Data

The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in August, 2021.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. MSS/HRLA/APS/HLDS/HNGS	Downlog	0	593	79	Caliper closed. Invalid APS and HLDS.
	Repeat	483	631	77.5	Recorded open hole
	Main	0	632	77.5	Depth reference run
2. FMS/DSI/GPIT/HNGS	Downlog	0	596	79	Caliper closed. Invalid FMS.
	Uplog	0	629	79

Hoe U1564C was the last hole to be logged during Expedition 395C, therefore due to time constarints only two logging strings were deployed. The MSS/HRLA/APS/HLDS/HNGS tool string was used first and collected a downlog and tow uplogs, followed by the FMS/DSI/GPIT/HNGS, which acquired a downlog and only one uplog. No problems were encountered during the recording. The Wireline Heave Compensator (WHC) was used to counter ship's heave whenever the tools were in open hole. The average ship's heave was 0.25-0.5 m.

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.

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/APS/HLDS/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 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.

The depth-matched logs have then been shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values observed on the FMS/DSI/GPIT/HNGS uplog at 2219 m WRF. This differs by 0.5 m from the sea floor depth given by the drillers (see above).

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

High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded 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 The HRLA is also acquired every 5.08 cm; in the database itis resampled 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 and upper and lower dipole modes in both passes. The velocities were computed from the slownessess. They compressional velocities are generally of good from about 320 m WMSF downward. Above this depth the velocity of the drilling mud was too close to the formation velocity. The shear velocities are of good quality up to about 131 m WMSF.

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 (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole is in gauge from 450 m WMSF downward. It is more irregular in the upper part with locally high readings around 16 inches.

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 395C.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.