Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1239A

Leg: 202

Location: Carnegie Ridge (equatorial SE Pacific)

Latitude: 0°40.32'S

Longitude: 82°04.85'W

Logging date: May 12-13, 2002

Bottom felt: 1424.5 mbrf (used for depth shift to sea floor)

Total penetration: 517 mbsf

Total core recovered: 515.10m (99.9%)

Logging Runs

Logging string 1: DIT/HLDT/APS/HNGS/TAP/MGT. This tool string was run three times; on the first pass the MGT tool was switched off. On the second and third pass the Schlumberger and TAP tools were switched off and main and repeat passes were made with the MGT tool.

Logging string 2: FMS/GPIT/DSI/SGT (2 passes)

No problems were encountered while logging Hole 1239A; all logs are of good quality. All passes reached the base of the hole. The wireline heave compensator was used to counter ship heave resulting from the calm 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/HLDT/APS/HNGS/MHT/TAP: Bottom hole assembly at ~ 81 mbsf

FMS/GPIT/DSI/SGT: Bottom hole assembly at ~ 81 mbsf (both passes)

Processing

Depth shift: The original logs were depth matched to the HSGR log from the DIT/HLDT/APS/HNGS pass and were then shifted to the sea floor (-1424.5 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. For Hole 1239A, it is the same as the "bottom felt" depth given by the drillers (see above).

Depth matching is 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: The HNGS and SGT data were corrected for hole size during data recording.

Acoustic data: The DSI tool was operated in the following modes for both passes: P&S monopole (mid-frequency), lower dipole (low frequency), and FMD (first motion detection) modes.

Four compressional wave velocity logs are available: 2 passes from the P&S monopole mode and 2 passes from the FMD. Pass 1 of the FMD is good down to 470 mbsf and is the best of the 4 logs. Pass 2 of the FMD is noisy and contains unrealistically high values between 264 and 455 mbsf. The two P&S monopole mode compressional velocity logs are similar to each other, but contain stepped drops to lower velocities. Between 200-370 mbsf the P&S monopole compressional velocity is slower than the FMD compressional velocity; the latter is possibly better. The shear wave velocity logs are good and repeat quite well.

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. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.

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 inter-comparison of all logging data. 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 by the caliper on the FMS tool string. The borehole had only small variations in diameter, ranging from 11.5 to 15 in.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 202 IR volume. For further questions about the logs, please contact:

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