| Title | Exploration Results and Resource Conceptual Model of the Tolhuaca Geothermal Field, Chile |
|---|---|
| Authors | Glenn Melosh, William Cumming, Dick Benoit, Max Wilmarth, Anna Colvin, Jeff Winick, Elizabeth Soto-Neira, David Sussman, Luis Urzúa-Monsalve, Tom Powell, and Adam Peretz |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Tolhuaca, Chile, MT, alteration, geothermometry, hydrology, geothermal exploration |
| Abstract | An exploration program conducted by GeoGlobal Energy Chile (GGE Chile) at its San Gregorio concession, including geology, geochemistry, T-MT-AMT and deep core hole drilling to 1073 m depth, discovered a geothermal resource and constrained the preliminary resource conceptual model at Tolhuaca volcano. Early reconnaissance exploration indicated the presence of a geothermal system based on cation geothermometry from mixed chloride springs of 160°C and gas geothermometry from the Muro fumarole of 220 to 250°C. Following several years of surface access negotiations, a detailed T-MT-AMT geophysical survey was completed while a helicopter-supported core hole rig was mobilized in early 2009. Geologic mapping and detailed geochemical sampling were run in parallel with the 70 station T-MT-AMT survey. The T-MT-AMT was optimized to effectively acquire data in the rugged, relatively inaccessible terrain on the glaciated lava flows covering much of the prospective area. The first 10 T-MT-AMT stations showed that the Muro fumarole located 1800 m to the south of the more easily accessed Sola fumarole was closer to the most intensely altered part of the clay cap, and the initial well location was shifted to that area while the rig was mobilizing. The low resistivity clay encased a resistive zone that, in conjunction with the gas chemistry, was interpreted to be a permeable steam cap. The well Tolhuaca-1 was continuously cored to 1073 m depth. Drilling paused for a flow test demonstration of the shallow 150°C to 160°C steam reservoir between 120 m and 320 m depth. At 1073 m, the declining temperature gradient and propylitically altered rocks are consistent with a conventional >289°C permeable geothermal reservoir with neutral pH and low gas content, implying that power generation from this resource would have low CO2 emissions. The T-MT-AMT survey imaged a >10 km2 low resistivity clay cap that extends beyond the known fumaroles on the lower flanks of the glaciated volcano. Although the shallow zone is hot enough to support binary or low pressure flash geothermal power generation, GGE Chile’s first priority will be targeting additional wells to produce the greater than >289°C reservoir. |