to the bottom of the hole (103.8 mbsf). After we retrieved the core barrel that was in place while washing and reaming from 99.0 to 103.8 mbsf (Core 25G; 0.48 m recovered), we resumed RCB coring. While cutting Core 26R (103.8–111.8 mbsf), the first 4.2 m drilled at a slow 1.3 m/h, but the last 3.8 m was penetrated in <3 min. Core 26R was recovered on-deck at 0830 h on 15 January. While retrieving the core, the drill pipe became stuck. We tried to free the drill string for over an hour before deciding release the bit as the next step in freeing the drill string. When lowering the MBR shifting tool with the sinker bars to release the bit, we attached the core orientation (FlexIt) tool so we could determine the hole inclination. We had to offset the ship ~260 m (~5% of water depth) to lower a tool joint down nearly 8 m to the rig floor so that the core barrels could be removed and the shifting/FlexIt tools deployed. Our attempt to shift the MBR sleeve and release the bit was unsuccessful, so we retrieved the shifting tool. Data from the FlexIt tool indicated the hole was ±3° from vertical. This put to rest one proposed theory that we had been tracking down a high angle fault and might never drill out of the fractured material. On our second attempt to release the bit, we added a core barrel to the shifting tool and pumped it down to the bit at 70 strokes/min. The sinker bars were then run into the hole to retrieve the shifting tool and release the bit. However, before the sinker bars reached the core barrel, the drill string worked itself free. The sinker bars were recovered, leaving the core barrel and shifting tool in place. If we had recovered the core barrel, the sleeve would have shifted, leaving the bit and MBR in the hole. Once the pipe was free, we were able to pull the drill string, and the bit was back on the rig floor at 0130 h on 16 January. Because of the continually problematic and deteriorating hole conditions and the diminishing return on recovering core samples for science, the decision was made to abandon Hole U1415J and move to a different location.

Holes U1415K–U1415N

Hole U1415K consisted of a failed attempt to establish reentry capability that penetrated to 35.3 mbsf without any coring except for a single ghost core (345-U1415K-2G) that recovered 4.72 m of surficial mud, gravel, and rocks. Hole U1415L consisted of a jet-in to 4 mbsf; no cores were recovered. Hole U1415M was a failed attempt to establish reentry capability that penetrated to 25.9 mbsf without any coring except for a single ghost core (345-U1415M-2G) containing 5.87 m of surface gravel and mud. Hole U1415N consisted of RCB coring that penetrated to 37.0 mbsf and recovered a total of 1.56 m (4%) of olivine-phyric basalt and gabbro.

Hole U1415K operations

After moving ~400 m northwest of Hole U1415J, we lowered a new BHA with a 14.75 inch tri-cone bit to the seafloor and prepared to conduct a short camera survey prior to spudding the hole. However, the camera developed problems during the trip in and had to be recovered. A spare camera was installed before it was redeployed. We conducted an expanding box survey extending out 10 m, and a location to start Hole U1415K was chosen. We verified the seafloor depth (4698.4 mbrf) by tagging the seafloor with the bit, retrieved the camera system, and started Hole U1415K at 2155 h on 16 January 2013. The 14.75 inch hole reached a total depth of 35.3 mbsf by 0400 h on 17 January. A wiper trip was performed, and the bit pulled back to 6.6 mbsf. A 16 inch FFF without any stinger was deployed to facilitate subsequent reentries. The driller waited 1.25 h before pulling out of the hole to allow time for the FFF to reach the seafloor. The bit was then pulled clear of the seafloor at 2310 h on 17 January. We deployed the camera to observe the FFF cone; the cone was not upright and appeared to be nearly on its side. We felt that the base of the FFF cone was still in or immediately adjacent to the hole. We decided to retrieve the bit, change to an RCB BHA, and attempt to reenter the hole (either through the FFF cone or by a bare rock reentry). The ultimate goal was to deploy a second FFF with 10.75 inch casing to stabilize the upper ~35 m of hole and allow deeper coring. The 14.75 inch bit arrived back on the rig floor at 1110 h on 18 January. A 36 m length of 10.75 inch casing string was assembled and hung off in the moonpool doors using C-plates and casing elevators. The RCB BHA was assembled and lowered through the casing and back to the seafloor. The camera was deployed, and a seafloor survey was conducted from 2333 h on 18 January until 0051 h on 19 January in an attempt to locate Hole U1415K. No discernible hole or cuttings mound could be identified during the survey, and it was decided that the hole was located at the base of the leaning FFF cone. A reentry was attempted by placing the bit at the base of the cone. This was accomplished relatively quickly (~45 min) and the bit was lowered into the seafloor, penetrating 1–2 m before taking weight. We decided to retrieve the camera and to attempt to walk the bit into the hole using light bit weight and low rpm. A perceived reentry into Hole U1415K occurred at 0140 h. Rotation was applied for ~2 h without any luck in penetrating further into the hole. We decided to abandon our attempts to continue operations in Hole U1415K, retrieve the RCB BHA, and start a new hole with a 14.75 inch tri-cone bit. As of 1200 h on 19 January, the RCB BHA was still being recovered back to the surface. The RCB BHA and coring bit was back on the rig floor at 1510 h on 19 January. The seafloor positioning beacon deployed at the start of our Hess Deep operations on 22 December 2012 was nearing the expected lifetime of its batteries, so we commanded it to release at 1503 h and it was back aboard at 1639 h.

