Understanding hydrothermal processes during production is critical to optimize geothermal reservoir operation and reduce the risk of its failure. The influence of the subsurface physical parameters, the design of the wells, and their operational settings on a high-enthalpy liquid-dominated geothermal operation has been investigated. For this purpose, a numerical model was developed, accounting for the flow, mass and heat transport in a single-phase aquitard-aquifer system, in the vicinity of a vertical 4-km well-doublet scheme. The sensitivity analysis varies the thermal power from 34.0 MWt to 58.1 MWt and the productivity index altered within the range 0-4.9 x 10(2)1s(-1) bar(-1). The parameters affecting both the hydraulic and thermal performances are (1) the reservoir permeability, (2) the injection temperature, (3) the production/injection rates, (4) the aquifer thermal conductivity, and (5) the length of the openhole section. These parameters provide a general control of the project and should be carefully estimated and designed. The predominant role of the aquifer parameters over the aquitard parameters is clearly demonstrated in this specific study. However, ignoring the caprock and bedrock in the model simulations would result in strongly and negatively biased estimates of the reservoir temperatures.