Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG

Well name: 766A

Leg: 123

Location: Exmouth Plateau (tropical SE Indian)

Latitude: 19° 55.925' S

Longitude: 110° 27.243' E

Logging date: October, 1988

Bottom felt: 4008 mbrf (depth used onboard by Schlumberger engineer to shift the data to sea floor)

Total penetration: 527.2 mbsf

Total core recovered: 347.5 m (66 %)


Logging Runs


Logging string 1: DIT/SDT/NGT

Logging string 2: ACT/GST/NGT (completely through pipe)

Logging string 3: LDT/CNTG/GPIT/NGT (upper section thorough pipe)

      Wireline heave compensator was used to counter ship heave


Bottom-hole Assembly/Pipe


      The following bottom-hole assembly/pipe 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 ~245 mbsf

      ACT/GST/NGT: Bottom-hole assembly from ~368 mbsf to total depth

      ACT/GST/NGT: Pipe at ~368 mbsf

      LDT/CNTG/GPIT/NGT: Bottom-hole assembly at ~245 mbsf (lower section)

      LDT/CNTG/GPIT/NGT: Recorded through pipe (upper section)




      Depth shift: Original logs were depth shifted to the sea floor onboard ( 4008 mbsf). Subsequently, they have been interactively depth shifted with reference to NGT from 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: Barite mud with addition of KCl (4 %) was used. Data from the DIT/SDT/NGT run recorded open hole have been processed to correct for borehole size and type of drilling fluid. No correction has been performed on the NGT from the ACT/GST/NGT run recorded through pipe and bottom hole assembly. Also, no processing has been performed on the NGT data from the LDT/CNTG/NGT run which was recorded after the geochemical run, with the formation possibly activated.


      Geochemical data: Due to technical problems, no geochemical data from this hole could be migrated into the online database. The results of the processing, however, can be viewed in the paper by Pratson, E. L. et al. (1992), Geochemical well logs from the Argo abyssal plain and Exmouth Plateau, Northeast Indian Ocean, Sites 765 and 766 of Leg 123. In Gradstein, F. M., Ludden, J. N. et al., Proc. ODP, Sci. Results, 123: College Station, TX (Ocean Drilling Program), 637-656. )


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 bottom-hole assembly and pipe should be used qualitatively only because of the attenuation on the incoming signal. Because of the poor quality, no data from the upper LDT/CNTG/GPIT/NGT section recorded through pipe are included in the database.

      In a hole stabilized with barite mud it would be expected to notice and steady increase of the density values towards the bottom of the hole, where barite tends to accumulate. In hole 966A, however, this effect is not observed; the density data from logs correlate remarkably well with the physical property data (see IR volume 123, back-pocket plate 1) down to ~425 mbsf. A sharp decrease of the density, not shown by other logging data, is observed below this depth.

      Hole diameter was recorded by the 3-arm mechanical caliper on the DIT/SDT/NGT tool string (HD). Based on the logging scientist's report, this tool was reading 1.41 " too high, according to calibration in casing performed at Site 765. This correction, however, has not been applied at Hole 766A, because it would result in portions of the hole with hole size < bit size (9 7/8").


      Details of standard shore-based geochemical processing procedures are found in the ODP SR Volume 123. For further information about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia