Analysis of tectonic related fractures in Jurassic and Cretaceous Formations in the Sibillini Mountains, Italy

Abstract

Secondary permeability created by fractures is an interesting property regarding reservoir purposes. In the Umbria-Marche Apennines these fractures have been digitized using software named Digifract. The goal of this research is to correlate these fractures to the lithology, and their relative position regarding the two main structures found in the area; the Sibillini thrust and the Fiastrone anticline. The lithology found in this area consists out of Mesozoic carbonate formations, which in some cases contain marls and cherts, and a siliciclastic turbidite formation. Digifract is used to quantify and analyze fractures determining the fracture length, fracture density, fracture orientation. When present, cherts and marls act as fracture boundaries in the carbonate formations. When present in the siliciclastic turbidite formation, shale layers prevent the fractures from propagating. The fracture density in the formations increases as the bedding thickness decreases. Mainly because of their relative small bedding thicknesses the Maiolica Fm and the Scaglia Rossa Fm have the largest fracture density. The Laga Fm and the Calcare Massiccio Fm have the largest fracture lengths. In the footwall of the Sibillini thrust a distinction can be made between a fault-controlled fracture zone and a fracture zone controlled by other stresses. The boundary between these zones in the footwall can be found between 150 and 225 meters. On the crest of the Fiastrone anticline the largest fracture density can be found regarding this structure, whereas the greatest fracture length is to be found on the limbs of the anticline.