Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG

Well name: 765D

Leg: 123

Location: Argo Abyssal Plain (SE Indian Ocean)

Latitude: 15° 58.54' N

Longitude: 117° 34.49' E

Logging date: October, 1988

Bottom felt: 5724.3 mbrf

Total penetration: 1194.9 mbsf

Total core recovered: 78.7 m ( %)


Logging Runs


Logging string 1: DIT/SDT/NGT (upper and lower sections)

Logging string 2: ACT/GST/NGT

Logging string 3: LDT/CNTG/GPIT/NGT

      No information could be found about use of wireline heave compensator.


Drill Pipe/Casing


      The following drill pipe/casing depths are as they appear on the logs after depth shift to the sea floor and differential depth shift (see "Depth shift" section). 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.


      The casing shoe is seen on the logs at ~ 928 mbsf.

      The DIT/SDT//NGT was recorded through drill pipe and casing in the uppermost 50 meters.

      The LDT/CNTG/GPIT/NGT was recorded through pipe and casing from 783 to 868 mbsf.




      Depth shift: Original logs were depth shifted to the sea floor (- 5728 mbrf) on board by the Schlumberger engineer and logging scientist. This amount differs 3.7 m from the "bottom felt" depth given by the drillers. No proprietary tapes of un-depth shifted data were brought back to the LDEO-BRG. On shore, differential depth shift has been performed of all logs with reference to ACT/GST/NGT run. 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 from the ACT/GST/NGT tool string have been processed to correct for borehole size and type of drilling fluid; subsequently, they have been corrected for the attenuation due to pipe and casing.


      Acoustic data processing: The array sonic tool was operated 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 appears in discrete core measurement files and also it 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 (CNTG, LDT) and a good contact with the borehole wall.

      Data recorded through casing and pipe should be used qualitatively only because of the attenuation on the incoming signal.

      The spherically focused induction resistivity log (SFLU) suffered from intermittent failures during both runs and is not included in the database.

      Hole diameter was recorded by the 3-arm mechanical caliper (MCD) on the DIT tool string. The caliper tool measured 1.4" too high, according to calibration performed on board in casing; the value has been corrected prior to using the caliper for borehole size corrections.


      Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 123. For further questions about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia