| Abstract |
Geothermal processes, in particular those in deep geological formations, can only be realistically modeled as long as reactive fluid-rock interactions are taken into account. This is especially true when CO2 is used as a heat extraction fluid, which dissolves into the resident brine and increases its acidity. The combination of this acidity increase together with high underground temperatures, stimulates geochemical reactions that can cause dissolution and precipitation of minerals, and consequently dramatic changes in rock properties, such as strength, porosity, and permeability. These rock transformations can ultimately hinder heat extraction if not well understood and properly managed. In this work, we present efficient and versatile computational methods for modeling fluid-rock interactions during geothermal processes and show examples in which such chemical interactions can be critical for proper behavior assessment of geothermal energy systems. The presented methods are capable of calculating thermodynamic equilibrium states in multiphase, multicomponent systems, such as the ones found in geothermal reservoirs that include rock-forming minerals, the heat extraction fluid (assumed here as CO2) and the resident fluid (brine). For such fluid-rock reactions (e.g., mineral precipitation) that are considerably slower than fluid flow, we present a method that computes their time evolution based on their chemical kinetics description. This allows a more realistic modeling of geochemical reactions taking place in geothermal systems. |