Page 106 - Reservoir Geomechanics

90 Reservoir geomechanics

a. 180
True vertical depth:
3065 meters
160 m = 0.9
i
140 Linear Mohr envelope Mohr Failure envelope
Shear stress (MPa) 120 P conf = 15 MPa

100
80
60 P conf = 10 MPa

40
P conf = 0
20
S 0 = 24 MPa
−20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
Normal stress (MPa)
T 0 = 6.3 MPa C 0 = 105 MPa

b.
450
DARLEY DALE SANDSTONE
400

350

300
(MPa) 250 n = 4.55
S 1
200

150

100
94.3 MPa
50
0 10 20 30 40 50 60 70
S (MPa)
3
Figure 4.3. (a) Laboratory strength tests at 0, 10 and 15 MPa confining pressure defines the Mohr
envelope for a sandstone sample recovered from a depth of 3065 m in southeast Asia. A linearized
Mohr–Coulomb failure envelope and resultant values of S 0 , C 0 and µ i are shown. (b) Illustration of
how strength values determined from a series of triaxial tests can be used to extrapolate a value of
C 0 .Asexplained in the text, the slope of this line can be used to determine µ i .