First Results of a Reinjection Experiment at Larderello

Reinjection, which began at Larderello in 1974 as a means of disposing of excess steam condensate, is now envisaged as a method for improving heat recovery. The behavior of the geothermal field when subjected to production and injection is difficult to predict because of the very heterogeneous fractured reservoir. More information is needed on circulation patterns and heat sweeping processes to estimate the long-term behavior of the reservoir and to avoid detrimental effects. A series of reinjection experiments is now under way in different parts of the Larderello reservoir, aimed at improving knowledge o f these points before starting a widescale injection program. This paper presents the results of about one year of injection in an area that has been exploited intensely for over 2 0 years. During this test the following were noted: almost complete vaporization of the injected water; significant production increases and no temperature decrease in the wells around the injector. Introduction Production from the Larderello field, under exploitation for more than 5 0 years, has been kept more or less constant during the last 30 years by drilling new wells. This policy has proved to be less than satisfactory during the last few years because of the large decrease in pressure throughout the field (Fig.l), and in the more productive zones in particular (Ferrara et a1.,1970; Celati et a1.,1977a; Baldi et a1.,1980). The success of the new wells is tied to the possibility, still to be verified, of recovering fluids from zones outside the present margins of the field and from deep horizons of the reservoir (more than 2 km depth).