3D multi-scale characterization and modeling of three fractured carbonatic outcrop analogues: Pag Croatia, Parmelan France, Gozo Maltese Islands

OBJECTIVES: To select the "best outcrop analogue" of a subsurface field/prospect is always challenging, especially when dealing with fractured carbonatic reservoirs. The candidate should match the mechanical stratigraphy, the depositional conditions, the diagenetic history, the tectonic evolution. This is almost impossible, considering that at least the exhumation phase and the associated diagenetic features will not be shared between the outcropping analogue and the buried reservoir. Nevertheless, the analysis of natural analogues can provide useful indications particularly in a complex matter as fracture distribution; in fact, large-scale outcrop analogues reveal their potential when trying to fill the gap between seismic- and borehole-scale structural characterization. METHODS, PROCEDURES, PROCESSES: In order to start building an "Atlas of Fracturing Facies" as a digital interactive catalogue of natural fractured analogues, three main cases have been studied: Pag (Croatia) and Parmelan (France) anticlines as analogues for folded and faulted platform carbonates affected by pre-folding extensional faulting, and the Gozo Island (Maltese Archipelago) as an example of carbonatic sequences affected by extensional tectonics. An integrated multiscale approach has been applied, from thin sections to outcrop scale analysis, from drone-based surveys to satellite image interpretation. This workflow leads to the reconstruction of 3D models, and to the quantification of the main parameters characterizing the fracture pattern and its variability. RESULTS, OBSERVATIONS, CONCLUSIONS: The Island of Pag, External Dinarides of Croatia, is a thrust-related anticline that involves Upper Cretaceous to Eocene shallow-water carbonate platform sequences affected by tight folding during Eocene - Oligocene times. The fold evolution is multiphase, expressed by pre-folding features developed during a layer-parallel shortening with a strong influence of structural inheritance, followed by fold- and thrust-related cataclastic flow in hinge zones. The Parmelan Anticline, in the Bornes Massif, Western Alps, is a box-fold involving Lower Cretaceous massive platform carbonates. It is characterized by steeply-dipping limbs, separated by a wide crestal plateau, delimited by narrow hinge zones localized on inherited extensional faults. Its polyphasic tectonic history has been reconstructed by analyzing the fracture and vein pattern, which highlighted the strong influence of structural inheritance during folding. The Gozo Island is a Late Oligocene-Late miocene carbonatic sequence, composed by platform carbonates with different facies, affected by two extensional events associated to a mult-sets fracture pattern. In Gozo, spectacular coastal outcrops allowed analyzing the structural and statistical relationships between fractures and faults, in terms of density, length, orientation, spatial distribution patterns, and topology. NOVEL/ADDITIVE INFORMATION: The Pag, Parmelan and Gozo case studies, together with several literature case studies, are the starting point of the implementation of an Atlas of Fracturing Facies, providing a multidisciplinary knowledge management and data repository platform to improve the prediction of fracture patterns in the subsurface, and its impact on porosity and permeability in reservoirs.