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doi:10.2204/iodp.proc.347.103.2015

Downhole measurements

Hole M0059B logging operations

Hole M0059B was drilled with an 210 mm (8½ inch) rotary coring bit (Rock Roller) from the seafloor to 204.03 m drilling depth below seafloor (DSF). In preparation for logging, the hole was circulated, the drill string was pulled back in the hole to 20 m wireline log depth below seafloor (WSF), and rig up of the Weatherford equipment began.

The gamma ray tool (MCG)/array induction tool (MAI), measuring NGR and electrical resistivity, was the first tool string to be run and reached 72.5 m WSF, where an uplog was started. Then the drill pipe was run again to 204 m DSF and set at 87 m WSF, and the MCG/MAI tool string was deployed again in order to log the bottom part of the hole. The tool string reached 186.4 m WSF, where an uplog was started. While pulling out of the hole, an overpull was observed, and the decision was made to set the pipe again at ~20 m WSF and deploy the MCG/spectral gamma ray tool (SGS)/sonic sonde (MSS) tool string, measuring total gamma ray, spectral gamma ray, and compensated sonic velocity. This tool string was run to 72.5 m WSF, and an uplog was started.

Hole M0059B logging units

Hole M0059B is divided into six logging units on the basis of the logs (Fig. F33). The uplog was used as the reference to establish the wireline log depth below seafloor depth scale. Total gamma ray values from the different tool strings correlate well. The olive-green total gamma ray was measured from 0 to 87 m WSF through pipe. The compensated sonic log remains relatively constant downhole, with some paired aberrations probably due to unwanted environmental effects such as hole rugosity.

Logging Unit 1: base of drill pipe to 50 m WSF

This logging unit is characterized by constant gamma ray values and dominated by thorium and uranium and extremely low potassium values. Electrical resistivity slightly increases because of increasing compaction. This corresponds to lithostratigraphic Subunit Ia (see “Lithostratigraphy”).

Logging Unit 2: 50–57 m WSF

Logging Unit 2 is characterized by a sudden drop in both NGR and electrical resistivity, which again increase through this unit. This shows a lithostratigraphic boundary from clay to silty clay with quartz silt. The separation of the different investigation depths (shallow, medium, and deep) of resistivity values show that the formation is permeable.

Logging Unit 3: 57–72.5 m WSF

In logging Unit 3 from 55 m WSF to the deepest part of this logging unit, NGR values are high again and slightly increase. The electrical resistivity data also slightly increase with some fluctuations.

Logging Unit 4: 88.5–145 m WSF

Logging Unit 4 is characterized by a decrease in NGR from ~80 to <40 gAPI and by a decrease in resistivity. Deeper than 125 m WSF, resistivities at different investigation depths are separated again, showing water infiltration into the formation. Fluctuations are observed in resistivity between 90 and 110 m WSF. They might be due to poor borehole conditions, but no caliper data are available for this hole.

Logging Unit 5: 145–164 m WSF

In logging Unit 5, an increase in NGR and an increase in electrical resistivity between 145 and 157 m WSF are observed. As no caliper data are available and core recovery was very low, it is difficult to deduce whether this corresponds to an interbedded glacial deposit or poor borehole conditions.

Logging Unit 6: 164–185 m WSF

Logging Unit 6 is marked by a sudden drop in NGR values at 164 m WSF to values <20 gAPI. Resistivity slightly decreases to very low values. This decrease corresponds to lithostratigraphic Unit VII, limestone with flint gravel (see “Lithostratigraphy”).

Hole M0059E logging operations

Hole M0059E was drilled with a 210 mm (8½ inch) rotary coring bit (Rock Roller) from the seafloor to 100.8 m DSF. In preparation for logging, the hole was circulated, the drill string was pulled back in the hole to 15 m WSF, and rig up of the Weatherford equipment began.

The first tool string was the MCG/MAI tool string, with total gamma ray and induction tools; it reached ~70 m WSF, where an uplog was performed. The second tool string was the MCG/microimager (CMI) tool string, with a total gamma ray tool and a microimager; it reached 59 m WSF. The last tool string was the MCG/SGS/MSS, with total gamma ray, spectral gamma ray, and sonic tools; it also reached 59 m WSF, where an uplog was started.

Hole M0059E logging units

Hole M0059E is divided into two logging units on the basis of the logs (Fig. F34). The uplog was used as the reference to establish the wireline log depth below seafloor depth scale. Total gamma ray values from the different tool strings correlate well. Resistivity shows a general increase downhole because of increasing compaction.

Logging Unit 1: base of drill pipe to 52 m WSF

The upper logging unit is characterized by slightly increasing gamma ray values and dominated by thorium and uranium and extremely low potassium values. Electrical resistivity slightly increases, with oscillations between 15 and 35 m WSF corresponding to an increased borehole diameter (cf. caliper log). This corresponds to logging Unit I in Hole M0059B. The sonic log increases from ~620 to 630 µs/m at 26 m WSF and then remains constant throughout this unit. The paired aberrations between 34 and 35 m WSF and 43 and 44 m WSF are due to unwanted environmental effects.

Logging Unit 2: 52–70 m WSF

Logging Unit 2 is characterized by an increase in NGR to high natural gamma ray values of 100 gAPI. The electrical resistivity data increase, with some fluctuations and separated logs for the different investigation depths (shallow, medium, and deep) indicating infiltration. This unit corresponds to logging Unit 3 from Hole M0059B.

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