Hole U1415L operations

We assembled a 14.75 inch tri-cone bit and drilling BHA with three stands of drill collars and lowered it to the seafloor. While the BHA was being lowered, we also deployed the camera system with the same positioning beacon (with new batteries) and the 3.5 kHz pinger. The seafloor positioning beacon was commanded to release at the Hole U1415K coordinates, but it did not immediately fall to the seafloor. After 40 minutes of working the camera system up and down, the beacon eventually came loose. At 0515 h on 20 January, we started a visual and 3.5 kHz subbottom seafloor survey by moving the ship 95 m east of Hole U1415K. Unfortunately, the 3.5 kHz pinger ceased working before the survey commenced, but we continued with the visual inspection of the seafloor. After we arrived at the target location, we conducted a box survey extending out 10 m to ensure that no large boulders or rubble were in close proximity. We also tagged the seafloor with the bit, revealing an approximate seafloor slope of ~14° to the south. Hole U1415L consisted of a 1 h jet-in test that penetrated to 4 mbsf through sediment and soft rubble. Hole U1415L was spudded at 0845 h on 20 January, and the bit was pulled clear of the seafloor at 0900 h.

Hole U1415M operations

After recovering the camera system, Hole U1415M was started at 1240 h on 20 January. The initial penetration from seafloor to 5 mbsf went relatively quickly, indicating that the formation was sediment/soft rubble. From ~5 to 9 mbsf, the formation became hard with a significantly slower ROP (0.5–1.0 m/h) and smooth torque, as is typical of massive hard rock. The ROP increased again to ~4.0 m/h from 9.0 to 11.0 mbsf. A hard rock reentry system (HRRS)-style FFF with a 26 inch opening was assembled around the drill string in the moonpool. We did not attach a stinger or base plate. The funnel was deployed at 2100 h on 20 January. We then deepened the hole to 19.6 mbsf, where the hole began to pack off. We spent the next 4 h washing and reaming the hole and circulating high-viscosity mud. Eventually the hole was stabilized, and we continued drilling down to 25.9 mbsf. At that depth, the bottom of the hole became problematic and the bit was unable to penetrate deeper than 24 mbsf, so we conducted a wiper trip by raising the bit up to 8 mbsf and then lowering it to the bottom of the hole. However, the bit still could not penetrate past 24 mbsf. Another high-viscosity mud sweep was pumped. The camera system was lowered to observe the orientation of the FFF cone, but it was obscured by clouds of mud and cuttings coming from the hole. Portions of the rim of the FFF cone, however, were discernible at times buried in cuttings. We pulled the bit out of the hole at 1602 h on 21 January and then waited for 1 h to let cuttings settle for better visibility. The top of the FFF cone was clearly visible in the cuttings mound. The camera was retrieved, the drill string raised to 4660 mbrf, the top drive set back, and we performed a slip and cut of 115 ft of drill line. After the slip and cut, the drill string was recovered, and the bit arrived back on the rig floor at 0330 h on 22 January. Our next step was to assemble 25 m of 10.75 inch casing and hang it off on the moonpool doors. We assembled a RCB BHA with a used C-7 core bit (2 h rotating time in Hole U1415K) and lowered it and the camera system to the seafloor. The top drive was installed and the drill string spaced out for reentry into Hole U1415M. An attempt was made to maneuver the vessel for reentry; however, because of the drill string space out, the bit was positioned nearly at the seafloor, and the driller was unable to raise the bit any higher. This resulted in the bit repeatedly tagging the cuttings mound and the FFF, creating clouds of debris in the water column and completely obscuring the FFF cone. We offset the ship south to slightly deeper water while a 30 ft knobby was laid out and a 20 ft knobby was picked up, giving an additional 3 m of room in the derrick. We moved back over Hole U1415M and reentered the FFF cone at 1645 h on 22 January. The cone appeared to tip/shift as the bit made contact with the inner surface. Circulation along with slow rotation was used in an unsuccessful attempt to find the 14.75 inch hole. No progress was made, and we retrieved the camera system so we could use more rotation. This also was not successful, so we redeployed the camera system and offset the ship in an attempt to drag the funnel out of the way. This also did not work, and the FFF cone appeared to be solidly in place in the cuttings mound, wedged sideways into a large boulder that had been hidden beneath the seafloor sediment. We reentered the FFF cone for one last failed attempt to find the hole below the FFF cone. We then decided to abandon Hole U1415M at 0000 h on 23 January. Ghost Core 2G (assumed to be from 0 to 3.5 mbsf) was recovered at 0230 h on 23 January containing 5.87 m of surface gravel and mud from the multiple failed reentry attempts.

