Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG

Hole: 960A

Leg: 159

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

Latitude: 34.979' N

Longitude: 2° 44.009' W

Logging date: January, 1995

Bottom felt: 2048.4 mbrf (used for depth shift to sea floor). NOTE: the mudline was originally established by the drillers at 2059.7 mbrf by direct pipe measurement. The corrected PDR reading was 2048.4 mbrf. The difference was attributed to the difficulty in "feeling" for bottom with drill pipe.

Total penetration: 451.2 mbsf (calculated using a "bottom felt" depth of 2059.7 m)

Total core recovered: 145.01 m (32.1 %)


Logging Runs


Logging String #1: DIT/SDT/HLDT/CNTG/NGT


Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.


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/HLDT/CNTG/NGT: bottom hole assembly at ~85 mbsf.





Depth shift: All original logs have been depth shifted to the sea floor (- 2048.4 m). Any correlation with core must take into account the difference of 11.3 m between core and log sub-bottom depth.


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.


High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm respectively. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDT pad and the borehole wall (low density correction) the results are improved, because the short-spacing have better vertical resolution.


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.


Data recorded through bottom hole assembly (NGT and CNTG above 85 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).


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