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doi:10.2204/iodp.proc.314315316.118.2009

Operations

Hole C0006A

The summary of operations in Hole C0006A is shown in Table T1. The drill string was spaced out in preparation for drilling, and the Schlumberger MWD and APWD tools were tested in preparation for drilling pilot Hole C0006A (initial target depth = 950 m LSF; drilled to 885.5 m LSF). The bottom-hole assembly (BHA) included polycrystalline diamond compact (PDC) bit, a crossover sub, MWD (PowerPulse) and APWD tools, a stabilizer and nine 6¾ inch drill collars, and one jar (see Fig. F1 in the “Expedition 314 methods” chapter; Table T2). Tools were assembled and we started running into hole between 0040 and 2045 h on 9 November 2007. Because of the high current, all pipe connections were checked while running in. Because water depth was deeper than the remotely operated vehicle’s (ROV’s) capability (3000 m), the hole was positioned based on ship position. After spud-in, drilling and MWD logging operations began at 0015 h on 10 November. Based on the cumulative length of drilling pipe, the seafloor depth was estimated to be 3903.5 m (3903.5 m drillers depth below rig floor [DRF]).

A time version of the surface drilling parameters and downhole MWD measurements of equivalent circulating density (ECD), average annular pressure (APRS), and gamma ray values (GR_RAB) is given in Figure F1. The hole was jetted-in to 3954 m DRF (50.5 m LSF) with a minimal (<2 kkgf) weight on bit (WOB) and standpipe pressure (SPPA). Surface pump flow was set to 520 gpm. After 50.5 m LSF, bit rotation (CRPM) was progressively increased to 80–100 rpm to 150 m LSF and then stabilized at ~120 rpm to TD (885.5 m LSF). Increase in CRPM was concomitant with increased SPPA and surface pump flow. A first wiper trip was conducted between 4210 and 4060 m DRF (306.5–156.5 m LSF; 1415–1530 h on 10 November) and a second wiper trip was conducted between 4504 and 4364 m DRF (600.5–460.5 m LSF; 0500–0545 h on 11 November). Drilling progressed smoothly with an average rate of penetration (ROP) of ~30 m/h. Normal hydrostatic increase with depth was observed on APRS and ECD. Annular temperature (ATMP) also gradually increased to 12°C at the bottom of the hole. Total depth of 885.5 m LSF was reached at 2045 h on 11 November, after 45 h of drilling operations. The BHA was then pulled out of the hole and the drill bit cleared the seafloor at 2400 h on 11 November. The drill bit was recovered on the rig floor at 1015 h on 12 November.

Hole C0006B

The summary of operations in Hole C0006B is shown in Table T1. Hole C0006B was spudded at 0045 h on 13 November 2007. The LWD-MWD drilling/​logging operations were conducted from the seafloor (3900.0 m DRF) to TD of 4785.5 m DRF (885.5 m LSF). As water depth exceeded the 3000 m ROV limitation, the position of the hole was determined by the position of the ship. At the time of spud-in, ship position was 33°01.6350′N, 136°47.6390′E.

Operations began with the makeup of the BHA (from 1115 to 2000 h on 12 November). The BHA included a PDC bit, various subs, LWD tools, one mechanical jar, nine 6¾ inch drilling collars, and an extra crossover sub to connect the BHA to the drill pipes (Table T3). The LWD tools (6¾ inch [17.15 cm] collars) included geoVISION, sonicVISION, MWD (PowerPulse), adnVISION (caliper-only mode), and seismicVISION tools (see Fig. F1 in the “Expedition 314 methods” chapter). Seafloor was tagged at 3900 m DRF (3871.5 meters below sea level) at 0045 h on 13 November (Table T1).

Hole C0006B was jetted-in with an initial pump rate of 500 gpm to ~40 m LSF. Real-time communication with the tools was poor because the pump rate was limited in the slipping mode interval to reduce washout. Graphic representation of drilling parameters and the gamma ray log is given in Figures F3 and F4. Real-time communication with the LWD tools was lost at 1800 h on 13 November (274 m LSF) because the mud pulse telemetry system failed. Drilling progressed smoothly at a constant ROP of 40 m/h. CRPM progressively increased from 80 rpm (40 m LSF) to 100–120 rpm to the end of operation. Pump flow increased to 700 gpm, and SPPA was mostly maintained below 15 MPa. Major reaming operations were conducted during drilling as a result of an observed increase in hole deviation (~5° at 240 m LSF). A wiper trip was conducted from 4502 to 4350 m DRF (602.5–450.5 m LSF) at 0330–0415 h on 14 November. The target depth of 885.5 m LSF was reached at 1645 h on 14 November. The hole was killed by circulating heavy mud, and tools were pulled out at 1900 h. After the drill string was above the seafloor, the drilling equipment and derrick were checked before continuing pullout. LWD tools were recovered on the rig floor at 1715 h on 15 November, and all data successfully downloaded.

Transit to Hole C0001E

After pulling out of Hole C0006B, the D/V Chikyu moved ~ 14 nmi to Site C0001 with an average speed of 3.5 kt at 1700 h on 15 November 2007 and arrived at the location at 2100 h.

After recovering the ROV, the Chikyu moved to proposed Site NT2-01G over a distance of ~600 m with average speed of 0.3 kt at 0240 h on 6 November 2007 and checked the communication with beacons at the site at 0500 h.

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