A numerical modeling approach to investigate the safety aspects of the gas storage in a deep geological reservoir

The natural gas storage in underground structures, known as geological reservoirs, plays a key role in the Italian energy system. The gas storage satisfies several needs such as responding to the gas market demands, ensuring wide margins in the management of production facilities and transport nets and ensuring the maintenance of strategic reserves that are used exclusively to deal with exceptional situations. The numerical modeling is the only approach that allows preliminary analyses of operating scenarios and the assessment of the safety requirements connected to industrial process related to the natural gas production and storage. The methodology developed in order to characterize gas storage sites and to simulate the related fluid dynamic behaviours was documented by a test case application focused on the Sergnano site, located in Lombardia Region (Italy). The methodology pointed out for the site characterization includes the geological information collection, the creation of a static geological model and then the realization of a corresponding 3D fluid dynamic model. In the shown case, the geological reservoir is located in the conglomerate formation known as Sergnano Gravel while the caprock is identified in the overlying clay formation known as Santerno Clay. For this site, an accurate 3D numerical model, including geological and spatial discretisation, has been realized using GeoSIAM software system which allows to simulate the original conditions of the reservoir at the time of the discovery and to reproduce the industrial storage process, also taking into account the effect of the natural gas production and storage cycles on the geological structure. The results confirmed the goodness of the methodology based on the GeoSIAM system in terms of accuracy and reliability and its fundamental role to support sustainability analyses of geological gas storage.