Standard Wireline Data Processing
IODP operator and logging contractor: LDEO-BRG
Hole: 642E (ODP re-entry hole)
Expedition: 306
Location: Voring Plateau (Norwegian Sea)
Latitude: 67° 13.2' N
Longitude: 2° 55.8' E
Logging date: July 1985
Logging date: October 1983
Sea floor depth (driller's): 1289 mbrf
Total penetration: 1229.4 mbsf
Total core recovered: 372.6 m (41.1 % of cored section)
Oldest sediment cored: Fine-grained volcaniclastic sediment (Early Eocene)
Lithologies: Glacial muds, nannofossil and siliceous oozes, volcaniclastic muds, sandy muds, and sand (sediments); tholeitic basalt flows and basaltic-andesite flows (basement)
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/GPIT/HNGS/TAP | Uplog | 372.5 |
582.6 |
372.5 |
Temperature recorded downhole and uphole |
| 2. FMS/DSI/GPIT/SGT | Pass 1 |
355.5 |
591 |
372.5 |
|
| Pass 2 |
329.3 |
442.1 |
372.5 |
Hole 642E was drilled and logged during ODP Leg 104 and re-entered in IODP Expedition 306. Logging operations consisted of two logging strings. The DITAPS/HLDS/GPIT/HNGS/TAP was lowered to a depth of about 590 mbsf, where an unpassable obstruction prevented from reaching lower into the hole. Temperature was recorded logging down. A second attempt was made to pass the obstruction but it failed. The FMS/DSI/GPIT/SGT tool string was also lowered to about 580 mbsf and could not go any further. The second pass of the FMS/DSI/GPIT/SGT was logged from about 330 mbsf up.
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 NGT log from the main pass of the FDC/CNL/NGT from ODP Leg 104, and were then shifted to the sea floor (- 1289 m).
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 corresponds to the sea floor depth given by the drillers (see above), which was also used on ODP Leg 104.
Sonic data: The Dipole Sonic Imager was run in three modes on both passes: monopole P&S, cross dipole, and Stoneley mode. Velocity has been computed from the delay times acquired in each mode.
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). In the case of Hole 642E, the data was also compared to the excellent data acquired during ODP Leg 104; the data acquired during Expedition 306 is of very good quality. Good acoustic (compressional, shear and Stoneley) data allow for an accurate definition of the acoustic properties of the basalt flows and interbedded sediments (only compressional data had been acquired during ODP Leg 104).
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). The HLDS caliper did not work properly in Hole 642E; the caliper data acquired by the FMS tool indicate a generally smooth hole (about 10 inches) with large washouts opposite the sedimentary beds and two restrictions just below 450 and 520 mbsf.
A null value of -999.25 may replace invalid log values.
Additional information about the logging operation can be found in the Operations section of the Site Chapter in IODP Expedition Reports volume 306. Information about drilling and previous logging is included in the Site Chapter in ODP Preliminary Reports, volume 104. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia