Numerical models of anthropic land subsidence due to gas and
groundwater withdrawals
G. Gambolati, M. Putti, P. Teatini, D. Bau'
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
We develop a set of mathematical models which are suited to simulate land
subsidence of anthropogenetic origin in the area underlying the coast of
the upper Adriatic Sea.
Land subsidence due to groundwater withdrawals from the most recent
Quaternary sediments is simulated by the use of two separate models.
The first model is a multi-layer model of flow within interconnected
aquifer and aquitard units of a sedimentary basin in response to an
assumed pumping plan.
Flow occurs horizontally in the aquifers and vertically in the
intervening aquitards and is fully coupled.
The hydrological model is primarily used on a regional or sub-regional
scale to provide the evolution of the groundwater contour profiles.
The land subsidence model is a vertical compaction model at selected
sites which makes use of the head decline predicted by the hydrologic
model.
By distinction, the model developed to simulate land settlement over the
gas fields underlying the coastline in the Ravenna area is a structural
model where the pore pressure decline is specified as a strength source
according to the general theory of poroelasticity.
The model addresses a fully 3-D environment with a gas field made of
several pools of arbitrary shape.
A fundamental solution for each pool is first calculated using an
axi-symmetric finite element model with the actual vertical soil
compressibility as was observed in the Ravenna area and mathematically
elaborated by the Commission for the Study of the Ravenna Subsidence
under the form of a constitutive relationship vs sediment depth.
The fundamental solutions are then introduced into integrals which are
performed over the volume of the reservoir.
The application of the model to the selected gas field to Angela-Angelina
is outlined.
