Study of the gas migration mechanism in the natural laboratories for the characterisation and monitoring of CO2 geological storage sites

The greenhouse gas effect and the global warning phenomenon are largely discussed by scientific community and government and, in the next years, a number of actions focused on the reduction of the greenhouse gases emissions have to be finalised. The reduction of greenhouse gas emissions can be achieved in several ways but probably, at the short/mid-term, the only way with an acceptable cost/benefit ratio is to avoid the CO2 emission from the fossil fuel power plant and, in parallel, strongly develop the renewable energies. A really interesting option for the reduction of CO2 emissions is CCS (CO2 capture and storage). This technique consists of capturing CO2 from power and industrial activities and storing it in deep geological reservoirs having different geological traps. The potential effectiveness of CCS is the reduction of 15% of the emission by 2050. A critical component of long term geological sequestration of anthropogenic CO2 will be our ability to adequately monitor a chosen site to ensure public and environmental safety. Near surface monitoring is particularly important, as it is possible to conduct sensitive and direct measurements at the boundary between the subsurface and the biosphere (i.e. surface water or atmosphere). In this work different aspects of direct gas measurements for the control and monitoring of CO2 storage sites were undertaken. In particular: i. the study of some fault systems at the Latera caldera allowed a better understanding of the gas migration mechanisms; ii. soil gas surveys carried out at “Concessione mineraria Monte Sinni” and at Kaniow allowed baseline characterization and the test of this approach for the discontinuous post injection monitoring; iii. the design and development of an innovative and low cost monitoring system that can make possible the use of direct geochemical methods of measurement where the currently required costs make them unsuitable. The obtained results seem to confirm the potent of the geochemical approach, both in terms of sensitivity and cost/benefit ratio. In fact the discontinuous monitoring applied at Kaniow defined micro-leaks close to the injection site and the monitoring system tested at Panarea Island successfully worked highlighting a good sensitivity and repeatability of the measures. Finally, in the framework of the CCS activities, it is important to consider the importance of the “public acceptance” of this process. In this regards, although a number of well-tested (i.e. in the oil exploration), indirect geophysical monitoring techniques can be used, the monitoring of the storage site by direct geochemical measurements in the near-surface environment can provide a clearer observation phenomenon and can be easier understood and accepted by local stakeholders.