Wireline Standard Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 564
Leg: 82
Location: Mid-Atlantic Ridge (central N Atlantic)
Latitude: 33° 44.36' N
Longitude: 43° 46.03' W
Logging date: October 1981
Sea floor depth (drillers' mudline): 3830 mbrf
Sea floor depth (step in GR log): 3830 mbrf
Total penetration: 365 mbsf
Total core recovered: 34.75 m (43 % of cored section)
Oldest sediment cored: early Oligocene
Lithologies: nannofossil chalk, limestone (sediments), basalt (basement).
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 February 2004.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. DLL/GR |
main
|
99
|
353
|
99
|
|
|
repeat
|
275.5
|
353
|
|
|
|
| 2. FDC/CNL/GR |
main
|
0
|
300
|
99
|
reference
|
|
repeat
1
|
276
|
355
|
|
|
|
|
repeat
2
|
276
|
345
|
|
reference
|
|
|
repeat
3
|
273
|
344
|
|
|
|
| 3. HRT |
See
below
|
0
|
343
|
|
|
| 4. LSS/GR/MCD |
pass
1 main
|
90
|
340
|
97
|
|
|
pass
1 rept 1
|
269
|
340
|
|
|
|
|
pass
1 rept 2
|
94
|
168
|
98
|
|
|
|
pass
2
|
268.5
|
341
|
|
SWF recorded
|
|
|
pass
3
|
260.5
|
339
|
|
SWF recorded
|
|
|
pass
4
|
310
|
340
|
|
SWF recorded
|
|
| 5. HRT |
See
below
|
0
|
340
|
|
|
Logging at Hole 564 was successful, with all logging tool strings entering the basement section (at 282 mbsf) and reaching close to the bottom of the hole. The HRT temperature probe was weighted by placing it in a perforated core barrel, after HRT runs in the previous holes in the leg had failed to reach the bottom of the hole. The two HRT runs comprise a downlog and an uplog, and those logs were subdivided into upper, middle, and lower sections. A storm was anticipated during logging, but never fully developed. However, there are some signs of ship heave in the logs, for example, the porosity logs show the sediment-basement contact has a peak of basement-like values above it in some logs, but not in others. Alternatively, the basement section could be azimuthally heterogenous, and the repeat logs may record data from different sides of the borehole.
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 (-3830 m). The FDC/CNL/GR main pass was chosen as the reference run because it was the only run to cross the sea floor. The FDC/CNL/GR second repeat pass was used as the depth reference in the basement section, below the extent of the main pass. The GR logs from the other passes were matched to the GR log from the reference runs. The match between GR logs was unclear in runs and intervals. In such cases, the simplest depth match was chosen, and for the LSS/GR/MCD tool string pass 1 repeat 2, and passes 2-4 were not differentially matched.
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 3830 mbrf. This is the same as 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 generally free of the artifacts present in the velocities derived directly from DT and DTL. For this hole, probably the more reliable velocities are from LSS/GR/MCD pass 1. The other passes appear to give low values in places in the basement, and don't repeat well.
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 caliper readings do not repeat very well from pass to pass. The basement section reads between 8-10.5 inches wide, and between 11-14 inches in the sediment section. The LSS/GR/MCD main caliper indicates small thin bridges throughout the section, but these might be some kind of artifact.
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 82. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia