Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: 395A
Expedition: 336
Location: Mid Atlantic Ridge (central tropical N Atlantic)
Latitude: 22° 45.35' N
Longitude: 46° 04.9' W
Logging date:
Sea floor
depth (driller's):
4494 m DRF
Sea floor
depth (logger's):
4494 m WRF
Total
penetration: 664 m DSF (5158 m DRF, drilled durimg DSDP Leg 45)
Total core recovered: 88.36 m (47.9 % of cored section)
Oldest sediment cored: calcareous brown clay (Upper Miocene)
Lithologies: foram-nanno ooze and calcareous brown clay (sediments), basalt, serpentinized peridotite, and gabbro (basement).
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 2011.
Tool string |
Run/Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
|
MTT/DEBI-T/GPIT/HNGS |
Pass 1 downlog
|
58 |
Casing depth 116 m DSF |
||
" |
Pass 1 uplog
|
" |
" |
||
"
|
Pass 2 downlog
|
200 |
" |
||
" |
Pass 2 uplog
|
" |
" |
||
"
|
Pass 3 downlog
|
" |
" |
||
" |
Pass 3 uplog
|
" |
" |
Hole 395A was a re-entry hole. Three logging passes were conducted with the MTT/DEBI-T/GPIT/HNGS tool string without major incidences, except for running onto a ledge at (182 m WMSF) during pass 1. The sea state was relatively calm with a peak-to-peak heave of ~ 0.5 to 1 m. Therefore, the wireline heave compensator was not used during logging.
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 using the sea floor depth of - 4494 m determined by the step in gamma ray values during ODP Leg 174B. All logs from the three passes were then depth matched to the logs acquired during Leg 174B using the gamma ray curve (i.e., HSGR) reference.
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 data were corrected for hole size during the recording.
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 density log).
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.
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 reports,
Proceedings of the Integrated Drilling Program, Expedition 336.
For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia