Resource assessment of the Copahue geothermal field

This paper assesses the electrical generating capacity of the Copahue geothermal field. Because it plays a critical role in driving financial support, we discuss these results in terms of its geothermal project. We performed a set of estimates, including the volumetric method and wellhead output calculations. The former was supported by a 3D-geological model that allowed us to subdivide the reservoir into blocks to constraint the parameters to each zone better. The probability models estimate that the proved resource can produce more than 10.2 MWe and 13.5 MWe at 90 % and 50 % confidence level, respectively. The wellhead power output calculations were supported by long- and shortperiod discharge test performed at three production wells and one slim hole and by the analysis of its decline paths. We estimate 10 MWe in the most optimistic prediction ruling out the identified power plant decline, above 5 % per year. Regardless of the method, our results support less than half of the previously calculated proven power output (i.e., 30 MWe) used to scale the offered tenders to develop a power plant. Overestimation cases worldwide invite us to be even more restricted over our power capacity estimations. Moreover, a tighter characterization of the reservoir volume (e.g., Chilean ranking) could redefine it from proven to probable, increasing the uncertainty over the resource. Throughout its 50 years of history the Copahue Geothermal Project reached significant milestones (first power plant on South America, a district -heating system, and four drilled wells). However, an in-depth review of the project history revealed several setbacks (closure of the power generation and direct use projects because of technical issues, developer retreatments, inadequate tenders) that partially explain its current on-hold status. We concluded that more work is needed before advancing towards the development stage of the project. The vast heat storage at Copahue is beyond doubt, but it is mandatory to improve the estimations of the steam supply, enhance the success rate of wells by a new drilling exploration stage, resize the projected power plant and perform a more accurate feasibility report. New attempts to attract investors and future developers should consider these goals and the project history to avoid new setbacks.