Standard Wireline Data Processing

ODP logging contractor: LDEO-BRG

Hole: 1275D

Leg: 209

Location: Mid-Atlantic Ridge (tropical NW Atlantic)

Latitude: 15° 44.4396' N

Longitude: 46° 54.2173' W

Logging date: June 30 - July 1, 2003

Bottom felt: 1565 mbrf _used for depth shift to sea floor)

Total penetration: 209 mbsf

Total core recovered: 104.63 m (50.1 %)

Logging Runs

Logging string 1: DIT/HLDS/APS/HNGS/TAP

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

Logging string 3: DSI/GPIT/SGT (2 passes)

All passes reached 103 mbsf, where the hole was bridged. The HLDS caliper arm was difficult to open; it opened at 67 mbsf, but would not close again, so no repeat DIT/HLDS/APS/HNGS/TAP pass was made. The wireline heave compensator was used to counter ship heave only on the DIT/HLDS/APS/HNGS/TAP pass; it started malfunctioning for the other tool strings. Heave varied from 0.73 to 1.06 m.

Bottom Hole Assembly

The following bottom hole assembly (BHA) 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. Typical reasons for depth discrepancies are ship heave, use of wireline heave compensator, and drill string and/or wireline stretch.

DIT/HLDS/APS/HNGS/TAP: bottom hole assembly at 26 mbsf

FMS/GPIT/SGT: bottom hole assembly at 26 mbsf

DSI/GPIT/SGT: bottom hole assembly at 26 mbsf.

Processing

Depth shift: The original logs were depth matched to the DIT/HLDS/APS/HNGS/TAP tool string (the reference run) and were then shifted to the sea floor (-1565 m). A combination of gamma ray and caliper logs was used to depth match the other passes to the reference. The sea floor depth was not determined directly because there is no clear step in gamma radiation values, which are very low in this hole. The sea floor depth given by the drillers was used.

Depth matching is typically 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 manually. 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.

Environmental corrections: The HNGS and SGT data were corrected for hole size during the recording. The APS and HLDS have been corrected for standoff and hole diameter respectively 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 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.

Sonic data: On the first pass the DSI tool was run in P&S monopole, upper dipole and cross-dipole modes; in the second pass, P&S monopole, lower dipole, and cross-dipole modes were used. Low-voltage and DSST hardware fault messages were received from the DSI tool. The data quality is fair to poor.

Quality Control

null value=-999.25. This value may replace invalid log values or results.

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, 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 casing 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 on the FMS tool (C1 and C2). The borehole was in very good condition, typically 10 inches wide, apart from thin wider sections at 78 and 96-99 mbsf.

Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 209. For further questions about the logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia