Hydrothermal fluid flow modeling using numerical simulation to identify potential reservoir zones in the Mount Rajabasa geothermal field

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The exploration of geothermal resources on Mount Rajabasa is still at an exploratory stage. Various exploration methods and conceptual models have been developed, however, there is no accurate numerical model for hydrothermal fluid movement. In this study, we use numerical simulations to develop a preliminary model of hydrothermal fluid flow to identify the reservoir potential zone in Mount Rajabasa. The numerical simulation method was conducted using the USGS HYDROTHERM code. Input and validation parameters were calculated based on manifestation measurements and previous studies. Results from the study indicate that the geothermal reservoir lies below Mount Rajabasa and Balirang, with dimensions of approximately 4 ​km long and a thickness of 2–2.5 ​km. The water mass flow model also exhibited similarities to field conditions, including fluids at temperatures more than 100 ​°C that appeared in the W. Simpur, G. Botak, W. Merak, and Pangkul manifestation areas in the 40,000th iteration year as a steady-state condition. The mass movement model of the steam reaches 1×10−7g/s.cm2 forming a centered pattern under the peaks of Mount Rajabasa and Balirang with a pattern consistent with the resistivity distribution model of the previous magnetotelluric study. The model predicts a reservoir fluid temperature range of 250–380 ​°C. Furthermore, the model indicates that the reservoir is located between 800 and 1200 ​m below the surface. The model estimates that the reservoir contains a majority of water in the two-phase zone, with a thick layer of cap rock beneath the Rajabasa peak.