Standard Wireline Data Processing
Science Operator: Texas A&M University
Hole: U1498B
Expedition: 366
Location: Celestial Seamount (Tropical NW Pacific)
Latitude: 16° 27.3716' N
Longitude: 147° 10.1166' E
Logging date: January 29, 2017
Sea floor depth (driller’s): 3296 m DRF
Sea floor depth (logger's): 3297.5 m WRF (MSS/HRLA/HLDS/EDTC-B/HNGS Main Run)
Total penetration (RCB coring): 3556 m DRF (260 m DSF) .
Total core recovered: 82.82 (31.9%)
Oldest sediment recovered: n/a
Lithology: Serpentinite muds with ultramafic clasts
The logging data
were recorded by Schlumberger in DLIS format and processed at the
Borehole Research Group of Lamont-Doherty Earth Observatory in January 2017.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. MSS/HRLA/HLDS/EDTC-B/HNGS
|
Downlog
|
~50 |
Caliper closed. Invalid HLDS. |
||
Repeat |
Invalid HLDS.
|
||||
Main
|
~50 |
Depth reference. Invalid HLDS. |
The logging operation was carried out using one tool string (MSS/HRLA/HLDS/EDTC-B/HNGS) only.The HLDS tool was included in the tool string with the sole purpose of acquiring hole size data with the caliper. For safety reasons, noradioactive source was mounted, therefore the density data are invalid. The HLDS Caliper was opened only during the main and repeat run. The tool string encountered a soft obstruction at a depth of 3522 m DRF and thus did not reach the total depth of 3556 m DRF. As a result, all three passes were recorded from this depth up.
.
The sea state was high with a peak-to-peak heave of ~ 2.5 m. The 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 (-3297.5 m). The sea floor depth was determined by the step observed at the mudline in the gamma ray value (Main Run). This differs for 1.5 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 run.
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 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 and HRLA data were corrected for hole size during the recording.
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 features similar to the sonic velocity log).
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The hole condition was generally good, with the lower section (225-145 m WMSF) relatively narrow (11-13") and smooth but the upper section (145-51 m WMSF) larger (14-17") and rugose.
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 366.
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