Ternary fluid infiltrating with constant composition produces more than twelve reaction sequences controlled by rock composition

In many applications a fluid is injected into rocks for example for CO₂ storage, in enhanced geothermal reservoirs, or during oil and gas recovery. The fluid may be out of equilibrium with the rock resulting in chemical reactions at depth. The correct prediction of reaction front velocities depends on a thorough understanding of the theory of chromatography and the changes of density and porosity in reactive transport models. We study the systematics of reaction fronts in multi-component systems. The methodology is based on a finite difference approach for solving the transport problem in combination with precomputed thermodynamic equilibria. These lookup tables are calculated using Gibbs’ minimization and a linear programming approach. They are validated against full analytical solutions of the Gibbs minimization problem. Porosity and density evolution is predicted based on mass conservation. We focus on ternary ideal fluid or melt solutions in equilibrium with pure phases as exact solutions are feasible and here first consider the isothermal case. For a fixed incoming fluid composition, over twelve reaction sequences may form depending on initial rock composition. Within one type of reaction sequence, bulk rock composition still plays are role in determining the speed of the reaction front as well as the fluid compositions that develop along the path. This theoretical understanding allows better predictions of the formation of reaction sequences and the consequences on rock properties upon injection of fluids with dissolved chemical components.