Gas storage in compartmentalized reservoirs: a numerical investigation on
possible "unexpected" fault activation
P. Teatini, M. Ferronato, A. Franceschini, M. Frigo, C. Janna, C. Zoccarato
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Italy
G. Isotton
M3E S.r.l., Padova, Italy
ABSTRACT
Underground gas storage (UGS) is a practice that is becoming widely implemented
to cope with seasonal peaks of gas consumption. When the target reservoir is located
in a faulted basin, a major safety issue concerns the reactivation of pre-existing
faults, possibly inducing (micro-) seismicity. Faults are reactivated when the shear
stress exceeds the limiting acceptable strength. It
has been observed in The Netherlands that this occurrence can happen "unexpectedly"
during the life of a UGS reservoir, i.e. when the actual stress regime is not
expected to reach the failure condition. A numerical analysis by a 3D FE-IE
elasto-plastic geomechanical simulator has been carried out to cast light in this
respect, by investigating the mechanisms and the critical factors
that can be responsible for a fault reactivation during the various stages of UGS
in reservoirs located in the Rotliegend formation.
The model outcomes show that the settings (in terms of reservoir and fault
geometry, geomechanical parameters, and pressure change
distribution) more prone to fault activation during primary production are
also the most critical ones during cushion gas injection and UGS cycles.
