Environmental Engineering Reference
In-Depth Information
Figure 7.10.
Isotropic compression of a limestone at different
degrees of saturation [BRI 95]
We now consider the gas fields in the Northern Adriatic Basin in Italy (see
Figure 5.1 of Chapter 5 and Figure 7.11) in general and then one field in particular,
the Ravenna Terra [AGI 96]. The reservoirs are made of weakly consolidated sands
that show no detectable traces of cementing material, neither of a calcareous type,
nor of a siliceous type [MOR 94]. This fact rules out dissolution as a possible source
of reservoir compaction. The sandy reservoirs, from which gas is produced, have
porosities from 10-40%. The degree of water saturation varies between 35 and 65%.
Hence the reservoirs are in the capillary range described above. The existence of
capillary pressures, the nature of the soils involved and the fact that reservoir sands
are weakly consolidated suggest the possibility of collapsible behavior occurring
when the degree of saturation increases (and suction reduces) during the relevant
phases of gas production and reservoir pressure recovery.
Figure 7.11.
Location of the gas field in the region around
the city of Ravenna [GAM 91]
