< Standard Processing - ODP Leg 131, Hole 808E

Wireline Standard Data Processing

 

ODP logging contractor: LDEO-BRG

Hole: 808E

Leg: 131

Location: Nankai Trough (NW Pacific Ocean)

Latitude: 32° 21.11' N

Longitude: 134° 56.61' E

Logging date: May, 1990

Bottom felt: 4684.5 mbrf (used for depth shift to sea floor)

Total penetration: 1200 mbsf

Total core recovered: none.

 

Logging Runs

 

Logging string 1: DIT/BHC/NGT (main and downhole)

         No wireline heave compensator was used to counter ship heave

 

Casing

 

         The following casing depth is as it appears on the logs after differential depth shift 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, lack of wireline heave compensator, and drill string and/or wireline stretch.

         DIT/BHC/NGT: Bottom-hole assembly at ~524 mbsf

         NGT: Recorded through casing.

 

Processing

 

         Depth shift: Original logs have been interactively depth shifted with reference to NGT from the main DIT/BHC/NGT run and to the sea floor (- 4684.5 m). The program used is an interactive, graphical depth-match program which allows to visually correlate logs and to define appropriate shifts. The reference and match channels are displayed on the screen, with vectors connecting old (reference curve) and new (match curve) shift depths. The total gamma ray curve (SGR) from the NGT tool run on each logging string is used to correlate the logging runs most often. In general, the reference curve is chosen on the basis of constant, low cable tension and high cable speed (tools run at faster speeds are less likely to stick and are less susceptible to data degradation caused by ship heave). Other factors, however, such as the length of the logged interval, the presence of drill pipe, and the statistical quality of the collected data (better statistics is obtained at lower logging speeds) are also considered in the selection. A list of the amount of differential depth shifts applied at this hole is  available upon request.

 

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

 

         Acoustic data processing: The borehole-compensated (BHC) sonic logs are of good quality and did not need any processing.

 

Quality Control

 

         null value=-999.25. This value generally appears in discrete core measurement files and also it may replace recorded log values or results which are considered invalid.

         During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. The quality of the data recorded at hole 808B is generally good.

         Data recorded through casing should be used qualitatively only because of the attenuation on the incoming signal.

         No hole diameter was measured at Hole 808B.

 

         Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 131. For further questions about the logs, please contact:

 

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia