Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Well name: 679E

Leg: 112

Location: Peru Margin (tropical SE Pacific)

Latitude: 11° 3.78' S

Longitude: 78° 16.34' W

Logging date: November, 1986

Bottom felt: 461.7 mbrf (used for depth shift to sea floor)

Total penetration: 359.3 mbsf

Total core recovered: 36.3 m (31.8 %)

Logging Runs

Logging string 1: DIT/LSS/GR (main and repeat)

Logging string 2: ACT/GST/NGT

Logging string 3: LDT/CNTG/NGT

No information available about use of wireline heave compensator to counter ship heave.

Bottom-hole Assembly/Drill Pipe

The following bottom-hole assembly and 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 and drill string and/or wireline stretch.

DIT/LSS/GR: Bottom-hole assembly at ~75 mbsf

ACT/GST/NGT: Bottom-hole assembly at ~74 mbsf

LDT/CNTG/NGT: Bottom-hole assembly at ~70 mbsf

LDT/CNTG/NGT: Drill pipe at ~48 mbsf.

Processing

Depth shift: Original logs have been interactively depth shifted with reference to NGT from LDT/CNTG/NGT run and to the sea floor (- 461.7 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.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid. Because no valid caliper measurement was available uplog and the caliper recorded downlog was not retrievable from the original tapes, a constant diameter of 14" has been used in the correction. This value correspond approximately to the average diameter measured downlog.

Acoustic data processing: The long-spacing (8-10-10-12') sonic logs have been processed to eliminate the few cycle skips 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 data: Due to technical problems, no processed geochemical data from this hole could be migrated into the online database. The results of the processing at Hole 679E, however, can be viewed in the paper by Anderson, R. N. and Greenberg, M. L. (1990), Composition of sediments and pore fluids in the Peruvian continental margin from geochemical and geophysical well logs, Site 679, Leg 112. In Suess, E., von Huene, R. et al., Proc. ODP, Sci. Results, 112: College Station, TX (Ocean Drilling Program): 481-489.

Quality Control

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

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.

Data recorded through bottom-hole assembly and pipe, such as the gamma ray data recorded during the LDT/CNTG/NGT run, should be used qualitatively only because of the attenuation on the incoming signal.

Hole diameter was recorded by the 3-arm mechanical caliper device (MCD) during the downlog run only, as the tool failed during the uplog; unfortunately, this data was not retrievable from the original tape at the time of processing. Because previous documentation indicates the hole to be around 14 inches in diameter, a constant value of 14 inches has been used for borehole correction of the NGT logs.

The resistivity, gamma ray, and acoustic data from the main and repeat DIT/LSS/GR runs have been merged at 100 mbsf.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 112. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia