Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG
Hole: 1165C
Leg: 188
Location: Prydz Bay (Antarctic Ocean)
Latitude: 64° 22.8' S
Longitude: 67° 13.1' E
Logging date: February 13-14, 2000
Bottom felt: 3548.7 mbrf
Total penetration: 999.1 mbsf
Total core recovered: 69.3%

Logging Runs

Logging string 1: DIT/APS/HLDS/HNGS + TAP tool

Logging string 2: FMS/GPIT/DSI/NGT (1 main and 2 repeat passes)

After several drilling interruptions due to the approach of icebergs, Hole 1165C was prepared for logging. On the first attempt, the DIT/APS/HLDS/HNGS tool string could not penetrate more than 50 m into the open hole; on a second attempt, after lowering the pipe to 175 mbsf, the DIT/APS/HLDS/HNGS reached total depth. The logs were of very good quality, except in the vicinity of a bridge at around 310 mbsf. The FMS/GPIT/NGT tool string reached about 590 mbsf, then the vertical axis accelerometer on the GPIT tool failed, followed by a complete communications loss to the FMS tool. FMS tool problems were also encountered during the recording of two repeat runs. Only DSI and NGT data are valid.

The Wireline Heave Compensator was used to counter ship heave.

Bottom-hole Assembly

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, drill string and/or wireline stretch, and tides.

DIT/APS/HLDS/HNGS: Bottom-hole assembly at 175 mbsf

FMS/GPIT/DSI/NGT: Bottom-hole assembly at 175 mbsf.

Processing

Depth shift: The original logs were depth matched to the HNGS from the DIT/APS/HLDS/HNGS run and were then shifted to the sea floor (-3546.5 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. This depth differs by 2.2 m from the driller’s sea-floor depth, which was determined by the mudline in the hole 1165A.

Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent), and then the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed automatically, and the result checked and adjusted as necessary. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.

The depth match between the different passes of the tool strings at 1165C is generally robust, except where the DIT/APS/HLDS/HNGS tool string became trapped for a short time under a bridge at about 310 mbsf.

Gamma-ray processing: NGT data from the FMS/GPIT/DSI/NGT run have been processed to correct for borehole size. The HNGS data from DIT/HLDS/APS/HNGS was corrected for hole size during the recording. The HNGS data are statistically better than the NGT data. While total gamma ray counts (HSGR and SGR) are reproducible and show very similar features, the potassium, thorium, and uranium logs are less robust, due to the statistical nature of the gamma ray measurement.

Acoustic data processing: The DSI tool was operated in P&S and lower dipole modes. The waveform data from were processed during logging to give DTCO (compressional wave slowness), and DTSM (shear wave slowness). While the DTSM appears to be good data (corresponds to features observed in the resistivity logs), much of the DTCO has values are too high (velocities are too low). Since trying to correct for this would involve making up data (subjectively), the original data are given in the data files. The compressional and shear slownesses were then converted to velocities.

High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDS pad and the borehole wall (low density correction) the results are improved, because the short-spacing has better vertical resolution.

Quality Control

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

Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (APS, HLDS) and a good contact with the borehole wall. In general, Hole 1165C was moderately smooth, varying between 13-15 inches in diameter below 550 mbsf, and between 14-18 inches above 550 mbsf. APS and HLDS data quality is reduced in the rough and/or wide intervals. Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and on the FMS string (C1 and C2) (repeat passes 1 and 2 only).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 188. For further questions about the logs, please contact:

Cristina Broglia
phone: 845-365-8343
fax: 845-365-3182
email: Cristina Broglia