Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Great Australian Bight (SW Pacific Ocean)
Latitude: 33° 30.5613' S
Longitude: 128° 3.9844' E
Logging date: October, 1998
Bottom felt: 795 mbrf (used for depth shift to sea floor)
Total penetration: 463.3 mbsf
Total core recovered: 40.5 m (12.9 %)
Logging string 1: DIT/APS/HLDS/HNGS
Logging string 2: SDT/GPIT/GHMT/NGT
Logging string 3: WST
Wireline heave compensator was used to counter ship heave but it malfunctioned a few times: during the first run at 227 and 325 mbsf and during the second run at 165 mbsf. During the third run it stopped working at the second before the last station and was not restarted.
The following bottom-hole assembly and drill 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/APS/HLDS/HNGS: Bottom-hole assembly at ~116 mbsf
DIT/APS/HLDS/HNGS: Pipe at~40 mbsf
SDT/GPIT/GHMT/NGT: Bottom-hole assembly at ~116 mbsf.
Depth shift: Original logs have been interactively depth shifted
with reference to NGT from DIT/APS/HLDS/HNGS run and to the sea floor (-795 m).
The depth match was difficult, due to the low gamma ray signature and the poor
quality of the NGT logs. 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: The HNGS data from DIT/HLDS/APS/HNGS was corrected for hole size during the recording. Because of the low quality of the NGT logs, no borehole correction has been applied.
Acoustic data processing: The array sonic tool was operated in two modes: linear array mode, with the 8-receivers providing full waveform analysis (compressional and shear) and standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') and short-spacing (3-5-5-7') logs. 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 has been 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.
Data recorded through bottom-hole assembly and drill pipe should be used
qualitatively only because of the attenuation on the incoming signal.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL).
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR Volume 182. For further questions about the logs, please contact:
E-mail: Cristina Broglia