Search

This paper presents an investigation of naturallyoccurring CO2 emissions from the Florina natural analoguesite in Greece. The main objective was to interpretpreviously collected depth sounding data, convert theminto surfaces, and use them as input to develop, for thefirst time, 3D geological models of the Florina basin. Byalso locating the extent of the aquifer, the location of theCO2 source, the location of other natural CO2 accumulations,and the points where CO2 reaches the surface, wewere able to assess the potential for CO2 leakage. Geologicalmodels provided an estimate of the lithological compositionof the Florina Basin and allowed us to determinepossible directions of groundwater flow and pathways ofCO2 flow throughout the basin.Important modelling parameters included the spatial positionsof boundaries, faults, and major stratigraphic units(which were subdivided into layers of cells). We used variousfunctions in Petrel software to first construct a structuralmodel describing the main rock boundaries.We thendefined a 3D mesh honouring the structural model, andfinally we populated each cell in the mesh with geologicproperties, such as rock type and relative permeability.According to the models, the thickest deposits are locatedaround Mesochorion village where we estimate thataround 1000 m of sediments were deposited above thebasement. Initiation of CO2 flow at Florina Basin couldhave taken place between 6.5 Ma and 1.8 Ma ago. The NESWoriented faults, which acted as fluid flow pathways,are still functioning today, allowing for localised leakageat the surface. CO2 leakage may be spatially variable andepisodic in rate. The episodicity can be linked to the timingof Almopia volcanic activity in the area.

Natural CO2 fields can be used to identify trapping mechanisms, the fate and the geochemical consequences of geologically stored CO2 in shallow aquifers. The Florina Basin in Greece is regarded as a CO2 naturally leaking analog due to millions of years of gas accumulation in a Tertiary sand formation. This research was conducted in order to identify the CO2 fingerprints and to investigate and evaluate the factors controlling the groundwater quality in the basin. Leaking CO2 is observed in the aquifers and at the surface. The basin is filled with clastic sediments. It can provide information regarding the fate of CO2 and the possible impacts that can be used as reference in demonstration and industrial projects. Water sampling campaigns were conducted to determine the impact of the gas-water long-term interactions in the shallow aquifers. The CO2 has increased the concentration (in relation to other water samples from the basin) of certain elements like Fe, Mn, Na, Cl, and Br but only in few cases exceeds the EU drinking limit. The chemistry of the groundwater in the Florina Basin aquifers was found to be controlled mainly by the CO2-water-rock interactions due to the mineralogy of the aquifers (calcite and silicates including pyroxenes and chlorite). Metal attenuation processes have prevented the aquifers from brine contamination. Considering the Florina Basin is a natural analog for studying the leaking and migration pathways of stored CO2 and that only minor affects have been identified in the groundwater chemistry, the conclusions of this research are promising for the possible usage of a basin of similar geology and lithology for deep CO2 storage. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]