Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Well name: 700B
Location: NE Georgia Rise (central S Atlantic)
Latitude: 51° 31.977' S
Longitude: 30° 16.688' W'
Logging date: April, 1987
Bottom felt: 3611.5 mbrf (used for depth shift to sea floor)
Total penetration: 489 mbsf
Total core recovered: 50.2 m ( %)
Logging string 1: DIT/NGT
Logging string 2: ACT/GST/NGT
Wireline heave compensator was used to counter ship heave.
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/NGT: Bottom-hole assembly at ~138 mbsf
ACT/GST/NGT: Bottom-hole assembly at ~138 mbsf.
Depth shift: The data had been depth originally depth shifted to the sea floor onboard (-3611.5 m). On shore, the logs have been interactively depth shifted with reference to NGT from ACT/GST/NGT. 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.
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 elemental waveforms necessary to the processing.
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. The data is generally of good quality: invalid gamma ray data were recorded in the 297-308 mbsf interval during the DIT/NGT run.
Data recorded through bottom-hole assembly 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).
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:
E-mail: Cristina Broglia