Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 735B

Leg: 176

Location: SW Indian Ridge (SW Indian Ocean)

Latitude: 32° 43.395' S

Longitude: 57° 15.959' E

Logging date: October and December, 1997

Bottom felt: 731 mbrf (used for depth shift to sea floor)

Total penetration: 1508 mbsf

Total core recovered: 865.99 m (86.3 %)

Logging Runs (Phase 1)

Logging string 1: DLL/APS/HLDS/HNGS

Logging string 2: FMS/DSI/GPIT/NGT

Wireline heave compensator was used on all runs to counter ship heave.

Logging Runs (Phase 2)

Logging string 1: APS/HLDT/HNGS

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

Logging string 3: DLL/GPIT/NGT

Logging string 4: VSP (with BGKT three-component tool)

Wireline heave compensator was used on all runs to counter ship heave.

Casing

The logs show the casing shoe at ~ 52.5 mbsf.

Processing

NOTE: Because of the low quality of the data recorded during phase 1 and because phase two covered the newly drilled interval from 500 to 597 mbsf as well, only the data from the second phase of logging have been processed.

Depth shift: Original logs have been first depth shifted to the sea floor (- 731 m) and subsequently interactively depth shifted with reference to NGT and DLL logs recorded during Leg 118. The newly drilled interval from 500 to 597 mbsf was also logged during leg 176 and depth shifted as follows: the APS/HLDT/HNGS as well as the FMS runs have been depth tied to the DLL/GPIT/NGT depth shifted run. 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 or HSGR) from the NGT/HNGS 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: The HNGS data have been corrected in real time for borehole size and type of drilling fluid during the recording. The NGT data have been corrected for borehole size and type of drilling fluid during the processing.

Acoustic data processing: The acoustic data were recorded with the Dipole Sonic Imager (DSI). No Good DSI data were acquired from logging Phase 1. During Phase 2, the DSI recorded cross-dipole and P-and S-wave modes during the first pass and cross-dipole, upper dipole, and Stoneley modes during the second pass. Though the data is of good quality, processing from the waveforms may be necessary to get better results.

High-resolution data: No high resolution data recorded with the APS and HLDS tools.

Quality Control

null value=-999.25. This 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. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (APS, HLDT) and a good contact with the borehole wall. 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 hydraulic caliper on the HLDT tool (CALI) and by the caliper on the FMS string (C1 and C2). The former, however, displays a very blocky character, though its readings are usually within the range of values measured by the FMS caliper; for this reason use of the latter one is recommended.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 176. For further questions about the logs, please contact:

Cristina Broglia
phone: 845-365-8343
fax: 845-365-3182
email: Cristina Broglia