Data

The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of Lamont-Doherty Earth Observatory in March, 2022.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. MSS/HRLA/HLDS/APS/HNGS/EDTC	Downlog	0	485	79	Caliper closed. Invalid HLDS and APS.
	Repeat	354	524	Recorded open hole	Neutrons not enabled. Invalid APS.
	Main	0	522	79	Depth reference.
2. FMS/DSI/HNGS/EDTC	Downlog	0	487	80	Caliper closed.
	Pass 1	126	523	Recorded open hole
	Pass 2	0	521	80
3. UBI/GPIT/HNGS/EDTC	Uplog	386	504	Recorded open hole

After the completion of coring operations, the MSS/HRLA/HLDS/APS/HNGS/EDTC tool string was first deployed for logging, followed then by the FMS/DSI/HNGS/EDTC and UBI/GPIT/HNGS/EDTC toolstrings.

Sea condition was intermediate with ship's heave in the range of 1 to 1.5 m. The wireline heave compensator (WHC) was used in the open hole intervals to counter the ship heave while logging.

The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 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.

Processing

Depth match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the main pass of the MSS/HRLA/HLDS/APS/HNGS/EDTC tool string (reference 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 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.

The depth-matched logs were then shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values at 2571.0 m WRF observed on the MSS/HRLA/HLDS/APS/HNGS/EDTC main pass. This value differs for 0.5 m from the sea floor depth given by the drillers (see above).

Environmental corrections. The HRLA and HLDS data were corrected for hole size during the recording. The APS data were corrected for standoff during the recording.

High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded at sampling rates of 2.54 and 5.08 cm, respectively, 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 were recorded at sampling rates of 5.08 and 15.24 cm. The HRLA is also acquired every 5.08 cm; in the database it is re-sampled at 15.24 cm, for ease of comparison with the other logs.

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipole, and cross dipole. The sonic velocities were computed from the slownesses 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). Repeatability between logging runs is generally good for Hole U1580A.

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.

The logged interval was a series of slow and fast formations which made the real-time labeling difficult to be correct for all the depths. The labeling corrections were made by the Schlumberger engineer in playback. The upper dipole shear data had the best coherency between the lower and the upper dipoles. The monopole compressional and shear (P&S) data were of excellent quality as well. The calculated sonic velocities correlate closely with the resistivity logs of the borehole formations.

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. For hole U1580A, the caliper was near 10" for most of the logged hole interval with variations reaching up to 12"; it did extend to 14-15" at 150 m WMSF and above. As a result, log data above this depth level 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 report, Proceedings of the International Ocean Discovery Program, Expedition 392. 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:

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu

Gilles Guerin

Phone: 845-365-8671

Fax: 845-365-3182

E-mail: Gilles Guerin