Page 39 - Reservoir Geomechanics

23 The tectonic stress field

0 1E 2E 3E 4E 5E 6E 7E
62N 62N
100 km
Tampen Spur Visund
Snorre

Gulfaks Viking Graben
61N 61N

Troll

Oseberg

60N 60N
Frigg Bergen

Heimdal

Hermod
59N 59N

Gudrun

0 1E 2E 3E 4E 5E 6E 7E
Figure 1.8. Stress map of the northern North Sea as determined principally from drilling induced
tensile fractures and wellbore breakouts in wells (modified from Grollimund and Zoback 2000;
Grollimund, Zoback et al. 2001).

stress field (see Chapter 9), the state of stress in the northern North Sea represents both a
counter-clockwise rotation of stress orientation and an increase in stress magnitudes (to
a strike-slip/reverse stress field) in areas most affected by the former ice sheet margin.
As I discuss in Chapter 9, this modification of the stress field may be the result of
deglaciation in just the past ∼15,000 years.
Figure 1.9 presents a generalized stress and seismotectonic map of northern South
America (Colmenares and Zoback 2003). The east–west oriented strongly compressive
stresses observed in the Ecuadorian Andes province reflect the influence of convergence
between the Nazca and the South American plates as the direction of maximum com-
pression is the same as the direction of motion of the Nazca plate (single arrow) with
respect to the stable interior of South America. To the north, the compression direction