| Title | Understanding geothermal reservoirs using 3D modelling techniques: A case study of the Ebino prospect, Southern Japan |
|---|---|
| Authors | E. Humphrey, H. OKeeffe, J. OBrien and H. Honda |
| Year | 2017 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Ebino, geothermal exploration, geological model, Leapfrog, Seismo-Electric, Japan |
| Abstract | Current success rates for geothermal exploration wells are approximately 50% (IFC, 2013) and whilst results have improved over time, this still poses a high risk for small scale geothermal development. This project integrates existing and recently acquired data to create 3D geological models which identify higher potential drilling targets and mitigate exploration-based risk. The Ebino prospect, located in southern Japan, has been previously explored by the Japanese government in the early 1990`s where exploration data determined the area prospective for geothermal development. The survey area is situated on the northwest side of the Kirishima Volcanic Complex, segmented by two main valleys that straddle Quaternary-aged lava flows. Subsurface geology consists of sub-horizontal lava flows and pyroclastic deposits that have been partially fractured by NW-SE fault zones. Because of challenging topographic conditions, identifying an accessible wellsite for cost-effective drilling is necessary. Seismo-Electric (SE) surveying (Skokan & Chi, 1993) was selected for its mobility in challenging topographies and ability to vertically detect fluids without the need for large horizontal areas compared with other surface geophysical methods. A static geological model was initially created using existing borehole and geophysical data. The models display geological geometries and structural variations, whilst borehole temperature data creates isotherms to characterize reservoir conditions. SE data later updated the original model to define the architecture of fluid-saturated fracture zones to improve well planning and design. The model allows visualization of subsurface geology and reservoir architecture, helping to identify higher potential drill targets. Geological modelling indicated that higher potential drill targets exist closer to fault zones in the southern part of the prospect area. This project illustrates the effectiveness of a synthetic study of geological datasets that support decisions for geothermal well planning and design. Integrated geological modelling techniques can reduce exploration-based risk in decisions for geothermal development. |