Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1450B
Expedition: 354
Location: Bengal Fan ( tropical N Indian Ocean)
Latitude: 8° 0.4192' N
Longitude: 87° 40.2586' E
Logging date: March 10, 2015
Sea floor depth (driller's): 3666.3 m DRF
Sea floor depth (logger's): 3666 m WRF
Total penetration: 4478.2 m DRF (811.9 m DSF)
Total core recovered: 46.67 m (22.9 % of cored section). Drilled without coring to 608 m DSF.
Oldest sediment recovered: Upper Miocene
Lithology: claystone, silt, marlstone, and limestone
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in March 2015.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.HRLA/MSS//HLDS/EDTC-B/HNGS
|
Downlog
|
81 |
No HLDS radioactive and caliper closed. Invalid HLDS data. |
||
Uplog
|
81 |
In preparation for logging the drillers circulated 35 barrels of mud to clear the cuttings from the bottom of the hole, released the bit and filled the hole with weighted mud (11.5 ppg barite). The drilled string was raised to 82.7 m DSF. The HRLA/MSS//HLDS/EDTC-B/HNGS tool string, without the HLDS radioactive source and with the caliper closed reached only 50 m below the drill pipe, where it encountered a bridge in the hole. The tool string got initially stuck in the hole but after applying an overpulled it got free and was quickly brought back to the surface. Further logging operations were therefore cancelled. The Wireline Heve Compensator was not used because the tools had not reached a sufficient depth to switch it on. The ship's heave was minimal, therefore it is believed that it did not significantly affect the quality of the logs.
The depths in
the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, discrepancies may exist between the
sea floor depths determined from the downhole logs and those determined by the
drillers from the pipe length. Typical reasons for depth discrepancies are ship
heave, wireline and pipe stretch, tides, and the difficulty of getting an
accurate sea floor from a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3666 m). The sea floor depth was determined by the step in gamma ray values at 3666 m WRF. This differs by 0.3 m from the sea floor depth given by the drillers (3666.3 m DRF). The depth-shifted data from the downlog have then been depth-matched to the gamma ray log from the uplog of the HRLA/MSS//HLDS/EDTC-B/HNGS tool string.
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 no sudden changes in cable speed), 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 HRLA data were corrected for the weighted mud and bit sizeduring the recording.
High-resolution
data. Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
The quality of
the data is assessed by checking against reasonable values for the logged
lithologies, by repeatability between different passes of the same tool, and by
correspondence between logs affected by the same formation property (e.g. the
resistivity log should show similar features to the sonic velocity log).
The gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively, because of the attenuation of the incoming signal. The
thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
No caliper data were acquired in this hole, therefore it is not possible to provide a quantitative assessment of the borehole conditions, though the bridge encontered at about 130 m WMSF would indicate that they were far from ideal for logging.
A null value of
-999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition 154. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu