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doi:10.2204/iodp.proc.347.106.2015

Downhole measurements

Logging operations

Downhole logging measurements in Hole M0062D were made after completion of coring to a total depth of 21 m drilling depth below seafloor (DSF). In preparation for logging, the hole was circulated with seawater and the pipe was pulled back to ~2 m wireline log depth below seafloor (WSF).

For downhole logging in Hole M0062D, two tool strings were deployed:

• The gamma ray tool (MCG)/array induction tool (MAI) tool string, measuring natural gamma ray and electrical resistivity, was run from the seafloor to 10.4 m WSF, where an uplog was started.
• The MCG/spectral gamma ray tool (SGS)/sonic sonde (MSS) tool string, measuring total gamma ray and spectral gamma ray, was run from the seafloor to 10.4 m WSF and an uplog was started.

The tools provided continuous and good quality log data.

Logging units

Hole M0062D was divided into two logging units on the basis of the logs (Fig. F20). The uplog was used as the reference to establish the wireline log depth below seafloor depth scale. There is a good correlation between the gamma ray logs of the two different tool strings.

Logging Unit 1: base of drill pipe to 5.1 m WSF

This logging unit is characterized by a generally increasing gamma ray with large fluctuations between the base of the pipe and 3.7 m WSF in both gamma ray and resistivity. No caliper was run in this hole, but these fluctuations are probably due to poor borehole conditions. The resistivity values decrease slightly from 3.7 to 5.1 m WSF.

Logging Unit 2: 5.1–10.4 m WSF

After a sudden drop in gamma ray values at 5.1 m WSF, NGR values again increase to reach a maximum of nearly 120 gAPI at 7.2 m WSF. Deeper than 7.2 m WSF, NGR remains at constant high values of ~100 gAPI. These high natural gamma ray values correspond to the thick greenish black intervals described in lithostratigraphic Subunit Ia (between ~6 and 8.5 mbsf, see “Lithostratigraphy”). Resistivity values are constant in this logging unit, with a slight increase deeper than 8.8 m WSF. Resistivity values are generally very low in this hole, showing limited compaction.

Both logging Units 1 and 2 correspond to lithostratigraphic Unit Ia.

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