TOUGHREACT Code Applications to Problems of Reactive Chemistry in Geothermal Production-injection Wells. First Exploratory Model for Ahuachap·n and BerlÌn Geothermal Fields

Abstract

The first preliminary simulations to study calcite and silica scaling problems at two geothermal fields in El Salvador have been performed using a non-isothermal multiphase reactive geochemical transport code TOUGHREACT. This code was developed by Earth Sciences Division at Lawrence Berkeley Laboratory introducing reactive chemistry into the code TOUGH2. Production well AH-33B at Ahuachapan geothermal field was used for calcite scaling problem. For the calcite scaling in the well AH-33B, simulation results agree well with the observation data collected at depth in the borehole. Increases in calcite volume fraction over time were obtained close to the wellbore, due to high concentrations of Ca+2 and HCO3-. Injection well TR-1A at Berlin field was used for studying silica scaling. The silica scaling simulation reproduces in same way the decline in injectivity in the well TR-1A. Amorphous silica and quartz precipitation was obtained in the simulation. Results indicate that the kinetics of silica deposition is very important for predicting the future injectivity decline in the permeable zone of injection wells under different geological and thermodynamic conditions. The reactive transport simulations could be helpful for understanding the physical and chemical processes occurring in geothermal reservoirs and the potential risk of calcite and silica scaling problems in new geothermal developments. The mineral dissolution/precipitation application (production/injection well scaling) was used as a baseline and first approach of the geochemical-hydrological model.