A New Discovery Well in the Upper Agua De Pau Geothermal System, Sao Miguel Island, Azores: Results of Drilling and Testing

Abstract

A successful exploration well, CL-1, was completed in February, 1989 in the upper Agua de Pau geothermal system on Sao Miguel. The 2022 meter deep well encountered a high temperature (>200C) geothermal reservoir with permeable zones distributed between about 725 m and 1,8000 m depth in fractured volcanic rocks. The reservoir penetrated by CL-1 is predominantly single phase hot water, but temperature surveys and results of flow testing indicate that the top of a reservoir contains a steam cap, which underlies a cap rock of clay rich altered pyroclastics. Three weeks of flow testing in 1989 yielded total mass flow rates of at least 125 tons/hr. The calculated transmissivity and productivity index of CL-1 are average for deep, self flowing geothermal well, and reservoir fluid chemistry is typical of volcanic hosted meteoric hydrothermal systems. No evidence of calcite scaling, which has caused problems in earlier wells drilled in the lower Agua de Pau system, was found during testing.