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 July 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	277	~ 85.5	Caliper closed. Invalid APS and HLDS.
	Repeat	170	314	Recorded open hole
	Main	0	316	~ 85.5	Depth reference run
2. VSIT/HNGS		69	122		4 stations acquired
3. FMS/DSI/GPIT/HNGS	Downlog	0	277	~ 85.5	Caliper closed. Invalid FMS.
	Repeat	140	309	Recorded open hole
	Main	0	311	~ 85.5

The hole conditions at U1563B quickly deteriorated after drilling was completed, therefore it was decided to log only the sedimentary interval of the hole. The MSS/HRLA/APS/HLDS//HNGS tool string was run first: a downlog, with the caliper closed and the APS tool source turned off acquired data from the mudline to 1705.4 m WRF. Some difficulty, however, was experienced while getting out of the drill pipe; several attempts were needed to remove the blockage at the bottom of the pipe before logging operations could proceed. A repeat pass was acquired next with the caliper open and the APS source on. This was followed by a main pass, which extended to the mudline. Due to a false start of this main pass, the bottom of the interval was radioactively activated, which resulted in a sharp spike at about 1704 mWRF. The second logging run consisted of the VSI/HNGS tool string; after a brief pass uplog to depth-tie any upcoming shots to the MSS/HRLA/APS/HLDS/HNGS main pass, four stations were acquired at 1712.87, 1713.91, 1723.77, and 1733.66 DRF (285.37, 286.41, 296.27 and 306.16 m WMSF) but only two acquired good shots (see VSP processing notes). The logging operations were completed by running the FMS/GPIT/HGNS tool string last, which acquired three passes.

The Wireline Heave Compensator (WHC) was used 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 at 1427.5 m WRF. This differs by 1.6 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. 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 P&S monopole and upper and lower dipole modes in all three passes. The velocities were computed from the slowness. Compressional velocities were of very poor quality in the larger section of the hole above 215 m WMSF, where the measured velocity was slower than that of the drilling mud. Shear wave velocities are of better quality but processing from the sonic waveforms is recommended to improve the results.

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). There is generally a good repeatability between passes of the gamma ray logs: despite the low signature, they could be used for depth matching, with the exception of the lower 40 meters of the hole, where it becomes increasingly difficult to find good tie points.

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 HLDS caliper had trouble opening during the main pass of the MSS/HRLA/APS/HLDS/HNGS tool string. As a result, it recorded a steady value of 17 in. throughout the entire ilogged interval. The FMS caliper from the FMS/DSI/GPIT/HNGS or the repeat pass of the MSS/HRLA/APS/HLDS/HNGS should be used instead.

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.