Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Ontong-Java Plateau (NW Pacific Ocean)
Latitude: 2° 25.98' N
Longitude: 160° 32.46' E
Logging date: February, 1990
Bottom felt: 3424 mbrf
Total penetration: 656 mbsf
Total core recovered: 494.9 m (75.5 %)
Logging string 1: DIT/SDT/HLDT/NGT (HLDT invalid)
Logging string 2: FMS/GPIT/NGT
Logging string 3: ACT/GST/HLDT/NGT
Logging string 4: BHC/NGT (2 passes)
The BHC (Borehole Compensated Sonic Tool was run to collect reliable acoustic data, as the SDT did not function properly during the first run. The HLDT was run on the geochemical string as well, because the density data collected during the first run were not valid, due to malfunction of the caliper tool.
No information available from the logging report or log header about use of the wireline heave compensator to counter ship heave.
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/HLDT/NGT: Bottom-hole assembly at ~93.5 mbsf
FMS/GPIT/NGT: Bottom-hole assembly at ~90 mbsf
ACT/GST/HLDT/NGT: Bottom-hole assembly at ~88.5 mbsf
BHC/NGT: Recorded open-hole.
Depth shift: Original logs have been interactively depth shifted with reference to NGT from BHC/NGT pass 1. Due to the low signature of the NGT log, the depth match is very difficult, with the exception of one lithologic marker (ash layer) at 181.3 mbsf, which is clearly identified on each logging pass. In order to get a better depth match of the DIT/SDT/HLDT/NGT run, the resistivity log has been used to in the correlation with the sonic from the BHC/NGT. Again, the match is very difficult and, therefore, uncertain. 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. Finally, the logs have been depth shifted to the sea floor (- 3421.7 m); the amount of this shift differs from the “bottom felt” depth given by the drillers (see above) and has been applied to match the lithologic marker at 181.3 mbsf.
Gamma-ray processing: NGT data from the DIT/SDT/HLDT/NGT and ACT/GST/HLDT/NGT runs have been processed to correct for borehole size and type of drilling fluid.
Acoustic data processing: The array sonic tool did not function during the first run and a Borehole Compensated Sonic Tool was run twice as the last logging string. Good quality data were collected which did not require any processing, only some editing in the 98-106, 224-227, and 243-247 mbsf intervals; the delay time has been converted into compressional velocity.
Geochemical data: Due to malfunction of the Induced Gamma Ray Spectrometry tool, only the Aluminum Activation tool collected reliable data. No processing was performed due to the lack of a complete dataset.
null value=-999.25. This value may replace invalid log values or results (ex. processed sonic data).
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. The density data recorded with the ACT/GST/NGT tool string are valid up to 200 mbsf; above this depth they are shifted to unreliably low vales and for this reason they are not included in the database. 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 bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.
Hole diameter was recorded by the caliper on the FMS string (C1 and C2); the hydraulic caliper on the HLDT tool (CALI) malfunctioned and the data is invalid.
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:
E-mail: Cristina Broglia