Standard Wireline Data Processing
DSDP operator and logging contractor: Scripps Institution of Oceanography
Hole: 504A
Leg: 69
Location: Costa Rica Rift (tropical NE Pacific)
Latitude: 1° 13.58' N
Longitude: 83° 43.93' W
Logging date: September 1979
Sea floor depth (echo-sounding depth): 3468 mbrf
Total penetration: 277 mbsf
Total core recovered: 9.01 m (20.5 % of cored section)
Oldest sediment cored: Chert and siliceous limestone (Late Miocene)
Lithologies: Siliceous and nannofossil oozes, chalk, limestone and chert (sediments); pillow basalt (basement)
The logging data was recorded by Gearhart-Owen in LIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in April 2005.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. CDL/GR/TEMP |
Downlog
|
36.3
|
278
|
152
|
Temperature
only
|
|
Uplog
|
36
|
278
|
129
|
|
Hole 504A was logged twenty eight days after it had been abandoned 12 m into the basement after bit failure. Re-entering the hole disturbed the temperature in the top 180 m of the sediments, but in the lower 80 meters the hole had nearly returned to equilibrium. The uppermost 36 meters of temperature data were missing on the original data tape.
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 shift to sea floor: The original logs were depth shifted to the sea floor (- 3468 m). Because none of the logs reached the sea floor, tit was not possible to define the mudline on the logs; the echo sounding depth was used instead to shift the data to the sea floor. No "bottom felt" depth was available at this hole.
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). At Hole 504A only the temperature log was run twice (downhole and uphole); the two curves show excellent correlation.
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. Gamma ray was recorded open hole.
Hole diameter was measured by the hydraulic caliper on the CDL tool (CALI); the measurement, however, is invalid.
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 69. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia