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 July 2013.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. DIT/DSI/HLDS/EDTC-B	Downlog	0	288	89	Caliper closed. Reference.
	Pass 1	102	284	Open hole	Invalid HLDS (no radioactive source).
	Pass 2	44	283	89	Invalid HLDS (no radioactive source).

Hole U1420A was first flushed with 75 bbl of high viscosity mud and then displaced with heavy mud (10.5 ppg) for logging. Due to the poor and unstable hole conditions, a modified tool string consisting of the DIT/DSI/HLDS/EDTC-B tools was deployed to acquire high priority measurements with only one logging deployment (downlog and two passes). The tool string became stuck inside the drill pipe at the end of pass 2 but was eventually freed using the Kinley crimper/cutter system.

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 moderate, with a peak-to-peak heave in the range of 0.4-1.4 m. Wireline heave compensator was used during the logging operation.

Processing

Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (-259 m). The sea floor depth was determined by the step in gamma ray values at 259 m WRF. This differs by 0.4 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 downlog of the 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.

High-resolution data. Because the radioactive source was not used during the logging operation, no density logs from HLDS were obtained at this site. 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 velocity data from the monopole were excellent, but the shear velocity data from the dipoles were not as good due largely to the shallow depth of the hole. Waveform processing is recommended to improve the quality of velocity data.

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). 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. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.

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 data indicate a very large size (>18 inches) below 200 m WMSF) and above 140 m WMSF. Log data from these 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