Numerical prediction of land
subsidence over Dosso degli Angeli gas field, Ravenna, Italy
G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
W. Bertoni
Geologic Service, Municipality of Ravenna, Ravenna, Italy
ABSTRACT
Over the past 40 years the Ravenna area has experienced a widespread
land sinking due to both groundwater and gas withdrawal with a severe
impact on the coastal environment.
One of the major coastal gas fields is Dosso degli Angeli.
With a depth of burial close to 3000 m and a productive life started
in 1971, the pore pressure drawdown amounted to almost
300 kg/cm2 in 1992 at the reservoir depletion.
A numerical study of the land settlement that occurred over Dosso degli Angeli has
been performed using a linear 3-D finite element model with mechanical
soil properties which vary with depth by more than two orders of magnitude.
The influence of an active lateral waterdrive has been included as well.
The results point out a significant final land
settlement over the reservoir with a maximum value equal to 1 m, of which
0.45 m appears to have been contributed by the compaction of the waterdrive.
The outcome is to be viewed as a preliminary one since the reservoir
compressibility has been kept constant over the very large variation
experienced by the in situ effective stress and the lateral
aquifer has been assumed to
have infinite areal extent in all directions, with a perfect hydraulic
connection with the reservoir.
