Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 896A

Leg: 148

Location: Costa Rica Rift (tropical NE Pacific Ocean)

Latitude: 1° 13.006' N

Longitude: 83° 49.392' E

Logging date: March, 1993

Bottom felt: 3459 mbrf (used for depth shift to sea floor)

Total penetration: 469 mbsf

Total core recovered: 73.7 m (26.9 %)

Logging Runs

Logging string 1: ACT/GST/NGT

Logging string 2: DLL/SDT/NGT (upper and lower section)

Logging string 3: FMS/GPIT/NGT (2 passes)

Wireline heave compensator was used to counter ship heave.

Casing

The casing shoe was set at 191 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from NGT from DLL/SDT/NGT run and to the sea floor (- 3459 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. The NGT used in the geochemical processing consists of SGR/CGR from FMS pass 1 and THOR, URAN, and POTA curves laterally averaged from FMS passes 1 and 2 and DLL/SDT/NGT lower and upper sections.

Acoustic data processing: Because of the extremely noisy character of the sonic logs, no processing has been performed at this stage.

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 (ex. processed sonic data).

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close.

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 (MCD) and by the caliper on the FMS string (C1 and C2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 148. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia