Can gas withdrawal from Chioggia
Mare field affect the stability of the Venetian littoral?
D. Bau', G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
A major threat to the environment as well as the economy of the Upper Adriatic
coastal area is the anthropogenic land subsidence expected to occur from the
prospective development of 15 gas fields recently discovered by ENI-AGIP,
the Italian national oil company, north of the Po river delta in the Adriatic Sea.
To evaluate the consequences of gas production on the shoreline stability, and to
assist the Minister of Environment in making a decision on the sustainability of
the programme, a three-dimensional finite element (FE) model is developed for the
simulation of Chioggia Mare, the largest reservoir in the area and the nearest to
the Venetian littoral. Located at a depth of burial between 1000 and 1400 m in
lower Pleistocene sedimentary rocks, Chioggia Mare is planned to produce
5·109 Sm3 of methane during the 13 year production life with
a maximum pore pressure drawdown amounting to as much as 80 kg/cm2 in
the deepest pools. The model accurately accounts for the high geological
complexity of the field, the extensive lateral/bottom aquifer (waterdrive) and the
elasto-plastic deformation of the depleted sands based on in situ compaction
measurements obtained with the aid of the marker technique. The prediction is
extended over 12 years after the wells shutdown and is performed under a variety
of parametric scenarios intended to adequately address the parameter uncertainty.
The results from the FE analysis show that under the most pessimistic assumptions
the city of Chioggia may subside by 1 cm in 25 years while Venice turns out to be
unaffected by a measurable settlement. If the waterdrive depletion is contrasted
by two water injection wells drilled between the shoreline and the westernmost
point of the reservoir the 1 cm land subsidence isoline moves 5 km offshore with
Chioggia expected to rise by about 0.5 cm.
