Page 215 - Applied Petroleum Geomechanics

210 Applied Petroleum Geomechanics

In the central Graben of the North Sea, the minimum horizontal stress
calculated from shut-in data from both LOT and XLOT data follows the
following expression (Amundsen, 1995; Addis et al., 1998):
s h ¼ 0:017Z 1:09 ðZ 3; 500mÞ (6.45)
The minimum horizontal stresses measured from acid-gas injection
wells in the Alberta Basin, Canada, have a basin-wide average gradient of
16.6 kPa/m, although stress gradients vary locally between 13.6 and
19.5 kPa/m (Hawkes et al., 2005), i.e.:
s h ¼ 0:0166Z (6.46)

In situ stress results measured by hydraulic fracturing tests (e.g., DFIT) in
tight gas reservoirs (Xujiahe sandstones) in the Sichuan basin of China show
that the maximum horizontal stress is greater than the overburden stress
(s V ¼ 0.024e0.0245Z and s H z 0.03Z). This area is located in high
tectonic stress regime, and the pore pressures in deep formations are
overpressured. The minimum horizontal stress in this area is close to or even
higher than the overburden stress, which generally has the following
relation (refer to Fig. 7.26):
s h ¼ 0:0224Z (6.47)

6.4 Maximum horizontal stress
Predicting the maximum horizontal stress is much more challenging than
predicting the minimum horizontal stress. This section attempts to provide
various approaches and methods. In very complicated conditions, such as in
a strong tectonic stress region, multiple methods and integrated approaches
need to be applied to verify each other and calibrate the model.

6.4.1 Maximum horizontal stress from extended leak-off
test
6.4.1.1 No fluid penetration in the formation
In normal and strike-slip faulting stress regimes, the maximum horizontal
stress can be estimated from the multicycle XLOT or DFIT, as shown in
Fig. 6.12. Assuming that the rock behaves like elastic and isotropic material
and no fluid penetrates into the fracture, Haimson and Fairhurst (1967)
derived the following equation to calculate the fracture initiation pressure
that can be used for the leak-off test analysis in a vertical well, and they