Wireline Standard Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 462A (re-entry hole, see Leg 61)
Leg: 89
Location: Nauru Basin(tropical NW Pacific)
Latitude: 7° 14.5' N
Longitude: 165° 01.90' E
Logging date: November 1982
Sea floor depth: 5186 mbrf (determined during Leg 61)
Total penetration: 1209 mbsf
Total core recovered: 74.43 m ( 54.2% of cored section)
Oldest sediment cored: early Aptian
Lithologies: turbiditic ooze and chalk, chert, limestone, sandstone, and mudstone (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/Casing depth (mbsf) | Notes |
| 1. HRT |
downlog
|
0
|
516
|
|
|
|
uplog
|
0
|
512
|
|
|
Hole 462A was drilled and logged on Leg 61 (no analogs or digital logs available). It was re-entered on Leg 89, after about 4 years, and temperature logging was the first operation carried out to log the undisturbed borehole temperature profile. Slight obstructions were met at 470 and 515 mbsf, and the tool could not pass below 521 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: Because no GR logs were taken, depth matching could not be done, and a log-based sea floor depth could not be determined. The drillers' sea floor depth of 5186 mbrf was used to shift the temperature logs to the sea floor.
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).
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 89. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia