Hole: 1272A
Leg: 209
Location: Mid-Atlantic Ridge (tropical NW Atlantic)
Latitude: 15° 5.666' N
Longitude: 44° 58.300' W
Logging date: June 11-12, 2003
Bottom felt: 2571 mbrf
Total penetration: 321 mbsf
Total core recovered: 37.5 m (28.6%)
Logging
Runs
Logging string 1: DIT/HLDS/HNGS (2 passes)
Logging string 2: FMS/DSI/GPIT/SGT (2 passes)
All passes reached the base of the hole. The APS was not run because of a malfunction identified prior to logging. The wireline heave compensator was used to counter ship heave (1.7 m heave at the start of logging, decreasing to 1.45m).
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/HNGS: bottom hole assembly at ~38 mbsf (main pass)
FMS/DSI/GPIT/SGT: bottom hole assembly at ~38 mbsf (main pass.
Processing
Depth shift: The original logs were depth matched to the first pass of the DIT/HLDS/HNGS tool string (the reference run) and were then shifted to the sea floor (-2571 m). DIT/HLDS/HNGS pass 2 was matched to the reference run using SFLU resistivity; FMS/DSI/GPIT/SGT pass 1 was matched to the reference run using caliper and gamma radiation logs; FMS/DSI/GPIT/SGT pass 2 was matched to the depth-shifted FMS/DSI/GPIT/SGT pass 1 using the caliper logs. 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 HLDS has been corrected for hole diameter during the recording.
High-resolution data: Bulk density data was 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 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: In the first pass the DSI tool was
run in P&S monopole, upper dipole, and cross-dipole modes; in the second
pass it was run in P&S monopole, lower dipole, and cross-dipole modes. The
compressional wave data are very good; the shear wave data from the second pass
are better than in the first pass.
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 (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 is in good condition, typically between 10-13 inches wide, apart from occasional thin washouts, the largest of which is at 95 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