Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: New Zealand Continental Shelf (SW Pacific Ocean)
Latitude: 41° 47.1598' S
Longitude: 171° 29.9387' E
Logging date: September, 1998
Bottom felt: 3303.1 mbrf
Total penetration: 489 mbsf
Total core recovered: 451.4 m (92.3 %)
Logging string 1: DIT/HLDS/APS/HNGS
Logging string 2: FMS/SDT/GPIT/NGT (2 passes)
Logging string 3: GHMT/NGT (2 passes)
Wireline heave compensator was used to counter ship heave resulting from the rough sea conditions. Because the WHC reached its limit during GHMT/NGT pass 1, the tool string had to be lowered to the bottom of the hole to reset the WHC.
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/HLDS/APS/HNGS: Bottom-hole assembly at ~83 mbsf
FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~83 mbsf for both passes
GHMT/NGT: Bottom hole assembly at ~83 mbsf (pass 2).
Depth shift: Original logs have been interactively depth shifted
with reference to HNGS from DIT/HLDS/APS/HNGS run and to the sea floor (3303.5
m). This amount corresponds to the mudline as seen on the logs, which differs
2.4 m from the "bottom felt" depth given by the drillers (see above).
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
(HSGR or SGR) from the HNGS or 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 FMS/GPIT/SDT/NGT and GHMT/NGT runs have been processed to correct for borehole size and type of drilling fluid. The HNGS data from DIT/HLDS/APS/HNGS was corrected for hole size during the recording.
Acoustic data processing: The array sonic tool was operated in linear mode, with the 8-receivers providing full waveform analysis. The compressional transit time (DTCO) obtained from onboard MAXIS processing was of good quality and so no acoustic data processing other than removing some cycle skips and converting delay time to velocity was done.
High-resolution data: Neutron porosity data were recorded at a sampling rate of 5.08 cm.
Geological Magnetic Tool: The Geological Magnetic Tool collected data at two different sampling rates, the standard 0.1524 m rate and 0.0508 m. Both data sets have been depth shifted to the reference run and to the sea floor. Due to tool malfunction, only susceptibility data were acquired.
null value=-999.25. This value may replace invalid 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 (APS/HLDS) 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 bottom-hole assembly, such as the HNGS data above 80
mbsf, should only be used qualitatively because of the attenuation on the
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS string (C1 and C2).
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR Volume 181. For further questions about the logs, please contact:
E-mail: Cristina Broglia