Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 647A

Leg: 105

Location: Gloria Drift (Labrador Sea)

Latitude: 53° 19.876' N

Longitude: 45° 15.717' W

Logging date: October, 1996

Bottom felt: 3869 mbrf (used for depth shift to sea floor)

Total penetration: 736 mbsf

Total core recovered: 445.2 m (62 %)

Logging Runs

Logging string 1: DIT/LSS/GR (upper and lower sections)

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/LSS/GR: Bottom-hole assembly at ~120.5 mbsf (upper section)

DIT/LSS/GR: Bottom-hole assembly at ~236 mbsf (lower section).

Processing

Depth shift: Original logs have been interactively depth shifted with reference to GR from DIT/LSS/GR run (upper section) and to the sea floor (- 3869 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 gamma ray curve (GR) recorded 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.

Acoustic data processing: The long-spacing sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.

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. Data recorded at Hole 647A are generally of good quality. 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 3-arm mechanical caliper device; good caliper measurements were obtained during the downlog only.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 105. For further questions about the logs, please contact:

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