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 LWD/MWD services were employed in Hole C0002A:

geoVISION (RAB resistivity and gamma ray)

adnVISION: (no nuclear source deployed; only ultrasonic caliper data acquired)

sonicVISION (velocity)

MWD-APWD = Measurement-While-Drilling (azimuth, shock, fluid pressure and temperature,fluid circulating density)

In Hole C0004B, the rate of penetration ranged from 30 to approximately 45 m/hr below 33 mLSF and higher above.

Processing

Depth shift: The original logs have been depth shifted to the sea floor (- 2666 m). The sea floor depth was determined by the step in gamma ray and resistivity values at the sediment-water interface.

Gamma Ray data processing: Processing of the data is performed onboard by Schlumberger personnel after downloading of the data from the tool. Gamma Ray data is measured as Natural Gamma Ray (GR): the GR from the geoVISIONtool has been corrected for hole size (bit size), collar size, and type of drilling fluid.

Resistivity data: The geoVISION resistivity is sampled with a 0.03048 m (1.2 in) and 0.1524 m (6 in) sampling rate.

Acoustic velocity: The sonicVISION data for Hole C0004B were processed by a Schlumberger Data Consulting Services (DCS) specialist on board the Chikyu. A detailed description of the processing performed is provided in the Site Chapter of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 314. The compressional velocity has been computed from the the processed delay time (DTCO).

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 best data are acquired in a circular borehole. A data quality indicator is given by the four ultrasonic calipers (CC15, CC26, CC37 and CC48).

Additional information about the drilling and logging operations can be found in the Site Chapter of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 314 . For further questions about the logs, please contact:

Yoshinori Sanada
IODP Department, CDEX
Japan Agency for Marine Science Technology(JAMSTEC)
3137-25, Showama-machi, Kanazawa-ku
Yokohama, 236-0001, Japan
tel: +81-45-778-5649

fax: +81-45-778-5704
e-mail: sanada@jamstec.go.jp

For any web site-related problem please contact:
E-mail: logdb@ldeo.columbia.edu