Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 808C

Leg: 131

Location: Nankai Trough (NW Pacific Ocean)

Latitude: 32° 21.17' N

Longitude: 134° 56.66' E

Logging date: April, 1990

Bottom felt: 4685.5 mbrf (used for depth shift to sea floor)

Total penetration: 1327 mbsf

Total core recovered: 572.4 m (55 %)

Logging Runs

Logging string 1: The DIT/BHC/NGT tool string could not be lowered to the bottom of the hole due to an impassable bridge. No data was recorded.

Logging string 2: HLDT/CNTG/NGT (invalid density and caliper data)

Logging string 3: ACT/GST/NGT

No wireline heave compensator was used to counter ship heave.

Pipe

Both HLDT/CNTG/NGT and ACT/GST/NGT runs were recorded through bottom-hole assembly and drill pipe.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from ACT/GST/NGT run and to the sea floor (- 4685.5 m). The program used is an interactive, graphical depth-match program which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR) from the NGT tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. A list of the amount of differential depth shifts applied at this hole is available upon request.

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

Geochemical processing: The ACT/GST/NGT was recorded through bottom-hole assembly and drill pipe; this badly affected the quality of the data which for this reason have not been processed.

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).

The quality of the data recorded at hole 808C is very poor, as the data was not recorded in open hole. Use of the data from the qualitative point of view only is recommended.

Density data is invalid as the tool is a pad device that can be used only in open hole

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