Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 704B

Leg: 114

Location: Meteor Rise (central S Atlantic)

Latitude: 46° 52.785' S

Longitude: 7° 25.231' E

Logging date: May, 1987

Bottom felt: 2530.8 mbrf (used for depth shift to sea floor). Note that the "bottom felt" depth given in the IR volume is incorrect.

Total penetration: 671.7 mbsf

Total core recovered: 502.8 m (74 %)

Logging Runs

Logging string 1: DIT/BHC/GR

Logging string 2: LDT/CNTG/GPIT/NGT

Logging string 3: ACT/GST/NGT

Due to technical problems, the wireline heave compensator was not used to counter ship heave. Ship heave was about 3 m at the beginning of logging operations and diminished by the time the third logging run started.

Bottom-hole Assembly/Drill Pipe

The following bottom-hole assembly/drill pipe 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 ~124 mbsf

LDT/CNTG/NGT: Bottom-hole assembly at ~151 mbsf

ACT/GST/NGT: entirely logged through drill pipe and bottom hole assembly.

Processing

Depth shift: The overall quality of the gamma ray logs recorded on each logging run was so bad that no depth correlation was possible. The original logs have been depth shifted to the sea floor onboard (- 2530.8 m).

Gamma-ray processing: Only the NGT data from the LDT/CNTG/NGT run have been processed to correct for borehole size and type of drilling fluid. The ACT/GST/NGT run was completely recorded through drill pipe.

Acoustic data processing: The borehole compensated sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. 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 are more appropriate to determine changes in the macroscopic properties of the formation.

No geochemical processing could be performed at this hole because of the lack of proprietary tapes containing the geochemical waveforms necessary to the processing.

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. Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (CNTG, HLDT) and a good contact with the borehole wall.

Data recorded through bottom-hole assembly and pipe should be used qualitatively only because of the attenuation on the incoming signal.

Due to a computer crash during the LDT/CNTG/NGT run, data was lost in the 513-553 mbsf interval. Also, no valid data was recorded in the 261-268 mbsf interval.

Hole diameter was recorded by the 3-arm mechanical caliper device (MCD).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 114. For further questions about the logs, please contact:

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