Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 936A

Leg: 155

Location: Amazon Fan (equatorial NW Atlantic)

Latitude: 5° 37.932' N

Longitude: 47° 44.130' W

Logging date: April, 1994

Bottom felt: 3586 mbrf (used for depth shift to sea floor)

Total penetration: 433.8 mbsf

Total core recovered: 274.42 m ( 63 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNT/NGT

Logging string 2: FMS/GPIT/NGT (2 passes)

Logging string 3: ACT/GST/NGT

Wireline heave compensator was used to counter ship heave.

Bottom-hole Assembly/Drill Pipe

The following bottom-hole assembly/pipe 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 ~ 127 mbsf (main)

DIT/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~ 63 mbsf (repeat)

ACT/GST/NGT: Bottom-hole assembly at ~ 81 mbsf

FMS/GPIT/NGT: Bottom-hole assembly at ~ 85 mbsf (pass 1)

FMS/GPIT/NGT: recorded open hole (pass 2).

ACT/GST/NGT: Drill pipe @ 11.5 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from ACT/GST/NGT run and to the sea floor (-3586 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: Because of the good quality of the data, 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. 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 pipe and bottom hole assembly (such as the NGT recorded in the upper part of the hole) 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). During the repeat pass the HLDT caliper started closing at 92 mbsf, therefore the density data has not been corrected for borehole size in the interval from 92 to 63 mbsf.

The resistivity, gamma ray, density, caliper, neutron, and acoustic data from the DIT/SDT/HLDT/CNT/NGT main and repeat passes have been merged as follows:

resistivity: merged at 124 mbsf.

gamma ray: merged at 130 mbsf and 60 mbsf (ACT/GST/NGT)

density: merged at 130 mbsf

caliper: merged at 130 mbsf

neutron: merged at 130 mbsf

acoustic: merged at 130 mbsf.

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 155. For further information about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia