Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 994-D

Leg: 164

Location: Blake Ridge (NW Atlantic)

Latitude: 31° 47.1391 N

Longitude: 75° 32.726 E

Logging date: November, 1995

Bottom felt: 2810.1 mbrf

Total penetration: 670 mbsf

Total core recovered: 69.4 (80.5 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/NGT

Logging string 2: LDEO-SST

The 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/SDT/HLDT/NGT: Bottom-hole assembly at ~114 mbsf.

Processing

Depth shift. No depth shift necessary.

Gamma-ray processing: Data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The SDT was operated in long-spaced mode (8-1010-12 ft). The 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.

High-resolution processing: No high resolution logging performed at this 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 (HLDT) and a good contact with the borehole wall. The quality of the density data was affected by the degraded hole conditions which caused frequent low density (< 1.5 g/cm3). Invalid density /photoelectric effect spikes were observed at 203-211, 246, 324, 435, 467.5, 505, 523, 697.5 and 611.5 mbsf.

Data recorded through bottom-hole assembly, such as the NGT data above 114 mbsf, should be used qualitatively only because of the attenuation on the incoming signal. Invalid gamma ray data were recorded at 94-100 and 108-117 mbsf.

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

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