Stratigraphy, Temperature Profiles, and Flow Test Data from the PLTG-1 and PLTG-2 Coreholes, Platanares Geothermal System, Honduras

Abstract

Stratigraphy, temperature profiles, and flow test data from PLTG-1 and PLTG-2 coreholes in Platanares, Honduras, have been used to determine production characteristics from a 160°C fluid zone at 625 to 640 m depth and to estimate depth to the source geothermal reservoir. The two coreholes penetrate thin Quaternary deposits and several hundred meters of Miocene volcanics and Cretaceous to Eocene sedimentary rocks. Extrapolation of the deep thermal gradient of 139°C/km in PLTG-2 (depth 401 m) indicates the source reservoir of 220 to 240°C fluid occurs at 1.2 to 1.5 km depth. Flow tests of PLTG-1 from the 625 to 640 m zone show that 160°C geothermal fluids similar in composition to "end-member" hot springs originate from fractured meta-conglomerates of the Valle de Angeles Group. Pressure transient analysis indicates that this flow zone taps a localized reservoir having a volume on the order of 0.065 km (3). Maximum thermal power of PLTG-1 is roughly 3 MW(t). Scaling of arogonite results from flashing of the dilute, high ph, high HCO(3) fluid. Use of the shallow 160°C resource will require binary cycle power plants and, possibly, downhole pumps to successfully extract heat from the fluids for electrical applications.