Hole U1415N operations

Because we had the RCB coring system in place, we decided to offset the ship to immediately spud a single-bit unsupported hole. The vessel was moved 15 m west of Hole U1415M. We recovered the camera system, dropped a new core barrel, and started Hole U1415N at 0340 h on 23 January. Core 1R was cut from 0 to 14.9 mbsf and was recovered at 1315 h on 23 January with 0.45 m of roller rocks. After retrieving Core 2R (14.9–18.9 mbsf; 0.15 m recovery), 4.75 h were spent to work the bit down to bottom before beginning to cut the next core at 2330 h on 23 January. Core 3R was a full 9 m advance (18.9–27.9 mbsf; 0.50 m recovered), and then the ROP for Core 4R (29.7–37.0 mbsf; 0.46 m recovered) was very high. After recovering Core 4R, the drillers were never able to work the bit back down to bottom. The hole continued to pack off (high pump pressures) and had high/erratic torque, as seen during the expedition associated with the unstable/rapidly drilled intervals. We decided to abandon Hole U1415N at 1700 h on 24 January. The bit cleared the seafloor at 1740 h and was back on the rig floor at 0145 h on 25 January. The core barrel that was in place during the final attempts to clean out the hole back to bottom (Core 5G) was recovered at 0125 h on 25 January. The four cores recovered from Hole U1415N extended from 0 to 37.0 mbsf and recovered 1.56 m (4%) of basement rocks.

Hole U1415O

Our only operation here consisted of drilling a 14.75 inch hole to 17.0 mbsf. After reaching this depth, we prepared to establish reentry capability but had to abandon the hole because of poor hole conditions.

Hole U1415O operations

Following unsuccessful operations at Holes U1415K–U1415N on the shoulder, we decided to move back to the bench. The BHA was changed to a drilling assembly with a 14.75 inch tri-cone bit and lowered to the seafloor. While the BHA was being deployed, a new FFF cone was prepared for deployment. We deployed the camera system with the 3.5 kHz pinger attached and conducted a seafloor survey around the target drilling location. We also observed the bit tag the seafloor at 4861.0 mbrf. The survey was completed at 1536 h on 25 January 2013 and the camera system was back on board at 1815 h. Drilling in Hole U1415O started at 1900 h. The bit was washed down 1.5 mbsf and then drilled in a massive, hard formation to 5 mbsf. At 5 mbsf, the bit penetrated 10 m (to 15 mbsf) in only 15 min. The formation firmed up from 15.0 to 17.0 mbsf by 0345 h on 26 January. We then successfully conducted a wiper trip and started to prepare to deploy the FFF cone. At this time, the hole began to collapse, and our attempts to drill and ream back down to bottom failed; we could only get back to ~8 mbsf. We decided to abandon Hole U1415O at 0700 h on 26 January. The bit cleared the seafloor at 0710 h, ending Hole U1415O.

Hole U1415P

Hole U1415P was sited on the southern margin of a small promontory, between Holes U1415G and U1415O. From the onset, Hole U1415P was established as a reentry hole and was intended to be a nested FFF configuration with casing similar to that at Hole U1415J. However, after deployment the initial FFF cone tipped over and could not be used. Instead, we successfully reentered the bare hole and installed a FFF with 12.5 m of 10.75 inch casing.

The primary accomplishment in Hole U1415P was RCB coring that extended from 12.5 to 107.9 mbsf and recovered 30.57 m (32%) of gabbroic rocks. In addition, material was recovered in five ghost cores obtained during hole cleaning operations in previously drilled portions of the hole.

