Page 279 - Reservoir Geomechanics

260 Reservoir geomechanics

a. Borehole geometry
North

a

East

I

Apparent fast
direction plane

Down

b. Stress geometry c. Structural geometry
North North

East East
S Hmax f a
True fast
dip direction f d

Fast
Fn

Fast
plane

Down
Down
Figure 8.17. (a) Figure illustrating the geometry of the borehole with the plane in which the
apparent fast direction is measured with the sonic logs. (b) In the case of stress-induced anisotropy,
the apparent fast direction in the plane perpendicular to the borehole has an azimuth equivalent to
that of S Hmax , although the dip depends on the borehole trajectory. (c) Geometry used to compute
the apparent fast direction that will be observed on the dipole sonic tool for structural anisotropy
when the fast direction lies in an arbitrarily oriented plane. The angles f α , f d , F n are defined in the
text. After Boness and Zoback (2006).