Land subsidence spreading factor of the Northern Adriatic gas fields, Italy
D. Bau', M. Ferronato, G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
The land subsidence spreading factor X provides a useful
straightforward indication on how much of a gas/oil reservoir
compaction induced by field development migrates to ground surface
with a possible adverse impact on the stability of low-lying coastal
areas. This factor depends primarily on the ratio between the depth of
burial and a representative horizontal dimension of the
reservoir. However, an important influence is also exerted by the
active bottom/lateral aquifer hydraulically connected to the field (called
''waterdrive'' in reservoir engineering) which may undergo an
extensive depressurization also after the field abandonment, thus
contributing to enhance the overall land settlement. In the Northern
Adriatic basin, Italy, X is evaluated using a nonlinear finite element
model of three representative gas reservoirs (Chioggia Mare,
Dorotea and Dosso degli Angeli) surrounded by important
bottom/lateral aquifers in the interval depth between 1000 and
3300 m. Results show that X may easily approach and even
exceed one for the deepest field as well, contrary to the
prediction of land subsidence based on the compaction of the gas-bearing
formations alone, that can thus be largely underestimated.
