Wireline Standard Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1040C

Leg: 170

Location: Costa Rica Accretionary Wedge (tropical NE Pacific)

Latitude: 9° 39.697' N

Longitude: 86° 10.735' W

Logging date: November, 1996

Bottom felt: 4189 mbrf

Total penetration: 665 mbsf

Total core recovered: 377.3 m (74.6 %)

Logging Runs

Logging string 1: DITE/SDT/HLDT/GPIT/NGT

Wireline heave compensator was used to counter ship heave. The hole was deviated from the vertical; maximum deviation observed while logging was 11°.

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/SDT/HLDT/GPIT/NGT: Bottom-hole assembly at ~87 mbsf.

Processing

Depth shift: No differential depth shift was necessary as only one logging pass was recorded. The amount of depth shift to the sea floor (-4184m) differs 5m from the drillers' water depth; it corresponds to the depth of the sea floor as it is seen on the logs.

Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid.

Acoustic data processing: The array sonic tool was operated in standard depth-derived borehole compensated mode, including long-spacing (8-10-10-12') logs. The sonic logs have been processed to eliminate some of the noise and cycle skipping experienced during the recording. Using two sets of the four transit time measurements and proper depth justification, four independent measurements over a -2ft interval centered on the depth of interest are determined, each based on the difference between a pair of transmitters and receivers. The program discards any transit time that is negative or falls outside a range of meaningful values selected by the processor.

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 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 (HLDT) and a good contact with the borehole wall. Hole deviation can also affect the data negatively; density data at hole 1040C are of poor quality throughout the entire hole. Invalid spikes were frequently recorded (PEF curve) throughout the hole.

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).

Details of standard shore-based processing procedures are found in the "Explanatory Notes" chapter, ODP IR Volume 170. For further information about the logs, please contact:

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