LWD Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1188F

Leg: 193

Location: Manus Basin

Latitude: 3°43.686'S

Longitude: 151°40.188'E

Logging date: 21 December 2000

Bottom felt: 1653 mbrf

Total penetration: 386.7 mbsf

Total core recovered: 30.9m (18.3%)

Logging Runs

Logging string 1: DIT/HTGC (main and repeat passes)

Logging string 2: HLDS/APS/HNGS/HTGC (main and repeat passes)

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

Hole 1188F was cased to 190.5 mbsf. All logging strings run stopped 31m short of TD, due to a blockage; the rest of the hole was very wide (>18"). The first run recorded a bottom hole temperature of 86°C; the temperature increased to 100°C during logging operations.

The wireline heave compensator was used to counter ship heave except for the first logging string, when the heave was only about 15 cm anyway.

Bottom-hole Assembly and Casing

The following bottom-hole assembly and casing 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.

All logging strings: Bottom-hole assembly at 183 mbsf; casing at 190.5 mbsf

Processing

Depth shift: The original logs were depth matched to the SGR log from pass 2 of the FMS/GPIT/NGT/DSI/HTGC tool string. The logs were then shifted to the sea floor (-1652 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. It differs by 1m 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. The GR log from the HTGC tool was not corrected for borehole diameter and consequently has about 30-40% lower values.

DIT data: The IMPH log contains spikes that do not track the IDPH or SFLU logs, but do repeat in the repeat run. The IDPH and SFLU logs should be used in preference to the IMPH log.

DSI data: The first pass of the DSI was run in crossed dipole, stonely, and P&S modes, the second pass run in lower dipole, stonely, and P&S modes. The velocity logs generally repeat very well between the 2 passes.

High-resolution data: Bulk density data were recorded at a sampling rate of 2.54 cm. 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 replace recorded log values or results which are considered invalid.

Large (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization (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 only qualitatively 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). Hole 1188F was greater than 18 inches wide for nearly all of the logged interval.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 193 IR volume. For further questions about the logs, please contact:

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