Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Antarctic Peninsula (Antarctic Ocean)
Latitude: 63° 59.97002' S
Longitude: 65° 27.91901' W
Logging date: March, 1998
Bottom felt: 505 mbrf
Total penetration: 362.7 mbsf
Total core recovered: 44.5 m (12.3 %)
Logging string 1: DIT/HLDS/APS/HNGS
Logging string 2: GHMT/NGT (down and uplog)
Logging string 3: FMS/SDT/GPIT/NGT (2 passes)
Wireline heave compensator was used to counter ship heave resulting from the mild sea conditions. The WHC was turned off at the following depths:
logging string 1: 108 mbsf
logging string 2: 98 mbsf (during uplog)
logging string 3: 113 mbsf.
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.
DIT/APS/HLDS/HNGS: Bottom-hole assembly at ~86 mbsf
GHMT/NGT: Bottom-hole assembly at ~86 mbsf (uplog)
GHMT/NGT: recorded open-hole (downlog)
FMS/GPIT/NGT: Bottom-hole assembly at ~86 mbsf (pass 1)
FMS/GPIT/NGT: recorded open-hole (pass 2).
Depth shift: Original logs have been interactively depth shifted with reference to NGT from GHMT/NGT uplog and to the sea floor (- 502 m). This value corresponds to the water depth observed on the logs and differs 3 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.
Acoustic data processing: The array sonic tool was operated in linear array mode, with eight receivers recording full waveforms; however, because no valid travel times from the lower transmitters were collected and the upper transmitter travel times were of very poor quality, the standard sonic processing could not be performed. Processing of the raw sonic waveforms is recommended in order to get formation velocities.
null value=-999.25. This may replace invalid log 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 (APS, HLDS) and a good contact with the borehole wall. The APS bowstring, designed to ensure contact with the borehole wall, was lost during the trip to the bottom of the hole; as a results, the standoff is higher. Generally, however, the porosity data can be considered of good quality
Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. The very high gamma ray values observed on the GHMT/NGT and FMS/GPIT/SDT/NGT runs at about 83-92 mbsf are due to radioactive activation of the formation during the DIT/APS/HLDS/HNGS run, when the tool string got stuck.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) by the orthogonal calipers on the FMS string (C1 and C2).
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