Hole U1415P operations

After conducting a visual survey and selecting the position for Hole U1415P, we recovered the camera system, installed the top drive, spaced out the drill string, and started Hole U1415P at 1255 h on 26 January 2013. The 14.75 inch bit was washed without rotating to 2.0 mbsf (4866.0 mbrf), and drilling proceeded to 11.0 mbsf (4875.0 mbrf). We then assembled a HRRS-style FFF cone. The 26 inch interior diameter of this cone was reduced to 16 inches by attaching portions of a CORK fishing tool funnel (OF3620). In contrast to our previous FFF cone deployments, this time we attached a base plate to the bottom of the FFF. After the FFF cone was deployed to the seafloor, we continued drilling the hole to 12.5 mbsf. The camera was deployed to observe the orientation of the FFF cone and the bit pulling out of it. However, the FFF was very difficult to see through clouds of sediment. Eventually, we decided not to wait and pulled the bit out of the hole and through the FFF cone at 1545 h on 27 January. The bit appeared to heave down on the cone at least twice in the process. The bit was back on the rig floor at 0105 h on 28 January. We assembled 12.5 m of 10.75 inch casing and hung it off on the moonpool doors. Next, we assembled an RCB BHA, lowered it through the casing in the moonpool, and lowered it to the seafloor. The camera system was also lowered to the seafloor. Before we prepared to locate and reenter Hole U1415P, we had to slip and cut the drill line for the fourth time this expedition. After installing the top drive and spacing out for reentry, it was immediately apparent that the FFF cone was not sitting upright. Some camera perspectives looked as if the FFF cone was leaning to one side, whereas in other perspectives it appeared to be lying fully on its side. At the base of the FFF cone was a dark spot that appeared to be the top of the hole. Discussions alternated between attempting to reenter the cone or the hole. Eventually the pipe was maneuvered close enough to take a stab at cone reentry. The cone was indeed lying on its side at too high an angle for reentry, and this attempt failed. We then moved the bit over the dark area at the base of the FFF cone and successfully reentered Hole U1415P at 1450 h on 28 January. The total time expended after starting to search for the FFF cone was 2.6 h. The reentry of the bit into the open 14.75 inch hole with >4800 m (3.0 miles) of drill string deployed was quite an impressive feat achieved by the dynamic position and drilling staff. The camera system was recovered and the hole was redrilled from 8.0 to 12.5 mbsf and swept with high-viscosity mud. The core barrel used during washing and reaming this interval (Core 2G) was recovered with 2.36 m of rubble. Our next step was to assemble a FFF cone to the 12.5 m of 10.75 inch casing hung off in the moonpool. We free-fall deployed the 10.75 inch casing with the attached FFF and dropped a core barrel to start coring ahead. The driller could not identify the normal pressure spike that occurs when the core barrel has landed at the bottom of the BHA. When the pump pressure was increased to confirm the core barrel had landed properly, the rotary hose that supplies drilling fluid to the top drive suddenly burst. The hose failed on the top drive connection at 2400 psi even though the hose is rated to 5000 psi working pressure. After we installed a new hose, we reached the bottom of the hole (12.5 mbsf) at 0500 h on 29 January. We started RCB coring and Core 3R (12.5–18.1 mbsf) arrived on deck at 1225 h. We had some difficulty getting the bit through the transition from the 14.75 to 9.875 inch portion of the hole, but we were able to drill out this area (Core 4G; 12.5–16.5 mbsf). RCB coring resumed and Cores 5R–10R extended the hole from 18.1 to 45.6 mbsf and recovered 12.19 m (44%) of nicely cored pieces of gabbro. Core 11R was cut in only 45 min of rotating time. RCB coring continued to Core 18R, extending to 82.3 mbsf and recovered on deck at 0920 on 1 February. As the hole was deepened, we experienced faster coring rates through a formation inferred to be more fractured, leading to increasingly difficult hole cleaning. Eventually, we decided to pull out of the hole for a bit change because of increasing bit hours, decreasing recovery, and extended periods of washing/reaming back to bottom after recovering core barrels. We pulled the bit out of the hole, and the bit was back on the rig floor at 1845 h 1 February. After assembling a new C-7 RCB bit, we lowered the drill string, deployed the camera system, installed the top drive, and spaced out the drill string for reentry by 0530 h on 2 February. We reentered Hole U1415P at 0553 h. During reentry, we confirmed the top of the FFF cone was at 4862.5 mbrf. The height of the FFF from base plate to rim is 1.2 m, placing the base of the FFF at 4863.7 mbrf. The seafloor tag depth was determined to be 4864.0 mbrf on 26 January at slack tide. The FFF depth was established on 2 February when the tide tables indicated a high tide of 0.2 m. Therefore, the FFF appears to be installed right at the seafloor (4863.9 versus 4864.0 m).

