Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1352C
Expedition: 317
Location: Canterbury Basin (SW Pacific Ocean)
Latitude: 44° 56.2662' S
Longitude: 172° 1.3630' E
Logging date: December 20, 2009
Sea floor depth (driller's): 354.6 m DRF
Sea floor depth (logger's): 355 m WRF (DIT/HLDS/GPIT/HNGS main)
Total penetration: 1928 m DSF
Total core recovered: 655.02 m (50.5 % of cored section)
Oldest sediment recovered: Eocene
Lithology: marlstone, limestone, mud, sandy mud, and muddy sand, 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 in December 2009.
| Tool string |
Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
|
DIT/HLDS/GPIT/HNGS
|
Downlog
|
0
|
205
|
102
|
Invalid HLDS |
|
Main
|
0
|
205
|
102
|
Reference. Invalid HLDS |
The hole was drilled to a total depth of 1928 m DSF and then conditioned for logging by sweeping with 50 bbl of high viscosity, sepiolite/attapulgite mud. Because of the hole conditions, a modified triple combo tool string was run, which did not include the APS tool and employed the HLDS tool without radioactive source for a caliper measurement. Due to a possible obstruction at ~562 m WRF, only the downlog and main pass of the DIT/HLDS/GPIT/HNGS tool string were completed above this depth level and no FMS/Sonic tool string was attempted for logging thereafter. Heave was ~1.2 m (peak-to-peak), so the wireline heave compensator was used during logging.
The depths in the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). 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 a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor based on the logger's sea floor depth of 355 m WRF. The sea floor depth was determined by the step in gamma ray values observed on the DIT/HLDS/GPIT/HNGS main pass. The depth-shifted logs were then depth-matched to those of DIT main pass (reference).
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.
Environmental corrections. The HNGS logs were corrected for hole size during the recording.
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).
Gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe should be used only qualitatively because of the attenuation of the incoming signal. The thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). A wide (>12") and/or irregular borehole affects most recordings.. The caliper log indicates that the logged section of the borehole was washed to more than 17" and this may have adversely affected the tool response. Hence, log data from this hole should be used with caution.
A Null value of -999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition reports, Proceedings of the Integrated Drilling Program, Expedition 317.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.