Logging-While-Drilling Data Processing
IODP drilling and logging operator: CDEX
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 33° 10.0482' N
Longitude: 136° 39.8454' E
Logging-while-drilling date: December 26-27, 2012
Sea floor depth (as seen on logs): 2969 m LRF
Total penetration: 3263.5 m LRF (294.5 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 C0021A :
geoVISION-8 / arcVISION-8 / TeleScope (resistivity, resistivity images, velocity and gamma ray, azimuth, annulus fluid temperature and pressure)
The rate of penetration ranges from 35 to about 45 m/hr.
Depth shift: The original logs have been depth shifted to the sea floor (- 3113 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.
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 good.
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:
E-mail: Cristina Broglia
For questions about the procesing of the resistivity images, please contact:
E-mail: Tanzhuo Liu
For questions about the logs, please contact: