After the 1-hr, 8-nmi transit from Site 1173, we arrived at Site 808 at 1800 hr on 18 May. During the transit the drill crew slipped and cut the drill line. The seafloor positioning beacon was deployed at 1937 hr. The precision depth recorder indicated a water depth of 4674.5 mbsl (4685.4 mbrf). The vessel was offset 1 km west (upcurrent) to allow assembly of the casing while the ship drifted with the current. The reentry cone was positioned on the moonpool door. The drill floor was rigged up to run 20-in casing, and the drill crew started running the 20-in casing at 2215 hr on 18 May. The casing string included a shoe joint (10.63 m), 12 joints of casing, and a short (pup) joint of casing attached to the casing hanger. The casing running tool was attached to the casing hanger. A compound (Baker-Loc) was applied to each threaded connection to ensure that it did not come apart, and all casing connections were tack-welded. The casing was lowered and latched into the reentry cone by 0515 hr on 19 May. We then assembled the drilling BHA that included an 18.5-in drill bit, a 22-in underreamer (Smith Service 15000 DTU), a positive-displacement mud motor (Drilex Model D825MSHF), 16 drill collars, and the casing running tool. The drilling BHA was lowered into the reentry cone and casing and latched into the casing hanger. The casing, reentry cone, and drilling BHA were deployed through the moonpool at 0900 hr on 19 May. The drilling BHA (160.14 m) extended 3.54 m beyond the casing assembly (156.60 m).
The casing, reentry cone, and drilling BHA had been lowered to 3606.94 mbrf by 1500 hr on 18 May. The VIT camera was deployed, and we continued lowering the pipe to 4646.12 mbrf, where we spaced out the drill pipe in preparation to spud. Hole 808H was spudded at 1805 hr on 18 May. The casing was drilled into the seafloor from 0 to 126.70 mbsf (4685.004811.7 mbrf). While drilling ahead, we circulated sepiolite mud sweeps at 4710, 4735, 4780, 4792, 4802, and 4811 mbrf.
At 0230 hr on 20 May the downhole positive-displacement motor (mud motor) that provides rotational torque to the underreamer and drill bit appeared to stop working. At 0430 hr, we decided to pull the casing and reentry cone back up to the ship and replace the mud motor. The bit cleared the seafloor at 0615 hr on 20 May. The pipe trip continued until 0645 hr, when we began to recover the VIT camera; the pipe trip resumed at 0815 hr. The casing and reentry cone were set on the moonpool doors at 1625 hr. After unlatching the running tool from the casing, the BHA was taken apart until the mud motor was reached.
The mud motor was tested from 1800 to 1830 hr. The mud motor would not rotate when we pumped seawater through it at 165 gpm at 1025 psi. Testing prior to drilling operations showed that it freely rotated at 275 gpm with 125 psi. The mud motor was laid down, and the drill bit cleared the rig floor at 1910 hr on 20 May, ending Hole 808H.Hole 808I
After its installation at 1915 hr on 20 May, the backup mud motor was successfully tested with circulation rates of 25 spm at 50 psi, 50 spm at 225 psi, and 70 spm at 450 psi. The BHA and casing running tool were attached to it, and the entire assembly was lowered and latched into the casing and reentry cone; it was deployed through the moonpool at 2205 hr.
When the bit was at 3809.22 mbrf, the VIT camera was deployed. We continued tripping down to 4646.12 mbrf, where we spaced out the drill string in preparation to spud. Hole 808I was spudded at 0720 hr; the seafloor depth was 4686 mbrf. We successfully drilled the casing down to 160.14 mbsf (4845.14 mbrf). The average drilling parameters were a WOB of 515 klb and a flow rate of 400550 gpm (80110 spm) with 9001150 psi.
The casing running tool was released at 2110 hr on 21 May, and the bit cleared the seafloor at 2245 hr on 21 May. When the drill string had reached 4588.59 mbrf, the VIT camera was retrieved. With the bit at 124.06 mbrf, the casing running tool was removed, the BHA was disassembled, and the mud motor and underreamer were flushed with freshwater.
On 22 May at 1245 hr, the LWD/MWD BHA was made up with a new 9.875-in bit. The MWD mud pulse communications were tested with a flow rate of 305 gpm (61 spm). The trip down to the seafloor started at 1630 hr; the VIT camera was launched at 0030 hr when the bit had reached 4309.02 mbrf. While the VIT camera was being lowered, the drill crew slipped and cut the drill line. The drill string was tripped to 4654.13 mbrf, and we started searching for the reentry cone at 0315 hr on 23 May. The cone was successfully reentered at 0345 hr. The LWD/MWD tools were lowered from mudline (4686 mbrf) to 141.4 mbsf (4827.4 mbrf). After the VIT camera was retrieved at 0630 hr, the drill string was lowered to 160.14 mbsf (4846 mbrf). We began LWD/MWD logging/drilling at 0745 hr on 23 May.
The goal was to log/drill at a controlled rate of 50 m/hr. With connection times, the average ROP from 4846.14 mbrf (160.14 mbsf) to 5214.54 mbrf (528.54 mbsf) was 22.9 m/hr. Sepiolite mud sweeps (15 bbl) were pumped at 329, 413, and 471 mbsf to help remove cuttings and improve hole conditions. The drilling parameters used were a WOB of 520 klb, torque of 175225 A, and a flow rate of 67 spm (327 gpm) with 12501350 psi standpipe pressure.
On 24 May, the logging/drilling continued from 5214.54 mbrf (528.54 mbsf) to 5435.72 mbrf (749.72 mbsf), and the average ROP dropped to 21.0 m/hr. Twenty-barrel sepiolite mud sweeps were circulated at 557 and 634 mbsf, with a 30-bbl sweep at 749 mbsf.
Prior to continuing deeper into the hole, a wiper trip was made to determine hole conditions from 5435.72 mbrf (749.72 mbsf) to the casing shoe at 4846.14 mbrf (160.14 mbsf). The drill string was pulled with the top drive to 5230.73 mbrf (544.73 mbsf) with a maximum overpull of 20 klb and torque of 400 A. The top drive was then removed and the string pulled to 4827.4 mbrf (141.4 mbsf). The drill string was tripped back to 5256.51 mbrf (570.51 mbsf), where we picked up the top drive and reamed down to 5435.72 mbrf (749.72 mbsf). One tight spot was encountered at 5413 mbrf (727 mbsf).
Logging/drilling then continued from 5435.72 mbrf (749.72 mbsf) to 5474.26 mbrf (788.26 mbsf). The average ROP dropped to 15.7 m/hr as a result of the wiper trip and the time needed to make pipe connections. One 30-bbl sepiolite mud sweep was circulated at 759 mbsf. The drilling parameters were a WOB of 1520 klb at 60 rpm, torque of 200300 A, and a flow rate of 67 spm (327 gpm) with 1500 psi standpipe pressure.
On 25 May, LWD/MWD logging/drilling continued from 5474.26 mbrf (788.26 mbsf) to 5676.26 mbrf (990.26 mbsf). Sepiolite mud sweeps (20 bbl) were circulated at 846, 923, and 968 mbsf.
The décollement was encountered at 5654 mbrf (968 mbsf). We experienced drilling problems (high torque and high pump pressures) from 1115 to 2245 hr. Efforts to improve hole conditions included circulation, mud sweeps, and reaming up and down with the drill string. A short wiper trip was made from 5676.26 mbrf (990.26 mbsf) to 5615.39 mbrf (929.39 mbsf). During the wiper trip, the maximum overpull was 25 klb, maximum torque was 550 A, and the maximum pump pressure was 2200 psi.
Logging/drilling operations continued from 5676.26 mbrf (990.26 mbsf) to 5695.51 mbrf (1009.51 mbsf). The average ROP dropped to 13.3 m/hr due to connection times, hole conditioning, and the wiper trip. The LWD/MWD logging/drilling parameters were a WOB of 1520 klb at 60 rpm, torque of 275350 A, and a flow rate of 67 spm (327 gpm) with 1550 psi standpipe pressure. Sepiolite mud sweeps (20 bbl) were pumped at 958, 961, and 990 mbsf. Another wiper trip was made from 5695.51 mbrf (1009.51 mbsf) to 5615.39 mbrf (929.39 mbsf).
Most of 26 May was spent fighting the poor hole conditions, making wiper trips, and troubleshooting an overheating top drive. LWD/MWD logging/drilling extended from 5695.51 mbrf (1009.51 mbsf) to 5743.55 mbrf (1057.55 mbsf). The LWD/MWD logging/drilling parameters were a WOB of 1520 klb at 60 rpm, and torque of 275350 A with a maximum of 600 A. The pump pressure was 60 spm (300 gpm) with 1550 psi standpipe pressure. At 2330 hr, the drill string became stuck with the bit at 5702.08 mbrf (1016.08 mbsf). We were unable to rotate the drill string or move it up or down. Rotation and movement were successfully regained at 0045 hr on 27 May. We decided not to continue operations in this hole and began to trip out using the top drive for rotation and circulation up to 5432.72 mbrf (746.72 mbsf). The top drive was removed, and the bit cleared the seafloor at 0615 hr. The drill collars were racked back in the derrick and the LWD/MWD logging tools were laid down. The drill bit cleared the rig floor at 1710 hr on 27 May, ending Hole 808I. The thrusters and hydrophones were raised, and the seafloor positioning beacon was turned off. We began the transit to Kochi at 1715 hr on 27 May.Heave Compensation Experiments
At Site 808, we used the MWD tool to measure downhole drilling parameters, including downhole WOB, torque, and bit bounce. Given the strong MWD pressure signals obtained at the surface during Site 1173 MWD operations, we increased the MWD data transmission rates at Site 808 to 6 bps. Surface data from the RIS, including surface rotations per minute, torque, WOB, ship heave, pitch, and roll, were recorded synchronously. Ship heave was between 0.5 and 1.5 m during drilling at this site.
Eight experiments were conducted while drilling ahead with the AHC off (4917.154946.04, 5013.155032.10, 5118.595137.87, 5214.545233.73, 5320.175349.09, 5416.505435.72, 5522.335541.59, and 5724.375733.96 mbrf). One of these intervals (5522.335541.49 mbrf) was partially drilled with the AHC preloaded at a set surface weight to evaluate this practice in comparison to similar tests conducted at Site 1173. The comparison of downhole MWD parameters with the surface information will be analyzed postcruise to evaluate the shipboard heave compensation system and to compare drilling conditions with those encountered at Site 1173.
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