Numerical modeling was utilized to simulate natural state condition in Lahendong geothermal field. It is necessary to find out the reservoir characteristics, hydrogeology, location and total energy of the heat source. Lahendong geothermal field is a hydrothermal system which has sufficient fluids, high average thermal gradients, high rock permeability, and high porosity. Thermo-hydro-mechanical coupling model has been applied to enhanced geothermal systems (EGS), however it has seldom been utilized in the hydrothermal system. Several conceptual and numerical models have been created to do such investigation. In this study, we tried to improve the numerical model that was created. COMSOL Multiphysics (COMSOL 5.4, 2018) was utilized for modeling the 3D numerical model to predict the evolution of rock temperature and pore pressure in the natural state condition. The reservoir is treated as a fractured porous medium by adopting discrete fractured model (DFM) which uses grid nodes to represent flow relationship between fracture to fracture, fracture to matrix, and matrix to matrix. Based on the results, the natural state conditions have been reached when the numerical results corresponding to the wells pressure and temperature data. Although some uncertain mismatches between the field data and the model predictions, this model can be utilized to evaluate the sustainability of the reservoir, improve production performance, and develop a new geothermal resource.

1. Introduction

Geothermal energy is one of the alternative energies to reduce dependence on fossil fuels. In order to develop new geothermal sites and improve production performance, further theoretical research and numerical simulation in the geothermal field is still needed. A case study from the Lahendong geothermal field, Indonesia is simulated with three dimensional (3D) numerical model to study the characteristics of fluid flow, heat transfer and solid deformation in the geothermal field. The Lahendong geothermal field is located in Tomohon, North Sulawesi, Indonesia (Fig. 1).

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