Hole 1106A
A Holte CUB was made up to the SDS hammer drill, and using the same HDS BHA configuration as previously used, the assembly was lowered to the seafloor. The VIT camera was deployed for a seafloor survey. The Site 1104 holes were quickly located. So as not to confuse the Site 1104 holes with the Site 1106 holes, the ship was offset ~20 m to the north on the same outcrop. It was theorized that the nose TCI damaged on the previous bit may have resulted from the bit heaving off the seafloor as we attempted to keep the bit in place on the seafloor during retrieval of the VIT. The decision was made to spud Hole 1106A with the bit off bottom. Thus the VIT camera was retrieved with the bit clear of the seafloor.
Once the VIT was back on board, the pump was engaged and a flow rate of 200 gpm established. Circulation was maintained for several minutes to flush any air out of the system. While maintaining a 200 gpm flow rate, and no rotation of the drill string, at 1600 hr 12 May, the bit was lowered to the seafloor and Hole 1106A was spudded. The water depth was determined to be 740 mbrf by drill pipe measurement. The hammer began to cycle immediately and the flow rate was slowly increased. The heave at the rig floor was estimated to be 2 to 3 m and, as a result, the bit was heaved off bottom several times, causing the hammer to stop and restart. After ~10 min of drilling, penetration began to be made and the hammer operation settled out somewhat. Heave was still a major problem and, because of a cross swell, roll factored into the difficulties as well.
The drill bit had penetrated ~0.5 m when the torque began to increase and become erratic. The weather was deteriorating, and heave at the rig floor resulted in constant stop-start problems with the hammer. Several yellow (2%) automatic station keeping (ASK) system alerts occurred, indicating the dynamic positioning (DP) system was having a hard time holding the ship on station in the increasing wind. The DP operators also reported that the noise from the hammer was occasionally interfering with the acoustics of the ASK system. After ~3 hr drilling and 2 m penetration, 1000 psi was lost and the hammer quit running. The pump was stopped and the backup pump (#1) was engaged with similar results, indicating the problem was downhole. Drilling operations were suspended and the hammer retrieved for inspection.
With the hammer and bit on deck at 2230 hr 12 May, an inspection was carried out. The Holte CUB had suffered much the same damage as did the SDS bits (Fig. 24). All of the TCIs on the underreaming arms, except for the last one on the trailing edges, were broken off. Also, four TCIs near the shoulder of the pilot bit were broken off as well. Disassembly of the hammer revealed the valve was cracked similarly to the first cracked valve. The other internal parts of the hammer appeared to be in good shape.
Hole 1106B
A new valve was installed in the hammer, and a Holte eccentric underreaming bit was attached to the SDS hammer. The hammer and bit assembly was then deck tested. The hammer cycled immediately and was cycled for 6 min. The hammer and eccentric bit were made up to the HDS BHA and tripped to the seafloor. The VIT camera was deployed to locate a spud site. After locating the spud site and with the bit off bottom, the VIT was retrieved. The pump was engaged, and a flow rate of 150 gpm was established. At 0640 hr 13 May, the bit was lowered to the seafloor and Hole 1106B was spudded. The water depth was determined to be 741 mbrf by drill pipe measurement. After tagging bottom, the flow rate was slowly increased. It appeared as though the bit may have skidded downhill ~0.5 m during spudding. The hammer began to cycle smoothly and penetration was being made when the bit appeared to heave out of the hole and skid downhill ~1 m. The torque immediately increased and became erratic, causing the top drive to stall. Heave continuously opened the hammer bypass. After 1 hr of drilling with virtually no penetration, we stopped drilling and retrieved the bit for inspection.
Inspection of the Holte EUB revealed similar wear patterns as observed on the concentric bits (Fig. 25). The outer edge of the eccentric was severely abraded and most of the TCIs on the outer edged of the eccentric were broken. Several TCIs on the pilot bit shoulder were also broken. The EUB was determined not to be usable.
