Numerical modelling of regional faults in land subsidence prediction above
gas/oil reservoirs
M. Ferronato, G. Gambolati, C. Janna, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
The stress variation induced by gas/oil production may activate pre-existing
regional faults. This may enhance the expected land subsidence due to the
generation of mechanically weak points close to the
producing field. A class of elasto-plastic interface elements (IE), specifically
designed to address the mechanical behaviour of faults over a regional scale,
is integrated into a finite element (FE) geomechanical
model and used to investigate the role exerted by active faults in
anthropogenic land subsidence. The importance of regional faults depends on a
variety of factors including depth of the depleted reservoir,
fault number, orientation and size, geomechanical properties of porous medium,
pore pressure drawdown induced by fluid production, etc. With the aid of some
representative examples, a useful indication is
provided as to where and how fault activation may influence both magnitude and
extent of the land subsidence bowl above producing gas/oil reservoirs, pointing
to a generally limited impact on the ground
surface. The simulation of a real faulted gas reservoir in a complex 3-D setting
shows that the proposed IE can be simply and efficiently incorporated into a FE
geomechanical model, thus improving the quality
of the stress and displacement prediction.
