Geomechanical response to seasonal gas storage in depleted reservoirs: A case study in the Po River basin, Italy

Abstract

[1] Underground gas storage (UGS) in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand and occurs in many places in Europe and North America. In response to summer gas injection and winter gas withdrawal the reservoir expands and contracts essentially elastically as a major consequence of the fluid (gas and water) pore pressure fluctuations. Depending on a number of factors, including the reservoir burial depth, the difference between the largest and the smallest gas pore pressure, and the geomechanical properties of the injected formation and the overburden, the porous medium overlying the reservoir is subject to three-dimensional deformation with the related cyclic motion of the land surface being both vertical and horizontal. We present a methodology to evaluate the environmental impact of underground gas storage and sequestration from the geomechanical perspective, particularly in relation to the ground surface displacements. Long-term records of injected and removed gas volume and fluid pore pressure in the "Lombardia" gas field, northern Italy, are available together with multiyear detection of vertical and horizontal west-east displacement of the land surface above the reservoir by an advanced permanent scatterer interferometric synthetic aperture radar (PSInSAR) analysis. These data have been used to calibrate a 3-D fluid-dynamic model and develop a 3-D transversally isotropic geomechanical model. The latter has been successfully implemented and used to reproduce the vertical and horizontal cyclic displacements, on the range of 8-10 mm and 6-8 mm, respectively, measured between 2003 and 2007 above the reservoir where a UGS program has been underway by Stogit-Eni S.p.A. since 1986 following a 5 year field production life. Because of the great economical interest to increase the working gas volume as much as possible, the model addresses two UGS scenarios where the gas pore overpressure is pushed from the current 103%p i , where p i is the gas pore pressure prior to the field development, to 107%p i and 120%p i . Results of both scenarios show that there is a negligible impact on the ground surface, with deformation gradients that remain well below the most restrictive admissible limits for the civil structures and infrastructures. Citation: Teatini, P., et al. (2011), Geomechanical response to seasonal gas storage in depleted reservoirs: A case study in the Po River basin, Italy,

Efficient global optimization of reservoir geomechanical parameters based on synthetic aperture radar-derived ground displacements

“…Equation 2 is solved numerically by FEs using the code GEPS3D (Geomechanical Elasto-Plastic 3D Simulator developed at the University of Padova), which follows the infinite pore pressure gradient formulation (Gambolati et al, 2001). GEPS3D has been successfully used in several geomechanical applications over the past few years (Teatini et al, 2000(Teatini et al, , 2011Ferronato et al, 2003;Janna et al, 2012;Castelletto et al, 2013). An advanced block factored sparse approximate inverse with incomplete LU factorization preconditioner (Janna et al, 2010) is implemented in GEPS3D to effectively solve on parallel supercomputers the typically large linear systems arising from FE implementation.…”

“…The consequent adjustment of the stress field and the volumetric deformation of the geologic formations can reactivate faults located in the surroundings of the reservoir (Trugman et al, 2014), induce seismic events (Lei et al, 2013), produce localized ground ruptures (Li et al, 2000), land subsidence (Fielding et al, 1998;Motagh et al, 2008;Chang et al, 2014), or uplift (Vasco et al, 2010;Teatini et al, 2011). Thus, reservoir management raises serious concerns in terms of human health, safety of structures and infrastructures, economic risks, and environmental and hydrologic impact (Morton et al, 2006).…”

“…Advanced 3D viscoelastoplastic models have been used to reproduce the geomechanical behavior of complex, multipool, faulted reservoirs worldwide (Ferronato et al, 2003;Vasco et al, 2010;Teatini et al, 2011;Castelletto et al, 2013;Rinaldi and Rutqvist, 2013). Despite significative developments, model reliability in predicting localized (e.g., along fault systems) and/or distributed (e.g., land subsidence) deformations of subsurface systems due to change in pore pressure is hampered by large uncertainties in model parameters.…”

Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO2could leak

“…CO 2 storage in depleted gas fields has also been proven to be a safe option both at Otway, Australia (6) and at Lacq, France (5,8). Actually, CO 2 storage operates under conditions similar to natural gas storage, which has not induced felt seismicity for decades (10)(11)(12). The recent induced seismic events at Castor, Spain (13) appears to be the only exception.…”

On the importance of the heterogeneity assumption in the characterization of reservoir geomechanical properties

“…Teatini et al (2011) used these type of measurements to calibrate a finite element (FE) transversely isotropic model to simulate the behaviour of an underground gas storage (UGS) reservoir in Italy. The methodology provided an indirect estimate of the c M in loading/reloading conditions.…”