Simulation of land subsidence due to gas production at Ravenna coastline
P. Teatini, G. Gambolati, L. Tomasi, M. Putti
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
A large number of deep gas reservoirs are scattered both inland and
offshore in the Upper
Adriatic Sea sedimentary basin. Among these gas fields, the Angela
Angelina reservoir is of major concern for the CENAS project
because it is directly overlain by the shoreline extending from
Lido Adriano to Lido di Dante in the Ravenna area.
Angela Angelina is a very complex field consisting of 47
variously shaped pools located at a burial depth ranging between 3000
and 4000 m. The 31 largest pools will be depleted by 2014 with an
ultimate pressure decline that is expected to exceed 300 kg/cm2 in
some pools.
A numerical study of the reservoir compaction and land settlement
expected over
Angela Angelina is performed by a new three-dimensional nonlinear
finite element model. The constitutive
relationship of the most important parameter controlling the event,
i.e. the vertical soil compressibility vs the effective
intergranular stress, is derived from a number of oedometric
tests carried out on samples cored from deep boreholes scattered
throughout the Upper Adriatic Sea basin.
The results predict a final maximum land subsidence due to reservoir
depletion equal to 20 cm over the gas field central area and a
settlement of
12-14 cm on the coastal area directly overlying the reservoir.
An approximate evaluation of the influence of the active waterdrive
surrounding the gas
field is also given. Field measurements of land subsidence occurred
from 1977 to 1992 are shown to be sufficiently in agreement
with the simulated results.
