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 March 2010.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. DIT/APS/HLDS/GPIT/HNGS	Downlog	0	378	103	Invalid APS/HLDS. Caliper closed.
	Uplog	0	391	101.5	Reference
2. FMS/DSI/GPIT/HNGS	Pass 1	143.5	390	Open hole
	Pass 2	0	389	101

The hole was drilled to a total depth of 3465.5 m DRF. After re-entering the hole a short wiper trip was made and the hole was displaced with 10.2 lb/gal sepiolite/barite mud in preparation for logging. The DIT/APS/HLDS/GPIT/HNGS tool string was run first, followed by the FMS/DSI/GPIT/HNGS. Some difficulties were encountered while re-entering the drill pipe on the last FMS pass. The sea state was high with a peak-to-peak heave of 1-3 m and the wireline heave compensator 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 (- 3469.5 m). The sea floor depth was determined by the step in gamma ray values at 3469.5 WRF. This differs by 4 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 uplog of the DIT/APS/HLDS/GPIT/HNGS tool string (reference run).

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 data were corrected for hole size during the recording. The APS and HLDS data were corrected for standoff and hole size respectively during the recording.

High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded 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 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.

Acoustic data. The dipole shear sonic imager (DSI) was operated in P&S monopole and upper dipole modes using standard frequencies. The compressional data (DTCO) were originally good only below 150-160 m WMSF; they were reprocessed onboard to obtain valid data through the entire interval. The dipole shear data (DT2) were good below 345 m WMSF, but poor above this depth as slowness decreased below the capability of the acquisition software (<775 us/ft). Reprocessing of the shear data is to be performed at a later date.

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).

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 (APS, HLDS). Porosity logs showed average values of 60-70% , with many excursions to 100% as a result of the increased hole size and larger standoff. Density values ranged mostly around 1.6 - 1.8 g/cc with PEFL 2.5-4.0. Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole quality appeared to be fairly good as the caliper read mostly from 12-14" near bottom to around 205 m WMSF. Above this depth level up to to the drill pipe at 101 m WMSF, the hole size increased to 14-17" with some excursions to 18".

The spherically focused resistivity (SFLU) displayed an offset of about - 0.2 ohm with respect to the IMPH and IDPH logs.

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 318. For further questions about the logs, please contact:

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia