Optimum results are obtained from core fracture studies when the core can be oriented. There are two approaches to core orientation: downhole orientation and surface orientation. Downhole core orientation is most

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suitable for cores cut in formations where bedding is not visible. Drawbacks are encountered in highly fractured formations. Highly fractured cores are most effectively oriented at the surface provided that the bedding is visible or that other directional core parameters, such as paleomagnetic properties, can be measured.

The fold fracture classification presented differentiates between fracture systems associated with folds that result from horizontal compressive stress systems and those that result from vertical diapiric uplift. Each type of fold is characterized by two dominant fracture patterns. Fracture patterns 1 and 2 occur in association with compressive folds, and fracture patterns P and R are associated with diapiric structures. Potentially, each fracture pattern consists of an extension and two conjugate shear fractures. All four fracture patterns result from stresses generated during the folding process. Fracture patterns 2, P, and R result from extension parallel to the bedding, and are best developed where bed curvature is greatest.

Analysis of core-measured fracture patterns is best effected by plotting the poles to the fractures, with bedding plane orientation, on a stereographic projection. The fracture patterns distinguished can then be projected to other parts of the structure or to adjacent structures. Areas of maximum fracture potential can be distinguished by calculation of both cross-sectional and planar bed curvature.

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