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.

Logging Runs

Tool string	Pass	Top depth (mbsf)	Bottom depth (mbsf)	Bit depth (mbsf)	Notes
1. DIT/HLDS/APS/HNGS	Upper	0	233	119
	Downlog	265	659
	Lower	233	716	261	Reference
2. FMS/DSI/GPIT/SGT	Pass 1	280	718
	Pass 2	265	718
3. VSI		330	630		28 good stations

Hole 17B was a logging-dedicated hole, drilled after an attempted logging operation in Hole 17A only reached 144 mbsf. Prior to logging, Hole 17B was conditioned with a wiper trip and a 50 bbl sepiolite mud sweep, and then displaced with 260 bbl of 10.5 ppg barite mud. The first (upper) pass with the DIT/HLDS/APS/HNGS tool string reached only 233 mbsf, and so the pipe was lowered to 270 mbsf for the subsequent downlog and lower pass, which reached the bottom of the hole. The FMS/DSI/GPIT/SGT passes reached the bottom of the hole and went smoothly. The VSI tool reached 630 mbsf and collected data at stations at 5-m-intervals around the BSR, and 10-20-m-intervals shallower in the hole; 28 out of 32 stations recorded good data. The LDEO Wireline Heave Compensator compensated ship heave throughout the operation.

The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 'bottom felt' depth in soft sediment.

Processing

Depth match and depth shift to sea floor: The DIT/HLDS/APS/HNGS Lower Pass was used as the depth reference, and the other passes were matched to it using the gamma ray, SFLU, and caliper logs (the Upper Pass was not matched because it does not have an overlap with the other passes). All passes were then shifted to the sea floor (-1356 m), based on the step in gamma radiation at the sea floor in the DIT/HLDS/APS/HNGS Upper Pass. The DIT/HLDS/APS/HNGS Lower Pass was chosen as the reference run because it covered the majority of the open hole interval.

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 sea floor depth was determined by the step in gamma ray values in the DIT/HLDS/APS/HNGS Upper Pass at 1356 mbrf (after depth matching). This is the same as the sea floor depth given by the drillers (see above).

Environmental corrections: The HNGS and SGT data were corrected for hole size during recording. The APS and HLDS have been corrected for standoff and hole diameter respectively during the recording.

High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. 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. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

Acoustic data: The dipole shear sonic imager (DSI) was run in the following modes:

Pass 1: Low frequency monopole, low frequency upper dipole, standard (high) frequency lower dipole, and Stoneley modes.

Pass 2: Low frequency monopole, and low frequency crossed dipole modes.

Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide reliable results. Reprocessing of the original waveforms was required to extract meaningful compressional and shear velocities. The most reliable shear velocity value is the one derived from the upper dipole (VS2) during the first pass, where the lower source frequency used generated more coherent 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 acoustic log). The log data of Hole 17B is generally of good quality. In the lower section (319-717 mbsf) the hole is typically around 11-12 inches in diameter. There are several bridges: at 408-410 mbsf (DIT/HLDS/APS/HNGS only), 456-458 mbsf (FMS/DSI/GPIT/SGT passes only), 629-633 mbsf, 641-643 mbsf, and 674-675 mbsf. Some of these bridges caused increased cable tension, and consequently some small depth offsets may remain in the vicinity of the bridges (even logs from the same pass may have slight depth offsets). Small-scale washouts occur from 320-363 mbsf, and below 448 mbsf. The upper part of the hole is highly variable and in poor condition, varying from 4 to over 18 inches in diameter.

The APS data was unreliable in the DIT/HLDS/APS/HNGS Upper Pass.

Gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe should be used only qualitatively, because of the attenuation on the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.

A null value of -999.25 may replace invalid log values.

For further questions about the processing, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia