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doi:10.2204/iodp.proc.314315316.114.2009

Operations

Transit to Site C0002

The D/V Chikyu moved to a low-current area (14 nmi northwest of Hole C0001D) on 13 October 2007 in order to avoid shock and vibration from the Kuroshio Current while picking up and running in with the LWD bottom-hole assembly (BHA) and drill collars. The ship drifted to the location of Site C0002 at 1.5 kt while running the LWD BHA, and the ship arrived at the location at 2145 h.

Hole C0002A

Preparation for drilling began at 0400 h on 13 October 2007. Like the previous LWD-MWD-annular-pressure-while-drilling (APWD) holes, the LWD tools (6¾ inch [17.15 cm] collars) included the geoVISION tool with a 23.18 cm button sleeve, the sonicVISION tool (four-receiver array), the MWD (PowerPulse) tool, the seismicVISION tool, and the adnVISION tool. A breakdown of operations is given in Table T1, and the full BHA is described in Table T2.

Tools were assembled, and communication and function checks were conducted at 36.8 m drillers depth below rig floor (DRF) between 0730 and 0800 h. The radioactive source for density measurement was installed and the BHA was lowered to 700 m DRF. From 1430 to 2200 h, the Chikyu slowly drifted to the hole position while the bit was lowered to 1488 m DRF, where a second series of tests was successfully conducted. After tagging the seafloor at 1964.5 m DRF (1936 m mud depth below sea level [MSL]) the hole position was located and surveyed by remotely operated vehicle (ROV) from 2200 h on 13 October to 0045 h on 14 October.

Hole C0002A was jetted-in from 1964.5 to 2035 m DRF (0–70.5 m LWD depth below seafloor [LSF]) at 0045 h on 14 October with an initial pump rate of 714 gpm (2700 L/m). Drilling continued with an average rate of penetration (ROP) of ~30 m/h, normal collar rotation (80–100 rpm), and minimal weight on bit (WOB). Surface pump pressure maintained at 15 MPa while pump flow rate was decreased to ~2500 L/m. At 0445 h, a problem with the inline blowout preventer prevented real-time communication with the LWD tools. After repairs (0515 h), drilling continued to 709.5 m LSF (2674 m DRF) and the decision was made to relog the missing section (535.5–556.5 m LSF) during the next wiper trip. A wiper trip was conducted from 709.5 to 401.5 m LSF (2674 to 2366 m DRF) between 1500 and 1745 h on 15 October, and missing data were successfully collected. Drilling continued to TD of 1401.5 m LSF (3366 m DRF) at 0600 h on 17 October without any difficulties except moderate increase in equivalent circulating density (ECD) at each pipe connection, which was rapidly controlled with mud recirculation.

The hole was displaced with 100 m³ of kill mud (density 1.3 g/cm³). At 1400 h on 17 October, two stands of pipe were removed to create an offset in uphole check shots at every pipe disconnection. All LWD tools were recovered on the rig floor at 0800 h on 18 October, and all memory data were successfully downloaded. However, the seismicVISION battery failure before retrieval of the tool required that data be sent to the land base for processing. A time version of the surface drilling parameters and downhole ECD, annular pressure measurement (APRS), and real-time gamma ray log (GR_RAB_RT) is given in Figure F3.

Transit to Site C0003

As the BHA was rigged down from Hole C0002A, the ROV was deployed to pick up four beacons at 0800 h on 18 October 2007. The ship was then moved to the next site (proposed Site NT2-01D) at 1700 h for 6 nmi with average speed of 6 kt, and four beacons were deployed at 2130 h. At this site, the deployment plan was changed for greater efficiency and safety. The ship was moved against the Kuroshio Current by 12 nmi from 1400 h on 19 October for 3.5 h with average speed of 3.4 kt. The BHA was then made up and run into the sea as the ship drifted back at 1.5 kt from 2130 h. Upon arriving at the location at 0530 h on 20 October, running continued to 2480 m DRF. The bit was positioned, and a survey was made of the sea bottom.

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