Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 723B

Leg: 117

Location: Oman Margin (tropical NW Indian Ocean)

Latitude: 18° 3.079' N

Longitude: 57° 36.561' E

Logging date: September, 1987

Bottom felt: 861.7 mbrf (used for depth shift to sea floor)

Total penetration: 429 mbsf

Total core recovered: 295.4 m (73.8 %)

Logging Runs

Logging string 1: DIT/BHC/GR

Logging string 2: LDT/CNTG/GPIT/NGT

Logging string 2: GST/CNTG/GPIT/NGT (upper and lower sections)

No wireline heave compensator was used to counter ship heave.

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 and drill string and/or wireline stretch.

DIT/BHC/GR: Recorded open-hole

LDT/CNTG/GPIT/NGT: Recorded open-hole

GST/CNTG/GPIT/NGT: Bottom hole assembly at ~ 70 mbsf (upper section).

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from LDT/CNTG/GPIT/NGT downlog run and to the sea floor (-816.7 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. After differential depth shift and shift to the sea floor all data has been depth shifted 2.2 m downward to match some lithologic markers observed on the cores (dolomite stringers at 227.5, 247.5, 260, 300, 317, 327 374, and 407 mbsf). This was consistent with correlation procedure followed by the logging scientists during the leg (see ODP Initial Reports Downhole Measurements section).

Gamma-ray processing: NGT data from the LDT/CNTG/GPIT/NGT run have been processed to correct for borehole size and type of drilling fluid. No spectral data were available for processing for the GST/CNTG/GPIT/NGT runs.

Acoustic data. The borehole compensated data (BHC) from the uplog run have been processed to eliminate some minor baseline shifts. 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.

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 723B was carried out in 1988; revision of the results and their inclusion in the database will be carried out at a later date.

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, LDT) and a good contact with the borehole wall.

No hole diameter was measured successfully at Hole 723B.

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