ABI40 Image Data Processing
IODP-MSP
drilling and logging contractor: ESO
Hole: M0027A
Expedition: 313
Location:
New Jersey (NW
Atlantic)
Latitude: 39° 38.0406' N
Longitude:
73° 37.3015' W
Logging
date: May 19 - 21,
2009
Sea floor
depth (driller's):
50.15 m DRF
Sea
floor depth (logger's): 49.50 m WRF
Total
penetration: 631.01
m DSF
Total
core recovered:
471.59 m (86.21 % of cored section)
Oldest
sediment recovered:
Eocene
Lithologies: Clays to gravels
ABI40 Lower Section: 419.94 – 575.30 m WSF
ABI40 Middle Section: 194.25
– 328.15 m SWF
The acoustic images show the acoustic hardness of the lithologies within the depositional sequence.
In M0027A, acoustic images have been recorded in the lower
and middle sections of the borehole. Images have not been recorded in the
lowest part of the middle section (328 to 419 m WSF) due to borehole collapse and
bridge formation. For each interval of M0027A the image logs were acquired as
one continuous file. The ABI40 images of the
borehole wall were apparently unaffected by borehole fluid quality. The occurrence of dark
lines oriented at 180° indicates poor centralization of the tool, possibly related to an enlarged hole.
The ABI40 acoustic images in the
lower interval were acquired with a resolution of 72 samples x 4 mm (increasing in resolution in the upper few
metres of this section as a test) which results in a
pixel size of less than 5 (horizontal) x 4 (vertical) mm. In the middle
interval the acoustic images were acquired with a resolution of 288 samples x 4
mm. The presented values of the acoustic caliper were obtained by assuming a acoustic wave velocity of 1495 m/s through borehole fluid
and taking the mean value of the measurements at every sample (4 mm vertical
sampling).
The images of the borehole wall (360°),
corrected for decentralization effects when possible, are displayed into a
two-dimensional view as an unwrapped borehole cylinder. A dipping plane in the
borehole will appear as a sinusoid on the image with the amplitude of this
sinusoid proportional to the dip of the plane. The images are oriented with
respect tothe magnetic north, hence the strike of dipping
features can also be determined. A "static" normalization of the
images has been applied to enhance structure visualization. Images are provided
in PDF format at two different scales. The travel time and amplitude data for
each interval logged have also been output in ASCII format.
Jennifer
Inwood
Phone:
011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail: IODP-UK
Johanna Lofi
University
of Montpellier 2
Phone: 033-
467-149- 309
Fax: 033- 467-
143- 244
E-mail: IODP-UK
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