Wireline Standard Data Processsing

ODP logging contractor: LDEO-BRG

Hole: 1018A

Leg: 167

Location: Baja California Margin(tropical NE Pacific Ocean)

Latitude: 36° 59.300' N

Longitude: 123° 16.653' W

Logging date: May, 1996

Bottom felt: 2488.6 mbrf (used for depth shift to sea floor)

Total penetration: 426.9 mbsf

Total core recovered: 426.9 m (100 %0)

Logging Runs

Logging string 1: DIT/HLDT/APS/HNGS (upper and lower section)

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 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: Bottom-hole assembly at ~ 53 mbsf (upper section)

DIT/HLDT/APS/HNGS: Bottom-hole assembly at ~ 238 mbsf (lower section)

Processing

Depth shift: Due to lack of correlation in the limited overlapping section between the upper and lower section of the logged interval, no differential depth shift has been performed. Original logs have only been depth shifted to the sea floor (- 2488.6 m).

Gamma-ray and environmental corrections: HNGS data from the DIT/HLDT/APS/HNGS tool string were corrected in real-time during the recording.

High-resolution data: Bulk density and neutron porosity data were recorded with the HLDT and APS tools 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 have better vertical resolution.

Quality Control

null value=-999.25. This value generally appears in discrete core measurement files and also it may replace recorded log values or results which are considered invalid (ex. processed sonic data).

During the processing, quality control of the data is mainly performed by cross-correlation 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. Borehole conditions at Hole 1018A were extremely poor, the hole being affected by large washouts. In the lower section of the logged interval, the caliper closed at 270-286 mbsf, due to tool sticking problems; this resulted in suspiciously lower density readings.

Data recorded through bottom-hole assembly, such as the HNGS data above 53 mbsf (upper section) and 238 mbsf (upper section) 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).

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR volume 167. For further information about the logs, please contact:

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