| Title | The new geological and natural state model of Hululais geothermal field |
|---|---|
| Authors | S.S. Nainggolan, I. Prasetyo, Sardiyanto, M. Gravatt, J. OSullivan, K. Titus |
| Year | 2025 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | 3D Geological Model, Numerical Simulation, Natural State |
| Abstract | Hululais Geothermal field, operated by PT Pertamina Geothermal Energy (PGE), is situated in the Province of Bengkulu, Sumatra Island, Indonesia. This volcanic-high terrain geothermal system is controlled by the Sumatra Fault System, which provides a high-enthalpy, liquid-dominated reservoir. As of 2025, the pre-exploitation phase is still underway in this field, with production scheduled to commence in the near future. This paper aims to update the previous work by Nusantara et al. (2017) and Sisminardi (2019) by implementing the latest real subsurface datasets, hence yielding a well-constrained geological and natural state model of the Hululais field. Leapfrog geothermal software was used to create the three-dimensional geological model, while PyTOUGH coupled with AUTOUGH2 software was used to run the numerical simulations. The geological model shows the lithology and stratigraphy sequences of the field, as well as the faults and alteration zone. The geological model was discretized and converted into the model grid for the numerical simulation. Temperature and pressure data acquired from previously conducted surveys were used for calibration. After extensive trial and error with manual calibrations, the natural-state model provided a satisfactory and reasonable temperature match. The average RMS error of the natural-state model is 15.1°C, meaning that 80% of the model is within 20°C difference with the downhole temperature. The model shows that the high-temperature reservoir in the vicinity of well pads A, C, and E has a temperature of > 250 °C. In contrast, the lower temperature outflow zone lies in the vicinity of well pads B, D, P, and Q with a maximum temperature of 210°C. The temperature distribution also corresponds with the conceptual model, proving the relationship between the high-temperature upflow zone around Mount Beriti and Mount Gedang in the South with the lower temperature outflow zone in the Mount Cemeh area in the North. |