Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 395A
Leg: 78B
Location: Mid-Atlantic Ridge (central tropical N Atlantic)
Latitude: 22° 45.35' N
Longitude: 46° 4.9' W
Logging date: March 1981
Sea floor depth ("bottom felt"): 4493mbrf (Leg 78B); 4485 mbrf (leg 45)
Total penetration: 664.09 mbsf (Leg 45)
Total core recovered: 88.36 m (47.9 % of cored section)
Oldest sediment cored: calcareous brown clay (Upper Miocene)
Lithologies: foram-nanno ooze and calcareous brown clay (sediments), basalt, serpentinized peridotite, and gabbro (basement) .
Hole 395A was drilled during DSDP Leg 45 and re-entered for logging during Leg 78B and ODP Leg 109. The logging data was recorded by Gerhart-Owen in Gerhart-Owen format. Data were digitized by Centerline Data in 2004 and processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in October 2004. In addition to the logs acquired with Gearhart-Owen tools, the Soviet downhole magnetometer and magnetic susceptibility tools were run as well. They were also digitized by Centerline Data.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. CDL/GR |
Main
|
122
|
624
|
|
Reference
|
|
Repeat
|
541
|
625
|
|
|
|
| Temperature |
Pass
1 Upper
|
0
|
237
|
|
Downlog
|
| Temperature |
Pass
1 Lower
|
242
|
625
|
|
Downlog
|
| 2. BHC/GR |
Upper
|
109.2
|
441.9
|
111.5
|
Invalid GR
data
|
|
Lower
|
427.2
|
612
|
|
Invalid GR
data
|
|
| 3. LL3/NL/GR |
Main
|
110.6
|
610.5
|
|
Invalid GR
data
|
|
Repeat
|
507.6
|
610
|
|
Invalid GR
data
|
|
| 4. Soviet Magnetometer |
Uplog
|
126.3
|
616
|
|
|
|
Downlog Upper
|
137
|
326.9
|
|
|
|
|
Downlog Lower
|
351.7
|
617.9
|
|
|
|
| 5. Magnetic Susceptibility |
Downlog
|
124.6
|
608.7
|
|
|
| 6. Temperature |
Pass
2
|
|
|
|
Missing
|
The temperature log was recorded downlog with the CDL/GR tool string and then again after running the Magnetic Susceptibility tool; the second pass of the temperature, however, was not included on the blueprints and could not be digitized. The GR recorded with the BHC/GR and LL3/NL/GR tool strings appeared to have malfunctioned and therefore were not processed. GR from the CDL/GR tool string is of good quality.
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 density log from the main pass of the CDL/GR tool string, and were then shifted to the sea floor (- 4483 m). The CDL/GR run was chosen as the reference run because it was the only tool string with three valid tool measurements (density, gamma ray, and caliper).
Depth matching is typically done in the following way. One log is chosen as reference (base) log (, and then the features in correlatable 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 after a comparison of the depth-matched logs with equivalent logs from ODP Leg 109. A shift of 4483 m was necessary to match equivalent features in ODP Leg 109 logs.
Sonic data: A velocity log was derived from the DT (acoustic 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). A good correlation could be established between Leg 78B and ODP Leg 109 logs, particularly the GR and density from the CDL/GR string and the laterolog from the LL3/NL/GR string. The neutron and acoustic logs are generally of poor quality.
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.
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 volumes 45 and 78B. See ODP volume 109 for additional logs. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia