Permeability distribution in the Lahendong geothermal field: A blind fault captured by thermal–hydraulic simulation

Subsurface fluid flow of reservoirs in active tectonic regions is mainly controlled by permeability of fault zones. Therefore, the characterization of fault zones is an important step toward performance assessment of a reservoir. The fluid flow is controlled also by pressure and temperature conditions. In this context, we simulated pressure and temperature fields to elaborate on the influence of permeability on subsurface fluid flow in the Lahendong geothermal reservoir. Thermal–hydraulic simulation is performed using a finite element approach. Adjusting the permeability through 370 different cases, modeling results converged to the observed data within a misfit range of 0–7 %. The best fitting models identified a deep-seated fault that has previously not been traced at the surface. Simulated temperature distribution suggests a prominent convective heat flow, driven by an upward migrating and SW–NE oriented fluid flow. This hydraulic gradient causes a pressure drop along the reservoir. High-pressure patterns are used to constrain recharge areas, in addition to infiltration measurements. Discharge flow occurs from SW to NE migrating also upward toward the hot springs. In that frame, thermal–hydraulic simulations identified previously unresolved subsurface faults, which now allow a better understanding of the subsurface permeability and its influence on fluid flow.