Impact of land subsidence due to residual gas production on surficial infrastructures: The Dosso degli Angeli field study (Ravenna, Northern Italy)

The Dosso degli Angell reservoir is located along the coast of the Adriatic Sea, approximately 20 km north of Ravenna, Italy, in the nearby of the Comacchio Lagoons. The field was discovered in 1968 and the production started in 1971. The production strongly decreased from 1998 to 2004 and suspended in 2004. In 2012 Eni, the oil company managing the reservoir, has planned to complete the exploitation of the residual reserves over the period from 2013 to 2023. An elasto-plastic FE model provided by Eni was used to measure the expected residual land subsidence, whose maximum value will amount to 2.8 cm. In this work the environmental impact assessment of the expected land subsidence has been quantified on the lowlying coastland above the reservoir. Initially, the subsidence map has been used to quantify the displacement gradient xi in correspondence of sensitive structures (bridges, pumping stations, lagoon embankments, historical buildings, power plants and a power lines) in order to assess the possible damages. Because the maximum xi value amount to 1 x 10(-5), i.e. 1 mm over 100 m, no damage is expected to the structures. Moreover, hydrological (HEC-HMS) and hydraulic (HEC-RAS) models have been used to evaluate the possible effects of the land subsidence on the efficiency of the main drainage networks used to keep dry the area, which is mainly located below the mean sea level. The results have shown a negligible loss of efficiency of the drainage system. The study allows concluding that land subsidence due to the residual gas production from the Dosso degli Angeli reservoir will not affects the environment, hydraulic safety, and infrastructures of the Comacchio Lagoons and the lowlying coastland surrounding this precious natural environment.