Wireline Standard Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 584A
Leg: 87
Location: Japan Trench (NW Pacific)
Latitude: 40° 28.0' N
Longitude: 143° 56.7' E
Logging date: August 1982
Sea floor depth (drillers'mudline): 4125 mbrf
Sea floor depth (step in GR log): 4124 mbrf
Total penetration: 901.5 mbsf
Total core recovered: 10.66 m (37 % of cored section)
Oldest sediment cored: early Middle Miocene
Lithologies: diatomaceous muds and mudstones, with silt and ash beds.
The logging data was recorded by Schlumberger in LIS format. Data were processed at the Borehole Research Group at the Lamont-Doherty Earth Observatory in November 2003.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. FDC/CNL/GR |
main
|
0
|
517
|
92
|
Reference run
|
|
repeat
|
398
|
496.5
|
|
|
A logging run with the DIT/LSS/GR/MCD tool was aborted due to failure of the LSS tool. A bridge prevented the FDC/CNL/GR tool string from logging the lowermost 400 m of the hole. The hole was filled with heavy mud prior to logging.
The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). Generally, discrepancies may exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the 'bottom felt' depth in soft sediment.
Depth match and depth shift to sea floor: The original logs were depth-matched to the GR log from the main pass of the FDC/CNL/GR tool string, and were then shifted to the sea floor (-4124 m). The FDC/CNL/GR main pass was chosen as the reference run because it had the longest open-hole coverage and passed the sea floor. The GR log from the other pass was matched to the GR log from the reference run.
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.
The sea floor depth was determined by the step in gamma ray values at 4124 mbrf. This differs by 1 m from the sea floor depth given by the drillers (see above).
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 (FDC, CNL). Hole diameter was recorded by the hydraulic caliper on the FDC tool (CALI). The caliper on the FDC tool reads between 11-12.5 inches, apart from a bridged section between 467-504 mbsf.
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 87. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia