Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Great Australian Bight (SW Pacific Ocean)
Latitude: 33° 28.45' S
Longitude: 128° 28.87' E
Logging date: November, 1998
Bottom felt: 490.6 mbrf (used for depth shift)
Total penetration: 1001.8 mbsf
Total core recovered: 442.05 m (86.6 %)
Logging string 1: DIT/HLDS/APS/HNGS (run
without density nuclear source)
Logging string 2: FMS/SDT/GPIT/NGT (main and repeat)
Logging string 3: GHMT/NGT/GPIT
Wireline heave compensator was used to counter ship heave. It was deactivated at 119.4, 129.4, and 119.4 mbsf during first, second, and third logging string respectively.
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 ~109.5 mbsf
FMS/GPIT/SDT/NGT: Bottom hole assembly at ~109.5mbsf (main pass)
FMS/GPIT/SDT/NGT Recorded open hole (repeat pass).
Depth shift: Original logs have been interactively depth shifted
with reference to HNGS from DIT/HLDS/APS/HNGS main run and to the sea floor
(490.6mbrf). 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
Gamma-ray processing: NGT data from FMS/GPIT/SDT/NGT and GHMT/NGT runs has 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 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 for both passes and so no acoustic data processing other than 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. 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 109.5
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). The FMS caliper operated correctly during the main pass but did not fully open on the repeat pass.
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