Geochemical Characteristics of Reservoir Fluid from NW-Sabalan Geothermal Field, Iran

Abstract

The first geothermal exploration activities in Iran were carried out in the Mt. Sabalan field. The discharge test measurements show that wells NWS-1and NWS- 4 produce predominantly from a single-phase, reservoir (liquid) with a temperature of 225oC and 223 oC. The chemical composition of the reservoir water was analyzed by standard methods and subsequently classified using Cl-SO4-HCO3 and Cl-Li-B triangular diagrams. A Na-K-Mg triangular diagram was used to classify waters according to the state of equilibrium at given temperatures. The geothermal waters are of sodium-chloride type and from a relatively old hydrothermal system. Thermal fluid is in equilibrium with reservoir rocks. The isotopic composition of the Well NWS-4 presents enrichment in ∂18O, typical characteristics of geothermal origin. The chemical geothermometers were used to predict subsurface temperature. Silica geothermometers give temperature more close to measured temperature whereas cation geothermometers show significantly higher temperatures than measured temperatures.