We washed and reamed down to the bottom of the hole (82.3 mbsf) slowly to clean out the hole in small increments as opposed to loading up the annulus with large amounts of fill/cuttings and then having to wash these out all at once. After we finished washing and reaming down to the bottom of the hole (82.3 mbsf), we recovered the core barrel used during this hole cleaning (Core 19G; 0.6 m recovered) at 1920 h. We resumed RCB coring and Core 20R was cut from 82.3 to 89.4 mbsf. Before retrieving Core 20R, the hole had to be washed and cleaned enough to attempt making a connection. At the time, several bit nozzles were also plugged. At 0030 h on 3 February, we were able to remove a drilling knobby so that Core 20R could be recovered (0130 h) with 2.42 m of nicely cored gabbro. A new core barrel was deployed, and the drillers were able to partially unplug the bit nozzles. Before coring could resume, the hole had to be washed and reamed from 79.0 to 89.4 mbsf. At 0900 h, the core barrel deployed during this reaming was retrieved (Core 21G). We had to wash and ream back to the bottom of the hole again but then continued coring from there. Cores 22R and 23R were recovered from 89.4 to 107.9 mbsf and recovered 4.87 m (26%). After retrieving Core 23R, hole conditions began deteriorating, with the hole packing off and the bit taking weight ~9 m above the bottom of the hole. As we had just added a joint of pipe and the bit was unable to pass below this depth, we had to offset the ship 100 m to reach a connection so that the driller could pull up and lay out the same piece of pipe. At this point, we raised to 76.0 mbsf, resumed hole cleaning, reamed back down to the bottom of the hole (107.9 mbsf), and recovered the core barrel used during the reaming (Core 24G). Once again, the hole packed off and circulation and rotation were lost while making the connection after laying out the barrel, so we offset the ship 100 m (2% of water depth) to reach a connection in order to remove more drill pipe. We raised the bit to 79.0 mbsf and started to work the bit back down. However, after making another connection the bit could not be advanced further because of high torque, packing-off, and plugged nozzles. Ultimately, we decided to stop trying to core and to conduct a wiper trip to prepare the hole for logging.

To prepare for logging, we raised the bit to 11.9 mbsf (inside the 10.75 inch casing) and then lowered it back down the hole. Problems were encountered at 41, 55–60, and 84–90 mbsf that had to be drilled through. We elected not to attempt to clean out the ~18 m of hard fill in the bottom of the hole. At 1215 h on 4 February, the bit was back up to 11.9 mbsf (inside the casing). We deployed the camera and pulled the bit clear of the hole at 1434 h. At 1449 h, we observed the bit successfully release from the BHA. The end of pipe reentered Hole U1415P at 1550 h after only 15 min of maneuvering. We recovered the camera, placed the end of pipe at 10 mbsf, and lowered the first logging string into the hole (caliper and Dipole Sonic Imager). We had decided to deploy a very short logging string because of the poor hole conditions and risk of the tools getting stuck. The logging tool string could not pass 24 mbsf (11.5 m below the 10.75 inch casing shoe). The logging tools were retrieved so that the end of pipe could be lowered past the trouble area. The drill pipe could not be lowered past 20 mbsf (7.5 m below the casing shoe), so we terminated our logging. We pulled the bit out of the hole at 0315 h on 5 February. RCB coring in Hole U1415P extended from 12.5 to 107.9 mbsf and recovered 30.57 m (32%) of gabbroic rocks. In addition, five cores were recovered from previously drilled portions of the hole during the hole cleaning operations.

Because there was not sufficient time remaining to conduct any further drilling operations as we had dropped the bit for logging, we deployed the camera and 3.5 kHz pinger to conduct a final seafloor survey across Hole U1415P. The survey was completed at 0845 h on 5 February. Although the drill string was back on board at 1745 h, the beacon retrieved at 1838 h, and the hydrophones raised by 1900 h, we delayed our departure until 2000 h so that inductively coupled plasma–atomic emission spectroscopy geochemical analyses that are sensitive to ship motion could be completed. After we raised the thrusters, we started our transit to Balboa, Panama, at 2048 h, about a half day ahead of the scheduled departure time. During the transit, ship local time was shifted ahead 1 h on 7 February (to UTC – 6) and 1 h on 9 February (to UTC – 5). The ~1467 nmi transit from Hess Deep to Balboa took 6.5 days at 9.3 nmi/h. Expedition 345 ended with the first line ashore at 1151 h on 12 February 2013.

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