Massachusetts Institute of Technology. Earth Resources Laboratory
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.Massachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation
Consortiu
