Data

The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in August 2017.

Logging Runs

Tool string	Run	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe (m WMSF)	Notes
MSS/HRLA/DSI/HLDS/HNGS/EDTC-B	Downlog	0	816	70.5	Caliper closed. Invalid HLDS.
	Repeat	740	865
	Main	0	862	70.5	Reference run.

The tool string, consisting of MSS/HRLA/DSI/HLDS/HNGS/EDTC-B tools was lowered to total depth without incident. It acquired a downlog of very good quality, indicating good hole conditions. A repeat pass was recorded from TD up to 4320 m WRF (743.7 m WSF), and then the tools were returned to TD for the main pass.

The Active Heave Compensator (AHC) was switched on once the tools were a safe distance outside the pipe, although the heave at that time was only about 0.3 m peak-to-peak. Throughout the course of the run, the heave did go as high as 1.2 m peak-to-peak, so the AHC was a prudent measure.

Processing

Depth match and depth shift to sea floor. The logs were first depth-matched to the reference run (MSS/HRLA/DSI/HLDS/HNGS/EDTC-B main pass) and then depth-shifted to the sea floor (-3579.3 m). The sea floor was not clearly visible on the GR log due to a very low GR signature in the upper part of the hole, so the driller’s sea floor depth was used to depth shift the logging data.

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, HLDS, and HRLA data were corrected for hole size during the recording.

High-resolution data. Bulk density (HLDS) data were recorded at 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 are 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. The HRLA is also 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 and upper and lower dipole for all three passes. The velocities were computed from the DTCO (compressional), DT1 and DT2 (shear) delay times. They are generally of good quality. Post-cruise processing is required to obtain accurate shear velocities from the cross dipole data.

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 overall quality of the data from Hole U1507B is good.

Gamma ray logs recorded through the drill pipe should be used only qualitatively because of the attenuation of the incoming signal.

Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). 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 “hard rock” portion of the hole at the bottom, approximately the lower 300 m of the hole, was of excellent quality and in gauge. Accordingly, the log data over this interval were excellent, most notably the sonic data. The softer ooze formation in the upper part of the hole was still good, on average, but several spots in the area above 233 m WMSF were found to be significantly under gauge (>12-15"). As a result, the density log readings above 233 m WMSF should be used with caution.

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 371. 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