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 services were employed in Hole C0002F :

geoVISION-8 / arcVISION-8 / sonicVISION-8 / TeleScope (resistivity, resistivity images, velocity, gamma ray, azimuth, annulus fluid temperature and pressure)

In Hole C0002F a main log was acquired while driling, and three short repeat sections were acquired uphole (ream up 1) and downhole (ream down 2 and 3) to check repeatability.

The rate of penetration was approximately 35 m/hr until about 1006 m LSF; below this depth it dropped to about 12 m/hr.

Processing

Depth shift: The original logs have been depth shifted to the sea floor (- 1967.5 m) by JAMSTEC personnel.

Gamma Ray data: Gamma Ray data is measured as Natural Gamma Ray (GR): it is assumed that the GR from the GVR tool has been corrected for hole size (bit size) and type of drilling fluid, though there is no mention of any environmental correction in either the IODP Proceedings or the logging report posted on the JAMSTEC web site.

Resistivity data: The geoVISION resistivity is sampled with a 0.03048 m (1.2 in) sampling rate.

Sonic data. The acoustic compressional data were of good quality; no shear velocity was acquired because formation velocities lower than the velocity of the drilling fluid cannot be independently picked form the recorded waveform data.

Quality Control

During the processing, quality control of the data is performed by inter-comparison of all logging data to ensure that reasonable values are returned for expected lithology types and features on the logs reflect true formation characteristics and are not artifacts.

The overall quality of the logs was good and good repeatability was observed.

Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition reports, Proceedings of the Integrated Drilling Program, Expedition 338. For further questions about the online database please contact:

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

For questions about the processing of the resistivity images please contract:

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu

For questions about the logs, please contact:

Yoshinori Sanada

E-mail: sanada@jamstec.go.jp

Yukari Kido

Email: ykido@jamstec.go.jp

Yuichi Shinmoto

Email:shinmoto@jamstec.go.jp