West Macedonia water sampling campaign with chemical analysis including isotopes, helium, methane and hydrogen as part of the Pilot Strategy Horizon2020 project

Previous field investigations under the PilotSTRATEGY project on CO₂ storage identified promising seal rocks but failed to confirm the presence of suitable reservoir rocks. To address this knowledge gap, water sampling campaigns were conducted in areas with elevated natural gas emissions as a proxy to detect subsurface formations with potential reservoir properties. Although the sampled formations are themselves unsuitable for CO₂ storage due to leakage, they provide valuable analogues. By identifying these leaky units, geologists can better recognize similar, yet properly confined, formations in the region that may offer secure CO₂ storage potential.

Field observations, including anecdotal evidence, some publicly shared via platforms such as YouTube coupled with visible indications of gas-rich springs, guided site selection. The local geology was assessed, leading to the conclusion that the investigated springs are suitable candidates for preliminary exploration.

Four water sampling campaigns were subsequently carried out. Field measurements included pH, dissolved oxygen (mg/L), conductivity (μS/cm), and temperature (°C). Laboratory analyses comprised ICP elemental analysis and the detection of key gases and isotopes, including:

• He, H₂, CH₄, CO₂

• Helium isotopes (³He, ⁴He)

• Deuterium in hydrogen (δ²H-H₂), methane (δ²H-CH₄), and water (δ²H-H₂O)

• Oxygen-18 in carbon dioxide (δ¹⁸O-CO₂) and water (δ¹⁸O-H₂O)

• Carbon-13 in methane (δ¹³C-CH₄), carbon dioxide (δ¹³C-CO₂), and dissolved inorganic carbon (δ¹³C-DIC)

• Carbon-14 in dissolved inorganic carbon (¹⁴C-DIC)

The results confirmed the presence of methane (CH₄), hydrogen (H₂), helium (He), and carbon dioxide (CO₂), indicating active gas migration and suggesting a potential link with deeper geological formations.