The importance of poro-elastic coupling in dynamically active aquifers of the
Po river basin, Italy
G. Gambolati, P. Teatini, D. Bau', M. Ferronato
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
Uncoupling between the flow field and the stress field in pumped
aquifers is the basis of the classical groundwater hydrology.
Recently some authors have disputed the assumption of uncoupling with
regards to both fluid dynamics and porous medium deformation.
The issue is very important as it could undermine the traditional
approach to simulate subsurface flow, analyze pumping tests and
predict land subsidence caused by fluid withdrawal.
The present paper addresses the problem of coupling vs uncoupling in the
Po river plain, a normally consolidated and normally pressurized basin
which has experienced in the last 50 years a pronounced pore pressure
drawdown because of water and gas removal, and where a large
hydromechanical database is available from the ground surface down to
4000 m depth.
A numerical study is performed which shows that the
matrix which relates flow to stress is very similar to the capacity
matrix of the uncoupled flow equation.
A comparison of results obtained with the finite element integration of
the coupled and uncoupled models indicates that pore pressure is
rather insensitive to coupling anywhere within the pumped formation
while in the adjacent aquitard-aquifer units coupling induces a slight
overpressure which quickly dissipates in time with a small initial
influence on medium deformation, and specifically on land subsidence.
As a major consequence the uncoupled solutions to the fluid dynamic and
the structural problems appear to be fully warranted on any time scale
of practical interest in a typical normally consolidated and pressurized basin.
