Logging Tools

The downhole logs were recorded by Halliburton-Sperry Drilling Services using LWD/MWD (Logging-While-Drilling/Measurement-While-Drilling) system, which employs logging 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 in real time up to the ship during drilling.

LWD data were collected after coring from 2163 to 2218.5 m DSF. The cored interval was logged while reaming and enlarging the hole, while the the formation below was logged while drilling.

The following services were employed in Hole C0002P:

AGR / AFR / EWR-M5 / PWD (gamma ray, resistivity, resistivity images, annulus fluid temperature and pressure)

The rate of penetration ranged from 5 to about 50 m/hr but most of the time was between 30 and 40 m/hr.

Processing

The AFR memory data could not be downloaded at the end of the logging operations due to a damaged data recovery port. The raw data were examined at the Halliburton processing center in Thailand and subsequently transmitted back to the ship. The original XBAT velocity and caliper data were forwarded to the Halliburton processing center in Kuala Lumpur for processing.

Depth shift: The AFR original logs have been depth shifted to the sea floor (- 1967.5 m) by JAMSTEC personnel. The rest of the data files were depth-shifted by the same amount at LDEO-BRG, as the depth-shifted data provided on the JAMSTEC web site reported incorrect top and bottom depth that prevented the use of the data in the GeoFrame system.

Environmental corrections: The gamma ray and resistivity tools have been corrected for borehole size and type of drilling mud.

Acoustic velocity: Compressional and acoustic velocities were computed at LDEO-BRG from the corresponding slownesses.

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. Unlike in hole C0002N, the exposure times in hole C0002P were generally low, due to the steady drilling, which stopped only twice.

The overall quality of the EWR-M5 resistivity, AFR ring deep and shallow resistivity, and AGR gamma ray data is good. The resistivities from the two different tools track each other consistently. The bit resistivity is invalid. About 36.8% of the AFR data points recorded by the high resolution sensor was missing from the memory data set, nonetheless the remaining data is sufficient for interpretation. The missing points resulted from sudden increases in the rate of penetration, which prevented the acquisition system from acquiring all the readings.

The quality of the compressional acoustic slowness measured with the monopole source is good, while the shear slowness measured with the dipole source is poor. The two curves show no correlation.

The borehole is enlarged and elliptical in shape, mostly at the top of the logged interval, between 2135 and 2210 m LSF.

Note: the PWD annular pressure was missing from the dataset provided on the JAMSTEC web site, thus no value could be posted online on this web site.

Additional and more detailed information about the drilling and logging operations and the quality of the measuremets performed can be found in the Operations and Logging sections of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 348.

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 procesing of the resistivity images, please contact:

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