3D geomechanics in UGS projects. A comprehensive study in northern Italy.

The 3D geomechanical response to seasonal gas storage is investigated for a gas field managed by Stogit. The 1200-m deep reservoir is located in the Po basin, Italy, and a UGS program is under way since 1986 following a 5-year primary production life. The use of: i) a basin-scale geomechanical characterization of the Po basin, ii) a detailed knowledge of the subsurface geology made available by 3D seismic surveys, iii) almost 30-year measurements related to the gas field activities, and iv) an advanced PSInSAR analysis providing the vertical and horizontal West-East displacements of the ground surface above the field from 2003 to 2007, has allowed for the development, setup, and calibration of a representative 3D fluid-dynamical model and a transversally isotropic nonlinear geo-mechanical model. The latter successfully reproduces the largest vertical and horizontal seasonal land displacements, on the range of 8-10 mm and 6-8 mm, respectively, as observed above the reservoir. The model is then used to investigate the ground surface displacements in connection with UGS future programs where the maximum overpressure achieved in the field is planned to be raised to 107% pi and 120% pi, with pi the original in-situ pore pressure.