Residual land subsidence near abandoned gas fields raises concern
over Northern Adriatic coastland
D. Bau', G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
In the last half century many gas fields have been detected
in the Northern Adriatic basin. Gas production started in the early
1950s with some reservoirs depleted as of today and others currently
under production or planned for development in the near future.
One major environmental consequence of gas
withdrawal is land subsidence. This can be a matter of great concern
if the field is located below or close to low lying and densely
urbanized coastal areas where the loss of ground elevation of only a
few centimeters can enhance the ingress of sea water inland and increase
the exposure of the shore to flooding during high tides and severe
storm events.
Contrary to the general belief, rock compaction in response to gas
withdrawal may continue for a long time after the cessation of pumping
due to a dynamically active aquifer surrounding the reservoir where pore
pressure decline keeps on propagating also after the end of the
field production life. In the vicinity of abandoned gas or oil field this
process may produce a ''residual'' delayed land subsidence, an unexpected
event which can prove difficult to relate to the original source.
A numerical study shows that gas production from Dosso degli Angeli, a
major reservoir in the Northern Adriatic basin developed from 1971 to 1992
and later abandoned, may still induce almost 10 cm settlement in the next
50 years, with an adverse impact on the resort coastal area north of Ravenna,
Italy.
