Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Great Australian Bight (SW Pacific Ocean)
Latitude: 33° 25.2114' S
Longitude: 127° 36.1398' E
Logging date: November, 1998
Water depth (as seen on logs): 497.5 mbrf
Total penetration: 894.7 mbsf
Total core recovered: 23.3 m (24.27 %)
Logging string 1: DIT/HLDS/APS/HNGS (2
Logging string 2: FMS/SDT/GPIT/NGT (2 passes)
Logging string 3: WST
Wireline heave compensator was used to counter ship heave. It was shut down during pass 1 of the first logging string due to overheating. It was deactivated at 137.5 mbsf during the second pass of DIT/HLDS/APS/HNGS and at 127.5 mbsf during both passes of FMS/SDT/GPIT/NGT.
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 ~107.5 mbsf (pass 1)
DIT/HLDS/APS/HNGS: Bottom-hole assembly at ~112.5 mbsf (pass 2)
FMS/GPIT/SDT/NGT: Recorded open hole (pass 1)
FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~99 mbsf (pass 2).
Depth shift: Original logs have been interactively depth shifted
with reference to HNGS from DIT/HLDS/APS/HNGS pass 2 and to the sea floor
(497.5 mbrf). This amount corresponds to the water depth as seen on the logs,
which differs 2 m from the drillers' "bottom felt" depth. 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 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.
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 112 and 107.5 mbsf, should be used qualitatively only, because of the attenuation on the incoming signal. In addition, the HNGS data recorded through BHA during pass 2 is clearly affected by radioactive activation from the first pass, resulting in slightly higher values though BHA.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS string (C1 and C2).
Because the better DIT/APS/HLDS/HNGS pass (pass 2) is shorter than pass 1, the data have been spliced as follows:
HNGS: 0-112.5 mbsf (pass 1), 112.5-295 mbsf (pass 2), 295-352 mbsf (pass 1)
DIT: 109-300 mbsf (pass 2), 300-370 mbsf (pass 1)
HLDS: 121-300 mbsf (pass 2), 300-365 mbsf (pass 1)
APS: 109-300 mbsf (pass 2), 300-357 mbsf (pass 1)
Caliper from HLDS: 110-300 mbsf (pass 2), 300-365 mbsf (pass 1).
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