Standard Wireline Data Processing
IODP logging contractor: LDEO
Hole: U0060A
Expedition: 344S
Location: Baffin Bay (Labrador Sea)
Latitude: 75°42' 58.3531 N
Longitude: 65°57' 12.1941 W
Logging date: September 27-28, 2012
Sea floor depth (driller's): 592.2 m DRF
Sea floor depth (logger's): 594 m WRF (HRLA/DSI/MSS/EDTC-B/HNGS Uplog)
Total penetration: 239.1 m DRF (831.3 m DSF)
Total core recovered: 62 % of cored section
Oldest sediment recovered: Turonian-Cenomanian
Lithologies: organic-rich carbonaceaous mudstones, siltstones and sandstones, and sandy mudstones.
The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in October 2012.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
| 1. HRLA/DSI/MSS/EDTC-B/HNGS |
Downlog
|
0
|
194.7
|
45
|
|
|
Uplog
|
0
|
196.8
|
45
|
Depth reference
|
Hole U0060A was reported to be in good condition for logging.
The first and only logging run consisted of the HRLA/DSI/MSS/EDTC-B/HNGS tool string (the DSI replacing the APS). The tool string reached a depth about 40 m above total depth. After three unsuccessful attempts to go past this depth, an uplog was recorded. About 10 m after entering the drill pipe there was a significant overpull, believed to be due to debris stuck to the tools. Eventually, the tools were able to pass freely all the way to the surface. No repeat uplog pass was recorded.
During the logging operations sea conditions remained calm (~ 0.2 m peak to peak) and the wireline heave compensator was not used.
The depths in the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). 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 a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 594 m WRF). The sea floor depth was determined by the step in gamma ray values at 594 m WRF observed on the HRLA/DSI/MSS/EDTC-B/HNGS uplog. This differs by 1.8 m from the sea floor depth given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the uplog of the HRLA/DSI/MSS/EDTC-B/HNGS tool string.
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 in turn matched to it. 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.
Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording.
High-resolution data. Gamma Ray data from the HNGS and EDTC-B tools were recorded at sampling rates of 5.08 and 15.24 cm.
Acoustic data. The dipole shear sonic imager (DSI) was operated with standard frequency in P&S monopole, lower dipole and Stoneley modes in both passes. The upper dipole was recorded in low frequency. The velocities were computed from acoustic slownesses. They are generally of good quality.
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 of 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. Hole diameter was recorded by the FMS tool (C1 and C2). Hole conditions were generally excellent.
A Null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the expedition report.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.