enhanced oil recovery CO2 chemical conversion CO2 emission sources CO2 storage CO2 utilization CO2 utilization options Carbon capture Carbon capture and storage Gravity survey Histria Old Danube Romanian Subcarpathian bend region UAV acoustic impedance ancient cities biological conversion transformations of CO2 captured CO2 utilization critical points dioxide carbon fluvial islet frequency modulation geology in-depth investigations magnetic anomalies magnetic method magnetic susceptibility modelling monitoring morphologic changes necropolis oil fields orthophotomap photogrammetry protonic magnetometer reservoir characterization rezistivity survey salt cavern site selection thermoremanent magnetization tumulus utilization and storage vertical resolution well correlation