Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1394B
Expedition:
Location: Lesser Antilles, off Montserrat (Caribbean Sea)
Latitude: 16° 38.4375' N
Longitude: 62° 2.2819' W
Logging date:
Sea floor
depth (driller's):
1125.6 m DRF
Sea floor depth (logger's): 1124 m WRF (HRLA/HLDS/MSS/EDTC-B/HNGS main)
Total
penetration: 1307 m DRF 181.4 ( m DSF)
Total core
recovered: 141.15 m (
77.8 % of cored section)
Oldest
sediment recovered:
Lithologies: Volcaniclastic turbidites, mixed volcaniclastic-bioclastic turbidites, hemipelagic sediments.
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 March 2012.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/HLDS/MSS/EDTC-B/HNGS
|
Downlog
|
80.5 |
Invalid caliper
|
||
Main
|
80.5 |
Reference |
|||
Repeat
|
recorded open hole |
||||
| 2. VSI | recorded open hole |
Failed |
|||
3. FMS/DSI/GPIT/EDTC-B
|
Downlog
|
80.5 |
Invalid caliper |
||
Main
|
80.5 |
||||
Repeat
|
recorded open hole |
Hole U1394B was prepared for logging with 30 barrels of high viscosity mud sweep and then displaced with 71 barrels of 10.5 ppg mud. Owing to hole stability issues the HLDS 137Cs source was not used during the HRLA/HLDS/MSS/EDTC-B/HNGS logging run; while no density data were acquired, caliper measurements are available for the main and repeat runs. The VSI logging operation failed due to the tool string's difficulty in passing through the drill bit.
,
The sea state was low with a peak-to-peak heave of 1.0 m or less. Wireline heave compensator was used during the logging operation.
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 of (- 1124 m). This sea floor depth differs by 1.6 m from that given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the HRLA/HLDS/MSS/EDTC-B/HNGS main run (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 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.
High-resolution data. The HNGS data were corrected for hole size during the recording.
Acoustic
data. The dipole sonic imager (DSI) was operated in P&S monopole and upper and lower dipole modes. Standard frequency was used in P&S monopole and upper dipole modes, low frequency in lower dipole mode. The velocities were computed from the P&S monopole compressional and upper and lower dipole shear slownesses. They are
generally of good quality. Reprocessing of the sonic waveforms is recommended for better results.
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 hydraulic caliper on the HLDS
tool (LCAL). The hole diameter is generally in gauge (~12") for much of the open hole, but with a ~10-m enlarged (~16") interval
just below the drill bit.
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 340.
For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia