--> Abstract: Structural and Stratigraphic Controls on Fold-Related Fracturing in the Zagros Mountains, Iran: Implications for Reservoir Development, by Ben Stephenson, Anton Koopman, Heiko Hillgartner, Stephen Bourne, Jon Noad, Keith Rawnsley, and Harry McQuillan; #90039 (2005)
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Structural and Stratigraphic Controls on Fold-Related Fracturing in the Zagros Mountains, Iran: Implications for Reservoir Development

Ben Stephenson1, Anton Koopman2, Heiko Hillgartner2, Stephen Bourne2, Jon Noad2, Keith Rawnsley2, and Harry McQuillan3
1 Shell Canada, Calgary, AB
2 Shell International Exploration and Production, Rijswijk, Netherlands
3 Zagros Orchard, Nelson, New Zealand

New observations of mega-scale (>150m) fold-related fracture corridors, planes of bedding-parallel slip and a mega-scale spaced cleavage (~50m) are integrated with sedimentological descriptions of the Asmari Formation to understand the main controls on the development of fractures in the Zagros Mountains of Iran. The main control on the lateral variation of fold-related fracture corridors in Kuh-e Pahn is the interplay between the mechanisms of Previous HitbedNext Hit-parallel slip and tensile fracturing due to outer arc extension. Fold-related fracture corridors occur in the crest of the fold, due to neutral surface folding, and are axis-parallel (NW-SE), but at a certain critical dip of the beds (~15º in this case) bedding-parallel slip, due to flexural slip folding is the predominant mechanism. This Previous HitrelationshipNext Hit is substantiated by curvature calculations. Crestal fractures have a large vertical extent in mechanical unit B (>150m) primarily due to the lithological homogeneity of the Asmari Formation, comprising massive packstone beds with relatively little marl content. Fracture corridors inherited from basement faults have been mapped out from satellite imagery, trend N-S and E-W, and are spatially unrelated to the folds. Observations from an adjacent eroded box fold, Kuh-e Mish, with much more steeply Previous HitdippingTop limbs (60°), revealed a complete contrast in the style of deformation in the limbs. We interpret Kuh-e Pahn and Kuh-e Mish to represent different stages in the evolution of a box fold and a conceptual model has been devised for the development of reservoir scale structures through time.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005