Standard Wireline Data Processing
IODP-USIO logging contractor: LDEO-BRG
Hole: U1318B
Expedition: 307
Location: Porcupine Seabight (eastern N Atlantic)
Latitude: 51° 26.148' N
Longitude: 11° 33.019' W
Logging date: May 10, 2005
Sea floor depth (“drillers’): 419.8 mbrf
Sea floor depth (step in GR log): 421 mbrf
Total penetration: 244.6 mbsf
Total core recovered: 213 m (87.08 % of cored section)
Oldest sediment cored: Siltstone (Miocene)
Lithologies: Silty clay, sand, conglomerate, siltstone and sandstone
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 |
Uplog
|
0
|
241.2
|
69.5
|
|
| 2. FMS/DSI/GPIT/SGT |
Pass
1
|
53.3
|
238.8
|
65
|
Reference
|
|
Pass
2
|
0
|
238.3
|
55
|
|
Logging operations at Hole U1318B were carried on with only some minor difficulties, such as going through the bit and re-entering the drill pipe during the second pass of the FMS/DSI/GPIT/SGT tool string.
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 depth-matched to the GR log from the DIT/APS/HLDS/HNGS tool string, and were then shifted to the sea floor (- 421 m). The sea floor depth was determined by the step in gamma ray values at 421 mbrf on the DIT/APS/HLDS/HNGS tool string. This differs by only 1.2 m from the sea floor depth given by the drillers (see above).
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.
Sonic data: The DSI was operated in four modes: monopole P&S, upper and lower dipole, and Stoneley. Velocities have been calculated from the different delay times.
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). The data is generally good, with the exception of the acoustic data, which show good correlation with the resistivity and density data only in the lower half of the hole.
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 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 (LCALI) and by the caliper on the FMS tool string (C1 and C2). The hole constantly varies in diameter, with value ranging from 12 to 15 inches.
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 and Downhole Measurements section of the Site Chapter in IODP Expedition 307 Report. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia