The viability and sustainability of geothermal energy development are subject to several reservoir (subsurface) and economic parameter uncertainties. Determining the optimal operational parameters of the geothermal system, in the presence of uncertainty, require hundreds, if not thousands, of permutations of the different uncertain or naturally variable reservoir, operational and economic parameters for any specific hydrothermal system. The key task of this project is to quantify reservoir and economic uncertainties and to examine their effects on the techno-economic performance of the hydrothermal doublet system. What are the ranges of permissible reservoir conditions (parameters) to render a geothermal system economically viable? What are the trade-offs between these parameters? What are the ‘acceptable uncertainties’ and the ‘optimized values’ for a geothermal-energy producer in the economic decision-making? These kinds of questions will be addressed in this project, by means of scanning the related parameter-space via a very large number of numerical simulations, to then derive first-order ‘reduced model metrics’ that help to derive simplified decision-making quantities. In this study, we will develop a novel generalized non-dimensional expression of power generation over time to characterize the optimal operational parameters for various combinations of the reservoir parameters, and to determine which combination of the parameters depletes the reservoir heat the fastest. This methodology will further be applied to evaluate and compare the performance of geothermal systems that use in-situ brine or (sequestered) CO2 as the heat-extraction fluid, with emphasis on Saudi Arabia’s geological and economic conditions. Finite element/volume simulators such as TOUGH2/3, DARTS, or CMG, and wellbore-power system models will be used to conduct comprehensive simulations and to stochastically assess the system’s power and lifetime based on a range of available subsurface parameters (e.g., depth, thickness, permeability, porosity, permeability anisotropy), operational parameters (e.g., flow rate, injection temperature, well spacing) and economic parameters (e.g., drilling cost, heat cost, electricity cost, etc.). The candidate must have the willingness to learn basic geoscience and reservoir engineering concepts. Affinity with programming (preferably MATLAB/Python) and Paraview or related visualization tools is an advantage.