In the most cases, the numerical simulation is the only approach that allows to assess the behavior of a geological reservoir when it is interested by the injection or extraction of fluids both with storage and energy production purposes, accounting for the effects of fluid dynamics, rock mechanics and chemical interactions in the short, medium and long period. The SIAM (Integrated System for Modeling Analysis), realized in RSE in the frame of the RdS projects funded by the Ministry of the Economic Development, is an integrated modular system, available for the most common calculation platforms and equipped with an interactive interface, that can be used for studies in the frame of the CO2 geological storage and for analyses involving geological reservoirs as for the geothermal energy production, natural gas storage and CAES applications.As a matter of fact, SIAM allows to perform all the analysis tasks required for the characterization of a complex geological site as the 3D geological modeling, the storage capacity evaluation, the simulation of different injection/extraction scenarios, the check of the reservoir safety and the simulation of seismic monitoring results. The system can be managed by means of a graphic interactive interface properly realized, that allows the use time by time of the modules devoted to calculations and pre and post processing of data in a workflow automatically linked, so the user is led to perform a correct analysis procedure. SIAM has been developed with criteria of maximum portability and modularity, using OpenSource languages and tools. SIAM also offers interface for importing the 3D geological models realized with the support of Petrel software platform realized by Schlumberger. At first, SIAM has been used to study CO2storage both in sandstone and carbonate reservoirs, in a lot of different geological complex situations, often faulted, with presence of anticline, syncline and heterogeneities, simulating the evolution in time and space of the CO2 behavior, considering both horizontal and vertical wells also in a multiple configuration, and finally treating also the safety aspects. Some examples regarding both on-shore and off-shore reservoirs are presented with the injection scenarios realized. Currently, SIAM is used to investigate the aspects involved in the energy production from geothermal reservoirs. A simple study case designed to analyze the phenomena connected to the hydraulic fracturing in heat rocks is presented.