Logging Tools

The downhole logs were recorded using the LWD/MWD (Logging-While-Drilling/Measurement-While-Drilling) system, which employs instruments that are part of the drill string itself. The advantages of this technique include being able to log in formations that would not provide a stable hole for wireline logging (e.g. the upper section of sedimentary formations) and logging a hole immediately during drilling, so that it is in good condition and largely free of wash-outs. The data is recorded in the tool's memory and downloaded when the drill string returns to the rig floor. A small subset of the data is transmitted up to the ship during drilling. The following data was processed by the logging specialists and the Schlumberger engineer aboard the Chikyu, with additional processing performed onshore by Schlumberger Information Solution. In order to meet the format constraints of the LogDB online database, some additional data reduction has been performed by personnel at the Borehole Group of the Lamont-Doherty Earth Observatory.

The following LWD/MWD services were employed in Hole C0002S :

LWD

arcVision ((phase and attenuation resistivity, gamma ray, annulus temperature and pressure, equivalent circulation density)

MicroScope (Gamma ray, resistivity, resistivity Images)

SonicScope (velocity)

TeleScope (drilling parameters)

seismicVision (seismic data)

MWD

TeleScope (torque, drilling weight on bit)

Multiple runs were carried out at Hole C0002S:

LWD/MWD tools	Run	Top Depth (m WMSF)	Bottom Depth (m WMSF)	Casing Depth (m WMSF)	Notes
Telescope	1			~2802	Real Time only
arcVision/MicroScope/SonicScope/TeleScope/seismicVision	2	2772	2933	~2802

Drilling went smoothly in hole C0002S.The first run acquired only MWD data in real tim, without downhole torque or weight on bit data. The second run acquired a full suite of LWD/MWD logging data.

During run 2 the rate of penetration was stable at about 2 m/hr. The high ROP observed between 2876 and 2880 LSF is an artifact due to tripping after an orientation survey.

Processing

Depth shift: The original have been depth shifted to the sea floor (- 1967.5 m) by the logging scientists aboard the ship using Schlumberger's Techlog software. This value matches the water depth used in the C0002P hole drilled during expedition 348 and hole C0002Q drilled in expedition 358. The sea floor depth was originally determined by the step in gamma ray and resistivity values at the sediment-water interface. The sonic waveforms were depth-shifted by personnel at the Borehole Group of the Lamont-Doherty Earth Observatory.

Gamma Ray data processing: The Gamma Ray logs have been environmentally corrected for bit size (8.5 in) and mud properties by the Schlumberger engineer aboard the ship.

Acoustic data: The data was processed onhore by Schlumberger personnel at Schlumberger Information Solution, who provided both compressional and shear wave outputs. The data was acquired in three modes: monopole, monopole-low frequency, and quadrupole mode. Compressional and shear data were obtained only between about 2802 and 2884 mLSF from the monopole and quadrupole mode data. However, the compressional velocity values are generally lower than in Hole C0002P in the 2836-2869 mLSF interval; this is believed to be caused by the pervasive drilling damages occurring in the proximity of Hole C0002S, casued by previous logging operations. Below 2869 mLSF, the hole is considered to be undamaged and the compressional velocities are consistent with C0002P and are therefore more reliable. Only spotty shear velocities could be computed and they are of questionable quality.

Sampling rates: The data was acquired with the following sampling rates:

Attenuation and Phase Resistivity (arcVision): 15.24 cm

Button Resistivity (MicroScope): 3.04 cm

Computed e-caliper (Microscope): 3.04 cm

Computed e-caliper (arcVision): 15.24 cm (published curve not available; recomputed at LDEO)

Gamma ray (arcVision): 15.24 cm

Miscellaneous (arcVision, TeleScope): 15.24 cm

Slowness/Velocity (SonicScope): 5.08 cm

Sonic waveforms (SonicScope): 5.08 cm

Temperature / Pressure (arcVision): 15.24 cm

IMPORTANT: Because Hole C0002S is a sidetracked hole, there is a difference between the measured depth (MD) and the true vertical depth (TVD). Because the difference is small (~1-2 m in total in expedition 358 Holes C0002Q and C0002S), the scientists decided to use the the measured depth instead of the true vertical depth for all the measurements reported in the IODP Proceedings. Accordingly, we have used the measured depth in the files included in the LogDB online database.

Quality Control

Additional information about the drilling and logging operations can be found in the Site Expedition Report and in the Methods section, Proceedings of the International Ocean Discovery Program, Expedition 358.

For questions about the logging operations and the processing performed onboard, please contact:

Yukari Kido

E-mail: ykido@jamstec.go.jp

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.