Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Ontong-Java Plateau (tropical NW Pacific)
Latitude: 3° 36.39' N
Longitude: 156° 37.48' E
Logging date: March, 1990
Bottom felt: 2817 mbrf (used for depth shift to sea floor)
Total penetration: 1528.4 mbsf
Total core recovered: 252.8 m (33.8 %)
Logging string 1: DIT/LSS/NGT
Logging string 2: ACT/HLDT/NGT (only ACT data recorded)
Logging string 3: FMS/GPIT/NGT (2 passes)
No information available from log report about use of wireline heave compensator to counter ship heave.
The casing shoe was located at 349.8 mbsf. On the logs it appears to be at 350 mbsf.
Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/LSS/NGT run and to the sea floor (- 2817 m). 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 (SGR) from the 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 vailable upon request.
Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.
Acoustic data processing: The long-spacing (8-10-10-12') 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.
Geochemical data: Due to malfunction of the neutron source on the Induced Gamma Ray Spectrometry tool, only the Aluminum Activation tool was run. No processing was performed due to the lack of a complete dataset.
null value=-999.25. This value may replace invalid log values or results (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 (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 casing, such as the gamma ray data above 350 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 on the FMS string (C1 and C2).
E-mail: Cristina Broglia
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