Wireline Standard Data Processing
IODP-USIO logging contractor: LDEO-BRG
Hole: U1327E
Expedition: 311
Location: Cascadia Margin (NE Pacific)
Latitude: 48° 41.895' N
Longitude: 126° 51.906' W
Logging date: October 10-11, 2005
Sea floor depth (drillers'): 1314.6 mbrf
Sea floor depth (loggers'): 1313.4 mbrf
Total penetration: 300 mbsf
Total core recovered: 11.42 (91.4 % of cored section; only 12.5 m were cored)
Oldest sediment cored: Pleistocene
Lithologies: clay and silty clay
The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. DIT/DSI/SGT | Main |
0
|
289.4
|
71.5
|
Reference
|
| Repeat 1 |
147
|
287.4
|
|
LDEO WHC
|
|
| Repeat 2 |
|
|
|
Schlumberger WHC
|
The tool string reached a depth of 287.4 mbsf, only 12.6 m off the bottom. One main and two repeat passes were made; pass 1 with the LDEO-BRG Heave Compensator, pass 2 with the Schlumberger Heave compensator. The WHC appeared to work well on both passes, with heave slightly less than 3 m during the entire logging. The data from the second repeat pass overlaid with the main pass and therefore has not been processed.
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.
Depth match and depth shift to sea floor: The repeat pass was depth-matched to the IDPH log from the main pass of the DIT/DSI/SGT tool string; both passes were then shifted to the sea floor (- 1313.4 m). The main pass was chosen as the reference run because it was the longer one and the only run to cross the sea floor.
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 at 1313.4 mbrf. This differs by 1.2 m from the sea floor depth given by the drillers (see above).
High-resolution data: 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 P&S monopole, upper and lower dipole, and Stoneley modes on both main and repeat pass. 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 is the one derived from the upper dipole (VS2), where the lower source frequency used generated more coherent waveforms.
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 U1329E is of very good quality, the velocity log correlating well with the resistivity. It is assumed that the hole was in good condition, though no caliper log was acquired.
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. The base of the BHA is shown on the logs at 71 mbsf on the main pass.
A null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operation can be found in the Operations section of the Site Chapter in IODP Expedition Reports volume 311. For further questions about the logs, please contact:
Cristina Broglia
phone: 845-365-8343
fax: 845-365-3182
E-mail: Cristina Broglia
Gilles Guerin
Phone: 845-365-8671
Fax: 845-365-3182
E-mail: Gilles Guerin