Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1213B

Leg: 198

Location: Shatsky Rise North (NW Pacific Ocean)

Latitude: 31°34.658' N

Longitude: 157°17.862' E

Logging date: October 9, 2001

Bottom felt: 3894 mbrf

Total penetration: 494.4 mbsf

Total core recovered: 60.5 m (19.8 %)

Logging Runs

Logging string 1: DIT/HLDS/APS/HNGS

The DIT/HLDS/APS/HNGS tool string reached 430 mbsf, 64 m short of the total depth. The log was stopped at 188 mbsf because the tool string became stuck. Additionally, the HLDS caliper arm would not close, so the tool string could not be lowered back down the hole. The Lamont MGT tool was in the tool string but was not used. An approaching storm forced the ship to leave the site before a second tool string could be rigged up.

The wireline heave compensator was used during logging.

Bottom-hole Assembly/Pipe

The data was recorded open-hole.

Processing

Depth shift: Normally, the sea floor depth is determined from the step in gamma radiation at the sediment-water interface. However, the sea floor was not logged, so the "bottom-felt" depth of 3894 mbrf was used to shift the logs to the sea floor. Depth differences between logs and cores can occur because of wireline/drill pipe stretch, tides, heave, incomplete core recovery, etc.

Gamma-ray processing: The HNGS data were corrected for hole size during the recording.

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 HLDT/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 recorded log values or results.

During the processing, quality control of the data is mainly performed by cross-correlation of all logging data.

The principal control on log quality is the hole diameter. This was measured by the hydraulic caliper on the HLDS (LCAL) tool. Hole 1213B diameter varies between 11 inches at the base of the hole to 17 inches in some washed out sections. The caliper indicates a very narrow hole between 310 and 325 mbsf; in this interval logs should be used with caution. Softer lithologies are more easily washed out of the borehole wall; as a result of this, each chert layer forms a small ledge (1 or 2 inches), so the borehole wall can be quite rough - not ideal for the tools that require good contact with the borehole wall (density, porosity). The DRH and STOF logs provide measures of quality for the density and porosity logs, respectively.

On the other hand, resisitivity logs are relatively insensitive to hole diameter. The SFLU (shallow penetration resistivity) shows an offset from the IMPH and IDHP (medium and deep penetration resistivity) for much, but not all, of the hole. The offset is too large to be explained by high-salinity formation water. It could possibly be caused by the SFLU being preferentially affected by the cherts, because SFLU is a current-based measurement rather than an induction-based measurement like IDPH and IMPH.

Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 198. For further questions about the logs, please contact:

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