reservoir geomecanics

108 Reservoir geomechanics
a.
300
Mu - Bi Gneiss
s 0
m i
Shear stress (MPa)
200
100
c 0
b
b
0
0 100
200
300
Normal stress (MPa)
400
b. b.
350
300
35
Strength, s 1 (MPa)
250
200
150
20
5
100
50
0
30 60
90
b
Figure 4.13. Fit of compressive strength tests to the theory illustrated in Figure 4.12 and defined by
equation (4.33). Modified from Vernik, Lockner et al. (1992).
of overburden formations (where many wellbore instability problems are encountered)
are almost never available for testing. To address this, numerous relations have been
proposed that relate rock strength to parameters measurable with geophysical well logs.
The basis for these relations is the fact that many of the same factors that affect rock
strength also affect elastic moduli and other parameters, such as porosity.