Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Queensland Plateau (tropical SW Pacific Ocean)
Latitude: 17°49.985 ' S
Longitude: 149° 30.831' E
Logging date: August, 1990
Bottom felt: 531.4 mbrf (used for depth shift to sea floor)
Total penetration: 300 mbsf
Total core recovered: 162.4 m (54.1 %)
Logging string 1: DIT/SDT/HLDT/NGT
Logging string 2: FMS/GPIT/NGT (2 passes)
No information available about use of Wireline heave compensator.
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/SDT/HLDT/CNTG/NGT: Bottom-hole assembly at ~ 57.5 mbsf
FMS/GPIT/NGT: Bottom-hole assembly at ~ 57.5 mbsf (repeat pass)
FMS/GPIT/NGT: Logged in open hole (main pass).
Depth shift: No depth shift necessary. Original logs have been depth shifted to the sea floor (- 531.4 m).
Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.
Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.
null value=-999.25. This value generally appears in discrete core measurement files and also it may replace recorded log values or results which are considered invalid (ex. processed sonic data).
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 (CNTG, HLDT) 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 NGT data above 57.5
mbsf, should be used qualitatively only because of the attenuation on the incoming signal.
Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI), and the caliper on the FMS string (C1 and C2).
For further information about the logs refer to the ODP Initial and Scientific Results, volume 133 or contact:
E-mail: Cristina Broglia