EXPEDITION 304 OPERATIONS SUMMARY

Port Call

The Ponta Delgada, Azores Islands (Portugal), port call was completed in 3.5 days. Pacing items for the port call were loading of specialty hardware required for the advanced diamond core barrel system and the hard rock reentry system (HRRS), delayed incoming airfreight, and maintenance on the active heave compensator (AHC).

The last line away from Berth 12, Ponta Delgada, was at 2012 h on Saturday 20 November 2004. The transit was uneventful, with the ship averaging 11.1 kt over the 939 nmi distance. The vessel arrived at location (based on Global Positioning System coordinates) and launched a beacon at 0830 h on 24 November.

After arriving at Site U1309, we assembled the BHA and ran the pipe to just above the seafloor. Operations began with a VIT camera bottom survey to determine suitable locations to spud the pilot hole and to install the HRRS. The survey was completed in <2 h, and an appropriate area was selected for drilling (devoid of large boulders or rubble). A water sample and temperature measurement were collected with the Water Sampling Temperature Probe (WSTP) from just above the mudline. The first hole (Hole U1309A) was a punch core with the RCB assembly to capture the surface sediments. Rotary coring commenced in Hole U1309B (without moving ship location) at 0050 h on 25 November. Weight on bit started at 4000 lb with a rotation of 30 rpm and was gradually increased to 12,000 lb at 55 rpm as the BHA drilled into the hard formation. Penetration rates started at <1 m/h but increased to >2 m/h with the increased weight on bit and increased rotation. A brief test of the AHC system was conducted at the start of coring operations, but the vessel heave (4–5 m) proved too large for the AHC. Previous experience limits the use of the AHC to ~2.5 m maximum heave.

Coring continued to 101.8 mbsf (Table T1), when penetration ceased, likely owing to bit failure after >86 rotating hours. The mechanical bit release (MBR) was activated, and the bit was released at the bottom of the hole. The annulus was displaced with drill (fresh) water for logging and the pipe pulled back to 25 mbsf. Three logging runs were completed including the triple combo and FMS-sonic tool strings and a test of the logging heave compensation winch. Logging was completed and operations in Hole U1309B ended at 0805 h on 1 December.

The HRRS was run in an attempt to install 31.5 m of casing in Hole U1309C, 20 m west of Hole U1309B. The hammer-in casing attempt started at 0945 h on 2 December. After ~5–6 m penetration, high torque and loss of pipe rotation dictated an inspection with the subsea camera. This inspection revealed that the casing running tool had prematurely released, disconnecting the BHA with the hammer from the casing string. With no further advancement possible, Hole U1309C was abandoned. A 25 m length of 13³/₈ inch casing was left sticking out of the seabed at Hole U1309C. A new drilling target (Hole U1309D) was selected, the HRRS system was prepared, and the vessel was offset 20 m north of Hole U1309B. Hole U1309D was spudded at 0120 h on 4 December. The HRRS was drilled to 20.5 mbsf, leaving 4.5 m of casing above the seafloor. After running the reentry cone, the VIT was deployed to inspect the HRRS. All components appeared to be in place. The BHA was pulled clear and tripped back to surface. An RCB BHA was then assembled to reenter Hole U1309D to core ahead from 20.5 mbsf.

The first reentry into Hole U1309D was accomplished in 10 min by 0240 h on 6 December. Cores 304-U1309D-1R to 22R (20.5–131.0 mbsf; recovery = 51%) were predominantly 4.5 m penetrations, but two ~9.5 m cores (Cores 16R and 17R; 89.0–107.9 mbsf) were cut to compare recovery rates. Penetration rates and operating parameters were similar to pilot Hole U1309B. Coring was terminated at 60.75 bit rotating hours to prevent bit deterioration from affecting hole conditions. After the bit cleared the top of the reentry cone at Hole U1309D, the vessel was moved to Site U1310 using the dynamic positioning (DP) system.

During the DP transit to Site U1310, drill pipe was added to reach the estimated 2580 m of water depth. A subsea camera survey located a target for Hole U1310A, and after a punch test to determine sediment thickness, the pipe was recovered. The bit cleared the rotary table at 1520 h on 10 December, officially ending Hole U1309D and starting Hole U1310A. The bit was in poor condition, with numerous missing and broken teeth and three loose cones.

The HRRS was assembled and tested at the rig floor prior to deployment. During the initial assembly, an error was discovered in the length measurement of the new nonagon design bit. This resulted in the overall casing length being too short for the BHA. The bottom joint of casing had to be removed and the ring bit removed from the casing and reinstalled on a longer joint of casing. The completed assembly was then deployed to the seabed and a drill pipe measurement to the seafloor was recorded at 2594 meters below rig floor (mbrf). The HRRS was spudded at 0000 h on 12 December. Hammer drilling continued for the next 6.75 h with little penetration. The HRRS was pulled back to the surface, and it was clear that the nonagon design bit had failed. The drive bit had pushed through the ring bit and could not have been engaging during hammer operation. The nonagon pilot bit and nonagon ring bit were changed to a wing bit with an open casing shoe.

After 6 h during this HRRS installation attempt, penetration stopped and we were unable to maintain rotation. We pulled the hammer assembly from the seafloor, moved 10 m north, and attempted a third penetration. After 5 h, penetration stopped again with ~6 m of hole, so we pulled and inspected the hammer system. The bit was missing gauge buttons from the outside of the wings. The casing was shortened to a single joint, and a new wing-style reamer bit was installed. We elected to reenter the short hole started with our previous installation attempt to reduce the required depth of penetration. After a total of ~13 m of penetration, the penetration rate was so slow we decided to release the casing and continue with the reentry funnel deployment. However, we could not extract the pilot bit from the hole even after multiple attempts. After a several-hour struggle, we were finally able to extract the assembly, casing in tow, from the seabed. When brought to the rig floor, we determined the running tool had released the casing, but the wing-style reamer bit was lodged in the lower end of the casing, preventing extraction of the bit. One reamer arm was missing and the lower part of the casing was bent. Since no installation was successful, but basalt pieces were recovered from behind the arms of the hammer and within the casing, we elected to call all the attempts collectively Hole U1310A and curated the material recovered as Core 304-U1310A-1M (miscellaneous).

