Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1480G
Expedition: 362
Location: Sumatra Seismogenic Zone (Equatorial SE Indian Ocean)
Latitude: 3° 2.0550' N
Longitude: 91 ° 36.3370' E
Logging date: September 5, 2016
Sea floor depth (driller's): 4158.7 m DRF
Sea floor depth (logger's): 4158.7 m WRF (HRLA/EDTC-B/HNGS main run)
Total penetration: 5590.3 m DRF (1431.6 m DSF)
Total core recovered: 329.16 m (49 % of cored section)
Oldest sediment recovered: Miocene
Lithology: Bioturbated clay with some silt and fine sand, tuffaceous sandstone and congomerates, basalt
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 September 2016.
Tool string | Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
1.HRLA/EDTC-B/HNGS
|
Downlog
|
0 |
803 |
757.1 |
|
Repeat |
743
|
808 |
open hole |
||
Main |
0 |
808 |
757.1 |
Reference |
Hole U1480G was drilled to a depth of 5590.3 m DRF (1431.6 m DSF). A 10 3/4" casing was lowered to a depth of ~ 4220.7 m DRF (62 m DSF). The original plan was to log the entire open hole interval to 5590.3 m DRF (1431.6 m (DSF). However, the hole collapsed as the drill pipe was being pulled out in preparation for logging. Therefore it was decided to deplo a modified tool string without nuclear source, consisting of HRLA/EDTC-B/HNGS. The Active Heave Compensator (AHC) was engaged as soon as the tool string approached he sa floor. A downlog was recorded to 4967.6 m WRF (808.0 m WSF) where the string encountered an obstruction. A repeat pass was conducted from that depth uphole for about 70 m. The main run was recorded from 808 m WSF to the sea floor.
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 (-
4158.7 m). The sea floor depth
was determined by the step in gamma ray values at 4158.7 m WRF on the HRLA/EDTC-B/HNGS main run. The depth-shifted logs have then been depth-matched to the gamma ray log from the main
run of the HRLA/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 hole size during 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).
Gamma ray logs
recorded through bottom hole assembly (BHA) and casing should be used only
qualitatively, because of the attenuation of the incoming signal. The
thick-walled casing attenuates the signal more than the thinner-walled drill pipe.
Hole
conditions could not be assessed due to the lack of a caliper log.
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 . For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition 362.
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