Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 819A

Leg: 133

Location: Central Great Barrier Reef (tropical SW Pacific)

Latitude: 16° 37.439' S

Longitude: 146° 19.486' E

Logging date: September, 1990

Bottom felt: 576.4 mbrf (used for depth shift to sea floor)

Total penetration: 400 mbsf

Total core recovered: 339.5 m (84.9 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/NGT

The logging report did not provide any information about use of wireline heave compensator.

Bottom-hole Assembly

The following bottom-hole assembly depths is as it appears on the logs after 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/SDT/HLDT/NGT: Bottom-hole assembly at ~67.5 mbsf.

Processing

Depth shift: As only one run was recorded, no differential depth shift was required. The original logs have been depth shifted to the sea floor (- 576.5 m).

Gamma-ray processing: NGT data have been processed to correct for borehole 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 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 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. Logging data at hole 819A are mostly of good quality, except the density measurement which, due to the lack of proper eccentralization and therefore of contact with the borehole wall, is locally too low (i.e. 185-215, 240-250, and 280-300 mbsf intervals).

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

Neither the 3-arm mechanical caliper device (MCD) nor the hydraulic caliper on the HLDT tool were operational at this site.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 133. For further questions about the logs, please contact:

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