For fear that the missing reamer arm lay at the bottom of Hole U1310A, the vessel was offset 10 m to the east and an RCB coring assembly was deployed to initiate a bare rock penetration in Hole U1310B. Hole U1310B was spudded at 2250 h on 15 December. The first coring interval (Core 304-U1310B-1R; 0–18.5 mbsf; recovery = 7%) required 30 h to complete. High torque and rubble falling into the hole were relentless during the coring operation. After recovering Core 304-U1310B-1R, 3 m of fill had to be cleared from the hole before continuing coring. Cutting Core 304-U1310B-2R required an additional 16.5 h. When the wireline failed to retrieve the core barrel (after two attempts), the operations team surmised we had lost the lower part of the BHA. Recovery of the pipe proved this to be the case and ended operations at Site U1310.

A <1 nmi transit brought us to our alternate hanging wall drilling location. After a brief subsea camera survey, Hole U1311A was spudded with an RCB assembly at 2040 h on 18 December. Core 304-U1311A-1R (0–12 mbsf) required >26 h to cut.

After the first core had been cut in Hole U1311A there was at least 3 m of fill in the 12 m deep hole. We attempted to clear the hole for several hours, without success, and the hole was abandoned. Based on our prespud bottom survey, we elected to move ~100 m north, survey another location, and attempt another hole at this site.

Since we had not been able to keep a hole clear of fill at Site U1310 or in Hole U1311A, we decided to attempt to drill a large-diameter bore without coring. We hoped this strategy would allow deployment of a casing to isolate the upper part of the formation and allow deeper penetration. The two options left in our arsenal of drilling tools were a large rotary bit and the wing-style, reaming hammer bit. We surmised that the rotary bit was not likely to be successful, based on our attempts with rotary coring bits. The larger bit face would translate to less weight on bit per unit area, thus yielding even slower penetration rates. In addition, the size difference between the top of the bit and the BHA would provide ample space for rocks falling into the hole to trap the bit. After a brief subsea camera survey, we chose a location with a smooth sediment cover to deploy the hammer bit. Although there was an initial rapid penetration rate, at a depth of only a few meters below seafloor penetration virtually ceased. High torque stalled rotation, and picking the bit up off bottom to regain rotation allowed rock to cascade into the hole underneath the bit. We hammered for ~19 h, but could gain no headway, so operations at Site U1311 were terminated.

Following a pipe trip to install an RCB BHA, we reentered Hole U1309D through the HRRS and recommenced coring at 131 mbsf. Cores 304-U1309D-23R to 47R (131.0– 252.4 mbsf) were cut, with an average recovery of 64%. We made a pipe trip to pick up a fresh bit, and coring continued through Core 304-U1309D-78R with 74% recovery (average recovery for Hole 1309D = 58%). We terminated coring at 401.3 mbsf after the RCB bit had accumulated 56 rotating hours. The hole was cleaned and filled with freshwater in preparation for logging. A shallow-penetration hole (Hole U1309E) was cored to 3.8 mbsf 10 m east of Hole U1309D (Core 304-U1309E-1R). Continuing with efforts to capture the oldest sediments draping the central dome of Atlantis Massif, as well as the detachment surface, we moved the vessel in DP mode to a site 275 m northwest of Hole U1309D. Hole U1309F was initiated with the RCB and cored to 4.8 mbsf (Core 304-U1309F-1R). Since RCB coring was not successful in recovering the uppermost basement in either Hole U1309E or U1309F, we tripped the pipe in preparation for logging.

We reentered Hole U1309D with a new APC/XCB bit, and our intention was to log the hole then attempt shallow cores with the XCB. The bit was positioned in the casing, but the logging tools were unable to pass an obstruction at ~40 mbsf. Since the XCB bit would not fit in the RCB hole, we terminated the logging attempt and pursued shallow-penetration coring. We made a transit in DP mode to an alternate location on the dome, where a submersible dive had observed a hard carbonate cap (interpreted to represent the oldest sediment cover on the dome) directly overlying basement. Core 304-U1309G-1X was cored to 3.5 mbsf, but no hard carbonate or recognizable fault rock was recovered. We elected to make a final attempt to recover the lithified carbonate and upper basement with the APC. Only the upper half of the APC barrel returned. Subsequently, we chose to trip the pipe to install a logging bit to guide the pipe past the obstruction in Hole U1309D and accomplish our logging objectives in that hole. Triple-combo and FMS-sonic tool string runs were successful, but an Ultrasonic Borehole Imager (UBI) run was not attempted since the second FMS pass ended with fallen rock briefly trapping the tool in the hole. The tool was extracted with no significant damage.

After logging operations were concluded, there was sufficient time left in the expedition for a short bit run. We elected to attempt a single, short RCB core at the same location as Hole U1309G. Using the retired bit from our last coring run, we attempted coring to a depth of just more than 2 m below the soft sediment blanket, but the core barrel returned empty. With ~5 h of operations time left in the expedition, the bit was returned to the seafloor and Core 304-U1309H-1R was cut without circulation in the upper 0.5 m and low pump pressure for the remainder of coring (~3.5 m). The pipe was pulled and inspected, and we were under way for Ponta Delgada by 0700 h on 4 January 2005.