The Massepe Geothermal Field in South Sulawesi, Indonesia, presents sufficient geothermal energy potential as a promising greenfield site. This study focuses on assessing its resource capacity through uncertainty analysis and a natural state model, despite limited direct subsurface exploration. A comprehensive three-dimensional (3D) geological model of the Massepe field was developed using public data and reports, integrating geological, geophysical, geochemical, and spatial datasets with LEAPFROG Energy software. Key formations, fault structures, and the North-South Massepe fault were identified as critical components influencing geothermal fluid flow. Magnetotelluric data helped delineate the alteration zone, while surface manifestation data provided constraints on temperature distribution. A numerical model compatible with AUTOUGH2 and Waiwera was developed to simulate temperature distribution, fluid flow, and heat transfer processes. The model was calibrated by refining permeability parameters and simulating deep geothermal upflow to replicate the field’s natural state. High-performance computing enabled thousands of alternative model simulations, which were conditioned against sparse field data, particularly temperatures beneath the clay cap, primarily located below the Pajalele springs. These simulations underwent Approximate Bayesian Computation (ABC) to generate probabilistic power output estimates. The results confirm a strong geothermal upflow along the North-South Massepe fault, with lateral migration effectively constrained by geological structures. The estimated power output of the field ranges from P90, P50, to P10 values over a 25-year production period. This study enhances the understanding of geothermal systems in similar non-volcanic geological settings, providing valuable insights for strategic planning and the development of renewable energy resources in Indonesia. The refined resource assessment contributes to optimizing geothermal exploration efforts and supports sustainable energy initiatives in the region.

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