Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 908-A

Leg: 151

Location: Fram Strait (Arctic Ocean)

Latitude: 78° 23.11' N

Longitude: 1° 21.636' W

Logging date: August, 1993

Bottom felt: 1284.5 mbrf (used for depth shift to sea floor)

Total penetration: 344.6 mbsf

Total core recovered: 313.96 m (91 %)

Logging Runs

Logging String 1: DIT/DSI/NGT

Logging String 2: HLDT/CNTG/NGT

Logging String 3: FMS/GPIT/NGT (2 passes)

Wireline heave compensator was used to counter ship heave.

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/DSI/NGT: Bottom-hole assembly at ~77.5 mbsf

HLDT/CNTG/NGT: Bottom-hole assembly at ~75 mbsf

FMS/GPIT/NGT: Bottom-hole assembly at ~59.5 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from FMS/GPI/NGT (main pass) and to the sea floor (- 1284.5 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: No processing performed. Data recorded with the DSI tool were adversely affected by the irregular surface of the borehole (see caliper data) and the compressional log was difficult to obtain. For this reason, we have included in the database only compressional and shear wave data that show some correlation with other logs, i.e. the resistivity logs. Waveform processing is necessary to recover some of the invalid data recorded in the lower part of the hole.

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 bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. Invalid NGT readings from the HLDT/CNTG/NGT run were recorded at 32, 55, 64, and 69 mbsf.

Valid hole diameter measurements were recorded by the caliper on the HLDT tool (CALI) and on the FMS string (C1 and C2). As the HLDT caliper closed at about 92 mbsf, any density measurement above that depth is suspicious, as no real-time correction for borehole size could be performed and because the tool was not making proper contact with the borehole wall.

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 151. For further information about the logs, please contact:

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