Wireline Standard Data Processing
IODP-USIO logging contractor: LDEO-BRG
Hole: U1329D
Expedition: 311
Location: Cascadia Margin (NE Pacific)
Latitude: 48° 47.3617' N
Longitude: 126° 40.7159' W
Logging date: September 30, 2005
Sea floor depth (drillers’): 957.4 mbrf
Sea floor depth (loggers’): 956 mbrf
Total penetration: 211 mbsf
Total core recovered: 1.03 m (1.0.8 % of cored section. Note that this was a hole drilled for logging; only 9.5 m were cored at the bottom of the hole)
Oldest sediment cored: Late Miocene
Lithologies: 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 | Downlog |
18
|
183
|
62.5
|
|
| Main |
0
|
210
|
46
|
Reference
|
|
| 2. FMS/DSI/GPIT/SGT | Pass 1 |
80
|
195
|
85
|
|
| Pass 2 |
80
|
180
|
Open
hole
|
|
Hole U1329D was drilled without coring (except for a 9.5 interval at the bottom of the hole), with the sole purpose of reaching the target depth of 220 m (missed in Hole U1329C) and logging with a full suite of wireline tools. Drilling was carried out in very rough weather conditions; operations had to be stopped a couple of times, waiting for the weather to improve. In preparation for logging, the hole was displaced with barite. Logging with the DIT/APS/HLDS/HNGS/TAP tool string went smoothly on the way down, while two tight spots were encountered on the way up at 188 and 172 mbsf (caliper readings were less than 6 inches). Because of the degraded hole conditions below 128 mbsf, it was decided not to run any repeat pass. The FMS/DSI/GPIT/SGT tool string was lowered next and again it got temporarily stuck at 172 mbsf. For this reason, it was decided to run the second pass only from 169 mbsf upward.
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 original logs were initially depth-matched to the HSGR log from the main pass of the DIT/APS/HLDS/HNGS/TAP tool string, and were then shifted to the sea floor (- 956 m). The main pass was chosen as the reference run because it was the only run to cross the sea floor. After the initial depth shift, however, it was noticed that the APS/HLDS/DIT/HNGS logs from the downlog pass did not match the equivalent logs from the reference run. Therefore, additional shifts were applied to this subset of logs in order to correct the problem.
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 956 mbrf. This differs by 1.4 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.
Acoustic data: The dipole shear sonic imager (DSI) was run in P&S monopole, upper and lower dipole and Stoneley mode on both passes. 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 sonic velocity log). An acceptable repeatibility is observed on the gamma ray logs recorded with each pass. The presence of barite in the hole is clearly felt by the density curves; the photoelectric effect is unusually high from 125 mbsf downward (also corresponding to the top of the excavated section of the hole), while the bulk density shows an increasing trend in the bottom 40 m of the hole, a clear response to the sagging effect of barite. Caution is therefore suggested when using the density logs.
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 46 and 62.6 mbsf for the main and downhole pass of the DIT/APS/HLDS/HNGS/TAP tool string, and at 85 mbsf for the pass 2 of the FMS/DSI/GPIT/SGT tool string.
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). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by two orthogonal calipers on the FMS tool string (C1 and C2).
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