pH CALCULATION THROUGH THE USE OF ALKALINITY IN GEOCHEMICAL MODELING OF HYDROTHERMAL SYSTEMS

Abstract

An algorithm based on the alkalinity conservation is presented in order to calculate the natural water pH with incorporating the effects of heating, boiling, dilution and mixing of different types of fluids. Alkalinity with respect to the equivalence point of H2CO3 is defined as

Dissolution of gases (CO2, H2S, NH3) does not alter the alkalinity. Therefore it permits us to recalculate the deep reservoir liquid pH including the effect of separated vapor.
The back calculation procedure using conservation of energy and mass is implemented to compute the geothermal reservoir fluid physical-chemical parameters from the parameters measured at the surface in the geothermal fluid (vapor and liquid). The scheme is simplified with considering a steady state homogeneous two-phase flow and neglecting fractional pressure drop in comparison of gravitational and acceleration pressure drops in the well. The application of this method is demonstrated in calculating the pH together with other parameters of deep reservoir fluid in case of well M-19A at Cerro Prieto.