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 May 2017.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. DSI/HLDS/EDTC-B/HNGS	Downlog	0	840	745.3	Depth reference
	Repeat	786	875
	Main	0	875	745.3
2. VSI/EDTC-B	Uplog				six stations

In preparation for logging the pipe was positioned at a depth of 4522 m DRF (747.3 m DSF), about 23.6 m below the bottom of the casing, in order to avoid a ledge in the formation that had been encountered when lowering the RCB coring assebly for the first time. The plan was to run a modified tool string that included the DSI, HLDS and gamma ray tools (HNGS and EDTC-B). The tool string made it without incidents to 4650 m WRF, about 45.,5 m above the driller's total depth. A repeat pass was taken from that depth, then the string was lowered again to acquire a main pass.

While pulling up the pipe in preparation for the VSI experiment, the drill crew noticed that the hole was beginning to flow. They temporarily stopped pulling the pipe in order to pump down some seawater to kill the flow. The VSI experiment started immediately after, without completing the drill pipe pull-out.

Several attempts were made to get out of the casing and down to the bottom of the hole but the tool string appeared to be hanging on a ledge and was unable to pass into the open-hole section. Overall, eight stations were attempted through casing; six stations were successful, while the two deepest ones did not produce any usable signal. The tool string was then recovered without any incidents.

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.

The heave compensator was not required for any portion of the logging as the total heave was approximately 2 in throughout the entire operating time.

Processing

Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3774.7 m). The sea floor depth was determined by the step in gamma ray values at 3774.7 mWRF. This coincides with the sea floor depth given by the drillers (see above). The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog of the DSI/HLDS/EDTC-B/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.

Environmental corrections. The HNGS 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 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. 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: P&S monopole and upper and lower dipole on all passes. After acquisition, the SLB engineer adjusted the DSI labeling range so that it would pick up the correct peaks consistently. The velocities were computed from the delay times.

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 density log should show similar features to the sonic velocity log).

Gamma ray logs recorded through bottom hole assembly (BHA), casing and drill pipe should be used only qualitatively, because of the attenuation of the incoming signal. The casing joints are clearly visible as negative spikes occuring every 10 meters..

A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall ( HLDS). The hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The hole appears smooth and between 11-13 in in the bottom 45 meters; above that depth it is very irregular, with some readings of more than 16 in.

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 368. 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