Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG

Hole: 798B

Leg: 128

Location: Oki Ridge (Japan Sea)

Latitude: 37° 3.848' N

Longitude: 134° 79.961' E

Logging date: August, 1989

Bottom felt: 911.1 mbrf

Total penetration: 517.9 mbsf

Total core recovered: 514.4 m (99 %)


Logging Runs


Logging string 1: DIT/SDT/NGT

Logging string 2: FMS/GPIT/NGT (2 passes)

Logging string 3: LDT/CNTG/NGT

Logging string 4: ACT/GST/NGT

Wireline heave compensator was used to counter ship heave on all four logging runs.



Bottom-hole Assembly/Drill 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 and drill string and/or wireline stretch.

      DIT/SDT/NGT: Bottom-hole assembly at ~84 mbsf

      FMS/GPIT/NGT: Bottom-hole assembly at ~83 mbsf (pass 1)

      LDT/CNTG/NGT: Bottom-hole assembly at ~84 mbsf

      ACT/GST/NGT: Bottom-hole assembly at ~88 mbsf


      DIT/SDT/NGT: Drill pipe at ~23.5 mbsf

      ACT/GST/NGT: Drill pipe at ~28.5 mbsf.




      Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/SDT/NGT run and to the sea floor (- 907.5 m). This amount corresponds the water depth as seen on the logs and as such differs 3.6 m from the "bottom felt" depth given by the drillers.. 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 long-spacing (8-10-10-12') 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 may replace invalid recorded 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. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close.

      Data recorded through pipe and/or bottom hole assembly, such as the NGT and CNTG data recorded above 84 mbsf, should be used qualitatively only because of the attenuation on the incoming signal.

      Hole diameter was recorded by the 3-arm mechanical caliper device and the caliper on the FMS string (C1 and C2).


      Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 127-128. For further questions about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia