Standard Wireline Data Processing

Science operator: Texas A&M University

Hole: U1521A

Expedition: 374

Location: West Antarctic Ice Sheet (Ross Sea)

Latitude: 75° 41.0351' S

Longitude: 179° 40.3108' W

Logging date: January 20-21, 2018

Sea floor depth (driller's): 573.0 m DRF

Sea floor depth (logger's): 572.0 m WRF

Total penetration: 1223.1 m DRF (650.1 m DSF)

Total core recovered: 411.50 m (63.3 % of cored section)

Oldest sediment recovered: Early Miocene

Lithology: Diatom-rich mud to diatom-bearing sandy mud, diatom-bearing diamictite, siliceous mudstone, sandy mudstone.

Data

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.

Logging Runs

Tool string	Run	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe (m WMSF)	Notes
1. MSS/APS/HRLA/HLDS/EDTC-B/HNGS	Downlog	0	240	76	Caliper closed. Invalid HLDS and APS.
	Repeat	159	294	Open hole
	Main	0	289	66	Reference run.
2. FMS/DSI/EDTC-B/HNGS	Downlog	0	289	81	Caliper closed. Invalid FMS.
	Pass 1	93	287.5	Open hole
	Pass 2	0	287.5	65
3. VSIT/EDTC-B	Uplog	247	379	Open hole	96 shots acquired at 16 stations

No trouble was observed while drilling this hole and expectations were good for a stable hole. A sepiolite-seawater-barite based mud with a weight of 10.5 lb/gal was added to the hole before logging. The standard logging tool strings were utilized for this hole.

A downlog of the MSS/APS/HRLA/HLDS/HNGS/EDTC-B tool string with the caliper closed was acquired from 530.4 to 1222.7 m WRF. A repeat pass was acquired with the caliper open from 1223 to 1100.6 m WRF followed by a main pass from 1223 to 550.6 m WRF, both with the caliper open.

A downlog of the FMS tool string (FMS/DSI/HNGS/EDTC-B) was aquired from 528.1 to 1222.1 m WRF with calipers closed. Two uplog passes were acquired with the calipers opened: from 1220.7 to 674.4 m WRF and from 1220.7 to 561 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.

Processing

Depth match and depth shift to the sea floor. The original logs were depth-matched to the gamma ray log of the MSS/APS/HRLA/HLDS/HNGS/EDTC-B main pass before they were depth-shifted to the seafloor. The sea floor depth was determined by the step in gamma ray value at 572 m WRF. This differs by 1 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 APS, 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. Gamma ray data from the EDTC-B tool, neutron porosity data from the APS tool, and resistivity data from the HRLA tool were recorded at the sampling rate of 5.08 cm , in addition to the standard sampling rate of 15.24 cm.

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). In general the log data was very good, with good repeatbility 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 (APS and HLDS). The caliper readings showed a very smooth hole for the majority of the logged interval, with hole size often near bit size. The caliper readings were mostly in the 10-11 in. range from TD to 288 m WMSF and in the 11-14 in. range in the upper part of the hole.

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