Thermodynamics of thermite reactions for a new thermal plug and abandonment process

Thermites are powerful energetic materials able to release large amounts of energy in a self-propagating reaction. They have been widely applied in rail welding, pyrotechnics, and material synthesis, as they are highly exothermic. In recent years, there has been an increased interest on applying a thermite reaction in the plug and abandonment of wells due to the possibility of reducing the high cost of this process. However, some primary studies are required to understand these energetic materials and to select the most efficient thermite mixtures to be applied in a plug and abandonment scenario. Although they do not react as simple condensed-phase reactions because of all the complex physicochemical mechanisms involved, they can be characterized and understood by simple principles of thermodynamics. As so, this research presents the importance of the Gibbs free energy concept to determine the candidates of a thermite reaction, in addition to showing how important characteristics of these reactions such as adiabatic temperature and heat released can be calculated using thermodynamic principles. Lastly, the minimization of Gibbs free energy method for determining the final products of a reaction, considering chemical equilibrium, is presented and applied to predict the final products, as a function of temperature, for some of the most powerful thermite mixtures. The conclusion is that, although the 2Al–Fe _2 O _3 thermite reaction has the lower mass and volumetric heat of combustion in comparison with the 2Al–3CuO and 3Be–Fe _2 O _3 thermites, it can reach the highest adiabatic temperature observed due to the lower gaseous mass fraction in the products, which means fewer heat losses due to phase changes. So, the thermite mixture 2Al–Fe _2 O _3 is a promising candidate for the plug and abandonment of mature oil wells.