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doi:10.2204/iodp.proc.314315316.115.2009

Operations

Hole C0003A

Hole C0003A was spudded at 1300 h on 20 October 2007. LWD-measurement-while-drilling (MWD) operations were conducted from the seafloor (2481.5 m drillers depth below rig floor [DRF]) to a total depth of 3007 m DRF (525.5 m LSF), where the drill pipe became stuck and pipe connection was lost. In spite of numerous efforts to recover the bottom part of the bottom-hole assembly (BHA) (including the MWD-annular pressure while drilling [APWD]-LWD tools), the fishing operation was not successful and the hole was cemented on 30 October, leaving the tools behind. The summary of operations in Hole C0003A is shown in Table T1, and a schematic of the final hole condition at the time of plugging and abandonment is shown in Figure F3.

In detail, operations began with making up the BHA (at 2300 h on 18 October), tool initialization, calibration, and shallow (36.8 m DRF) communication tests (at 1830 h on 19 October). The BHA included a polycrystalline diamond bit, various subs, LWD tools, one mechanical jar, twenty 6¾ inch drill collars (12 below the jar and 8 above the jar), and an extra crossover sub to connect the BHA to the drill pipe (Table T2). As with Hole C0002A, the LWD tools (6¾ inch [17.15 cm] collars) included, from bottom to top, the geoVISION tool with a 23.18 cm button sleeve, the sonicVISION (four-receiver array) tool, the MWD (PowerPulse) tool, the seismicVISION tool, and the adnVISION tool (see Fig. F1 in the “Expedition 314 methods” chapter). Installing the radioactive source for density measurement was completed at 2100 h on 19 October, and the BHA was lowered to run into hole. Communication with all tools and function checks were conducted again at 348 m DRF between 2330 and 2345 h on 19 October. After the end of the dynamic positioning system calibration operation, the seafloor was tagged at 2481.5 m DRF (2453 m mud depth below sea level [MSL]) and hole position was confirmed and surveyed by the remotely operated vehicle (ROV) (at 1145 h on 20 October) (Table T1). At ~6 m above seafloor (from 1150 to 1210 h on 20 October), the surface air gun array was activated and the seismicVISION tool was tested again. Real-time data were of poor quality because of poor fluid pulse telemetry efficiency in the noisy environment caused by pipe vibration in the strong current. Hole C0003A was jetted-in at 1245 h on 20 October with an initial pump rate of 500–650 gpm to ~50 m LSF. Real-time communication with the tools was initially poor, as the pumping rate was limited in this jet-in interval to reduce washout. A graphic representation of the drilling parameters and gamma ray log is given in Figure F4. As the LWD tools were not recovered, only real-time data were ultimately available.

Below 50 m LSF, drilling progressed smoothly at a constant rate of penetration (ROP) of 35 m/h. Collar (bit) rotation speed (CRPM) progressively increased from 30 to 80 rpm at 80 m LSF to reach a constant value of 100 rpm until the end of operation. Pump flow increased to 650–680 gpm and standpipe pressure (SPPA) was maintained at 15 MPa (normal trend increase with depth to 18 MPa at 525 m LSF). Standard pipe connection procedure included circulation, hole sweep, and pumping high-viscosity gel. Surface weight on bit was kept to a minimum to 490 m LSF, where the first significant increase in equivalent circulating density (ECD)/APWD and torque were noticed (at 1000 h on 21 October). The hole was reamed at 8 m depth intervals until the tool string became stuck (at 1310 h on 21 October; 525.5 m LSF). While attempting to increase circulation and work the stuck pipe loose, the drill pipe broke at 1350 h, detected by the loss of ~10 tons of string weight.

A free-fall funnel was dropped, and the remaining string was pulled out of the hole at 0230 h on 22 October. After recovering the drill string, it was observed that 19 of the 20 drill collars and the entire LWD BHA assembly had been lost. The second to last pipe recovered on deck was plugged with cuttings and large pieces of mudstone and sandstone, and the bottom drill pipe threads were heavily damaged. After repair of a deformed 8⅛ inch overshot guide, a fishing assembly was made up, run in, reentered, washed down, and reamed from 2707 to 2785 m DRF. Between 0000 and 0745 h on 24 October, fishing was attempted seven times with one successful catch; however, the fishing tool failed to pull up. Therefore, it was pulled out to the rig floor at 1415 h on 24 October and run again with a 6¾ inch grapple assembly on 25 October. Reentry to the well was difficult and took 10 h to get into the hole. The overshot again failed to catch the fallen LWD assembly, and the decision was made to deploy a wireline fishing tool to retrieve the radioactive source from the adnVISION tool. The wireline was rigged up for a “dummy run” with a 7 m sinker bar instead of a fishing tool for the radioactive source at 2215 h on 25 October. After failing to pass through 2780.5 m DRF at 0145 h on 25 October, the dummy tool was retrieved. However, the sinker bar had unscrewed and dropped off, possibly into the hole. The overshot assembly was pulled out of the hole and recovered on deck at 0000 h on October 27.

After the overshot assembly was pulled out of the hole at 0000 h on 27 October, the D/V Chikyu sailed 14 nmi north-northwest to move away from the strong current and a typhoon. At 1600 h on 27 October the Chikyu sailed back to Hole C0003A and an 8⅛ inch overshot assembly with 6⅝ inch spiral grapple. After moving 6 nmi upstream, the overshot assembly began running into the water to 1800 m DRF, and the ROV dived while drifting back to position. The hole was reentered at 0315 h on 28 October and run in to 2774 m. Wireline equipment was rigged up at 0600 h and the overshot latched the pipe after several attempts. An attempt to pass the wireline past 2788 m DRF failed, and it was finally decided to rig down the wireline equipment at 1530 h. Fishing with the overshot continued until the decision was made to pull out at 1200 h on 29 October.

At 1900 h, the Chikyu sailed 500 m upstream and made up a cement stinger. The cement stinger was run in beginning at 2000 h, and a cement stand was rigged up and cement lines flushed at 0230 h on 30 October. After testing pressure, the first cement job was conducted at 0430 h and the drill string was displaced with seawater. A second cement job was conducted at 0730 h after pulling out from 2760 to 2612 m DRF. Seawater again was displaced and cement returned to the seabed was confirmed by ROV. After cementing, the cementing assembly was pulled out of the hole, the ROV was recovered, and the drill string was cleaned.

Transit to Site C0004

After picking up the beacons from Site C0003, the Chikyu moved to the proposed Site NT2-01I pilot hole location at 0330 h on 31 October 2007 with ROV and beacons in the water for 1 nmi at an average speed of 0.3 kt. The four beacons were set and calibrated until 1740 h. The ship then moved 4 nmi upstream at 1740 h with average speed of 2.4 kt and drifted back to the location at 2140 h at 1.3 kt.

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