Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 808B

Leg: 131

Location: Nankai Trough (NW Pacific Ocean)

Latitude: 32° 21.09' N

Longitude: 134° 56.61' E

Logging date: April, 1990

Bottom felt: 4685 mbrf (used for depth shift to sea floor)

Total penetration: 358.8 mbsf

Total core recovered: 59.7 m (24 %)

Logging Runs

Logging string 1: DIT/SDT/NGT (main and repeat)

Logging string 2: LDT/CNTG/NGT . The tool string eventually got stuck and all fishing attempts were unsuccessful. The hole was cemented and abandoned. No data was recorded.

Wireline heave compensator was not used because the sea was calm.

Bottom-hole Assembly/Pipe

The following bottom-hole assembly/pipe depths are as they appear on the logs after depth shift to the sea floor. As such, there might be a discrepancy with the original depths given by the drillers onboard. Possible reasons for depth discrepancies are ship heave, lack of wireline heave compensator, and drill string and/or wireline stretch.

DIT/SDT/NGT: Bottom-hole assembly at ~79.5 mbsf (main run)

DIT/SDT/NGT: Recorded through bottom-hole assembly and drill pipe (repeat run).

Processing

Depth shift: Because main and repeat do not overlap, no differential depth shift was necessary. The logs have been shifted to the sea floor (- 4685 m).

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The array sonic tool was operated standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.

Quality Control

null value=-999.25. This value generally appears in discrete core measurement files and also it may replace recorded log values or results which are considered invalid (ex. processed sonic data).

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The quality of the data recorded at hole 808B is generally good.

Data recorded through bottom-hole assembly and drill pipe, such as the data of the repeat section, should be used qualitatively only because of the attenuation on the incoming signal.

No hole diameter was measured at Hole 808B.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 131. For further questions about the logs, please contact:

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia