Wireline Standard Data Processing
IODP-USIO logging contractor: LDEO-BRG
Hole: U1324A
Expedition: 308
Location: Ursa Basin (Gulf of Mexico)
Latitude: 28° 4.786'N
Longitude: 89° 8.357'W
Logging date: June 19-20, 2005
Sea floor depth (driller's): 1065.5 mbrf
Sea floor depth (logger's): 1066.5 mbrf
Total penetration: 612.5 mbsf
Total core recovered: 0 m (LWD only)
Oldest sediment cored: LWD performed first, no coring. In U1324B: Quaternary
Lithologies: LWD performed first, no coring. In U1324B: clay, mud, silt, and sand
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. DSI/GPIT/HNGS |
Downlog
|
0
|
482
|
49
|
|
|
Pass 1
|
86
|
500
|
|
|
|
|
Pass 2
|
0
|
502
|
47
|
|
|
| 2. WST |
|
283.5
|
498.5
|
16 Stations
|
|
Hole U1324A was drilled with LWD, and then logged with wireline tool strings in order to get sonic velocity and travel-time information from the hole. The wireline heave compensator was used to counter minor ship heave.
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 DTCO logs were depth matched to the RHOB density log from the LWD of the same hole. This was done so that the LWD images would not have to be differentially depth matched, and so that the acoustic and density logs were well matched for potential use in synthetic seismogram generation. Gamma ray logs were used to check the depth matching, but they were generally lacking in correlatable features.
The sea floor depth was determined by the step in gamma ray values at 1066.5 mbrf in the LWD logs. This differs by 1 m from the sea floor depth given by the drillers (see above).
Acoustic data: The dipole shear sonic imager (DSI) gave good compressional wave logs for all three passes, in addition to shear and Stonely wave velocities for pass 2 (P&S monopole, lower-dipole, and Stonely modes).
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).
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 contac with the DSI/GPIT/HNGS tool string.
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 308. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia