Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 722B

Leg: 117

Location: Owen Ridge (tropical NW Indian Ocean)

Latitude: 16° 37.213' N

Longitude: 59° 47.755' E

Logging date: September, 1987

Bottom felt: 2033.2 mbrf (used for depth shift to sea floor)

Total penetration: 565.6 mbsf

Total core recovered: 385.9 m (68.2 %)

Logging Runs

Logging string 1: DIT/BHC/GR

Logging string 2: LDT/CNTG/NGT

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: Bottom-hole assembly at ~91 mbsf

LDT/CNTG/NGT: Bottom-hole assembly at ~95 mbsf (downlog)

LDT/CNTG/NGT: Recorded open-hole.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from DIT/BHC/GR run and to the sea floor (-2033.2 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. The borehole compensated data (BHC) from the uplog run have been processed to correct for a baseline shift at 178 mbsf in one of the short-spacing pairs. 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.

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. The density log was adversely affected by voltage fluctuations in the neutron porosity tool; all density readings were overcorrected, resulting in negative values. The correction has therefore been removed, thus yielding density readings that match reasonably well in both upgoing and downgoing runs (with the exception of the lowermost 100 meters). Because the removed correction usually accounts for the effect of lack of contact of the density tool pad with the borehole wall, the "uncorrected" values are very sensitive to the presence of washouts. The density data included in the database are the result of merging the best data from the up and downlogs:

95-230 mbsf (downlog)

230-550 mbsf (uplog).

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 722B.

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