Wireline Standard Data Processing


ODP logging contractor: LDEO-BRG

Hole: 1261B

Leg: 207

Location: Demerara Rise (equatorial NW Atlantic)

Latitude: 9° 2.918' N

Longitude: 54° 19.049' W

Logging date: February 21-22, 2003

Bottom felt: 1911 mbrf

Total penetration:  674.1 mbsf

Total core recovered:  92.49 m (62.16 %)


Logging Runs


Logging string 1: DIT/APS/HLDS/HNGS/TAP/MGT (two passes without MGT, followed by 2 passes with MGT only)

Logging string 2: FMS/SDT/SGT (two passes)

Logging string 3: WST


All of the passes except for the WST reached close to the hole total depth, despite the presence of some bridges in the upper section, particularly between 200-230 mbsf. The wireline heave compensator was used, but because of high ship heave (to > 3m), during the recording with the DIT/APS/HLDS/HNGS/TAP tool string it stroked out at 563-580 mbsf (pass 1) and at 410-434 and 470-488 mbsf (pass 2). DIT/APS/HLDS/HNGS/TAP pass 1 terminated at 310 mbsf because of loss of communication with the tools.



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/APS/HLDS/HNGS/TAP/MGT: bottom hole assembly at 111.5 mbsf (pass 2)

FMS/SDT/SGT: bottom hole assembly at 110 mbsf (pass 1)

FMS/SDT/SGT: bottom hole assembly at 109 mbsf (pass 2)





Depth shift: The original logs were depth matched to the ECGR log from the second pass of the FMS/SDT/SGT tool string, and were then shifted to the sea floor (-1899 m). FMS/SDT/SGT pass 2 was chosen as the reference run because it crossed the seafloor and the wireline heave compensator operated continuously through the run. FMS/SDT/SGT pass 1 and DIT/APS/HLDS/HNGS/TAP pass 1 and 2 and were matched to the reference run by total gamma ray, with cross checking using the caliper logs.


The sea floor depth was determined by the step in gamma ray values at 1899 mbrf. For Hole 1261B, this differs by 11m from the sea-floor depth given by the drillers (see above). The large depth discrepancy here is probably due to the difficulty in picking an accurate mudline or 'bottom felt' depth when using the RCB coring system. The logger's seafloor is well constrained in this case.


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.


Acoustic data: The four transit times from the SDT were processed using an in-house program that compares the slownesses derived from the 8 different transmitter-receiver pairs at each depth, and discards those times that are significantly different from the majority as bad data. This leads to improved compressional wave velocity logs that are mostly free of the artifacts present in the velocities derived directly from the recorded delay times (DTLN and DTLF). The velocities from the second pass have hardly any artifacts, but some are present 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 (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 hole was in excellent  condition below 380 mbsf, generally reading between 9 and 10 inches in diameter with only a few small washouts. From 375 mbsf to the base of the bottom hole assembly, however, the hole alternates between very tight (e.g. 4 inches) and washed out (> 18 inches): the HLDS, APS, and gamma radiation logs should be used with caution in this interval.


Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 207. For further questions about the logs, please contact:

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