Logging-While-Drilling
Data Processing
IODP coring and logging operator: CDEX
Hole: C0012H
Expedition: 338
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 32 ° 44.8783 ' N
Longitude: 136° 5.0351' E
Logging-while-drilling date: December 3-6, 2012
Total penetration: 4248 m LRF (710 m LSF)
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 C0012H :
geoVISION-8 / arcVISION-8 / sonicVISION-8 / TeleScope (resistivity, resistivity images, velocity, gamma ray, azimuth, annulus fluid temperature and pressure)
The rate of penetration exceeded 40 m/hr.
Depth
shift: The original logs
have been depth shifted to the sea floor (- 3538 m) by JAMSTEC personnel.
Gamma Ray data processing: Gamma Ray data is measured as Natural Gamma Ray (GR): according to the header of the printouts produced by Schlumberger, the GR has been corrected for bit and tool size, mud weight and potassium concentration in the mud.
Resistivity data: The geoVISION resistivity is sampled with a 0.03048 m (1.2 in) sampling rate. According to the header of the printouts produced by Schlumberger, the resisistivity has been corrected for bit size and mud resistivity.
Sonic data. Good quality compressional velocities were acquired throughout the drilled interval. Shear velocities were acquired only in two intervals in the basement section: from 574 to 604 m LSF and 655 to 687 m LSF.
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 logging data is fair.
Additional information about the drilling and logging operations can be found in the Operations and Logging-while-drilling sections of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 338.
For questions about the online database, please contact:
Cristina Broglia
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
Yuichu Shinmoto
Email: shinmoto@jamstec.go.jp