Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 738-C

Leg: 119

Location: S Kerguelen Plateau (Antarctic Ocean)

Latitude: 62° 42.54' S

Longitude: 82° 47.25' E

Logging date: January, 1988

Bottom felt: 2263 mbrf (used for depth shift to sea floor)

Total penetration: 533.8 mbsf

Total core recovered: 146.3 m (27 %)

Logging Runs

Logging string 1: DIT/LSS/GR (upper, middle, and lower sections)

Logging string 2: LDT/CNTG/GPIT/AMS/NGT

         Wireline heave compensator was not used to counter ship heave.

Bottom-hole Assembly

         The following bottom-hole assembly depths are as they appear on the logs after differential depth shift (see "Depth shift" section) and depth shift to the sea floor. As such, there might be a discrepancy with the original depths given by the drillers onboard. Possible reasons for depth discrepancies are ship and drill string and/or wireline stretch.

         DIT/LSS/GR: Bottom-hole assembly at ~92.5 mbsf

         LDT/CNTG/GPIT/AMS/NGT: Bottom-hole assembly at ~93.5 mbsf.

Processing

         Depth shift: No differential depth shift required. The logs have been depth to the sea floor (- 2263 m).

         Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.

         Acoustic data processing: The long spacing sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. The data has been spliced at 190 and 330 mbsf. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.

 

Quality Control

         Null value=-999.25. This value may replace recorded log values or results which are considered invalid (ex. processed sonic data).

         During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (CNTG, LDT) and a good contact with the borehole wall.

         Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.

         Hole diameter was recorded by the 3-arm mechanical caliper device which did not work properly as it recorded a constant 12.5-in diameter through the entire hole.

         The data from the DIT/LSS/GR runs has been spliced as follows:

resistivity: at 190 and 340 mbsf

gamma ray: at 185 and 335 mbsf

sonic: at 190 and 330 mbsf.

         Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 119.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.