3D quantitative microstructural analysis of deformation bands in sandstones and their role as regulators of fluids migration in field analogues: a potential support for reservoir geology characterization

Our aim was to investigate the fabric of quartz-rich sandstones of Numidian Flysch outcropping in central Sicily (Italy). In particular, our main goal was to infer microstructural data such as pore and clasts grainsizes to gain information useful to model permeability and fluid migration by considering such sandstones as a potential fluids reservoir. Recognition of different constituting phases and their volumetric size distribution in different portions of the same rock, which are characterized by a variety of compaction states, are then crucial constraints to further develop models for analogue reservoirs. The microtomography analyses made on sandstone specimens, characterized by the occurrence of diffuse deformation bands, provided very detailed 3D information about pores and clasts (volumetric distribution, grain sizes, phase interconnectivity) which was not possible to obtain by means of other techniques. Moreover, the peculiar aggregation state of such sandstones, often poorly cemented, had not permitted the use of classical porosimetric laboratory tests, because during specimen preparation procedure rocks easily were broken. Preliminary results highlighted how such samples consist essentially of three main portions distinguishable thanks to the adopted technique: - undeformed portion with bigger pores, larger quartz grains and high iron-oxides concentration; - deformed portion with smaller pores with respect the previous one without Fe-oxides minerals; - deformed portion with pore sizes similar to the undeformed part and high iron oxides concentration. Further investigations and 3D data rendering elaborations, which are still in progress, will allow us to formulate realistic models about fluid migration within such rocks.