Assessing groundwater impacts of geothermal development through integrated modelling: Insights from Ulumbu with broader application

Abstract

Social issues such as agricultural disruption, water scarcity, health risks, and natural disasters remain key challenges in geothermal energy development in Indonesia, often delaying project implementation and reducing public acceptance. This study investigates the impact of geothermal production at the Ulumbu Geothermal Field on the local water table and its potential implications for nearby agricultural areas.
A three-dimensional conceptual model was constructed using Leapfrog™, incorporating geological, structural, and alteration data. This model was then translated into a numerical reservoir model using AUTOUGH2. Refinements were applied to the shallow subsurface to ensure simulation stability and accurately capture water table responses.
Two calibration phases were performed. The first involved natural-state calibration by adjusting permeability values and introducing a hot plate to simulate subsurface heat input. This confirmed that Ulumbu is a vapor-dominated system with reservoir temperatures ranging from 220–240°C. The second phase matched production history by refining porosity and relative permeability to reproduce the enthalpy and mass flow of well ULB-02, which produced dry steam with enthalpy values between 2803 and 2787 kJ/kg from 2012 to 2025.
After calibration, pressure changes in blocks associated with agricultural zones were evaluated and converted into water table variations. Results indicate a maximum water table decline of only 4.6 mm, considered negligible and unlikely to impact agricultural sustainability. This study provides a robust modelling framework for assessing the groundwater impacts of geothermal production and contributes to addressing critical social concerns associated with geothermal development in Indonesia.