ABSTRACT

Breakout orientations measured in 35 wells in northern Alberta and British Columbia show that the principal horizontal stresses are deflected over the Peace River Arch. Instead of the regional northeast-southwest azimuth for S_Hmax, the larger horizontal principal stress is directed north-northeast - south-southwest.

Two-dimensional finite element modelling of this stress refraction shows that the cause could be lateral variations in the elastic properties of the rock. On the other hand, faults that are acting as free surfaces could also be locally deflecting the stresses. However, the consistency of the data, which comes mainly from Paleozoic sections, points to a regional cause.

Micro-frac and mini-frac records from some 30 wells on and around the Peace River Arch give indications of the magnitudes of S_Hmin, the smaller horizontal principal stress. The magnitudes appear to be laterally variable, with a tendency to be larger toward the Rocky Mountains, but there is insufficient information to recognize trends.

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