Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 952A

Leg: 157

Location: Madeira Abyssal Plain (tropical NE Atlantic)

Latitude: 30° 47.488' N

Longitude: 24° 30.570' E

Logging date: August, 1994

Bottom felt: 5442.7 mbrf (used for depth shift to sea floor)

Total penetration: 425.9 mbsf

Total core recovered: 415.18 m (98 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNTG/NGT (3 sections)

The wireline heave compensator was used to counter ship heave resulting from the mild sea conditions (0.2-0.7 m).

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 (main, upper section): Bottom-hole assembly at 92 mbsf

DIT/SDT/HLDT/CNTG/NGT (repeat, upper section): Bottom-hole assembly at 76 mbsf

DIT/SDT/HLDT/CNTG/NGT (lower section): Bottom-hole assembly at 181 mbsf.

Even though three intervals were logged, only the upper two ones have meaningful data. For this reason, these two zones are referred to as upper and lower section.

Processing

Depth shift: No differential depth shift necessary in the upper part of the hole. Upper and lower sections do no present sufficient overlap for depth correlation. All logs have been depth shifted to the sea floor (-5442.7 m).

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

Acoustic data processing: The SDT was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. Because of the good quality of the logs, no processing has been performed.

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 should be used qualitatively only because of the attenuation on the incoming signal. NGT data was recorded through BHA in the 168-180 mbsf interval and above 76 mbsf.

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).

The data has been merged as follows:

gamma ray: data spliced at 100 and 168 mbsf

density and caliper: data spliced at 125 mbsf

neutron: data spliced at 125 and 181 mbsf

resistivity: data spliced at 100 and 195 mbsf (no good IDPH resistivity recorded n the lower section)

sonic: data spliced at 105 mbsf

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 157. For further information about the logs, please contact:

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