Wireline Standard Data Processing
ODP logging
contractor: LDEO-BRG
Hole: 1179D
Leg: 191
Location: Shatsky Rise (NW. Pacific Ocean)
Latitude: 41° 4.788' N
Longitude: 159° 57.7868' E
Logging date: August 5, 2000
Bottom felt: 5577 mbrf
Total penetration: 475 mbsf
Total core recovered: 194 m (25.96 %)
Logging
Runs
Logging string 1: DIT/HLDT/APS/HNGS/MGT/TAP (main and repeat passes)
The repeat pass was conducted first, in the upper part of the open-hole (203-300 mbsf). The tool string, however, could not be lowered to total depth for the main pass due to a blockage at about 260 mbsf. A pass was made to collect MGT (Multisensor Gamma Tool) data (alone) before the main DIT/HLDT/APS/HNGS/MGT/TAP pass. The wireline heave compensator was used to counter ship heave; it stopped once during the main pass.
The following bottom-hole assembly and pipe 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/TAP (main pass): Bottom-hole assembly at 154.5 mbsf
DIT/HLDS/APS/HNGS/MGT/TAP (main pass): pipe at 64 mbsf
DIT/HLDS/APS/HNGS/MGT/TAP (repeat pass): recorded open hole.
Processing
Depth shift: The original logs were depth matched to the HSGR from the main pass and were then shifted to the sea floor (-5573.5 m). The sea floor depth is determined by the step in gamma ray values at the sediment-water interface. It differs by 3.5 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.
Gamma-ray processing: The HNGS data were corrected for hole size 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 HLDT pad and the borehole wall (low density correction) the results are improved, because the short-spacing has better vertical resolution.
Quality
Control
null value=-999.25. This value generally replaces invalid log data.
Hole diameter was recorded by the hydraulic caliper on the HLDT tool (CALI).
The caliper log indicates a rough borehole between 248 and 287 mbsf, ranging from 7 to 16 inches. Above this, the caliper remains at its maximum value, 16.5 inches. The very high apparent log porosity indicates lack of good contact with the borehole wall and a hole diameter some inches in excess of 16.5".
The far detector on the HLDT had a voltage regulation problem during logging, resulting in erroneous spikes in the RHOB and PEF logs. Because the PEF log is highly disturbed, it has not been included in the online database.
During the processing, quality control of the data is mainly performed by cross-correlation of all logging data. Large (>12") and/or irregular borehole width affects most recordings, particularly those that require eccentralization (APS, HLDT) and a good contact with the borehole wall. Hole deviation can also affect the data negatively.
Data recorded through bottom-hole assembly should be used qualitatively only because of the attenuation on the incoming signal.
Main and repeat pass were merged at the following depths:
APS: 230 mbsf
Caliper: 230 mbsf
DIT: 230 mbsf
HLDT: 243 mbsf
HNGS: 211 mbsf
Additional information about the logs can be found in the "Explanatory Notes" and Site Chapter, ODP IR volume 191. For further questions about the logs, please contact:
Cristina
Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia