FMS Image Data Processing

ODP logging contractor: LDEO-BRG

Hole: 900A

Leg: 149

Location: Iberian Abyssal Plain (NE Atlantic Ocean)

Latitude: 46° 40.994' N

Longitude: 11 ' 36.252' W

Logging date: May, 1993

Bottom felt: 5048.5 mbrf (used for depth shift to sea floor)

Total penetration: 805 mbsf

Total core recovered: 519.6 m (65 %)

Logging Runs

Logging string 1: DIT/DSI/NGT (upper and middle sections)

Logging string 2: FMS/GPIT/NGT (2 sections in the lower part of the hole)

Wireline heave compensator was used to counter ship heave resulting from the mild 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/DSI/NGT: Bottom-hole assembly at ~ 137.5 mbsf (upper section) and ~330 mbsf (middle section)

FMS/GPIT/NGT: Both sections recorded open-hole.

Processing

Depth shift: No differential depth shift necessary as the runs do not overlap. Original logs have been depth shifted to the sea floor (- 5048.5 m).

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

Acoustic data processing: Due to the characteristics of the formation logged (soft sediments with high porosity), the sonic data recorded with the DSI are of very poor quality. Extensive processing from the original waveforms is required to obtain meaningful results. No such processing has been performed at this stage.

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. Hole deviation can 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. The NGT data from the FMS/GPIT/NGT passes in the lower part of the hole have been spliced at ~ 716 mbsf.

Hole diameter was recorded by the caliper on the FMS string (C1 and C2).

Additional information about Hole 900A logs can be found in the Site Report, ODP IR Volume 149. For further information about the logs, please contact:

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