| Title | Well-scale permeability classification on the Indonesia conventional geothermal reservoir |
|---|---|
| Authors | M. Ikhwan, R.M. Tofan, J. Anggraini |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | permeability, geology, structure, image log |
| Abstract | Effective permeability characterisation in geothermal wells is paramount for optimising geothermal energy production. This study investigates the interpretation of permeability control using image log data and injection spinner logs to classify and capture the various permeable zones within geothermal reservoirs from a well-scale perspective. The classification delineates five primary types of permeable zones: highintensity fracture zones, large aperture fracture sets, permeable fault cores, pores or microfracture-supported formations, and permeable unconformities or lithological contacts. High-intensity fracture zones, typically occurring in brittle formations such as lava or welded tuff, are identified by closely spaced fractures with small apertures. These zones are well captured by image logs and exhibit a gradual response in spinner logs if they are permeable. Large aperture fracture sets, characterised by noticeable and continuous conductive fractures, show abrupt responses in spinner logs, indicating high permeability. However, the conductivity of these fractures can be biased by the presence of conductive minerals, impacting the actual permeability estimation. Permeable fault cores are marked by significant displacements or washouts in the borehole wall, often recorded as drilling breaks. These zones can pose challenges in logging due to caliper disorientation and image loss, making it difficult to determine the actual fault orientation. Porous formations and lithological contacts, which include interconnected pores and microfractures, enhance permeability and are well captured by image logs and under microscopic analysis. Lithological contact or unconformities, particularly angular unconformities or disconformities, can create permeable zones, but may sometimes be misinterpreted as faults. Integrating multiple log analyses, including image, sonic, and density logs, is crucial for accurately identifying productive fractures and permeable zones. This approach addresses key challenges such as fracture continuity beyond the borehole, actual fracture permeability, and the geometry of fault planes in space. Additionally, understanding fracture kinematics through geomechanical analysis provides valuable insights into fracture characterisation. Non-fracture permeability, facilitated by porous formations and lithological contacts, also plays a significant role in well productivity. By comprehensively analysing these various permeable zones, this study enhances the understanding of reservoir hydrology and supports the effective planning and optimisation of geothermal wells, ultimately contributing to the successful exploitation of geothermal energy resources. |