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, 2014.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. HRLA/MSS/HLDS/EDTC-B/HNGS	Down	0	384	95	Closed caliper. Invalid HLDS.
	Pass 1	140	370
	Pass 2	0	304	95	Malfunctioning caliper. Invalid HLDS.
2. FMS/DSI/GPIT/EDTC-B/HNGS	Down	0	286	95	Closed caliper. Invalid FMS.
	Pass 1	140	285
	Pass 2	0	285	77

The HRLA/MSS/HLDS/EDTC-B/HNGS tool string was run first; it was lowered to a depth of ~ 3560 m WRF (387 m WSF) where it got stuck. Three attempts to pass the obstruction failed. The second pass also tried to pass the blockage without success. The FMS/DSI/GPIT/EDTC-B/HNGS tool string was run next; it got stuck at an even shallower depth (3459 m WRF or 288 m WSF) and all attempts to pass the blockage failed.

Sea condition was ideal for logging, with a peak-to-peak heave of ~0.8 m. Because the heave was forecast to increase during the day, it was decided to use the Wireline Heave Compensator (WHC) during the entire logging operations.

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 reading from a 'bottom felt' depth in soft sediment.

Processing

Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (-3173 m). The sea floor depth was determined by the step in gamma ray values at 3173 m WRF on the HRLA/MSS/HLDS/EDTC-B/HNGS downlog. The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog of the HRLA/MSS/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, HLDS and HRLA 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 are smoothed to match the long-spacing ones, 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, upper and lower dipole, and Stoneley in all three passes, with the upper dipole in low frequency and all others in standard frequency. The soniic velocities were computed from the delay times. They are generally of good quality.

Quality Control

The quality of the data can be 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 acoustic data are generally of good quality and correlate well with the resistivity data. Usable density data were collected only during the first pass as the caliper was closed during the downlog and was malfunctioning during the second pass.

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 has most diamter values in the range of 11-15", thus resulting in overall good 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 reports, Proceedings of the Integrated Drilling Program, Expedition 352.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.