Experimental and numerical investigation of the effect of alumina on thermite reation propagation for thermal plug and abandonment of oil wells

•Experimental tests demonstrate that a 20 % alumina dilution significantly reduces peak temperatures, burning velocity, and expelled mass, presenting benefits for wellbore sealing.•The diluted system, with alumina, formed a thicker plug, contrasting with the non-diluted system.•Numerical data was validated with experimental observations, and also indicated smooth burning, no apparent ejection of molten metal, and mitigation of peak temperatures in diluted systems. Thermite has been considered as a potential alternative for the wellbore plug and abandonment process. This new technology, thermal P&A, may substitute cementation as a cheaper and more compelling material. In this way, different thermite systems and additives are being explored in this scenario. The present study aims to examine the effects of diluting the Fe2O3–2Al thermite system with alumina in search of a more controlled reaction by observing effects on total ejected mass, burning velocity, and temperature levels. Small-scale experiments were conducted where stainless-steel tubes were filled with the thermite system. Thermocouples welded to the tube's external surface allowed us to obtain the temperature profiles at different positions and the overall reaction propagation velocity. The 20 % diluted system suppressed the measured peak temperature, burning rate, and expelled mass of about 10%, 60%, and 45%, respectively, compared to a non-diluted system. Simplified numerical simulation assuming a zero-order kinetics mechanism presented consistent results with the experimental peak temperatures at most positions analyzed. The simulation revealed that the diluted system would not reach the aluminum vaporization temperature as observed in the non-diluted system. Still, instead, it would be limited to the alumina melting temperature of 2327 K. In summary, the diluted system showed substantial reductions in peak temperature, burning rate, and expelled mass, indicating potential cost-effective and controlled applications in Thermal P&A processes.