Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1522A
Expedition: 374
Location: West Antarctic Ice Sheet (Ross Sea)
Latitude: 76° 33.2262' S
Longitude: 174° 45.4652' W
Logging date: January 27-28, 2018
Sea floor depth (driller's): 568.5 m DRF
Sea floor depth (logger's): 568.0 m WRF
Total penetration: 1270.3 m DRF (701.8 m DSF)
Total core recovered: 279.57 m (39.8 % of cored section)
Oldest sediment recovered:
Lithology: Massive clast-rich muddy to sandy diamict and clast-poor sandy diamictite
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 2018.
Tool string |
Run
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe (m WMSF) |
Notes |
1. MSS/HRLA/DSI/HLDS/EDTC-B/HNGS
|
Downlog
|
0 |
597 |
89.5 |
Caliper closed. No radioactive source. Invalid HLDS. |
Repeat |
514 |
650 |
Open hole |
No radioactive source. Invalid HLDS. |
|
Main |
0 |
650 |
74 |
Reference run. No radioactive source. Invalid HLDS. |
|
| 2. FMS/GPIT/EDTC-B/HNGS | Downlog |
0 |
196 |
90 |
Calipers closed. Imvalid FMS. |
Pass 1 |
103 |
195.5 |
Open hole |
||
Pass 2 |
0 |
193 |
75 |
||
| 3. VSIT/EDTC-B/HNGS | Uplog |
249.5 |
294 |
Open hole |
53 good shots from 8 stations |
During drilling at hole U1522A high torque was noted as well some local overpull while pulling the drill string to the logging depth. As a result, it was decided to run the density tool (HLDS) without radioactive source and to leave out the porosity tool (APS) tool, which was replaced by the sonic tool (DSI). A sepiolite-seawater-barite based mud with a weight of 10.5 lb/gal was added to the hole before logging.
A downlog of the MSS/HRLA/DSI/HLDS/EDTC-B/HNGS tool string was acquired from 521.1 to 1218.6 m DRF with the caliper closed. A repeat pass was acquired from 1218.4 to 1082.2 m WRF, followed by a main pass from 1218.4 to 560.2 m WRF, both with the caliper open. Caliper reading (LCAL) was used for hole size correction for both repeat and main passes. The tools were logged up through drill pipe after closing the caliper and raising the drill pipe about 15 m for additional logging.
A downlog of the FMS tool string (FMS/GPIT/EDTC-B/HNGS) was started at 544.1 m WRF and stopped at 764.6 m WRF due to a bridge. After all attempts to pass the bridge failed, FMS pass 1 log was acquired from 763.5 to 670.6 m WRF. The calipers were closed and the tool string was lowered back to the bridge depth, where all attempts to pass it failed again. FMS pass 2 log was acquired from 761.2 to 561.6 m WRF.
The average heave was estimated at 0.2-0.3 m while logging. The motion heave compensator was utilized whenever the tools were in open hole.
Depth match and depth shift to the sea floor. The original logs were depth-matched to the gamma ray log of the MSS/HRLA/DSI/HLDS/EDTC-B/HNGS main pass before they were depth-shifted to the seafloor. The sea floor depth was determined by the step in gamma ray value at 568 m WRF. This differs by 0.5 m from the sea floor depth given by the drillers (see above).
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.
Environmental
corrections. The HNGS and HRLA data were corrected for hole size during the recording using the caliper readings acquired in the main and repeat pass. The HNGS and HRLA recorded in the downlog were corrected using the bit size (9 7/8 in).
High-resolution
data.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole and upper and lower dipole for all three passes. The velocities were computed from the DTCO (compressional), DT1 and DT2 (shear) delay times. In general, the sonic data was of excellent quality. Reprocessing of the sonic data was done by Schlumberger engineer on board to improve the labeling.
Quality Control
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). All measurements showed good repeatability between passes.
Gamma ray logs recorded through the drill pipe should be used only qualitatively because of the attenuation of the incoming signal.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). The caliper indicates a hole generally smooth and in gauge (11-12 in.) from TD to near 382 m WMSF, with occasionally higher readings. Above this depth the caliper is mostly in the 14-16 in. range, with locally lower readings of 12 in. Notable washouts are at 194-167 m WMSF which incidentally was a problem area for the logging with the FMS tool string. At 511 m WMSF, the caliper was required to be closed momentarily to lower the tool string and correct the cable wraps on the winch drum. This resulted in a small 1 m interval where the caliper is shown to be about an unlikely 4 inches in diameter.
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 374. 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