Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1131A

Leg: 182

Location: Great Australian Bight (SW Pacific Ocean)

Latitude: 33°19.5654' S

Longitude: 128° 28.8720' E

Logging date: November, 1998

Bottom felt: 345 mbrf

Total penetration: 962 mbsf

Total core recovered: 37.64 m (60.24 %)

Logging Runs

Logging string 1: DIT/HLDS/APS/HNGS
Logging string 2: FMS/SDT/GPIT/NGT
Logging string 3: WST

Wireline heave compensator was used to counter ship heave. It was deactivated at 146 mbsf during both DIT/HLDS/APS/HNGS and FMS/SDT/GPIT/NGT passes.

Bottom-hole Assembly

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 ~102 mbsf
DIT/HLDS/APS/HNGS: Drill pipe at ~29 mbsf
FMS/GPIT/SDT/NGT: Bottom-hole assembly at ~102 mbsf.
FMS/GPIT/SDT/NGT: Drill pipe at ~29 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to HNGS from DIT/HLDS/APS/HNGS main and to the sea (349 mbrf). This amount corresponds to the water depth as seen on the logs, which differs 4 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 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 and so no acoustic data processing other than converting delay time to velocity was done.

High-resolution data: Neutron porosity data were recorded at a sampling rate of 5.08 cm.

Quality Control

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 and NGT data above 102 mbsf, should only be used qualitatively because of the attenuation on the incoming signal.

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 182. For further questions about the logs, please contact:

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia