Investigating high permeable zones in non-volcanic geothermal systems using lineament analysis and fault fracture density (FFD): northern Konawe Regency, Indonesia

Indonesia has high geothermal potential comprising 40% of the world’s potential geothermal energy, volcanic and non-volcanic systems. Volcanic systems have witnessed more exploration activities for geothermal resources compared to non-volcanic systems. A high potential non-volcanic system in Indonesia is located in the northern part of Konawe, Southeast Sulawesi. Previous research had identified surface temperature anomaly (high temperature) and some surface manifestations for this area, specifically in the northeast part of Wawolesea. However, the source of surface manifestations and permeable zones as an implication of a good reservoir are still unknown. Therefore, this research aims to investigate the permeable zones and geothermal potential in the non-volcanic geothermal system of north Wawolesea by applying lineaments analysis and the fault fracture density (FFD) method. A total of 1694 major and minor lineaments were manually delineated using ArcGIS based on Digital Elevation Model Nasional (DEMNAS). FFD map and rose diagrams displayed the orientation of all lineaments and structures with the major lineaments trending NNE–SSW, whereas the minor lineaments showed irregular distribution and orientation. Field measurements also show the same azimuth orientation for the mapped fractures. Five zones were characterized by high FFD values (2.81–4.54 km/km2). One of the extensively fractured zones (Zone C) is located between Meluhu and Lembo, covering an area of around 19.39 km2. This area is interpreted to be highly permeable and suggestive of a recharge area that contributes to surface manifestation in the Wawolesea. Therefore, the area between Meluhu and Lembo in the northern part of Konawe shows high geothermal potential due to its planar morphology and high FFD values. This study allows an improved understanding of how fracture geometry, distribution and density control the permeability in geothermal reservoirs.