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doi:10.2204/iodp.proc.332.106.2011

Results

SmartPlug retrieval at Site C0010

Acceleration data from drill pipe VIV during SmartPlug recovery at Site C0010, along with current, drifting speed, and course data during retrieval, are plotted in Figure F4. Two types of acceleration are observed in the data. One type is VIV, correlated with drifting speed and angle between drifting direction and sea current direction. The methodology of attaching ropes (24 mm OD) to the drill string from 1200 m DRF to the surface successfully reduced acceleration from VIV to <1 g. The second type is due to shock transmitted to the drill string by contact with the rotary table while running pipe (Fig. F4); the peak-to-peak amplitudes of these accelerations were close to 1.5 g.

Peak-to-peak amplitude reached 6 g (as recorded by the accelerometer near the rotary table), with greater acceleration in the horizontal direction when lowering drill pipes began. This contrasted with peak-to-peak amplitudes recorded during recovering drill pipe, where the horizontal acceleration reached 0.5 g. Two other acceleration events (shocks) were recorded during Site C0010 reentry (>2.5 g) and SmartPlug recovery (Fig. F4).

LTBMS installation at Site C0002

The LTBMS CORK assembly deployment began in the LCA (<1 kt), with Accelerometer 1 attached just above the CORK head running tool and Accelerometer 2 attached at 1720 m DRF (Fig. F3). To reduce VIV while drifting to Site C0002, the Chikyu’s drifting speed was set at ~0.5 kt and the angle between drifting direction and sea current was set to be <45°. Drifting toward the site began at 0830 h on 6 December 2010, arriving at Site C0002 at 0045 h on 8 December (Fig. F5).

A large set of acceleration data was collected during the LTBMS installation, and the full data set is shown in Figure F5. These results show that VIV amplitude was reduced to <0.5 g, whereas the amplitude of the vertical component of the acceleration was <0.2 g during drifting.

Two kinds of vibrations affecting the drill pipe are identified from the acceleration data. One is VIV, a direct result of the effects of the sea current, drifting speed, and angle between the Chikyu’s course and the current. VIV was successfully reduced to <0.5 g by attaching ropes (24 mm OD) to the upper section of the drill string. The second kind of vibrations originate from the drill string contacting the rotary table while running pipe and striking the wellhead during reentry, and depending on the strength of impact, may reach larger magnitudes than that originating from VIV (Fig. F5). One new component observed during LTBMS deployment was acceleration originating from the remotely operated vehicle (ROV) connecting to the CORK head and landing on the ROV platform; maximum peak-to-peak acceleration amplitudes of some of these events were close to 6 g.

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