Wireline Standard Data Processing
IODP-USIO logging contractor: LDEO-BRG
Hole: U1327D
Expedition: 311
Location: Cascadia Margin (NE Pacific)
Latitude: 48° 41.8954' N
Longitude: 126° 51.9059' W
Logging date: October 7-8, 2005
Sea floor depth (drillers'): 1314.6 mbrf
Sea floor depth (loggers'): 1314 mbrf
Total penetration: 217.7 mbsf
Total core recovered: 53.99(71.1 % of cored section; only 19.5 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/APS/HLDS/HNGS/TAP | Uplog |
0
|
295.3
|
61
|
|
| 2. WST |
|
|
|
16 stations
|
Both weather and hole conditions were not ideal during logging of Hole U1327D. Ship heave was around 3-3.5 m; the WHC stroke out a couple of times, was stopped (at 151 mbsf), and then restarted. In addition, the caliper showed a very enlarged and rough hole. While the caliper arm was closing before entering the BHA, a big swell caused the caliper arm to break off. After retrieval of the DIT/APS/HLDS/HNGS/TAP tool string, a downhole seismic experiment was run with the WST tool. 16 stations were succeesfully recorded between 276 and 181 mbsf until weather conditions further deteriorated (heave about 3.5 m) and it was assumed that the WST might have been damaged. This was confirmed upon retrieval of the tool string. Because Hole U1327D was in bad condition and deteriorating, it was decided to postpone the acquisition of acoustic logs to a new hole (see Hole U1327E).
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 Ôbottom feltÕ depth in soft sediment.
Depth shift to sea floor: The original logs were shifted to the sea floor (- 1314 m). The sea floor depth was determined by the step in gamma ray values at 1314 mbrf. This differs by 0.6 m from the sea floor depth given by the drillers (see above).
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.
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 density log). The quality of the data at Hole U1327D is impaired by the rough hole conditions and, for some logs, by the presence of barite in the drilling mud. Whereas the density log shows a good correlation with the resistivity logs, the PEF gets out of its normal range (0-10 barns/e-) at about 145 mbsf, possibly an effect of the segregation of barite in the lower part of the hole.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The caliper shows a very large and irregular hole, locally wider than 18 inches.
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 61 mbsf, the bottom of the drill pipe at 22 mbsf (with a collar joint at 11.5 mbsf).
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