Wahawa geothermal field: subsurface structure and direct use potential

Abstract

Sri Lanka, mainly depends on non-renewable energy sources. It is essential to meet the country’s energy demand by developing and adopting renewable sources. This study was conducted to assess the geothermal potential of Wahawa geothermal field through integrated geophysical and geochemical methods. The water samples collected from 12 locations of the field were used for the geochemical characterization. The geochemical characterization to calculate the reservoir temperature included in-situ measurements such as pH, electrical conductivity, and wellhead temperatures along with major anion and cation analysis using Ion Chromatography and Microwave Plasma-Atomic Emission Spectroscopy respectively. The gravity, magnetic and resistivity data obtained from the geophysical measurements were used in determining the geometry and the location of the heat source. Gravity, resistivity and magnetic results collectively supports the presence of a geothermal reservoir associated with the dolerite dyke intrusions. A hypothetical model was developed for the geothermal field using the geochemical and geophysical data obtained. The geothermometric calculations estimate the maximum reservoir temperature to be 186 °C, corresponding to an energy input of 697.2 kJ/mol. The Monte Carlo volumetric assessment shows with a 90% probability that the reservoir could produce 2.6 MWe over a period of 30 years.