Interpretation of hydrogeochemical results from the Zunil I geothermal field, Guatemala

Abstract

In Guatemala the first geothermoelectric plant of 15 MW is being scheduled for June 1993 in Zunil I, a geothermal field located approximately 200 km west of Guatemala city. The fluids of the springs in the Zunil I geothermal field are of different chemical compositions but they clearly define a deep fluid of high temperature. The chemistry of the fluid from well ZD-1, the first production well in the granodiorite basement is undersaturated with respect to calcite and quartz and the chemical geothermometer temperature calculated on the basis of its deep water composition is 290 C. This high temperature fluid has a high chloride content (1490 ppm) and a calculated enthalpy of 1291 kJ/kg. Thermal manifestations along the Samalá River are evaluated and their deep water composition is derived from the analyzed surface chemical composition using the WATCH3 programme. The temperature evaluated by geothermometers is about 280 C. There are three types of springs along the Samalá River, chloride, bicarbonate and sulphate springs. The first type is presumably derived from the mixing of geothermal fluid (probably boiled) with local groundwater, whereas the latter two derive from condensation of steam and mixing with surface water.