Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1536E
Expedition: 382
Location: Dove Basin (Scotia Sea)
Latitude: 59° 26.4496' S
Longitude: 41° 3.6392' E
Logging date: April 25, 2019
Sea floor depth (driller's): 3230 m DRF
Sea floor depth (logger's): 3227.5 m WRF (MSS/HRLA/HLDS/DSI/EDTC-B/HNGS downlog)
Total penetration: 3875.4 m DRF (645.4 m DSF)
Total core recovered:
Oldest sediment recovered:
Lithology: Silty-clay-bearing diatom ooze, diatom-bearing and diatom-rich silty clay, and mudstones with a few limestone interbeds
Data
The logging data was recorded by Schlumberger in DLIS format and processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in April 2019.
| Tool string | Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
1. MSS/HRLA/HLDS/DSI/EDTC-B/HNGS
|
Downlog
|
0
|
640 |
80.5 |
|
Uplog
|
0 |
640 |
80 |
Hole U1536E was prepared for logging by pumping seawater and 10.5 lb/gal heavy mud with barite. The hole conditions were sufficiently stable to run a density source even with the threat of icebergs. The sonic compressional data was a high priority, so the logging tool string was modified by adding the sonic tool (DSI) and removing the porosity tool (APS). The APS could not be added as it was not a priority and also would require more electrical power than available. Due to the threat of icebergs and the contingency necessary for stuck tools, it was decided to run only this tool string.
The active heave compensator was not used during the logging operation due to some technical problems. Average heave was estimated around ~2 m just prior to logging.
The depths in the above table are for the processed logs (after depth matching between passes and depth shift to the sea floor).
Processing
Depth match and depth shift to sea floor. The uplog arrays were first depth-matched to the downlog of the MSS/HRLA/DSI/HLDS/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 matched to it in turn. This matching is performed manually. The depth adjustments 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.
Both downlog and uplog data were then shifted to the sea floor by 3227.5 m. The sea floor depth was determined by the step in gamma ray at the sediment-water interface observed on the MSS/HRLA/DSI/HLDS/EDTC-B/HNGS downlog. The observed water depth differs 2.5 m from the driller's water depth (3230 m DRF). Generally, discrepancies may exist between the sea floor depths determined by the loggers from the gamma ray and those 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.
Environmental
corrections. The HNGS, HRLA, and HLDS data were corrected for hole size during the recording.
High-resolution
data. Bulk density
(HLDS) data was recorded with a sampling rates of 2.54 cm in addition to the 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 is 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 was recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic data. The dipole sonic imager (DSI) downlog data was recorded in P&S monopole (DTCO) and upper dipole (DT2) modes with standard frequency (15 and 2 kHz, respectively), and in lower dipole (DT1) mode with low frequency (0.2 kHz). The uplog data was recorded in the same modes but with lower frequency (5 kHz) in the monopole mode, in order to get better quality data. Post-cruise sonic data processing is recommended for better results.
Quality Control
The quality of
the log data can be 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.
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).
All readings appear normal with density close to 1.1 to 2 g/cc for much of the logged interval, with the very bottom interval (hardest material) being around 2 g/cc. The deep resistivity is mostly about 1-2 ohmm with the harder bottom interval reading 1-5 ohmm approximately. The caliper readings are around 10.5-11 inches from the bottom of the hole to about 420 m WMSF where they increase to a maximum of 17 inches depending on theformation. The caliper was closed at 485-483 m WMSF on the uplog as the tension became tight at 532-526 m WMSF. The gamma ray averages less than 50 GAPI in the lower, in-gauge part of the hole and progressively increases to 100 GAPI in the upper, larger section of the hole. The compressional velocities are around 2.2-2.7 km/s in the lower part of the hole and decrease upwards in the less dense material.
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 report, Proceedings of the International Ocean Discovery Program, Expedition 382. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
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