Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 960C

Leg: 159

Location: Ivory Coast-Ghana Margin (equatorial NE Atlantic)

Latitude: 3° 35.025' N

Longitude: 2° 43.990' W

Logging date: February, 1995

Bottom felt: 2046.3 mbrf (used for depth shift to sea floor)

Total penetration: 352.8 mbsf

Total core recovered: 160.67 m (69.8 %)

Logging Runs

Logging string #: DIT/SDT/NGT and HLDT without source

Logging string #: FMS/GPIT/NGT

Wireline heave compensator was used during the FMS/GPIT/NGT run to counter ship heave resulting from the mild/rough sea conditions. Due to electronics failure, no WHC could be used during the DIT/SDT/NGT run.

Bottom-hole Assembly/

The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see "Depth shift" section) and 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, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/SDT/NGT: bottom hole assembly at ~170 mbsf.

FMS/GPIT/NGT: bottom hole assembly at ~169 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT run and to the sea floor (- 2046.3 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: Data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The digital sonic tool was operated in linear mode, including long-spacing array mode. The quality of the data is impaired by the bad hole conditions. The borehole size variations induced frequent cycle skipping in the log, the result of the receivers picking incorrect first arrival times. Because of the extremely noisy character of the sonic logs, no processing has been performed at this stage.

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. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (CNTG, HLDT) and a good contact with the borehole wall. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close.

Data recorded through bottom hole assembly, such as the NGT data above 170 mbsf should be used qualitatively only because of the attenuation on the incoming signal.

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI) and on the FMS string (C1 and C2).

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 159. For further information about the logs, please contact:

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