Wireline Standard Data Processing

Well name: 728A

Leg: 117

Location: Oman Margin (tropical NW Indian)

Latitude: 17° 40.790' N

Longitude: 57° 49.553' E

Logging date: September, 1987

Bottom felt: 1433.4 mbrf

Total penetration: 346.4 mbsf

Total core recovered: 343.7 m (99.2 %)

Logging Runs

Logging string 1: DIT/BHC/GR

Logging string 2: GST/CNTG/GPIT/NGT

Wireline heave compensator was used to counter ship heave during run 1 and part of run 2.

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 heave, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/BHC/GR: Bottom-hole assembly at ~52.5 mbsf

GST/CNTG/GPIT/NGT: Bottom-hole assembly at ~83.5 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/BHC/GR main run and to the sea floor (- 1437 m). In addition to the main run of the GST/CNTG/GPIT/NGT, the upper part of the downlog has been shifted to match the DIT/BHC/GR run, as it is the only log that shows the sea floor. The sea floor appears to be 2.6 meters deeper than indicated by the drillers. The program used for depth matching 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 (SGR) or natural (GR) gamma ray curve from the GR or 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 from the GST/CNTG/GPIT/NGT run have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: Because of uncompacted nature of the sediments drilled at this hole, the signal coming from the formation is generally poor (the delay times translate in velocity lower than 1.5 km/s over most of the hole), particularly for the short-spacing transmitter-receiver pair. Processing of the sonic waveforms is recommended in order to get reliable results.

Geochemical processing: The elemental yields recorded by the GST tool represent the relative contribution of only some of the rock-forming elements (iron, calcium, chlorine, silicon, sulfur, hydrogen, gadolinium, and titanium - the last two ones computed during geochemical processing) to the total spectrum. Because other rock-forming elements are present in the formation (such as aluminum, potassium, etc.), caution is recommended in using the yields to infer lithologic changes. Instead, ratios (see acronyms.doc) are more appropriate to determine changes in the macroscopic properties of the formation.

Processing of the geochemical data of Hole 728A was carried out in 1988; revision of the results and their inclusion in the database will be completed at a later date.

Quality Control

null value=-999.25. This may replace invalid log values or results.

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

No hole diameter was measured at hole 728A.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 117. For further questions about the logs, please contact:

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