Page 40 - Reservoir Geomechanics

24 Reservoir geomechanics

−85 o −80 o −75 o −70 o −65 o −60 o −55 o
15 o 15 o
CARIBBEAN PLATE
N

FB
10 o MB 10 o
CR-P UA SS - EP
Eastern
Microplate Venezuela
Barinas-Apure basin
basin
Llanos
Orientales
5 o COCOS basin SOUTH AMERICAN 5 o
PLATE PLATE
NAZCA
PLATE Caguán-Vaupés Stress Regime
basin
Thrust faulting
0 o Strike-slip faulting 0 o
Combination strike-slip
and thrust faulting
Amazonas km Combination strike-slip
basin and normal faulting
Stress provinces
EA 0 100 200
−5 o 20 mm/year −5 o
−85 o −80 o −75 o −70 o −65 o −60 o −55 o
Figure 1.9. Generalized tectonic map of northern South America. The inward-pointed double
arrows indicate the direction of either S Hmax whereas the outward pointed double arrows indicate
the direction of S hmin (as explained in the inset). The stress provinces shown in the figure are
discussed by Colmenares and Zoback (2003) and are abbreviated as follows: Ecuadorian Andes
(EA), Upper Andes (UA), San Sebastian – El Pilar (SS-EP). GPS (Global Positioning System)
velocity vectors (single arrows) denote velocities with respect to South America.

rotates to northwest–southeast and is slightly less compressive as more strike-slip fault-
ing is observed. Toward the Merida Andes and the Maracaibo basin in Venezuela, the
subduction of the Caribbean plate beneath the South American plate may affect the
observed direction of maximum compression in the area. Further to the east, the stress
orientation continues to rotate and stress magnitudes continue to decrease. Overall, the
stress field in northern South America is affected by a diversity of complex geologic
processes. Nonetheless, as was the case in the southern San Joaquin valley, careful
analysis of the available data reveals uniform stress fields within specific regions and
systematic variations of the stress field from region to region.

Frictionless interfaces

Because principal stresses are perpendicular and parallel to any plane without shear
stress, the orientation of principal stresses is likely to be affected by the presence of weak
salt bodies or severely overpressured formations. In the case of both formations, the