Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: West Antarctic Peninsula Rise (Antarctic Ocean)
Latitude: 67° 34.009' S
Longitude: 76° 57.82608' W
Logging date: March, 1998
Bottom felt: 3163.7 mbrf
Total penetration: 3771.4 mbsf
Total core recovered: 409.9 m (84.2 %)
Logging string 1: APS/HLDS/HNGS (upper, middle, and lower section)
Logging string 2: GHMT/NGT (2 passes)
Wireline heave compensator was used to counter ship heave due to the mild sea conditions.
The following bottom-hole assembly/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, use of wireline heave compensator, and drill string and/or wireline stretch.
APS/HLDS/HNGS: Bottom-hole assembly at ~94 mbsf (upper section)
APS/HLDS/HNGS: Recorded open-hole (middle section)
APS/HLDS/HNGS: Bottom-hole assembly at ~355 mbsf (lower section)
APS/HLDS/HNGS: Drill pipe at ~295 mbsf (lower section)
GHMT/NGT: Recorded open-hole (pass 1)
GHMT/NGT: Bottom-hole assembly at ~359.5 mbsf (pass 2)
GHMT/NGT: Drill pipe at ~295 mbsf (pass 2).
Depth shift: Original logs have been interactively depth shifted with reference to NGT from GHMT/NGT pass 2 and to the sea floor (- 3164.5 m). This value corresponds to the water depth observed on the GHMT/NGT pass 2 and differs 0.8 m from the drillers' "bottom felt" depth. 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 or HSGR) from the NGT/HNGS 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: HNGS and NGT data have been processed to correct for borehole size and type of drilling fluid; the former were corrected in real-time during the recording while the latter were corrected on shore.
High-resolution data: Neutron porosity data were recorded at a sampling rate of 5.08 cm in addition to the standard sampling rate of 15.24 cm.
Geological Magnetic Tool: The Geological Magnetic Tool collected data at two different sampling rates, the standard 0.1524 m rate and 0.0508 m. Both data sets have been depth shifted to the reference run and to the sea floor.
null value=-999.25. This may replace recorded log values or results which are considered invalid.
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 (APS/HLDS) and a good contact with the borehole wall. In the upper and middle sections of the hole the density tool did not provide valid measurements, due to malfunction of the long spacing detector. Due to the poor pad contact (as indicated by the caliper measurement and by the standoff curve of the APS tool) it has not been possible to recover decent density data from the short-spaced detector. The density readings are acceptable in the lower section, though the caliper did not function properly.
Gamma ray 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 hydraulic caliper on the HLDS tool (LCAL). The caliper did not work properly in the lowermost section of the hole, therefore no data is provided. In the upper and middle sections of the hole the caliper readings resulted consistently too low; a gain offset was calculated once the tool returned to the surface and the original caliper measurements was corrected accordingly.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 178. For further questions about the logs, please contact:
E-mail: Cristina Broglia