In order to discuss the interferences between an existing geothermal reservoir and reservoir to be developed, reservoir evaluations for a complex model were carried out, changing some of the parameters of the reservoir and the aquifer, and the conditions of production and reinjection. From the results, it is fairly clear that the interference increases as the flow rate of production increases and the reservoir porosity decreases. Larger coefficients of permeability of the aquifers and shorter aquifers seem to increase the interference during the early production stages. However, under the same conditions, the interference is reduced in the later stages of production.