Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1186A

Leg: 192

Location: Ontong-Java Plateau (tropical NW Pacific Ocean)

Latitude: 0° 40.7873' S

Longitude: 159° 50.6519' E

Logging date: October 27-28, 2000

Bottom felt: 2740 mbrf

Total penetration: 1034 mbsf

Total core recovered: 88.6 m (26.32 %)

Logging Runs

Logging string 1: DIT/HLDS/APS/HNGS (main pass and repeat pass in upper section)

Logging string 2: FMS/GPIT/NGT/DSI (3 passes)

The hole was logged from 678 to 1031 mbsf, in order to cover the cored interval (the top part of the hole was washed down without coring). The DIT/HLDS/APS/HNGS tool string was also run from 162.5 m to the seafloor to obtain depths for the seafloor and the base of the bottom hole assembly. Two passes of the FMS/GPIT/NGT/DSI tool string were recorded over the cored interval, and a third just in basement.

The wireline heave compensator was used to counter ship heave. Sea conditions were excellent.

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 123 mbsf.

Processing

Depth shift: The original logs were depth matched to the HSGR log from the main pass of the DIT/HLDS/APS/HNGS run and were then shifted to the sea floor (-2736 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. It differs by 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 3 passes of the DSI tool were converted to velocities. P&S DSI mode compressional slowness was used in all three passes. Lower dipole DSI mode shear wave slowness was used for passes 2 and 3, and P&S DSI mode shear wave slowness was used for pass 1. Note that the pass 1 shear wave values are reliable only for the basement section. No editing was performed on the data.

Resistivity data: The SFLU log has consistently low values, although the shape of the curve matches the IMPH and IDPH curves. This is likely due to a problem with the DIT tool.

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 recorded log values or results which are considered invalid.

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). The hole was mostly smooth in basement, between 12 and 15 inches in diameter, apart from two enlargements at 994 and 998 mbsf, which appear to have caused anomalous values in some of the other logs (e.g. IMPH, IDPH) at the same depths. From 680 to 810 m the hole was between 12 to 18 inches in diameter. From 810 to 930 mbsf the hole was beyond the maximum extent of the caliper arm, 19 inches. The HLDS caliper arm was not opened for the repeat DIT/HLDS/APS/HNGS run in the upper part of the hole, therefore both HLDS and APS data should be used with caution.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 192 IR volume. For further questions about the logs, please contact:

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