Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG
Hole: 1170D
Leg: 189
Location: South Tasman Rise (Tasman Sea)
Latitude: 47° 9.04'S
Longitude: 146° 2.991'E
Logging date: April, 2000
Bottom felt: 2715.8 mbrf
Total penetration: 779.8 mbsf
Total core recovered: 287.69 m (81.1 %)

Logging Runs

Logging string 1: DIT/APS/HLDS/HNGS (2 passes)

Logging string 2: GHMT/DSI/NGT (2 passes)

Logging string 3: FMS/DSI/NGT (4 passes)

The plan at this hole was to log in two stages: first the lower part, with the pipe set at about 533 mbsf (below anticipated bridges), and then the upper part after raising the pipe. Good logging data was obtained for the lower 250 m of the hole; the anticipated logging of the upper part of the hole, however, was not possible, because after logging the lower part, the pipe was found to be stuck and had to be exploded off just above the BHA. The DSI did not record logs during passes 2, 3 and 4 of the FMS/DSI/NGT tool string.

Bottom-hole Assembly

The following bottom-hole assembly depths are as they appear on the logs after depth matching (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 533 mbsf (pass 1)

GHMT/DSI/NGT: Bottom-hole assembly at 533 mbsf (passes 1 and 2)

FMS/DSI/NGT: Bottom-hole assembly at 533.5 (pass 4)

Processing

Depth shift: Since the depth match between the total gamma of the DIT/APS/HLDS/HNGS and GHMT/DSI/NGT logging runs is somewhat ambiguous, the conductivity from the GHMT (MAGC) was matched to the DIT from the DIT/APS/HLDS/HNGS second pass. Then the SGR gamma ray logs from the FMS/DSI/NGT tool string were matched to the shifted SGR log from the GHMT/DSI/NGT tool string (pass 1) because the FMS/DSI/NGT lacked a resistivity or conductivity log. Finally, all the logs were shifted to the sea floor (-2711.8 m). The mudline was not logged; according to the logs, however, the end of the bottom hole assembly was 4 m shallower than according to the drillers. Therefore the logger's sea-floor is also taken to be 4 m shallower.

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 wireline heave compensator stopped at certain intervals during logging, because of excessive ship heave. Depth control is degraded in these intervals, and consequently the match between different runs, and even between different tools on the same tool string will be poor. These intervals are: 662-693 and 736-763 mbsf (DIT/APS/HLDS/HNGS pass 1), 631-672 mbsf (DIT/APS/HLDS/HNGS), 712-747 mbsf (GHMT/DSI/NGT pass 1), 584-610 mbsf (GHMT/DSI/NGT pass 2).

Gamma-ray processing: The gamma ray logs from the NGT have been re-processed to account for borehole size and drilling fluid. The HNGS data were corrected for hole size during logging.

Acoustic data processing: The DSI waveform data were processed during logging to give DTCO (compressional wave slowness) and DTSM (shear wave slowness). DTCO and DTSM from the main pass (pass 4) are good and match well to the repeat passes (GHMT/DSI/NGT pass 2 and FMS/DSI/NGT pass 1). The DTSM appears to have unreasonable values from 268-273 mbsf. From 300-538 mbsf there is high amplitude DTCO variability that has no corresponding variability in the DTCO, thus the shear velocity data in this interval should be regarded with caution. No editing was performed, and 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. The logged portion of Hole 1170D was smooth, with a hole diameter between 10-11 inches, with only one washout at 647-649 mbsf. Consequently, the log quality is generally excellent.

Data recorded through bottom-hole assembly, such as the gamma ray data, 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) and by the caliper on the FMS tool string.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 189. For further questions about the logs, please contact:

Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia