Page 298 - Reservoir Geomechanics

276 Reservoir geomechanics

Normal faulting
7000

6000

5000
S hmin , frictional constraint (psi) 4000

3000

= 0.6
2000

1000
Sandstone Siltstone
Shale Limestone
0
0 1000 2000 3000 4000 5000 6000 7000
S hmin , measured (psi)

Figure 9.5. Comparison of calculated least principal stress magnitudes (ordinate) using Coulomb
faulting theory (normal faulting) and a coefficient of friction of 0.6 with measured values (abscissa)
in all lithologies of the Travis Peak formation in east Texas (see text).

faults in situ. Had lower coefficients of friction been applicable, the magnitude of the
least principal stress could not have been as low as the values measured.
It is well known that active normal faulting is pervasive throughout the offshore
Gulf of Mexico area. Because it is frequently important to be able to predict the mag-
nitude of the least principal stress in advance of drilling, a number of researchers
have proposed empirical methods to predict stress magnitudes from logs. These tech-
niques are discussed later in this chapter. Figure 9.7 allows us to examine how well
Coulomb faulting theory works in the South Eugene Island, Block 330 area. In this
field, oil and gas are produced from a number of extremely young (Plio-Pleistocene)