Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1087C

Leg: 175

Location: Cape Basin (SE Atlantic)

Latitude: 31° 27.9137' S

Longitude: 15° 18.6541' E

Logging date: October, 1997

Bottom felt: 1385.9 mbrf

Total penetration: 491.9 mbsf

Total core recovered: 478.3 m (97.2 %)

Logging Runs

Logging string 1: DIT/SDT/NGT

Wireline heave compensator was not used during the main run due to malfunction.

Bottom-hole Assembly

The main run of the logs was recorded open-hole.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT downlog and to the sea floor (- 1385 m). This amount corresponds to the sea floor depth observed on the logs and differs 0.9 m from the drillers' "bottom felt" depth. 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 bit size and type of drilling fluid.

Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs are of excellent quality and do not need processing.

Quality Control

null value=-999.25. This value may replace recorded log values or results which are considered invalid.

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The logs recorded at hole 1087C are generally of good quality, with the exception of the deep resistivity data between 230 and 240 mbsf.

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.

No measurement of hole size was recorded at this hole.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 175. For further questions about the logs, please contact:

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