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doi:10.2204/iodp.proc.319.104.2010

Logging and data quality

Logging results

Logging data collected during MWD and with the LWD geoVISION resistivity tool (GVR) are presented in Figure F5. Logging data included gamma radiation and resistivity, as well as drilling parameters (rate of penetration [ROP], stick-slip, etc.). Two sets of data were collected corresponding to two data sets of drilling operations (See "Operations"): Run 1 for the interval between 2590 and 3033 m LWD depth below rig floor (LRF) and Run 2 for the interval between 3034 and 3107 m LRF, with a repeat log interval between 2900 and 2972 m LRF. Detailed discussion and interpretation of individual logs are incorporated into the subsequent disciplinary sections (i.e., lithology, structural geology, and physical properties).

Depth correction of LWD/MWD data

Depth references are shown graphically in Figure F6. The height of the rig floor (rotary table) is 28.3 m above sea level (presuming minimal variation in this parameter during drilling operations), and the water depth is reported as 2523.7 m. LWD/MWD log depths are tied to the drillers depth at the rig floor, such that LWD/MWD depth is equal to drilling depth (LRF = DRF, LWD depth below seafloor [LSF] = DSF).

Operations

The Hole C0010A borehole assembly included TeleScope MWD and GVR, which measure resistivity, gamma ray, resistivity image, and drilling parameters. After making up the MWD-GVR assembly at 1230 h on 6 August 2009, a shallow tool string hole test was conducted at 1345 h before running into the water while the Chikyu drifted to a low-current area. At 1230 h on 7 August, the drilling assembly reentered Hole C0010A through the 20 inch conductor pipe to 41 m DSF, and drilling began at 1315 h at a controlled ROP of 20 m/h (16.6 m/h average). The section between 2846 and 2858 m LRF was relogged during this run (Run 1) because of poor data quality. Stick-slip increased with depth (Fig. F5), so sweeps of Hi-Vis mud were conducted at pipe connections, and a wiper trip was conducted at 1615 h to 2573 m LRF (inside the conductor pipe). A repeat section was logged again between 2921 and 2928 m LRF, and the hole was reamed at several other depths to improve data quality and reduce stick-slip. Drilling stopped at 1245 h on 9 August to move the Chikyu away from a typhoon's path. At 0300 h on 12 August, the Chikyu returned to the drillsite. After reentry at 0600 h, the bit was run to 2900 m LRF to relog the critical interval in the vicinity of the megasplay fault between 2900 and 2970 m LRF. At 1145 h, drilling resumed from 3034 m LRF at a controlled ROP of 30 m/h. Stick-slip decreased in this interval, and drilling finished at 1715 h after reaching a target depth of 3107 m LRF.

Log data quality

Available data

Hole C0010A was jetted down for the 20 inch conductor pipe and then drilled from 2593 m DRF to 3107 m DRF (TD) with a 12¼ inch MWD-GVR drilling assembly (see Fig. F3 in the "Methods" chapter). Real-time data from both MWD and GVR and memory data from GVR were environmental and inversion corrected. Available data from the MWD-GVR are listed in Table T2 in the "Methods" chapter.

Repeatability

To improve data quality, we conducted a repeat log between 2900 and 2972 m LRF in Run 2 (after hole reentry on 7 August). Comparison between the first logs (Run 1) and the repeat section (Run 2) indicate significant differences in both the gamma ray and resistivity data and in the bit resistivity images. It is not clear whether these differences are related to seawater invasion during ~2 days of WOW or to borehole rugosity changes because of reaming and relogging.

Data quality

In comparison to the data from Hole C0004B, which is 3.5 km east along strike, Run 1 for the top section of the Hole C0010A exhibited continuous high stick-slip. In addition, high heave (1.2–2.5 m) because of a passing strong typhoon from the west and another coming from the south may have affected data quality. The image data from Site C0010 showed conspicuous horizontal banding with sharp contacts between zones of differing resistivity. The bands were typically ~20 cm thick in data collected during Run 1. In the repeated log of the interval between 2900 and 2972 m LRF during Run 2, the horizontal bands are less conspicuous. Nevertheless, these artifacts of the logging process obscured shallowly dipping structures and biased our interpretation toward features with steep dips. Logs from the repeated log section (Run 2) showed enlarged breakouts relative to Run 1. Overall, we would rate the quality of the data of both runs as fair; however, data from Run 1 are of higher quality because of reduced effects from reaming the hole. Primary conditions that may have affected log quality include the relatively high heave and significant stick-slip in tool rotation during imaging (Fig. F5). Unlike resistivity, gamma radiation exhibits less variability and changes gradually across the boundaries.

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