Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 541
Leg: 78A
Location:
Latitude: 15° 31.2' N
Longitude: 58° 43.7' W
Logging date: February 1981
Sea floor depth ("bottom felt"): 4961 mbrf
Sea floor depth (step in temperature log): 4961 mbrf
Total penetration: 459 mbsf
Total core recovered: 400.75 m (87.3 % of cored section)
Oldest sediment cored: radiolarian mudstone (Early Miocene)
Lithologies: calcareous ooze, radiolarian mud with ash beds
The logging data was recorded by Gearhart-Owen in GO format and subsequently translated into LIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. CDL/TEMP/GR |
Downlog
|
|
|
|
Temperature
tool only
|
Three logging attempts were made at Hole 541. During the first one, temperature was recorded downward before the tool string got stuck in clay about 10 m beyond the end of the pipe. A second logging attempt was aborted due to an electrical problem that developed about one third of the way through the drill pipe. On the third attempt, temperature was recorded to about 18 m beyond the pipe before getting stuck again in soft clay. After several attempts to work the tool past the bridge, log function switched to density-caliper-gamma ray mode to log the approximately 46 m of open hole that could be exposed by raising the pipe in the derrick. The tool, however, had been damaged by the attempts to pass the bridge and no log could be recorded. In summary, only a temperature profile was recorded dowhole through pipe and 18 m open hole.
The depths in the table are for the processed logs (after 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 temperature log was depth shifted to the sea floor (- 4961 m).
The sea floor depth was determined by the step in temperature value at 4961 mbrf. This coincides with the sea floor depth given by the drillers ("bottom felt").
The quality of the data is usually 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 the case of Hole 541, only one pass of the temperature log was recorded, thus no comparison could be performed.
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 78A. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia