Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG
Hole: 807A
Leg: 130
Location: Ontong-Java Plateau (tropical NW Pacific)
Latitude: 3° 36.42' N
Longitude: 156° 37.49' E
Logging date: March, 1990
Bottom felt: 2815.1 mbrf (used for depth shift to sea floor)
Total penetration: 822.9 mbsf
Total core recovered: 716.7 m (87.1 %)

Logging Runs

Logging string 1: DIT/SDT/NGT
Logging string 2: ACT/ HLDT/NGT (only ACT data recorded)
Wireline heave compensator was used to counter ship heave during the first run; after malfunctioning in the lower part of the hole (up to 323 mbsf) during the second run, the WHC worked well in the upper part.

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/NGT: Bottom-hole assembly at ~77 mbsf
ACT/ HLDT/NGT: Bottom-hole assembly at ~77 mbsf.


Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT run and to the sea floor (- 2815.1 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 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 are of excellent quality and do not need any processing. Compressional velocity has been computed from the delay times.

Geochemical data: Due to malfunction of the neutron source on the Induced Gamma Ray Spectrometry tool, only the Aluminum Activation tool was run. No processing was performed due to the lack of a complete dataset.

Quality Control

null value=-999.25. This value generally may replace invalid log values or results.
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, such as the NGT data above 77 mbsf, should be used qualitatively only because of the attenuation on the incoming signal. Invalid gamma ray data were recorded at 38-41, 47-49, and 72-74 mbsf during the  DIT/SDT/NGT run and at 70-74 mbsf during the ACT/HLDT/NGT run.
Hole diameter was measured by the hydraulic caliper on the HLDT tool (CALI); the caliper did not fully open until 784 mbsf, therefore the density data below this depth are unusually low and should not be used quantitatively.

Additional information about the logs can be found in the “Explanatory Notes” and Site Chapter, ODP IR volume 130. For further questions about the logs, please contact:

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