Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 858G

Leg: 139

Location: Middle Valley-Juan de Fuca Ridge (NE Pacific)

Latitude: 48° 27.360' N

Longitude: 128° 42.531' W

Logging date: September, 1991

Bottom felt: 2426.2 mbrf (used for depth shift to sea floor)

Total penetration: 432.6 mbsf

Total core recovered: 6.8 m (4 %)

Logging Runs

Logging string 1: DIT/HLDT/NGT (2 passes)

No information available from logging report about use of wireline heave compensator.

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 and drill string and/or wireline stretch.

DIT/HLDT/NGT: Bottom-hole assembly at ~56 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from Pass 1 and to the sea floor (- 2426.2 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: NGT data from Pass 1 have been processed to correct for borehole size and type of drilling fluid.

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.

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 (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.

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

Because of malfunction of the HLDT caliper in the second pass, the data is suspicious and is not included in the database.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 139. For further questions about the logs, please contact:

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