Fracture System Characterization and Evolution in the Cingoli Anticline, Italy

Petracchini, Lorenzo ¹; Scrocca, Davide ²; Antonellini, Marco ¹; Billi, Andrea ²; Bencini, Roberto ³
(1) Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Bologna, Italy. (2) Istituto di Geologia Ambientale e Geoingegneria, CNR, Roma, Italy. (3) Independent Resources plc, Roma, Italy.

Characterization of fracture patterns and quantification of their attributes are crucial in hydrocarbon exploration and production, particularly in the case of carbonate reservoirs. Understanding fracture arrays and evaluating the related contribution to rock permeability is also essential for exploiting geothermal and water resources, as well as storing methane and CO2.

Several field and subsurface studies have documented that fault-related folds in carbonate rocks are usually affected by intense but heterogeneous brittle deformations, which are particularly challenging when attempting to quantify and model the physical properties of these structures.

In this contribution, results of investigations carried out on the Cingoli anticline, a multilayer carbonate anticline located in the Umbria-Marche region, central Italy, are presented. Our work aims at better constraining the evolution of the fracture systems in the studied fault-related fold, which consists of a mechanically heterogeneous geological sequence.

Several exposures, spread homogeneously along the structure and involving two principal mechanical units (i.e., the Scaglia Rossa Formation made of thinly-bedded pelagic limestone and the Calcare Massiccio Formation made of shallow water platform massive limestone), were analyzed in detail.

For each fracture system, the type of fracture, angular relationship with beds, orientation, dimensions, aperture, filling and density distribution along several scan-lines and scan-areas have been characterised and quantified.

Furthermore, laboratory analyses (i.e., calcimetry, XR diffractometry analysis, thin sections) have been done to define the mineralogical composition of the collected samples. Fluid inclusion analysis has been also completed to obtain information about the environmental conditions during inclusion formation.

Our results suggest a conceptual model of fracture nucleation and growth remarkably different for the two formations. Fractures mostly related to flexural slip mechanisms developed in the Scaglia Rossa Formation, whereas the Calcare Massiccio Formation reacted as a massive rigid volume with fracture systems markedly in contrast with the Scaglia Rossa system.

This study shows that the evolution of the Cingoli anticline fracture systems depends not only on the structural position along the fold, but also on the mechanical properties of the rock, the deformation evolution, and folding mechanisms.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.