Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 479
Leg: 64
Location: Guaymas Basin (tropical NE Pacific)
Latitude: 27° 50.76' N
Longitude: 111° 37.49' W
Logging date: December 1978
Sea floor depth ("bottom felt"): 766 mbrf
Total penetration: 440 mbsf
Total core recovered: 272.8m (62 % of cored section)
Oldest sediment cored: Late Pliocene
Lithologies: hemipelagic diatom mud, dolomite.
The logging data was recorded by Gearhart-Owen in analog form only; it was and digitized by Centerline Data in 2004. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in September 2004.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. CDL/GR |
Main
|
94
|
434
|
94
|
Reference run
|
|
Repeat
|
377
|
429
|
|
|
|
| Temperature |
Pass
1
|
0
|
424
|
|
Downlog
|
|
Repeat
|
377
|
429
|
|
|
|
| 2. BHC/CL/GR |
Main
|
93
|
426
|
93.5
|
|
|
Repeat
|
369
|
427
|
|
|
|
| 3. LL3/NL/GR |
Main
|
90.5
|
431
|
93
|
|
|
Repeat
|
372
|
431
|
|
|
|
| 4. IEL |
|
94.5
|
430
|
94.5
|
|
| 5. Temperature |
Pass
2
|
0
|
428
|
|
Downlog
|
All tool strings reached close to the bottom of the hole and good quality logs were obtained.
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 CDL/GR tool string, and were then shifted to the sea floor (-766 m). This corresponds to the drillers' sea floor depth.
Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the 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.
Sonic data: Sonic velocity was calculated from the DT slowness log. The background levels in the sonic velocity logs (1.25-1.35 km/sec) are low compared to the expected values in sediments (>1.5 km/sec), indicating some systematic error in the tool. Most of the velocity logs are also rather flat and featureless, in contrast to the other physical property logs. However, the occasional peaks in velocity correspond to peaks in density (related to the dolomite layers).
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 (CDL, NL). Hole diameter was recorded by the hydraulic caliper on the CDL tool and the mechanical caliper on the BHC tool string: the hole is between 10 and 11 inches in diameter below 237 mbsf, with a wider range of diameters, to > 14 inches in some layers shallower in 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 64. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia