IODP-MSP
drilling and logging contractor: ESO
Hole: M0007B
Expedition: 310
Location:
Latitude: 17° 45.9462' S
Longitude:
149° 33.0682' W
Logging
date: October 16, 2005
Sea
floor depth (driller's): 56.16 mbrf (41.65 mbsl)
Sea
floor depth (logger's): 56.16 mbrf
Total
penetration: 47.93
mbsf
Total
core recovered:
27.02 m (56.37 % of cored section)
Oldest
sediment recovered:
Pleistocene sequence
Lithologies: Reef framework, algal crusts, and
microbialite matrix
The logging data was
recorded by the
Tool string |
Pass |
Top depth
(mbsf) |
Bottom depth
(mbsf) |
Pipe depth
(mbsf) |
Notes |
1. ASGR |
thru pipe |
0 |
45.08 |
48.44 |
|
2. DIL45 |
|
25.33 |
30.88 |
24.84 |
|
3. IDRONAUT |
|
23.94 |
31.04 |
24.84 |
|
4. ABI40 |
|
24.75 |
31.15 |
24.84 |
|
A complete
list of tool and log acronyms is available at http://brg.ldeo.columbia.edu/data/iodp-eso/exp310/exp_documents/iodp-eso-310-acronyms.html.
After completion of the coring, the drill string was pulled and the coring bit was changed for an open shoe casing to provide borehole stability in unstable sections and a smooth exit and entry of logging tools. In addition, a wiper trip was performed with fresh sea water (no drilling mud was used). Difficult borehole conditions often required the boreholes to be logged in key intervals where the HQ drill string was used as a temporary casing. All measurements were performed under open borehole conditions (no casing) with the exception of a few spectral gamma ray logs which were run through the steel pipes to obtain continuous geophysical information over the entire interval cored.
Hole M0007B
was drilled and logged during Expedition 310. Logging operations were conducted
from 45.08 mbsf upwards. A casing was placed at 24.84 mbsf with open borehole
logging only possible below this depth. Only a very short interval (<10 m) of
the open borehole was possible to log due to hostile borehole conditions with three
short logs acquired by the DIL45, IDRONAUT and ABI40 tools. A spectral gamma
log provided a continuous log through the drilled interval by running the tool
through the steel drill pipe.
The depths
in the table are for the processed logs (after applying a depth shift to the
sea floor). 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 the 'bottom felt' depth in soft sediment. However, for
Depth
shift: The original logs were first shifted to the sea floor
using the driller’s depth to seafloor (-56.16 m below rig floor). For
Environmental
corrections: None were applied.
Spectral gamma ray: Gamma ray logs recorded through drill pipe
should be used only qualitatively due to attenuation of the incoming signal.
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 acoustic log).
The quality of the ASGR Spectral Natural Gamma data is
directly related to lithology in combination with logging speed. Despite
logging speeds of 1.1 m/minute and a taking a sample every 10 cm (collecting
gamma ray emissions of the formation for approximately 6 seconds for every
sample) the amount of total counts obtained are still very low. This degrades
the quality of the statistics that separates the raw counts into activity
values of naturally occurring radioactive elements such as potassium (K),
uranium (U) and thorium (Th). Negative K values are indicative of incorrect
statistics. Gamma ray logs
recorded through drill pipe should be used only qualitatively due to
attenuation of the incoming signal. Gamma ray logs recorded through drill pipe
should be used only qualitatively due to attenuation of the incoming signal.
Due to a short time period between the completion of coring
(including wiper trip) and logging, the IDRONAUT data should be treated with
great care. The hydrological properties of the borehole fluid measured with
this tool represent more of a mixture between fresh sea water (used for coring
and for the wiper trips) and true formation pore water.
A wide
and/or irregular borehole affects most recordings, particularly those that
require eccentralization and a good contact with the borehole wall. No hole
diameter was measured in Hole M0007B, but can be calculated
from the acoustic imaging tool (ABI40).
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 section of the Site Chapter in IODP Proceedings of Expedition 310.
For further questions about the data, please contact:
Jennifer
Inwood
University
of Leicester
Phone:
011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail: iodp@le.ac.uk
For any web
site-related problem please contact:
E-mail: logdb@ldeo.columbia.edu