| Title | Rapid Exploration of the Tolhuaca Prospect, Southern Chile |
|---|---|
| Authors | Melosh, Glenn; Cumming, William; Sussman, David; Benoit, Dick; Soto, Elizabeth; Colvin, Anna; Wilmarth, Max; Winick, Jeff; Fredes, Luis |
| Year | 2009 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Exploration; Drilling; Geophysics |
| Abstract | GeoGlobal Energy LLC (GGE) performed detailed exploration and then drilled and tested a 1073 m deep core hole in southern Chile in a period of 5 months. The successful well test demonstrated discovery of a geothermal system in the Tolhuaca Prospect. Following earlier reconnaissance exploration and several years of surface access negotiations, a detailed geophysical resistivity survey was completed and immediately followed by helicopter-supported core hole drilling during the period from December 2008 through April 2009. The resistivity survey imaged a >10 km2 low resistivity clay cap that extended beyond the two known fumaroles on the lower flanks of Tolhuaca volcano. Geologic mapping and detailed geochemical sampling were run in parallel with the other work. Initially the well was targeted between the two fumaroles. However, early geophysical results showed that the fumarole to the south was in a broader and more intensely altered part of the clay cap. Details of the low resistivity pattern in this area along with the gas chemistry suggested the possible occurrence of a permeable steam cap. As staging for the rig mobilization began, a revised well target was selected near the southern fumarole on February 26. The well Tolhuaca-1 spudded on March 9 and was continuously cored from the surface to total depth. A 160°C dry steam reservoir entry was flow tested on March 25. Drilling continued to 1073 m and reached a maximum temperature of 289°C, with the temperature gradient and propylitically altered rocks suggesting that the well was very close to a permeable ~300°C reservoir. Drilling was suspended for winter on April 29, 2009 and the rig demobilized. |