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/HLDS//HNGS	DOWNLOG	0	141	~ 46	Caliper closed. Invalid HLDS.
	REPEAT	88	141	Recorded openhole
	MAIN	0	140	~ 46	Depth reference.
2.VSI/HNGS	DOWNLOG	0	141	~ 46
	REPEAT	60	140	Recorded openhole
	MAIN	0	141	~ 46	11 stations acquired.
3. FMS/DSI/GPIT/HNGS	DOWNLOG	0	141	~ 46	Caliper closed. Invalid FMS.
	REPEAT	87	142	Recorded openhole
	MAIN	0	141	~ 46
4. UBI/GPIT/HNGS	DOWNLOG	0	136	~ 46	No image acquired.
	REPEAT	72	135	Recorded openhole
	MAIN	39	124	~ 46

After coring in Hole U1566A was completed, a viscosity mud sweep was conducted, followed by cleaning of the hole with sea water. The MSS/HRLA/HLDS//HNGS tool string (no porosity tool was requested by the shipboard party for this run) was lowered to 2255 m WRF (142 m WSF), where it encountered an obtsruction and could not go nay further. A repeat and a main pass were acquired from that depth. The VSI was run next and as requested by the shipboard party the stations were recorded at 10 m intervals starting at 2250 m WRF (137 m WSF). No stations were acquired at 2170 and 2160 m WRF 57 and (47 m WSF, respectively), as the tool string would be partially inside the drill pipe while anchored and that would result in caliper arm damage. Also, the uppermost two stations inside the pipe were skipped, as it was noticed that the lower stations inside the pipe showed no coupling between the pipe and the formation, which resulted in useless data. The FMS/DSI/GPIT/HNGS tool string was lowered next and like in the case of the first logging run encountered an obstruction at about 2255 m WRF (142 m WSF). A repeat and a main pass were recorded from that depth without any problems. The UBI/GPIT/HNGS tool string was deployed last and acquired one downlog and two uplog passes.

The sea state was excellent, nonetheless the Wireline Heave Compensator was used whenever 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 MSS/HRLA/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 2113 m WRF. This differs by 2.7 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 with a sampling rate 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 on all passes. The velocities were computed from the delay times. Compressional and upper dipole shear velocities are generally of good quality, while the lower dipole shear output 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). Very good correlation exist between the the density, resistivity and compressional velocities.

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). Hole conditions were excellent, with the hole diameter in gauge, generally not exceeding 10.5 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 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