Wireline Standard Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 583F
Leg: 87
Location: Nankai Trough (NW Pacific)
Latitude: 31° 50.10' N
Longitude: 133° 51.30' E
Logging date: July 1982
Sea floor depth (drillers' mudline): 4665 mbrf
Sea floor depth (step in GR log): 4663 mbrf
Total penetration: 439.7 mbsf
Total core recovered: 46.7 m (16 % of cored section)
Oldest sediment cored: early Quaternary
Lithologies: hemipelagic mud, silt, and sand
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. DIT/LSS/GR/MCD |
Pass
1
|
95
|
274
|
|
|
|
Pass
2
|
82
|
254
|
91
|
|
|
|
Pass
3
|
88
|
254
|
91
|
LSS/GR only
|
|
| 2. FDC/CNL/GR |
Main
|
0
|
269
|
90.5
|
Reference run
|
|
Repeat
|
75
|
271
|
90.5
|
|
|
| 3. HRT |
Downlog |
0
|
260
|
|
|
|
Uplog
|
208
|
262
|
|
|
The two tool strings were run to about 270 mbsf but were prevented from logging deeper by a bridge or hole-fill. The third DIT/LSS/GR/MCD run recorded the full sonic waveforms and gamma ray data (but no data from the other tools).
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 (-4663 m). The FDC/CNL/GR main pass was chosen as the reference run because it covered the whole open hole interval. The GR logs from the other passes were 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 4663 mbrf. This differs by 2 m from the sea floor depth given by the drillers (see above).
Sonic data: The transit time data were processed using an in-house program that compares the slowness derived from the 8 different transmitter-receiver combinations at each depth, and discards those times that are significantly different from the majority as bad data. The 'points' column in the LSS data files is a measure of confidence: it records the number of transmitter-receiver pairs retained - a value of 8 means that no data was discarded. This processing leads to improved compressional wave velocity logs that are free of the artifacts present in the velocities derived directly from DT and DTL. For Hole 583F, the sonic velocities from Pass 3 are superior to those from Passes 1 and 2, for which velocities could not be determined for some long intervals.
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) and by the 3-arm MCD tool (CALI). The MCD caliper read between 9-10 inches for DIT/LSS/GR/MCD Pass 2. DIT/LSS/GR/MCD Pass 1 reads a near constant value of 9 inches. The caliper on the FDC tool appears to have maxed out at 13 inches, which it reads for most of the log, with some drops below this value. These inconsistencies make it difficult to interpret the hole diameter, though it is likely, given the bit size and the hole-fill, that the hole was wider than 13 inches for most of its length.
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