Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 528
Leg: 74
Location: Walvis Ridge (tropical SE Atlantic)
Latitude: 28° 31.49' S
Longitude: 2° 19.44' E
Logging date: July 1980
Sea floor depth ("bottom felt"): 3812 mbrf
Sea floor depth (step in GR log): GR logs did not reach the sea floor
Total penetration: 555 mbsf
Total core recovered: 272.8 m (62 % of cored section)
Oldest sediment cored: Nannofossil chalk (Maestrichtian)
Lithologies: Nannofossil chalk, foram-nannofossil ooze, volcanogenic sandstones and claystone (sediments), basalt (basement)
The logging data were recorded by Gearhart-Owen in GO format and were subsequently translated into LIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in November 2004.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. Temperature |
Downlog
|
85.5
|
308.2
|
110
|
Section 1
|
|
Downlog
|
286
|
332.3
|
|
Section 2
|
|
|
Downlog
|
331.4
|
337.5
|
|
Section 3
|
|
|
Downlog
|
347.9
|
552.3
|
|
Section 4
|
|
| 2. BHC/CL/GR |
Main
|
110
|
553.8
|
110
|
|
|
Repeat
|
486.6
|
555.5
|
|
|
The first log attempted was a temperature/density/gamma ray log; the density component, however, failed, and only a temperature log was acquired downhole. The acoustic log was successful, but further attempts to log had to be abandoned: the Schlumberger line apparently hung up in the bottom hole assembly, which resulted in several "cattails" and hence aborted the remainder of the logging program.
The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor).
Depth match and depth shift to sea floor: The original logs were depth-matched to the GR log from the main pass of the BHC/CL/GR tool string, and were then shifted to the sea floor (- 3812 m).
Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent and no sudden changes in cable speed), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.
Because no GR log reached the sea floor, the sea floor depth of 3812 m used to shift the logs was the "bottom felt" depth provided by the drillers.
Sonic data: A velocity log was calculated from the acoustic slowness for both main and repeat run. The data, however, is mostly of very poor quality and should be used with caution.
The quality of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of the same tool, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the sonic velocity log).
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (density and neutron logs). At Hole 528 the hole diameter was measured by the caliper tool on the BHC/CL/GR tool string. The hole is very enlarged and irregular, especially down to 333 mbsf. This affected most recordings, particularly the acoustic logs, which are very poor through most of the hole.
A null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operation can be found in the Operations section of the Site Chapter in DSDP Initial Reports volume 74. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: chris@ldeo.columbia.edu