Wireline Standard Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 899B
Leg: 149
Location: Iberian Abyssal Plain (NE Atlantic Ocean)
Latitude: 40° 46.347' N
Longitude: 12° 16.063' W
Logging date: May, 1993
Bottom felt: 5302.5 mbrf (used for depth shift to sea floor)
Total penetration: 562.5 mbsf
Total core recovered: 174 m (52 %)
Logging
Runs
Logging string 1: DIT/DSI/NGT
Logging string 2: HLDT/CNTG/SDT/NGT
Logging string 3: ACT/GST/NGT (GST tool not functioning)
Logging string 4: FMS/GPIT/NGT (aborted).
The initial run of the geochemical combination ACT/GST/NGT was aborted when the neutron source failed during testing at 160 mbsf; the string was then recovered and the failing tool replaced. Failure of the neutron source on the second tool, however, precluded any data acquisition with the Induced Gamma Ray Spectrometry tool. Only NGT and aluminum data were recorded.
Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.
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/DSI/NGT: Bottom-hole assembly at ~ 391 mbsf
HLDT/SDT/CNTG/NGT: Bottom-hole assembly at ~ 394 mbsf
ACT/GST/NGT: Bottom-hole assembly at ~ 393 mbsf.
Processing
Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/DSI/NGT run, and to the sea floor (- 5302.5 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 available upon request.
Gamma-ray processing: Data have been processed to correct for borehole size and type of drilling fluid.
Acoustic data processing: The sonic logs were recorded with both the array sonic digital tool (SDT) and the Dipole Sonic Imager, which also provide shear and Stoneley wave velocities. The array sonic tool was operated in standard depth-derived borehole compensated mode, including short (3-5-5-7') and long-spacing (8-10-10-12') logs. Because of the good quality of the data, no processing has been performed. Compressional velocities were computed for the short-spacing logs only.
Quality
Control
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 (HLDT, CNTG) and a good contact with the borehole wall.
Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).
Additional information about Hole 899B logs can be found in the Site Report, ODP IR Volume 149. For further information about the logs, please contact:
Cristina
Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia