Standard Processing - ODP Leg 190, Hole 1173A

Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG
Hole: 1173A
Leg: 190
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 32° 14.6634' N
Longitude: 135° 1.5085' E
Logging date: June 5-6, 2000
Bottom felt: 4801.9 mbrf
Total penetration: 734.34 mbsf
Total core recovered: 658.23 m (89.6 %)

Logging Runs

Logging string 1: DIT/HLDS/APS/HNGS (upper and lower passes)
Logging string 2: FMS/GPIT/DSI/NGT (2 passes)

The upper pass of the DIT/HLDS/APS/HNGS was blocked from further penetration by a bridge at 344 mbsf. The pipe was lowered beneath the bridge, but the lower pass logged only 85 m before being stopped by another bridge. The FMS/GPIT/DSI/NGT reached 376.5 mbsf.

The wireline heave compensator was used to counter ship heave resulting from the mild sea conditions.

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, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/HLDS/APS/HNGS (upper pass): Bottom-hole assembly at 78 mbsf
DIT/HLDS/APS/HNGS (lower pass): Bottom-hole assembly at ~350 mbsf
FMS/GPIT/DSI/NGT: Bottom-hole assembly at 64.5 mbsf.

Processing

Depth shift: The original logs were depth matched to the NGT from the first pass of the FMS/GPIT/DSI/NGT run and then shifted to the sea floor (-4801.5 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. It differs by 0.4 m from the "bottom felt" depth given by the drillers (see above).

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.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid. The HNGS data were corrected for hole size during the recording.

Acoustic data processing: The compressional and shear wave slownesses from the 2 passes of the DSI tool were converted to velocities. DTCO was used for the compressional wave slowness, DT2 (upper dipole) for the pass 1 shear slowness, and DT1 (low frequency lower dipole) for the pass 2 shear slowness. No editing was performed on the data, although the upper part of the compressional velocity logs seems to contain jumps to overestimated velocities. The two passes should be interpreted together. The shear velocity from pass 2 is of better quality than from pass 1 (invalid above 105 mbsf).

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 generally replaces invalid recorded 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. Hole deviation can also affect the data negatively; the FMS, for example, is not designed to be run in holes deviated more than 10 degrees, as the tool weight might cause the caliper to close.

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) and on the FMS string (C1 and C2).

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 190 IR volume. For further questions about the logs, please contact:

Wireline Standard Data Processing

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