Fracture distribution in the Mt. Catria anticline, Northern Apennines: from the field analogue to numerical predictions in reservoirs.

Thrust-tip folding has been recognised as a common mechanism developing at the toe of fold and thrust belts, that provide well known plays in hydrocarbon exploration. In such structural traps, fluid migration and accumulation is strongly controlled by fracture distributions and play a fundamental role on reservoir performance. Fracture patterns in thrust-tip anticlines relate to both the fold kinematics and the mechanical stratigraphy of the deformed multilayer. Understanding these relationships strongly contributes to the implementation of fracture predictive tools of folding-related structures.The Mt. Catria anticline (Northern Apennines, Italy) is about 6km wide and provides a well exposed natural analogue to investigate the relationships among mechanical stratigraphy, folding mechanism, and fractures development and distribution. A series of fieldwork campaign allowed the preparation of a geological, evolutionary model. This revealed that the anticline initially grew by the concomitant activity of a conjugate thrust pair, in a pop-up like fashion. In the late stage of folding, the frontal part of the structure was translated onto the foreland along a major forethrust and underwent further deformation by fault-bend folding. A detailed structural study was carried out to characterise fracture variability across the fold strike and from different formations in the same fold sector. The statistical analysis of normalised fracture spacing as a function of rock type and layering, indicates a correlation with the structural positions within the anticline, thus supporting a folding related origin. A balanced cross-section of the Monte Catria anticline was forward modelled using the HCA numerical technique, implemented in the FORC 2 software. Outputs of this tool include the spatial distribution of the stress-time integral across the modelled structure that correlates to the deformation intensity. The availability of the complete information on fracture distribution in the modelled cross-section, allowed the conversion of stress-time integral values into fracture type, orientation, and spacing values. These relationships between numerical predictions and natural fracture data impact on hydrocarbon exploration. In fact, they allow to make quantitative fracturing predictions in prospect anticlines developed in the same stratigraphical succession, once depth-converted geoseismic cross-sections are numerically modelled.