Wireline Standard Data Processing
ODP logging contractor: LDEO-BRG
Location: Marion Plateau (tropical SW Pacific Ocean)
Latitude: 20°14.554' S
Longitude: 151°58.991' E
Logging date: January 25, 2001
Bottom felt: 384.8 mbrf
Total penetration: 427.4 mbsf
Total core recovered: 89.2 m (28.1 %)
Logging string 1: DIT/HLDS/APS/HNGS/MGT (one main pass, one pass with MGT only)
Logging string 2: FMS/GPIT/NGT/DSI (one pass)
Logging string 3: FMS/GPIT/NGT/SDT (one pass)
Logging string 4: WST
The DIT/HLDS/APS/HNGS/MGT reached TD on both passes. The DSI tool failed before recording any data and was replaced by the SDT. Hole conditions were good for the first two logging strings but deteriorated for the last two, the WST reaching only 157 mbsf. The wireline heave compensator was used to counter the minor ship heave resulting from the calm sea conditions.
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/HLDS/APS/HNGS/MGT (main pass): Bottom-hole assembly at 76 mbsf
FMS/GPIT/NGT/DSI: Bottom-hole assembly at 77 mbsf
FMS/GPIT/NGT/SDT: Bottom-hole assembly at 77 mbsf.
Depth shift: The original logs were depth matched to the SGR log from the FMS/GPIT/NGT/DSI run after it had been speed corrected using the accelerometry from the GPIT tool. The logs were then shifted to the sea floor (-384.5 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. It differs by 0.3 m from the "bottom felt" depth given by the drillers (see above).
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 automatically, and the result checked and adjusted as necessary. 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. In this case, the speed-corrected SGR log was used as the reference, because it has greater depth accuracy than the gamma logs without speed correction.
Gamma-ray processing: NGT data have been processed to correct for borehole size and type of drilling fluid. The HNGS data were corrected for hole size during the recording.
Acoustic data processing: The travel time logs from the SDT tool 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, eight 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. The original data was noisy in intervals where the hole was narrow, but the processing did a good job of correcting for this.
No data were obtained by the DSI.
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.
null value=-999.25. This value generally replaces recorded log values or results which are considered invalid.
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 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 HLDS tool (LCAL) and on the FMS string (C1 and C2). The diameter of Hole 1194B varied from 13" at the bottom to 17" in the middle for the first two tool strings. For the third tool string, the caliper was closed between 240 and 257 mbsf due to over pull, and a section between 230 and 238 had closed to around 7". The WST met an obstruction at 157 mbsf and could not progress further downhole.
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP Leg 194 IR volume. For further questions about the logs, please contact:
E-mail: Cristina Broglia