Page 124 - Reservoir Geomechanics

108 Reservoir geomechanics

a. a.
300
Mu - Bi Gneiss
s 0
m i
c 0
200
Shear stress (MPa) b

100 b

0
0 100 200 300 400
Normal stress (MPa)

b. b. 350

300 35

250 20
Strength, s 1 (MPa) 200 5

150

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.