MODELING OF THERMO-HYDRODYNAMIC-CHEMICAL PROCESSES: SOME APPLICATIONS TO ACTIVE HYDROTHERMAL SYSTEMS

Abstract

Available data on secondary mineral distributions, host rock properties and chemical composition of deep geothermal fluids ("parent geothermal fluids") of nine geothermal fields: Mutnovsky, Pauzhetsky (Kamchatka), Sumikawa, Kakkonda, Uenotai, Okuaizu, Hachijo-jima , Ogiri, Fushime (Japan) were used for thermo-hydrodynamic-chemical (THC) models calibration study. THC processes in hydrothermal systems were modeled with the TOUGHREACT numerical code (Xu and Pruess, 2001). Steady-state flow and single-phase liquid conditions were assumed. Our initial studies assume a highly simplified geochemical system, which includes the following mineral phases: quartz, K-feldspar, Na-feldspar, and cristobalite. Fluid containing Cl-, Na+ and CO2 was recharged to geothermal reservoirs under a specified range (10-200oC) of temperatures. Based on the modeling the following results were obtained: (1) Model validation by Na-K and SiO2 geothermometers; (2) Precipitation (K-feldspar and quartz) dominates over dissolution (Na-feldspar), meaning that selfsealing of reservoir took place. This has been confirmed by K-feldspar abundance in production zones at the geothermal fields; (3) Model sensitivity of mineral phase change to pH, porosity and flowrate has been studied