Page 246 - Reservoir Geomechanics
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227 Determination of S 3 from mini-fracs
160
155
150
145
S Hmax (MPa) 140
135
130
125
120
0 20 40 60 80 100
w BO
0 50 100 150 MPa
Figure 7.11. The dependence of S Hmax on rock strength for given values of breakout width. The
square indicates the analysis shown in Figure 7.10.
vertical stress, the least principal stress as well as a reasonable estimate of rock strength
are also needed. Figure 7.11 shows the sensitivity of S Hmax determined from breakout
width as a function of rock strength. The square box shows the result from Figure 7.10;
for a breakout width of 45 and a rock strength of about 138 MPa, S Hmax is estimated
◦
to be about 130 MPa. Had the rock strength been mistakenly assumed to be about 150
MPa, a value of S Hmax of about 140 MPa would have been indicated. Had the strength
been mistakenly assumed to be as low as 100 MPa, a value of S Hmax of about 125 MPa
would have been inferred.
In the case studies presented in Chapters 9–12 (as well as many others), the tech-
nique of estimating S Hmax from breakout width has proved to provide reasonably useful
estimates of the value of S Hmax .Asa historical note, Hottman, Smith et al. (1979)
