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. Logging proceeded smoothly down to 3007 mLRF (525 m LSF), where the drill pipe became stuck and pipe connection was lost. Despite several efforts to recover the bottom part of the BHA (including the MWD-LWD tools) fishing was not successful and the hole was cemented.

The following LWD/MWD services were employed in Hole C0003A:

geoVISION (RAB resistivity and gamma ray)

adnVISION: (density, porosity, caliper)

sonicVISION (velocity)

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

In Hole C0003A, the rate of penetration was approximately 35 m/hr.

Processing

During normal logging operations, the data is recorded in the tool's memory and downloaded when the drill string returns to the rig floor. This was not possible at Hole C0003A, where only real-time data that are transmitted to the ship during drilling could be retrieved. This small data subset included many invalid data that were filtered out in order to obatin a continuous record.

The following depth-shifted and filtered LWD channels were received from CDEX in April 2010 and were put online:

geoVISION (deep, ring, bit resistivity and gamma ray)

adnVISION: (density, porosity, caliper)

sonicVISION (delay time and velocity)

Depth shift: The original logs have been depth shifted to the sea floor (- 2481.5 m). The sea floor depth was determined by the step in gamma ray and resistivity values at the sediment-water interface.

Acoustic velocity: The sonicVISION data for Hole C0002A 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; this is particularly true for the density tool, which uses clamp-on stabilizers to eliminate mud standoff and to ensure proper contact with the borehole wall. A data quality indicator is given by the density caliper (ADIA) measurement of hole diameter.

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