Hole 1106C
The SDS flat-face drill bit (Fig. 26) was the last hammer drill bit on board to test. Although the aim of the HDS is to drill in casing, which requires an underreamer bit, the drill bit was deployed in an effort to prove that (1) the hammer drill could drill hard rock and (2) it was the premature deterioration of the underreamer arms that was preventing deep penetration. In anticipation of a long drilling run, the hammer drill was disassembled and a new cartridge installed. The drill bit was attached to the refurbished hammer drill and the assembly deck tested. The hammer cycled perfectly and was run for ~2 min. We reduced the flow rate to 130 gpm and picked up the hammer to check the bypass, which opened as expected.
The drill bit and hammer drill were made up to the same HDS BHA and tripped to the seafloor. The VIT camera was deployed to locate a specific spud site for Hole 1106C. After retrieving the VIT camera, the pump was engaged at 150 gpm to flush air out of the system. While we maintained flow rate, the drill bit was set on the seafloor at 1840 hr 13 May, and Hole 1106C was spudded. Water depth was determined to be 742.5 mbrf by drill pipe measurement.
After ~25 min of drilling and 1 m penetration, the pressure began to increase and the hammer began to cycle intermittently. The bit was raised off bottom to open the bypass and flush the hammer. When the bit was set back on bottom, the pressure again began to rise and the hammer still cycled intermittently. The back-up pump (#1) was engaged and similar events occurred, indicating the problem was probably downhole. So, the hammer was retrieved for inspection. While the hammer was retrieved, the drill string stayed full of water. This was an indication that the hammer check valve was not allowing the water inside the drill string to drain out as it was retrieved.
Once on deck, the hammer was disassembled for inspection. The initial cartridge was removed, and the coating on the piston appeared to have chipped off, probably by cavitation erosion. The piston was found to have galled to the lower bushing and was stuck in the full up position. With the piston being stuck in the full up position, the check valve was prevented from opening and the water could not drain from the drill string. The piston sticking was also thought to be the cause of the high operating pressure and intermittent cycling. The drill bit was found to be in good condition and reusable.
Hole 1106D
The hammer was refurbished with another complete cartridge and the same flat-faced drill bit installed. The assembly was then deck tested, and the hammer performed as expected. The hammer and bit were then made up to the same HDS BHA and tripped to the seafloor. The bit was set on the seafloor and at 0340 hr 14 May, Hole 1106D was spudded with 2 m heave at the rig floor. The flow rate was slowly increased, and the hammer cycled normally.
After ~4 min of drilling, the pressure began to rise and the hammer began to cycle intermittently. The flow rate was reduced to stop the hammer and then increased slowly to restart the hammer. As before, the pressure continued to rise and the hammer cycled intermittently. The bit was raised off the seafloor to open the bypass and flush the hammer. When restarted, the hammer once again operated intermittently at higher than normal pressure. It was assumed that the piston and lower bushing had galled again, so the hammer was retrieved for inspection.
Once on deck, the hammer was disassembled for inspection. The initial cartridge was removed and the coating on the piston once again appeared to have chipped off, probably by cavitation erosion. The piston was found to have galled to the lower bushing and was stuck in the full up position. The extent of the galling did not appear to be as bad as that observed in the cartridge used in Hole 1106C. Once again, with the piston being stuck in the full up position, the check valve was prevented from opening, and the drill string had to be pulled full of water. The drill bit, however, was found to be in good condition and reusable.
Hole 1106E
The hammer was rebuilt with the same piston and valve. However, the lower bushing used in Hole 1106C had been repaired in the ship’s machine shop, and it was assembled in the hammer. The drill bit was still in good condition, so the hammer and drill bit were made up and deck tested. The hammer was cycled for 2 min at 200 gpm and 650 psi, which are nominal readings. A noticeable reduction in the stand pipe and derrick vibrations was observed, even though the flow rates and corresponding pressures were consistent with those of a new hammer.
