Wireline Standard Data
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 567A
Leg: 84
Location: Mid-America Trench Slope (tropical NE Pacific)
Latitude: 12° 42.99' N
Longitude: 90° 55.92' W
Logging date: January 1982
Sea floor depth (drillers’ mudline): 5529 mbrf
Total penetration: 501 mbsf
Total core recovered: 103.68 m (39 % of cored section)
Oldest sediment cored: late Cretaceous
Lithologies: Mudstone, with some limestone and sedimentary breccias. Gabbro, diabase, serpentinite, and occur below the logged interval.
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 January 2004.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. DIT/LSS/GR/MCD |
repeat
|
200
|
260
|
|
|
|
main
|
0
|
272
|
65.5
|
reference
|
|
| 2. LSS/GR |
lower
|
88.5
|
256
|
|
SWF recorded
|
|
upper
|
54
|
101
|
65.5
|
SWF recorded
|
|
| 3. FDC/CNL/GR |
repeat
|
204
|
253
|
|
|
|
main
|
63
|
260
|
65.5
|
|
The hole was logged to 272 mbsf, but the tool strings could not pass below a bridge at this depth. The pipe was then lowered through the bridge to within 100 m of the base of hole. Unfortunately, the tool string could not exit the pipe at this lower depth, and during retrieval of the tool string, thee pipe failed just below the ship. About 5000 m of pipe, the tool string, and the bottom hole assembly were lost.
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 DIT/LSS/GR/MCD tool string, and were then shifted to the sea floor (- 5529 m). The DIT/LSS/GR/MCD main pass was chosen as the reference run because it was the only run to cross the sea floor. 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 could not be determined from the gamma ray log because of the lack of a clear step in the log values (although there is a small step at 5520 mbsf), therefore the drillers' sea floor depth of 5529 mbrf was used. The lower and upper passes of the LSS/GR tool string had to be shifted upwards by 11 and 10m respectively to bring them in line with the reference pass.
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.
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).
Gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe should be used only qualitatively, because of the attenuation on the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe. (The CNL porosity can sometimes be used qualitatively through the BHA and pipe, but most of the other logs will not give usable data.)
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 hole was wider than the maximum extent of the FDC caliper (~13 inches) for most of the interval.
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 84. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia