Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 795B

Leg: 127

Location: Japan Basin (Japan Sea)

Latitude: 43° 59.23' N

Longitude: 138° 57.89' E

Logging date: July, 1989

Bottom felt: 3310 mbrf (used for depth shift to sea floor)

Total penetration: 762.2 mbsf

Total core recovered: 188.9 m (47 %)

Logging Runs

Logging string 1: DIT/SDT/HLDT/CNTG/NGT

        

No information available from the ODP Initial Reports about use of wireline heave compensator.

Bottom-hole Assembly

The following bottom-hole assembly depth is as it appears 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 heave and drill string and/or wireline stretch.

DIT/SDT/HLDT/CNTG/NGT: bottom hole assembly at 120 mbsf.

Processing

Depth shift: No depth shift necessary as only one tool string was run.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid (sea water with 2% KCl by weight).

Acoustic data processing: The SDT sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. 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, HLDT) and a good contact with the borehole wall.

        

Data recorded through bottom hole assembly, such as the NGT and CNTG above 120 mbsf should be used qualitatively only because of the attenuation on the incoming signal.

       

Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).

        

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 127.

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