Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1418F
Expedition:
341
Location: Gulf of Alaska (NE Pacific Ocean)
Latitude: 58°46.5883' N
Longitude: 144° 29.5986' W
Logging date:
Sea floor
depth (driller's):
3678 m DRF
Sea floor
depth (logger's):
3677.5 m WRF
Total
penetration: 4626.2 m DRF (948.7 m DSF)
Total core
recovered: 495.2 m (71.9% of 688.7 m; several drilled-down intervals)
Oldest
sediment recovered:
~1 Ma at 645 m DSF
Lithologies: Mud, interbedded mud and silt, diamict, diatom/biosiliceous ooze, calcareous mud, volcanic ash, volcaniclastic mud and sand
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 July 2013.
| Tool string | Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
| 1. MSS/HRLA/HLDS/HNGS/EDTC-B | Downlog
|
99 |
|||
Uplog
|
99 |
Depth reference |
|||
2. VSI |
No good shots | ||||
3. FMS/DSI/HNGS/EDTC-B/GPIT |
Downlog
|
100 |
Calipers closed. |
||
Uplog
|
99 |
Hole U1418F was prepared for logging with a wiper trip and 50 barrels of high viscosity mud sweep; seawater was used as logging fluid. The triple combo tool string (MSS/HRLA/HLDS/HNGS/EDTC-B) was run first. The recording operations were affected by intermittent problems with the winch, which caused the breaks to lock down without warning. The HLDS caliper arm was closed at 3910-3906 and 3943-3941 m WRF (232-237 and 268-269 m WSF, respectively) due to heavy pulls while logging up. The VSI tool string was run next with the standard caliper. Although more than 35 shots were fired between 3869 and 3882 m WRF (192 and 205 m WSF, respectively), no good shots were recorded due to difficulties in getting a good anchoring in the soft formation. The FMS/DSI/HNGS/EDTC-B/GPIT tool string was run last; because the upper part of the tool string became stuck inside the drill pipe at the end of the uplog pass and it was necessary to use the Kinley crimper/cutter system to free the tool string, no further pass was recorded.
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.
Sea state was
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3677.5 m). The sea floor depth was determined by the step in gamma ray values at 3677.5 m WRF. This differs by 0.5 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 main pass of the MSS/HRLA/HLDS/HNGS/EDTC-B tool string.
Depth matching
is typically done in the following way. One log is chosen as reference or 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 are 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
data were corrected for hole size and mud weight after the recording. The HLDS data were corrected for hole size after the
recording.
High-resolution
data. Bulk density
(HLDS) data were recorded with a sampling rate of 2.54 cm in addition to a standard sampling rate of 15.24 cm.
The enhanced bulk density curve is the result of Schlumberger enhanced
processing technique performed on the MAXIS system onboard. While in normal
processing short-spacing data are smoothed to match the long-spacing one, in
enhanced processing this is reversed. In a situation where there is good
contact between the HLDS pad and the borehole wall (low-density correction) the
results are improved, because the short spacing has better vertical resolution.
Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: low frequency for lower dipole, standard frequency for both upper dipole and P&S monopole. The compressional data were good with missing coherence mainly in washouts. Low frequency dipole had the best shear slowness projection in the slower mud-like formations. Towards the drill pipe the difference between the compressional and fluid wave became more difficult. The velocities were computed from the delay times. Waveform processing is recommended to improve 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).
The data from the MSS/HRLT/HLDS/HNGS/EDTC-B tool string are of variable quality. The density, resistivity, and gamma ray logs are very noisy in the uppermost 300 m of the hole section due to poor hole conditions, with some improvement below that depth. The MSS acquired good data show a clear downhole drift, possibly attributed to increase in tool temperature downhole.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). A measurement of the hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) The caliper shows a very irregular and wide borehole (~ 10 to >18 inches), with numerous washouts especially above 250 m WMSF. Accordingly, log data from such washout intervals should be used with caution.
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 341.
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