Environmental management of land subsidence: Compaction evaluation through radioactive marker technique

Subsidence is a key issue in managing the production of underground fluids, especially in environmentally sensitive areas. This is the case of the Italian Adriatic offshore in front of the historical city of Venice, where several gas fields have been recently discovered. Here, the alleged risks connected with possible land subsidence and coastal impairment are crucial for releasing the authorizations to start a development project. In order to probe such risks, it has been utilized the Radioactive Marker Technique (RMT), nowadays a quite developed method to measure reservoir rock compaction of deep formations, by which it is possible to estimate the uniaxial compressibility coefficients (C m). As it is well known, C m is the chief geomechanical parameter influencing compaction phenomena, and thus its evaluation is vital for subsidence predictions by means of mathematical modeling. Generally, C m can be evaluated by both in-situ and laboratory measurements. Recent field applications seems to confirm that RMT-derivcd C m's match with sufficient precision with the ones calculated from the surface subsidence observed over the field by means of surveys (levelling, GPS, SAR), but are not always in good agreement with laboratory measurements. The present study reports some field applications of RMT in the Italian Adriatic offshore, which confirm that C m's from laboratory measurements are overestimated with respect to the ones obtained by RMT.