Fractured reservoirs are common exploration targets in fold and thrust belts because of the relatively high levels of structural deformation. A recently completed effort to predict fracturing and its effect on reservoir quality in the Canadian Rocky mountain foothills has shown that: 1) lithology and structure are the primary controls on fracture intensity and orientation, 2) intensity of effective fractures is correlated to gas productivity, and 3) map curvature is a useful tool for predrill estimates of fracture intensity and expected flow rates. Methods used in the study included core and outcrop fracture description, petrophysical analyses, and productivity analysis.

Geologic factors having the greatest control on fracturing were quantified with respect to fracture characteristics. Fracture intensity was compared with whole core permeability and flow rates from wells with sustained production. Lithologic factors that enhance fracturing in these carbonate reservoirs are increased dolomite and silica content, low porosity, fine grain size, and lack of silt and clay. Structural factors that enhance fracturing are the amount of stratal bending, which is quantified by map curvature, and the presence of faults, especially in stacked duplexes of sliced forelimbs of fault propagation folds. Higher flow rates generally correlate well to higher fracture intensities and greater map curvature. Although curvature is highest along fold hinges, it varies significantly with changes in tightness along a single fold and between different folds. These results enable us to integrate lithologic and structural data from these complex settings for improved fracture prediction, which is important for prospect evaluation, target selection, and drilling and completion strategies.

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