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 September 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	196	72	Caliper closed. Invalid HLDS.
	Repeat	109	196	recorded open hole
	Main	0	195	72
2. FMS/DSI/GPIT/HNGS	Downlog	0	196	72	Caliper closed. Invalid FMS.
	Repeat	114	195	recorded open hole
	Main	0	195	72	Depth reference.

In preparation for logging, a 50-barrel high viscosity mud sweep was conducted to clean the hole. The first tool string deployment consisted of the MSS/HRLA/HLDS/HNGS, which reached total depth without any incidents. After a short repeat uphole the main pass was carried out, which reached the sea floor. After the tool string was recovered, the FMS/DSI/GPIT/HNGS tool string was rigged up next. It also successfully reached the bottom of the hole and acquired a repeat and a main pass. The sea was calm, and the Wireline Heave Compensator (WHC) was used when the tool string was 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 main pass 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 observedat 2221 m WRF. This differs by 2 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 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 was acquired every 5.08 cm; in the database it is resampled at 15.24 cm, for ease of comparison with the other logs. The GPIT and FMS caliper data were also resampled at 15.24 cm.

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipole, and Stoneley (all passe)s. The velocities were computed from the delay times. They are generally of good 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). The repeatability of the gama ray readings is excellent between passes. The density, resistivity, and sonic logs also correlate well and in most of the logged interval they seem to respond well to the main physical property changes in the formation.

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). Describe briefly the hole conditions.

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 196. 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