Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: West Antarctic Peninsula Rise (Antarctic Ocean)
Latitude: 66° 59.12659' S
Longitude: 78° 29.26987' W
Logging date: February, 1998
Bottom felt: 3852.6 mbrf
Total penetration: 570.2 mbsf
Total core recovered: 385.8 m (67.7 %)
Logging string 1: DIT/APS/HLDS/HNGS
Logging string 2: GHMT/NGT (pass 2)
Logging string 3: WST
Due to the very rough sea conditions during the initial phase of logging the ship heave exceeded the maximum stroke of the wireline heave compensator; for this reason, it was decided not to use it during the first logging run. With sea conditions improving, it was operational during the recording of the GHMT/NGT logs, with the exception of the 372-417 mbsf interval during pass 1, where it stopped working temporarily. The lack of WHC on the first logging run produced depth offsets ranging from 10 to 15 m.
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 and drill string and/or wireline stretch.
DIT/APS/HLDS/HNGS: Bottom-hole assembly at ~98 mbsf
GHMT/NGT: Recorded open-hole (pass 1).
GHMT/NGT: Bottom-hole assembly at ~99 mbsf (pass 2)
GHMT/NGT: Drill pipe at ~32 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 (- 3853 m). This value corresponds to the water depth observed on the GHMT/NGT pass 2 and differs 0.4 m from the drillers' "bottom felt" depth. The depth match of the DIT/APS/HLDS/HNGS logs to the reference run was very difficult because of the poor data repeatability. This was mostly due to the rough sea conditions during the recording and the lack of wireline heave compensator. 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 smapling 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 eccentralization (APS, HLDS) and a good contact with the borehole wall. The hole size ranged from 13 to 18 inches (maximum opening of the caliper arm), therefore contact of the APS/HLDS tools with the borehole wall was intermittent; this is indicated by the standoff curve as well, which shows very few point of contacts of the tool string with the borehole wall. The HLDS caliper broke at the beginning of the repeat run and therefore the data collected in the upper part of the hole (218 mbsf upward) should be used with caution as no correction could be applied.
No resistivity data could be collected during the repeat run due to tool malfunction.
Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal. HNGS gamma ray data collected during the repeat run through bottom-hole assembly and drill pipe have a very low signature and have not been processed.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) during the main run only.
Some spikes recorded on the HNGS and DIT logs have been edited during the processing.
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