Page 216 - Reservoir Geomechanics

197 Compressive and tensile failures in vertical wells

a.

1

2

3

b.
90

80

THEORY
q b [degrees]
70

60
EXPERIMENTAL

50
s
hmin
40
50 60 70 80
s (MPa)
Hmax

Figure 6.15. After the formation of wellbore breakouts, they are expected to increase in depth, but
not width. This is as shown theoretically in (a) after Zoback, Moos et al. (1985) and confirmed by
laboratory studies (Haimson and Herrick 1989). It can be seen photographically that breakouts in
laboratory experiments deepen but do not widen after formation. A shown in (b), measured
breakout widths compare very well with those predicted by the simple thoery presented in Zoback,
Moos et al. (1985) which form the basic for the breakout shapes illustreated in Figures 6.2 and 6.3.