Page 214 - Applied Petroleum Geomechanics

In situ stress estimate 209

stress and depth (mainly for shales). The following correlations are the
lower bound of the measured data for normally pressured formations in this
region:
s h ¼ 0:197D 1:145 ðD 11; 500ftÞ
(6.39)
s h ¼ 1:167D 4596 ðD > 11; 500ftÞ
where D is the depth in ft; s h is the minimum horizontal stress in psi. The
same units are used from Eqs (6.39e6.42).
The minimum horizontal stress in abnormally pressured formations in
the US Gulf Coast region can be estimated from the following correlations
(Breckels and van Eekelen, 1982):

s h ¼ 0:197D 1:145 þ 0:46ðP c P cn ÞðD 11; 500ftÞ
(6.40)
s h ¼ 1:167D 4596 þ 0:46ðP c P cn Þ ðD > 11; 500ftÞ
where P c is the pore pressure gradient in psi/ft; P cn is the normal pore
pressure gradient; and P cn ¼ 0.465 psi/ft.
A similar correlation was obtained from hydraulic fracturing tests in
Venezuela for 5900 ft < D < 9200 ft (Breckels and van Eekelen, 1982):

s h ¼ 0:21D 1:145 þ 0:56ðP c P cn Þ (6.41)
where P cn ¼ 0.433 psi/ft.
The mini-frac test data in the offshore Brunei appear to be subject to
higher compressive stresses than those in the US Gulf Coast; based on 15
data points, Breckels and van Eekelen (1982) obtained the following
relation (depth D < 10,000 ft):
s h ¼ 0:227D 1:145 þ 0:49ðP c P cn Þ (6.42)

From LOTs, Gibson-Poole et al. (2002) obtained the following cor-
relation between the minimum horizontal stress and depth in the Mesozoic
formations of the Petrel Sub-basin, NW Australia:
s h ¼ 0:0184Z (6.43)

where s h is in MPa; Z is the depth in meters. The same units are used from
Eqs. (6.43e6.47).
A similar correlation was obtained in the North Sea basins (Lønø, 1995)
based on XLOT data in the Ekofisk field:
s h ¼ 0:0185Z bml 2 ð500 Z bml 2; 900mÞ (6.44)