The bit and hammer were tripped to the seafloor with the same HDS BHA configuration. The pump was engaged at a low flow rate of 150 gpm to flush out any air in the system. After a few minutes of flushing, the bit was lowered to the seafloor and Hole 1106E was spudded at 1140 hr 14 May. The drilling depth was determined to be 741 mbrf by drill pipe measurement. During this time, the average heave at the rig floor was estimated to be 3 to 4 m, with occasional 5-m heaves.
After ~15 min of drilling, the hammer drill began to make significant penetration. Despite constant opening of the hammer bypass caused by heave, the hammer drill continued to advance the borehole. Torque was slightly erratic, ranging from 2500 to 5000 ft/lb for most of the drilling. Occasionally the top drive would stall. However, when this happened, the hammer was allowed to keep cycling, and it soon drilled itself off, allowing the drill string rotation to resume.
After ~1 hr and 40 min and 8 m penetration, the stand pipe pressure transducer nipple failed because of stand pipe vibration, and the pump had to be stopped to repair it. The bit was pulled 4.5 m off the bottom of the hole, with a momentary 20,000 lb overpull. Slow rotation of the drill string was maintained as the pump was shut down. The stand pipe bull plug containing the pressure transducer was removed and a blank bull plug was installed in its place. The repairs took ~5 min.
When the pump was engaged, little or no pressure was observed, consistent with pumping through open-ended drill pipe. The back-up pump (#1) was engaged with similar results, indicating the problem was downhole. The drill string was then lowered in anticipation of tagging the bottom of the hole. After the end of the pipe had been lowered 4.5 m below the last TD of Hole 1106E, we decided to pull the bit clear of the seafloor and deploy the VIT camera for observation.
Once the VIT camera had reached the end of the pipe, it appeared as though all of the drill collars were still intact, and the crossover sub between the drill collars and the jet sub on top of the hammer could be seen. However, the jet sub, hammer, and bit could not be seen. The end of the pipe and the VIT camera were lowered to survey the seafloor. Several boreholes were observed. One of the boreholes appeared to have something in it, but it could not be confirmed as being the hammer. The sea state at the time of the survey caused the view of the seafloor to move in and out of focus. A further survey of the seafloor did not reveal the hammer, so either the hammer was still in the hole, out of sight, or had dropped onto the seafloor and rolled down slope. The VIT camera and drill string were then retrieved.
When the end of the drill string was retrieved, all of the drill collars and the crossover sub between the drill collars and the jet sub were recovered. The jet sub, hammer drill, and bit were missing. The pin connection on the bottom of the crossover sub showed signs of having pulled out of the box connection on top of the jet sub. Two theories have been put forth as to when the failure may have occurred. The first theory is that the jet sub box connection had been weakened or even split by the pounding the bit was taking as a result of the excessive heave during spudding. When the bit was pulled off bottom and the momentary 20,000 lb overpull was observed, the bit may have hung up on the borehole wall and the crossover sub pin may have pulled out of the weakened jet sub box. The second theory is that while waiting on the stand pipe to be repaired with the hammer heaving in the borehole, the BHA may have leaned over, causing the jet sub box to fail. By pulling the bit 4.5 m off the bottom of the hole, the jet sub was positioned at, or near, the seafloor, compounding the bending problem.
Although enough spare parts were on board to assemble a second hammer drill, the decision was made to halt the hammer drill testing because there were no more hammer drill bits available to be tested that would have increased the hammer drill test data base. Also, because of the weather conditions, lack of reentry hardware, time constraints, and high probability of loss of the fishing equipment, it was not thought prudent to attempt to fish for the lost hammer. The 9-1/2-in drill collars used in the HDS BHA were inspected, with no cracks found, and laid down. The drillship was secured for sea and at 2312 hr 14 May, the JOIDES Resolution got under way for the next site.