Near-supercritical behaviour of LHD-47 Well, Lahendong Geothermal Field, North Sulawesi, Indonesia

Abstract

The Lahendong geothermal field is located in North Sulawesi Province approximately 30 kilometers south of the capital city, Manado. The field has been a key site for Sulawesi Island’s geothermal exploration and development since early 1980s. Initial exploration, led by PT Pertamina, identified two primary prospects: Lahendong in the northern area and Tompaso in the southern area. As the first geothermal power generation facility in North Sulawesi, the field is currently operated by PT Pertamina Geothermal Energy (PGE) with an installed capacity of 4 x 20 MW.
The Lahendong geothermal system consists of two main reservoir compartments: Linow and Kasuratan (Prasetyo, 2024). Production is primarily sourced from the Kasuratan compartment, which features a two-phase reservoir and more benign fluid derived from an ultra-high-temperature reservoir, particularly in the southern block. The reservoir temperatures reach approximately 300°C, with some wells recording maximum temperatures of up to 361°C at 2.5 km vertical depth, nearing supercritical condition. These temperatures represent the highest recorded among PGE-operated fields across Java, Sumatra, and Sulawesi Islands.
This study focuses on the performance and challenges associated with well LHD-47, which has produced from this near-supercritical temperature reservoir. Although the well demonstrated promising initial output, operational challenges arose, including a 76°C superheat condition, high total dissolved solids (TDS), and significant corrosion issues. The insights gained from operating this well provide valuable lessons for the future development and management of extremely high-temperature geothermal reservoirs as well as the potential of producing supercritical fluid at relatively shallow depth.