Wireline Satandard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1228A

Leg: 201

Location: Peru Margin (tropical SE Pacific)

Latitude: 11° 3.8724' S

Longitude: 78° 4.6700' W

Logging date: March 5, 2002

Bottom felt: 273 mbrf

Total penetration: 200.9 mbsf

Total core recovered: 126.3 m (64.2%)

Logging Runs

Logging string 1: DIT/HLDT/APS/SGT/HNGS (main and repeat passes)

No problems were encountered while logging Hole 1228A. Good quality logs were obtained. The wireline heave compensator was used to counter ship heave.

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/SGT/HNGS: Bottom Hole Assembly at 68 mbsf (main and repeat).

Processing

Depth shift: The original logs were depth matched to the HSGR from the main DIT/HLDT/APS/SGT/HNGS pass and were then shifted to the sea floor (-277 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. At Hole 1228A it differs by 4 m from 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 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 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, HLDT) and a good contact with the borehole wall. Hole deviation can also affect the data negatively.

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 HLDT tool (CALI). The borehole was smooth in character and ranged from 14" to 18" in diameter (the maximum extent of the caliper arm).

Repeatability was excellent except for a gamma ray spike at 163 mbsf in the main pass of the HNGS and SGT logs. Possibly this peak was not repeated in the repeat pass due to the orientation of the tool string in the hole.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 201 IR volume. For further questions about the logs, please contact:

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