In a geothermal doublet, cold water injection creates an expanding thermal front whose geometry depends on reservoir properties and well configuration. Monitoring this front through periodic injector well tests provides critical data for reservoir management. This thesis evaluates the feasibility of this monitoring approach by generating synthetic pressure data using two thermal modeling formulations in tNavigator®: the black-oil Temperature option (TEMP), which uses PVT tables for water viscosity, and the Compositional Thermal model (THERMAL), which uses the GERG-2008 equation of state. While both are industry standards, their quantitative discrepancies in geothermal applications have not been systematically examined. These models were compared using a simplified doublet geometry across two thermodynamic scenarios with 20 C water injection: a low-enthalpy, liquid-dominated reservoir (100 bara, 92 C) and a high-enthalpy, vapor-dominated reservoir (10 bara, 181 C), inspired by the Larderello-Travale field in Italy.