Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 478
Leg: 64
Location: Guaymas Basin (tropical NE Pacific)
Latitude: 27° 8.51' N
Longitude: 111° 30.46' W
Logging date: December 1978
Sea floor depth ("bottom felt"): 1913 mbrf
Total penetration: 464 mbsf
Total core recovered: 310.25m (67 % of cored section)
Oldest sediment cored: Late Pleistocene
Lithologies: diatom and mud turbidites, dolerite sills, dolomite.
The logging data was recorded by Gearhart-Owen in analog form only; it was 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
|
112
|
458
|
112
|
Reference run
|
|
Repeat
|
409
|
463
|
|
|
|
| Temperature |
|
0
|
466
|
|
Downlog
|
| 2. BHC/GR |
|
340
|
463
|
|
|
| 3. LL3/NL/GR |
Main
|
87
|
334
|
94
|
|
|
Repeat
|
268
|
340
|
|
|
|
| 4. IEL/GR |
|
94
|
332
|
94
|
|
The CDL/GR and BHC/GR tool strings reached the bottom of the hole; the BHC/GR string, however, became stuck at 340 mbsf, and during the attempt to free it, the cable head parted. Fishing could not retrieve the tool string. The remaining tool strings thus logged only the upper part of the hole above 340 mbsf.
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 (-1913 m). This corresponds to the drillers' sea floor depth. The CDL/GR main pass was chosen as the reference run because it was the only run recorded from total depth to 112 mbsf (bit depth). The GR logs from the other passes were matched to the GR log from the reference run. Additionally, the BHC and Neutron logs were originally offset by 1 m from the GR logs on the same tool strings; this has been corrected.
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 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). In Hole 478, most logs correlate very well and show clearly the major lithologic changes, such as the two dolerite sills at 220-23 and 253-257 mbsf.
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 (CALI): the hole is a constant 9.5 inches in diameter in the dolerite section, and varies from 10 to >14 inches in the sediments.
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