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This section summarizes ship and drilling operations during Expedition 315. Table T1 includes hole summary data for the expedition.
The Chikyu departed Site C0006, the last location of Expedition 314, at 1652 h on 15 November 2007. The 14 nmi transit was covered at an average speed of 3.5 kt. Rig maintenance was carried out upon arrival at Site C0001 at 2050 h on the same day.
After making up an HPCS/ESCS coring assembly with a 11-7/16 inch bit, we started running in hole at 0000 h on 17 November. A mechanical failure was found in a drawworks motor while running in hole to 1706 m drillers depth below rig floor (DRF). We pulled the assembly to the surface, and inspection of the drawworks was started at 2145 h. Trouble shooting of the drawworks A and B motors continued to 0200 h on 19 November. We made up an 11-7/16 inch HPCS/ESCS coring assembly and ran in hole to 2207 m DRF. We observed the HPCS core barrel drop through the core bit during running with core line at 1515 m DRF because of a loose connection from severe vibration induced by the strong current. The fishing operation started at 1645 h, and we successfully retrieved the core barrel at 0230 h on 20 November. We restarted running in hole to the seafloor and shot the first core at 2211.6 m DRF at 0410 h. The first core was on deck at 0500 h. HPCS coring continued until the morning of 21 November, and we cut 13 cores. Downhole temperature measurement was carried out with the APCT3 on Cores 315-C0001E-2H, 5H, 8H, and 11H. After shooting Core 315-C0001E-14H, the inner barrel could not be freed with 450 kN maximum overpull. We rotated the string under 450 kN of overpull by mistake, which resulted in a break of the inner barrel, which parted at the bottom of the second rod connection. An APCT3 tool was also lost in the hole, along with an HPCS inner barrel assembly (except for the middle/upper piston rod and landing shoulder sub). We displaced the hole with 1.3 SG kill mud and pulled out of the hole from 2335 to 2153 m DRF at 0830 h on 21 November.
After we abandoned Hole C0001E, we moved 20 m eastward and spudded Hole C0001F. After washing to 108 mbsf, we started coring with ~10 m of overlap with the previous hole. We cored 121.8 m and cut 19 cores with the HPCS. Our recovery rate was >100% for most cores; however, some of relatively deep cores showed obvious flow-in structure. Downhole temperature measurements were carried out using the APCT3 on Cores 315-C0001F-2H and 5H. Because the formation became stiff, we changed the coring system to the ESCS from the twentieth core and then cored 19.0 m and cut two cores. Core recovery was good for both cores; however, severe drilling disturbance was observed on X-ray CT scan imagery. Therefore, we decided to stop ESCS coring and switch to the RCB. We abandoned the hole by displacing with 1.3 SG kill mud and then pulled out of the hole and recovered the ROV under drifting with an average speed of 0.8 kt at 0500 h on 24 November.
We started making up a 10 ft 5/8 inch RCB assembly at 0845 h on 24 November and started running in hole from 1300 h. We spudded Hole C0001G at 0130 h on 25 November. After jetting to 74.5 mbsf, we started drilling. Just after drilling started, the ROV umbilical cable wrapped around the drill pipe. We stopped drilling and started pulling out of the hole at 0900 h. We safely recovered the ROV on board at 1500 h and confirmed it had no fatal damage.
After moving the vessel 6 nmi upcurrent with an average speed of 3.0 kt, we restarted running in hole at 1745 h on 25 November. We spudded Hole C0001H at 0330 h on 26 November, ~10 m away from the previous hole. After jetting to 74 mbsf, we started drilling with an RCB assembly with a center bit. Drilling to 230.0 m CSF, we retrieved the center bit and started RCB coring at 1445 h. The first RCB core arrived on deck at 1704 h. The ROV umbilical cable wrapped around the drill pipe at 0300 h on 27 November, but we recovered at 0530 h without retrieving it to the surface. After cutting Core 315-C0001H-20R at 412.5 m CSF, high torque to 18 kNm was observed. It reduced back to normal (3–5 kNm) after we twice pumped 10 m3 of Hi-Vis mud. Round mudstone gravel, typical of borehole caving, was observed at the top of Cores 315-C0001H-18R (~15 cm) and 20R.
Core recovery was generally as low as 30%–35% except for one core, which yielded almost full recovery. Correlation between drilling parameters and core recovery was uncertain. As weather was getting worse, we stopped coring at 448.0 m CSF after cutting Core 315-C0001H-24R and started free fall funnel installation at 1600 h on 28 November.
We completed installation of the free fall funnel by 0700 h on 29 November, and then we pulled the pipe to 35 m CSF and waited on weather for the rest of the day. As weather recovered at night, we started running in hole at 2330 h. After running the bottom-hole assembly (BHA) from 152 to 381 m CSF, we swept and reamed with Hi-Vis mud for the interval 381 to 448 m CSF. We restarted coring at 0600 h on 30 November and cut two cores from 447.2 to 457.8 m CSF. The pipe stuck while coring and was released with 350 kN overpull; we then decided to stop coring. We displaced the hole with 1.3 SG kill mud and started to pull out of the hole at 1230 h. The pipe was recovered at the surface by 2145 h. As the current was too strong to retrieve the ROV, we had to wait until the current was below the operational limit. Meanwhile, we made up a 10-5/8 inch drilling assembly. After moving the vessel 8.6 nmi to a low-current area at 0730 h on 1 December at an average speed of 0.7 kt, we retrieved the ROV at 2045 h while drifting. We started moving the vessel 5 nmi upcurrent of the well location at 2045 h with an average speed of 3.1 kt. Meanwhile, we repaired a ROV cursor cable.
We started running in hole at 0200 h on 2 December. We launched the ROV at 0630 h and dove into the location at 0900 h. Positioning the vessel to set the bit above the free fall funnel at 1030 h, we reentered the hole at 1235 h. After washing and reaming from 299 to 458 m CSF, we started drilling at 1930 h. We reached 600 m CSF, the starting depth for coring, at 2200 h on 3 December and then repeated reaming and wiper trips several times for coring. After we spotted 57 m3 of 1.3 SG kill mud, we started pulling out of the hole at 2030 h and retrieved the BHA to the surface at 0500 h. We moved the vessel 6 nmi upcurrent and meanwhile made up an RCB coring assembly without a center bit. We started running in hole at 0900 h and launched the ROV at 1330 h. The vessel was on location at 1845 h. We reentered the hole at 2010 h and continued running in the hole to 264 m CSF. We then started washing and reaming from 268 m CSF at 2200 h. Despite repeated washing and reaming, borehole conditions did not improve. After washing and reaming to 449 m CSF, we finally decided to abandon the hole at 1300 h on 5 December. We displaced the hole with 50 m3 of 1.3 SG kill mud and picked up the coring assembly to the seafloor. We moved the vessel 60 m eastward and spudded a new hole (C0001I).
We dropped a center bit and then spudded the new hole at 1600 h on 5 December. After jetting to 70 mbsf, we started drilling at 1700 h with a 10-5/8 inch RCB assembly with a center bit. Drilling to 425 m CSF was relatively smooth. At every pipe stand, 10 m3 of Hi-Vis mud was spotted. On 6 December, while picking up from 458 to 340 m BSF to change the wash pipe, both upper and lower Inline Blow-Out Preventors (IBOPs; back valves at the top drive) were repaired. Running in hole started at 1400 h. We started drilling from 458 m CSF at 1630 h. After drilling to 520 m CSF, we repeated washing and reaming to 520 m CSF. While backreaming from 434 to 464 m CSF, we had a pipe stick at 464 m CSF. We managed to free the pipe with 700 kN of overpull. After escaping from this zone, we gave up further drilling and coring at 0315 h on 7 December. After displacing the hole with 35 m3 of 1.5 SG kill mud, we started pulling out of the hole at 0900 h and finished at 1400 h. The ROV dove to retrieve transponders at 1600 h. Meanwhile, we changed the saver sub and repaired a leak on the top drive system. Four transponders were recovered at 0230 h on 8 December. We left the location for Site C0002 at 0230 h.
The Chikyu departed Site C0001 at 0230 h on 8 December 2007. The 7 nmi transit was covered at an average speed of 2.8 kt. We arrived at Site C0002 at 0530 h on the same day.
The vessel was on location at 0530 h on 8 December. Deployment and calibration of four transponders occurred from 0530 h to 1930 h. The vessel moved 4 nmi upcurrent from 1930 to 2215 h at an average speed of 1.6 kt. We started making up and running a 10-5/8 inch RCB assembly at 2215 h. In the meantime, minor troubleshooting of the dynamic positioning system was carried out. We spudded the hole at 0600 h on 9 December. After jetting to 50 mbsf, we started drilling with an RCB coring assembly with a center bit at 0745 h. While drilling to 181 m CSF, a problem with the top drive was discovered at 1300 h. We checked it and made repairs to the changing bolt until 1815 h. We started running in hole at 1815 h, and we restarted drilling from 181 m CSF at 1830 h. We reached the starting coring depth (475 m CSF) at 0215 h on 10 December and installed a sinker bar. We retrieved the center bit and then dropped an inner barrel and started coring at 0530 h. We continued coring until 0700 h on 11 December and cut 22 cores in the interval from 475 to 675 m CSF. As leaking was found on the Crown-Mounted Heave Compensator (CMC) booster line at 0700 h, we spotted 10 m3 of Hi-Vis mud and retrieved an inner barrel and a sinker bar. Repairs were completed by 1530 h. After washing and reaming from 634 to 669 m CSF, we installed a sinker bar and restarted coring at 1730 h. After cutting Core 315-C0002B-23R, we could not recover the inner barrel. A swivel assembly shaft of the inner barrel was left down the hole. We ran a fishing tool (core catcher) in the hole with the coring line and were able to retrieve the assembly at 2230 h. We restarted coring at 2315 h on 11 December and cut 39 cores by 1645 h on 13 December. The drill pipe stuck twice, once at 1029 m CSF at 1650 h and another time at 1030 m CSF at 1715 h on 14 December, but came free with 300 kN of overpull each time. After cutting four more cores, hole conditions became worse below 1057 m CSF at 2230 h. The drill pipe was packed off and was freed by 300 kN of overpull. We washed and reamed the hole repeatedly with sweeping Hi-Vis mud until the next morning; however, hole conditions did not become better. We finally decided to stop RCB coring and abandon the hole at 1345 h on 15 December. We displaced the hole with 1.3 SG kill mud and pulled out of the hole until 2100 h. The ROV was recovered at 1835 h. We moved the vessel 6 nmi upcurrent at 2100 h on 15 December, at an average speed of 1.5 kt.
The vessel was on location at 0130 h on 16 December. We made up an 11-7/16 inch HPCS assembly at 0630 h and started running in hole at 0830 h. We installed a sinker bar and an inner barrel at 1530 h and cut two HPCS cores until 1815 h. We moved the vessel 10 m away from the hole for the next hole coring.
The vessel was on location at 1830 h on 16 December, and we continued HPCS coring at 1830 h. We cut 13 cores with the HPCS until 0830 h on 17 December. With 450 kN of overpull on Core 315-C0002D-13H at 120 m CSF, we overdrilled from 110 to 113 m CSF. We pulled the core line winch to the surface and found that we had not recovered the inner barrel (the sinker bar pin was sheared). We installed a new latch head and ran back in and latched. After another 2 m of overdrill, we attempted to pull free and released the inner barrel with 400 kN of overpull. We changed the latch head and replaced shear pins and V-packings on the inner barrel. We continued HPCS coring from 114 to 120 m CSF. We had high overpull (450 kN) again and overdrilled 5 m; the barrel came free with 400 kN of overpull. After recovering this core, we dropped the ESCS BHA for drilling. Having verified its landing, we started drilling at 1600 h from 129 m CSF. We ran a sinker bar assembly in the hole and recovered the ESCS. We then ran the APCT3 in the hole and performed HPCS coring at 150 m CSF. To free the barrel, 200 kN of overpull was needed. We recovered the HPCS core and dropped the ESCS again. We verified its landing and then started drilling from 159 m CSF at 2015 h. We ran the sinker bar assembly in the hole and recovered the ESCS at 2300 h. The final HPCS core was taken from 200 m CSF at 0110 h on 18 December. A total of 18 cores were cut in this hole. Downhole temperature measurement by the APCT3 was attempted on Cores 315-C0002D-2H, 4H, 6H, 8H, 10H, 12H, 16H, and 18H; six of these were successful. We displaced the hole with 26 m3 of 1.3 SG kill mud and pulled out of the hole to the surface from 0215 h to 0545 h. We moved the vessel and then launched the ROV at 0730 h and retrieved four transponders by 1345 h. The vessel left for Expedition 316 Site C0004 at 1345 h on 18 December.