Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 454A
Leg: 60
Location: Mariana Trough (Philippine Sea)
Latitude: 18° 00.78' N
Longitude: 144° 31.92' W
Logging date: April 1978
Sea floor depth (bottom felt): 3829 mbrf
Sea floor depth (step in GR log): 3829 mbrf
Total penetration: 171.5 mbsf
Total core recovered: 40.92m (28.7% of cored section)
Oldest sediment cored: early Pleistocene
Lithologies: mudstones and tuff, pillow basalts.
The logging data was recorded by Gearhart-Owen, and digitized from the paper plots by Centerline Data in 2004. Data were then 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/GR |
Pass
1
|
88
|
149
|
|
|
|
Pass
2
|
88
|
149
|
|
|
|
|
Pass
3
|
0
|
149
|
78
|
Reference
|
|
| 2. BHC/GR |
Main
|
80
|
149
|
|
|
|
Repeat
|
43
|
149
|
78
|
|
|
| 3. LL3/GR |
Main
|
55
|
147
|
79
|
|
|
Repeat
|
98
|
147
|
|
|
|
| 4. IEL/GR |
Main
|
0
|
148
|
78
|
|
|
Repeat
|
67
|
149
|
78
|
|
|
| 5. Temperature |
Pass
1
|
0
|
148
|
|
|
|
Pass
2
|
0
|
151
|
|
|
All the logging passes reached to within about 20 m of the base of the hole. Ship and tool heave conditions, on the order of 2 m, had a noticeable effect the logs.
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 and RHOB logs from the Pass 3 of the CDL/GR tool string, and were then shifted to the sea floor (-3829 m). Because of the tool heave, there are some mismatches between logs in the same tool string, as well as between tool strings, which makes depth matching difficult. The GR logs from IEL/GR and LL3/GR passes were matched to the GR log from the reference run; the BHC/GR and CDL/GR logs were already on depth.
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 3829 mbrf in the LL3/GR main pass. This occurs at the same depth as given by the drillers (see above).
Sonic data: DT slowness logs were converted to velocity.
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.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (CDL). Hole diameter was recorded by the hydraulic caliper on the CDL tool (CALI). The hole varies from 10-13 inches in diameter.
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 60. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia