A positioning beacon was deployed at 1925 hr 29 April, establishing Site 1104. The hammer drill was prepared for deployment for the first series of spudding and drilling tests without casing. The bottom-hole assembly (BHA) used for the HDS testing was made up of SDS concentric bit #1, hammer drill, jet sub, crossover sub (OG0726), four 9-1/2-in drill collars (OG0244), crossover sub (OG0725), one 8-1/4-in drill collar (OL1040), one tapered drill collar (OG0300), six joints of 5-1/2-in drill pipe (OG0052), and a crossover sub (OG1010) to 5-in drill pipe.
The BHA was tripped to the seafloor and the VIT camera deployed for a seafloor survey. The point of reference for the survey was the hard rock guide base at Hole 735B. Once Hole 735B was located, the ship was offset ~75 m west to the primary HDS testing site. Massive, sediment-free outcrop was observed at the primary test site. However, based on the most recent survey information received from H.J.B. Dick aboard the James Clark Ross (pers. comm., 1998), a second test site was explored ~200 m northwest of Hole 735B. Massive, sediment-free outcrop was also observed at the second site, and the decision was made to begin the hammer drill testing at the second site. For better positioning of the ship, a second positioning beacon was deployed at 0224 hr 30 April.
Site 1104 Spud Test
Water depth was determined to be 740 meters below rig floor (mbrf) by drill pipe measurement. With the VIT camera deployed and no rotation of the drill string, several spud tests were conducted. The hammer performed well during the spud tests, and the decision was made to recover the VIT and move on to the drilling tests.
Hole 1104A was spudded at 0620 hr 30 April, with an SDS underreaming bit. The pointed pilot bit did not skid as the hole was initiated. However, it is suspected that the bit heaved off bottom occasionally, thus starting a new hole. Only enough weight on bit (WOB), ~8000 to 10,000 lb, was applied to the hammer to keep the bit on bottom and the hammer bypass closed. It appeared that once the pilot bit was below the seafloor, the hammer performed better. Heave constantly caused the hammer bypass to open, causing the hammer to stop cycling and then restart. After ~1 m penetration the torque increased and became erratic. Excessive vibration in the stand pipe and derrick was noted.
After ~45 min of hammering and 1.5 m penetration, the bit was pulled clear of the seafloor with a slight overpull of 10,000 to 15,000 lbs. The VIT camera was deployed to observe the borehole, which was found to be a clean symmetrical circle in the rock outcrop. The bit was set back on the seafloor, and while maintaining WOB, the VIT camera was retrieved in preparation for another drilling test.
With the VIT camera back on board, Hole 1104B was spudded at 0830 hr 30 April. The water depth was determined to be 739 mbrf by drill pipe measurement. The hammer began cycling smoothly as the flow rate was slowly increased with no rotation of the drill string. After a few minutes of spudding, the top drive was engaged to begin rotation of the drill string. Excessive vibration in the stand pipe and derrick were once again noted. At 0900 hr 30 April, the rig air pop-off valve failed and drilling had to be stopped, while the bit remained in the hole. The pop-off valve was soon isolated and drilling resumed. Torque soon increased and became erratic. The hammer bypass was constantly opened, presumably by heave, causing the hammer to stop cycling and then restart. At 1130 hr 30 April, after hammering for ~2 -1/2 hr with 1.5 m penetration, the bit became stuck. The bit was freed at 1150 hr 30 April, and kept on bottom as the VIT camera was deployed to observe the bit and borehole. The bit was pulled clear of the seafloor at 1230 hr 30 April, and appeared to be intact. The borehole was somewhat oval shaped, presumably from being spudded on a slope.
The bit was set back on the seafloor and while WOB was maintained, the VIT camera was retrieved in preparation for spudding Hole 1104C. With the VIT camera back on board, the pump was engaged, and the flow rate slowly increased, but the hammer would not cycle. The hammer was pulled clear of the seafloor to open the bypass and be flushed. However, similar results occurred when the bit was set back on the seafloor, closing the bypass. The standby pump (#1) was engaged to make sure a problem with the pumps did not exist. The same pressure drops vs. flow rates were recorded, and the hammer did not cycle. The hammer and bit were retrieved for inspection.
Once back on board, the hammer was disassembled and it was determined that the hammer valve had cracked, allowing fluid to bypass it and thus preventing the hammer from cycling. It is theorized that the pressure transients across the valve created by the constant opening and closing of the hammer bypass may have been the cause of the cracking. A new valve was installed in the hammer, and the hammer was deck tested. The hammer was cycled for ~6 min at 100 gpm and 330 psi and at 200 gpm and 560 psi, with no problems. The pressure vs. flow rate curve was the same as for the new hammer, possibly indicating that no appreciable wear had occurred on the piston or other internal parts of the hammer during the two previous runs. The SDS CUB was not reusable. The TCIs on all three of the underreaming arms were sheared or broken off, except for the last one on each of the trailing edges (Fig. 21). Heavy abrasion was also observed on the gage surfaces of all the underreaming arms. The pilot bit was in good shape, except for one chipped TCI.
With a new bit (SDS CUB #2) installed on the refurbished hammer, the BHA was tripped back to the seafloor. The VIT camera was deployed and a spudding location chosen. The bit was set on the seafloor and, while maintaining WOB, the VIT was retrieved. Once the VIT was back on board, Hole 1104C was spudded at 0105 hr 1 May. The water depth was established at 739 mbrf by drill pipe measurement. The pump was engaged and the flow rate increased slowly with 5 to 10 rpm drill string rotation. After ~10 min of drilling and 0.5 m penetration, there was a pressure loss observed, presumably from the hammer bypass opening, and the flow rate was slowed. The flow rate was once again increased with normal pressure versus flow rate correlation and the hammer restarted smoothly.
After ~30 min of drilling with 0.5 m penetration, the bit heaved off bottom, causing the hammer to stop, and the flow rate was reduced. It was thought that the bit may have heaved out of the hole and a new hole started as the flow rate was increased and the hammer restarted. Almost immediately the torque increased and became erratic. The drill string rotation was erratic, from 10 to 50 rpm, as a result of slip stick. The hammer had to be stopped and restarted several times because of high torque buildup resulting in top-drive stalling.
At 0225 hr 1 May, a 2-in nipple on the stand pipe manifold failed because of the vibration in the stand pipe. Drilling had to be stopped so that the pump could be shut down for manifold repair. The bit remained in the borehole while the manifold was repaired, and the VIT camera was deployed. Near the hole with the bit in it, three other holes were observed, confirming that the bit had indeed heaved out of the hole and started new holes. The bit appeared to be 0.5 m below the seafloor. The VIT was retrieved and, with the stand pipe manifold repaired, drilling resumed at 0334 hr 1 May.
The flow rate was slowly increased and the hammer began to cycle. Torque was low and erratic, but increasing. Drill string rotation was going through slip stick. The top drive stalled on several occasions, and the hammer was stopped and the torque released. Each time the hammer restarted without any problems. At 0410 hr 1 May, the bit became stuck and may have heaved out of the hole as it was freed. Drilling resumed until 0425 hr 1 May, when the stand pipe transducer failed because of stand pipe vibration. Because the pumps had to be shut down to remove the pressure transducer from the stand pipe for repair, the bit was pulled clear of the seafloor.
The stand pipe pressure transducer nipple was blanked and Hole 1104D was spudded at 0445 hr 1 May. The water depth was determined to be 739 mbrf by drill pipe measurement. The pump was engaged, and the flow rate slowly increased. The bit heaved off the seafloor several times, causing the hammer to stop and restart. The torque soon increased and became erratic, eventually stalling the top drive. At 0510 hr 1 May, drilling was halted and the VIT camera was deployed while the bit remained on the seafloor. It appeared that several new holes had been spudded because of the bit heaving out of the hole during spudding. At 0615 hr 1 May, the bit was pulled clear of the seafloor and the VIT camera retrieved. The bit was also retrieved for inspection because of a lack of penetration.
Once on deck the bit was inspected revealing the leading two TCIs on each of the underreamer arms were sheared or broken off (Fig. 22). The gauge surfaces of the SDS bit #2 underreamer arms were not as heavily abraded as those on the SDS bit #1. Except for the pilot bit nose TCI having been sheared or broken off, the rest of the pilot bit appeared to be in good shape. The pilot bit nose TCI was probably damaged as the bit was heaved off the seafloor during spudding.
It appeared that the underreaming arms were preventing the hammer drill from advancing the borehole. To test this theory, parts of the underreaming bits used during the previous tests were converted into a drilling bit.
Bit Modification 1
Using a torch, the underreaming arms of SDS bit 1 were trimmed such that when opened, they would not extend past the outside diameter of the pilot bit and driver. Upon reassembly of the bit, the modified underreamer arms, when opened, did not appear to be strong enough to withstand drilling in hard rock. Therefore, bit modification 1 was abandoned.
Bit Modification 2
The second attempt at modifying an underreamer bit into a drill bit involved removing the underreamer arms and pilot bit from SDS bit 1. The pilot bit shank was shortened such that when installed in the driver, the underreamer arm gap was closed. The pilot bit was then installed and welded directly to the driver. Unfortunately, the pilot bit cracked during the welding process, and the bit could not be deployed.
Bit Modification 3
The third attempt at modifying an underreamer bit into a drill bit involved replacing the pilot bit with the broken nose TCI on SDS bit 2 with a new pilot bit. The original, damaged underreaming arms from SDS bit 2 were left in place. However, the underreaming arms were welded in place in the closed position. Since the underreaming bit was fixed in the closed configuration, new waterways had to be cut through the toes of the underreaming arms, using a torch and grinder.
The modified SDS bit was made up to the hammer drill BHA and tripped to the seafloor. The VIT camera was then deployed to locate a spud target. The modified bit was place on the seafloor ~1 m from Holes 1104C and 1104D. Maintaining WOB, the VIT was retrieved and Hole 1104E was spudded at 0140 hr 2 May. Water depth was established at 740 mbrf by drill pipe measurement. The weather had began to deteriorate, and the rig floor was experiencing 1 to 2 m heave resulting in the WOB having to be increased to 10,000 to 12,000 lb to keep the bit on bottom and the hammer bypass closed.
The pump was engaged, and the flow rate slowly increased. The hammer cycled smoothly but there appeared to be ~100 psi less pressure at any give flow rate than in past tests. There was also a noticeable reduction in the vibration in the stand pipe and derrick. At ~0155 hr 2 May, the hammer heaved off bottom, opening the bypass, and thus the hammer quit cycling and had to be restarted. The flow rate was increased slowly once again, and once again the hammer began to cycle.
After ~1 m penetration the torque began to increase and become erratic. Heave at the rig floor had increased to 3-m. The top drive stalled at 24,000 ft/lb. An overpull of 40,000 lb was applied to the bit without freeing it. The BHA was lowered to close the hammer bypass. The hammer was restarted and cycled at 400 gpm at 1720 psi. The pipe was worked again with up to 40,000 lb overpull, and still the bit could not be freed. Finally the drill string was rotated left, the direction one would normally rotate to close the underreaming arms, and the bit came free. It was assumed that the welds had failed allowing the underreaming arms to open, so the bit was pulled clear of the seafloor and the VIT camera deployed to verify. Once the VIT had reached the end of the pipe, the underreamer arms could be seen clearly in the open position. The VIT and BHA were retrieved for inspection. Once on deck, it was observed that every weld on the modified bit had failed, allowing the underreaming arms to open. Also, ~2 in of the leading edge of all three of the underreaming arms was broken off (Fig. 23). The pilot bit looked to be in good condition.
To 179 HDS Testing Hiatus
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