The use of gas chemistry and isotope geothermometry to study the effects of exploitation and reinjection on the fluids at Larderello, Italy

Isotopic and chemical analyses of the steam and gas from producing wells since exploration until 1992, were used to define the effects of the exploitation and reinjection of waste fluids. Maps showing zonations of the isotopic composition of the steam and chemical concentrations of the gas mixtures in the Larderello geothermal system are derived independently. Inspection of the maps obtained before and after reinjection reveals good discrimination between the natural inflow of meteroic water subsequent to exploitation and of man-made recharge using waste fluids. Chemical variations of Ar appear to be a valuable tool for evaluating a recovery factor of reinjected water. Isotopic variations in H2, CH4 and CO2 are used to describe disequilibrium conditions between gas components induced by the establishment of a liquid plume at the production zone of the reservoir. (author). 12 refs, 14 figs, 1 tab