| Abstract |
Towards large increase in geothermal power generation, one of the most important subjects is accurate positioning of production wells by reducing exploration drilling cost. For this challenge, we aim to develop a method of specifying ‘steam spot’ for suitable location of production wells by targeting the Patuha geothermal field, West Java, Indonesia. ‘Steam spot’ means permeable fracture zone acting as a main path of hydrothermal fluid that enables large and long-term power generation. The steam-spot detection was examined by integrating lineament-based fracture system, spatial and temporal features of radon (Rn) concentrations using shallow wells, compositions and isotopic features of waters, distribution of hydrothermal alteration minerals, and reservoir simulation. Lineaments were extracted from a high-resolution digital elevation model produced from LiDAR data. At high Rn concentration sites, the concentrations became almost constant with time suggesting a constant supply of gas from the depths. Potential map of steam spot existence was prepared by weight summing of three factors: Rn concentrations, major ion (Al and SO4) concentrations in spring water samples, and lineament density. Based on the potential map, two drilling sites were selected in high potential zones and two temperature core holes (TCHs) were drilled with total length of 506.5 m. Fluid inclusion analysis and mineral identification were implemented using the TCH cores and the mineral composition was applied to multi-geothermometer for estimating reservoir temperature. Both the homogenization and reservoir temperatures were higher at the higher potential site, which consequently demonstrates effectiveness and correctness of the proposed method of steam-spot potential mapping. |