Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1354C
Expedition: 317
Location: Canterbury Basin (SW Pacific Ocean)
Latitude: 44 °50.8487' S
Longitude: 171° 47.2080 ' E
Logging date: January 2, 2010
Sea floor
depth (driller's):
125 m DRF
Sea floor
depth (logger's):
122 m WRF (DIT/DSI/GPIT/HNGS main pass)
Total
penetration: 509.2 m DRF
Total core
recovered: 133.37 m (
42 % of cored section; no coring 0-65 m DSF)
Oldest sediment recovered: late lower Pliocene (4.0-4.3 Ma
Lithologies: mud, sandy mud, muddy sand, marl, sandy marl, clay
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in January 2010.
Tool string |
Pass |
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
1. DIT/DSI/GPIT/HNGS
|
Downlog |
0
|
383 |
109 |
|
Main
|
0 |
383 |
109 |
Reference |
|
Repeat
|
317 |
383 |
Open hole |
The hole was drilled to a total depth of 509.2 m DRF
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 based on the logger's sea floor depth of 122 m WRF, which differs 3 m from the driller's sea floor depth (125 m DRF). The sea floor depth was determined by the step in gamma ray values observed on the main pass. The depth-shifted downlog and repeat pass were then depth-matched to the DIT/DSI/GPIT/HNGS main pass (reference).
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.
Acoustic data. The dipole shear sonic imager (DSI) was run with the medium frequency monopole, the standard frequency upper dipole and the low frequency lower dipole for downlog, and with the standard frequency monopole (others remain unchanged) for both repeat and main passes. Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide consistently reliable results. Reprocessing of all the original waveforms was performed to validate the original data or extract meaningful compressional and shear velocities. The most reliable shear velocity value is the one derived from the lower dipole (VS1), where the lower source frequency used generated more cohert waveforms.
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 null value of
-999.25 may replace invalid log values.
Additional
information about the drilling and logging operations can be found in the
Operations and Downhole Measurements sections of the expedition reports,
Proceedings of the Integrated Drilling Program, Expedition 317.
For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu