Page 42 - The Geological Interpretation of Well Logs

- THE GEOLOGICAL INTERPRETATION OF WELL LOGS -

shear fallure zone extensional hydrautic
SHmin pega titled fracturing or open pre-existing
< ~ rtical fractures
sje a where compressive ve
breakout i strass is concentrated SHmin
cps
spall zone
SHmax SHmax SHmax SHmax
q

original <>

borehole shape
(bit size
SHmin
2 Cae
callbration)
SHmin
B. Fracture enlargement
A. Breakout
Figure 4.12 Horizontal stress field relationship to borehole shape. a. Breakout formation due to
spalling during drilling, in the direction of minimum horizontal stress (Sh_,,). b. Hole enlargement
along drilling induced extensional fractures oriented in the direction of maximum horizontal stress
(Sh,,,,) (modified from Dart and Zoback, 1989 and Hillis and Williams, 1992).

N

h
Sh, SP

9 5

Led
km

Figure 4.13 Consistently oriented breakouts, identified from
dipmeter caliper data in an offshore field, indicating the
present day, horizontal stress field. Depth of analysed interval
from 2.5 to 3.5 kilometres. Sh, = minimum horizontal stress,
Sh, 4, = Maximum horizontal stress,

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