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doi:10.2204/iodp.proc.347.104.2015

Downhole measurements

Logging operations

Downhole logging measurements in Hole M0060B were made after completion of coring to a total depth of 85.7 m DSF. In preparation for logging, the hole was circulated with seawater and the pipe was pulled back to ~17.5 m WSF.

For downhole logging in Hole M0060B three tool strings were deployed:

• The gamma ray tool (MCG)/array induction tool (MAI) tool string, measuring total gamma ray and electrical resistivity,
• The MCG/spectral gamma ray tool (SGS)/sonic sonde (MSS) tool string, measuring total gamma ray, spectral gamma ray, and sonic velocity, and
• The MCG/microimager (CMI) tool string, with total gamma ray and microimager tools.

The MCG/MAI tool string was lowered and downlogged to 67 m WSF. The hole was then uplogged to the seafloor. The wireline depth to the seafloor was determined from the step increase in gamma ray values.

The MCG/SGS/MSS tool string was lowered to 61 m wireline log depth below seafloor (WSF) and an uplog was started.

The MCG/CMI tool string was lowered to 56 m WSF with the calipers closed. The hole was then uplogged with open calipers at high resolution.

The tools provided continuous and good quality log data.

Logging units

Hole M0060B is divided into two logging units on the basis of the logs (Fig. F23). The uplog was used as the reference to establish the wireline log depth below seafloor depth scale.

Logging Unit 1: base of drill pipe to 23.5 m WSF

This logging unit is characterized by a fluctuation in gamma ray between 40 and 60 gAPI. Gamma ray values are driven by thorium and uranium; no potassium is measured in logging Unit 1. Resistivity values also show fluctuations and infiltration of borehole fluid into the formation (deep, medium, and shallow resistivity show different values). Sonic values are increasing. The fluctuations observed might be due to poor borehole conditions, but in this interval, no caliper data are available. The generally lower NGR values are explained by the sandy clayey silt as described in lithostratigraphic Unit II (see “Lithostratigraphy”).

Logging Unit 2: 23.5–67 m WSF

NGR values vary between 80 and 100 gAPI and are higher than in logging Unit 1. This can be explained by the increase in clay content from lithostratigraphic Units II and III (see “Lithostratigraphy”). Resistivity is constant throughout this unit, and the sonic log slightly decreases with depth. The caliper data in logging Unit 2 shows good borehole conditions with the hole slightly closing in the top part of the unit.

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