Page 102 - Reservoir Geomechanics

86 Reservoir geomechanics

0 S 0 S 1

0 S 0

HYDROSTATIC UNIAXIAL
S 0 0 = S = S = S 3 S ≠ 0, S = S = 0
2
1
2
1
3
S 1 S 3
S 1

S 1
S 3 S 3
S 1 S 2
S 3

TRIAXIAL
TRIAXIAL POLYAXIAL
EXTENSION
S > S = S 3 S = S > S 3 S ≠ S ≠ S 3
2
1
1
2
1
2
Figure 4.1. The most common types of rock mechanics tests. While it is common for petrophysical
properties to be measured as a function of hydrostatic pressure, strength is typically measured via
either uniaxial or triaxial tests. As discussed in the text, triaxial extension and polyaxial tests are
rare. Pore pressure is frequently accommodated as an independent variable in these tests by using a
flexible, impermeable sleeve outside the sample. For obvious reasons, pore pressure is not used in
uniaxial tests. It is also not used in polyaxial tests because of the experimental difficulty of sealing
pressure within the samples.