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 October, 2021.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. MSS/HRLA/HLDS/HNGS	Downlog	0	212	105	Caliper closed. Invalid HLDS.
	Repeat	142	212	Recorded open hole
	Main	0	212	106
2. FMS/DSI/GPIT//HNGS	Downlog	0	256	105	Caliper closed. Invalid FMS. Depth reference.
	Repeat	147	255	Recorded open hole
	Main	0	252	105

After coring was completed, a mud sweep was conducted with high viscosity mud, followed by hole displacement with 110 barrels of 10.5 ppg mud. The MSS/HRLA/HLDS/HNGS was lowered first and recorded a downlog starting at about 10 m above the sea floor. The tool string hung up at about 3015 m WRF (81 m WSF) but was eventually freed and descended to 3046 m WRF (212 m WSF), where it hung up again. After a few unsuccessful attempts to free it, a repeat and a main pass were acquired from that depth, which was 50 m higher than the drilled total depth. A second run, with the FMS/DSI/GPIT//HNGS tool string, reached total depth at 3096 m WRF (262 m WSF) and acquired an uplog from that depth to 2980 m WRF (146 m WSF). During the descent for the second pass, however, the tool string got stuck at 3004, 3016, and 3024 m WRF (170, 182, and 190 m WSF, respectively). All three times, the tool string got free and eventually reached a depth of 3089.5 m WRF (255.5 m WSF). Upon retrieval of the tool string, the FMS was found to be missing one of its pads ; this does not seem to have affected the quality of the data, as images are available from all four pads. It is therefore inferred that the damage may have occurred during the attempt to get back into the pipe, when there was an apparent obstruction that prevented the tool string from a smooth reentry.

The Wireline Heave Compensator (WHC) was used whenever the tools were in open hole.

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 downlog of the FMS/DSI/GPIT//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 2834 m WRF. This differs by 2.4 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 HLDS data were corrected for hole size during the recording.

High-resolution data. Bulk density (HLDS) data were recorded at sampling rates of 2.54 cm, 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 acquired every 5.08 cm; in the database it is 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, upper and lower dipole, and Stoneley mode (all passes). The velocities were computed from the delay times. They are of acceptable quality but the results could be improved by processing the original waveforms.

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). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole size above 170 m WMSF is extremely large (>16-17"), which may have affected the quality of the logging data.

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 396. 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