Interpreting Ground Deformation and Microgravity Changes in the Travale-Radicondoli Geothermal Field (Italy)

Abstract

Since 1973, when industrial exploitation of the Travale Radicondoli geothermal field started, ground vertical movements have been monitored by means of precise topographic levelling. Up-to-date methods have also been applied (EDM, and GPS).
The elevation changes, detected so far are rather modest and show a regular temporal trend, so that it is possible to make a precise determination and interpretation of the subsidence that has occurred.
Right in the small central area of the field, which has been the most productive for many years, the maximum subsidence rate exceeds 1 cm per year. This can be interpreted as the result of pressure depletion related to poorly connected reservoirs located at different depths. These reservoirs have different rates of pressure stabilisation depending on their exploitation history.
Since 1979, micro gravity changes have also been monitored by a network of permanent bases that coincide with selected topographic benchmarks used for subsidence monitoring.
The gravity changes, corrected for elevation change effects, are very small and show flat trends. This allows us to make some interesting evaluations in terms of mass balance and is encouraging as regards the sustainability of geothermal production in time.
The on-going monitoring results indicate that the effects on the environment are negligible, which should help in overcoming any resistance on the part of the local community and convince them of the benefits of geothermal development for the region.