Is the mountain front of the Apennines a reliable analogue for reservoirs in the Adriatic foredeep? The role of late-thrusting extension on the fracture pattern in the Sibillini Fronal Anticline, Northern Apennines (Italy).

Stefano Tavani, Fabrizio Storti, Stefano Mazzoli, and Josep A. Muñoz

Thrust-related anticlines exposed in thrust-and-fold belts typically provide natural analogues to address fracture pattern predictions in foredeep-foreland basin system reservoirs. Due to geographic proximity, mountain fronts are frequently considered reliable analogues. Relationships between pre-, syn- and post-folding deformation mechanisms can be exhaustively studied there and exported into reservoir modelling tools to populate fracture distribution scenarios. Syn-folding fracture patterns are commonly more “evolved” in the anticlines exposed at the surface rather than in buried structures. This implies filtering natural dataset from additional complexities to prevent severely biassed applications to reservoirs.

In this work, we present a case study from the Sibillini thrust sheet, the mountain front in the Umbria-Marche sector of the Northern Apennines (Italy). In the frontal anticline of the thrust, extensional and compressional deformation structures strike roughly parallel to the fold axial trend. Compressional structures developed during thrust propagation and fold growth, while extensional ones developed before or in the early stages of fold growth and, mostly, during latestage thrusting, when the transition from layer-parallel shortening to layer-parallel extension in the uplifting anticline caused syntectonic relaxation in the crestal region.

In the Sibillini anticline, fractures associated with this late stage deformation represent a significant component of the total fracture pattern and, if not properly recognised, they might drive different interpretations, like outer arc extensional fracturing. This would result in a wrong fracture density versus curvature relationship and in a subsequent dramatic overestimation of fracture density when exporting this relationship into reservoirs of the Adriatic region.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013