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 November 2015.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1.HRLA/DSI/HLDS/EDTC-B/HNGS	Downlog	0	114	103.5	Caliper closed and no HLDS source. No density data.
	Uplog	0	156	103.5	Caliper closed and no HLDS source. No density data.

Logging at Hole U1470B was carried out on short notice; while hole conditions were known to be far from ideal, scientists were hoping to get some wireline data. Therefore, it was decided to run a modified tool string combination, which included resistivity, sonic, density and gamma ray tools (HRLA/DSI/HLDSEDTC-B/HNGS). The HLDS was included in order to get a caliper emasurement, but no nuclear source was mounted. The total drilling depth of 754.5 m DRF was never reached; there was a significant loss of tension at 520 m WRF, about 10 m outside the drill pipe. After several attempts to go deeper the string finally reached 463 m WRF but it would not go any further. Data were acquired uplog from that depth and logging operations were terminated.

The sea state was calm, therefore no Wireline Heave Compensator (WHC) was used.

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 shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 405.5 m). The sea floor depth was determined by the step in gamma ray values observed on the HRLA/DSI/HLDS/HNGS downlog at 405.5 m WRF. This differs by 5.3 m from 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 HRLA/DSI/HLDS/HNGS tool string. Though the downlog was shorter than the uplog, it was chosen as the reference run because the sea floor was more clearly identified than on the uplog.

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

High-resolution data. 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 dipole, and Stonely mode in standard frequency, and lower dipole mode in lower frequency. However, the open hole logged interval was too short to acquire any acoustic 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). In hole U1470B a very limited dataset was acquired, as only a 50 m interval was logged in open hole with a 45 m-long tool string. The only valid data are the gamma ray and the resistivity. There are no bulk density (HLDS) data as the tool was run without source.

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.

The caliper tool on the HLDS tool, which measures the hole diameter, was kept closed during the entire logging operations in order to minimize the risk of losing the tool string in the rapidly deteriorating hole.

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 359. 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