Source Radiation Patterns In Cased Boreholes
Name
1997.4 Rao et al.pdf
Size
1.19 MB
Format
Adobe PDF
Checksum (MD5)
760d35bd080b23df6d3b4ac24d48441a
Author(s)
Rao, Rama V.N.
Turpening, Roger M.
Nafi, M. Toksoz
Date Issued
1997
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1997-04
Abstract
Source radiation from open and cased boreholes are well documented. The effect of
an unbonded casing on the radiation patterns of volume, radial stress and axial stress
sources in a borehole has received less attention and is modeled and analyzed here in
the context of performing single well imaging. Radiation patterns were evaluated using
a global matrix approach and wavenumber integration. 'While a borehole with a bonded
casing has a single propagating mode at low frequencies, the stoneley mode, the borehole
with unbonded casing has three propagating modes. Of the two additional modes that
are due to the unbonded casing, one is present mainly in the cross-section of the casing
and has a phase speed close to the speed of longitudinal waves in steeL Because of
its large phase speed (~ 5400 m/s), this mode radiates into almost all formations and
influences the radiation pattern of all source types. Test data and the predicted radiation patterns were used to identify the annulus material behind the casing.
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