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Sulcis site characterization for the construction of a test site for CO2 injection

The deep aquifer located at a depth of about 1000-1500 m within fractured carbonate in the Sulcis coal basin constitutes a potential reservoir for the development of a pilot-scale CO2 storage site. In order to select the location to host a pilot plant (test site) for CO2 storage tests, several geologic investigations have been performed in the area of the “Monte Ulmus” Mining Permit.

Structural surveys, both surface and underground in the “Nuraxi Figus” coal mine, have been performed in order to evaluate caprock integrity and the available potential carbon storage volume of the reservoir. In parallel, the results of seismic reflection surveys made it possible to outline the underground stratigraphic and structural framework. Tests performed on core samples of the formations of interest led to the petrographic, hydraulic and geophysical characterization of the rock formations of the caprock-reservoir system. Moreover, a seismic temporary station network led to the seismic baseline definition in the studied area. A hydrogeologic study defined the hydrogeologic framework and highlighted interchanges between superficial water and underground water circulating in fissured rocks.

Well water sampling and analysis by ion chromatography led to the recognition of hydrogeochemical facies and the detection of trace elements such as bromine and lithium, a clue to hydrotermalism. In parallel, some wells in the area have been sampled to analyse the main and trace gaseous species to determine the geochemical baseline. In some of the wells in the area of interest, continuous monitoring probes have been installed to detect and record the water’s temporal variations of dissolved CO2, temperature, pH and CH4.

Since the first year of the project, the natural seismicity has been monitored, in order to define the background seismicity of the area. The south-western sector of Sardinia is characterized by both low instrumental and historical seismicity.