Numerical study of phase-change heat transfer in multilayer wellbores under moving heat sources

In order to investigate the melting behavior of low-melting-point alloys subjected to a moving heat source during downhole thermal plugging operations, an axisymmetric two-dimensional transient heat transfer–phase change coupled finite element model is developed. The enthalpy method is employed to account for latent heat effects, enabling stable numerical treatment of strongly nonlinear phase-change processes. The model incorporates a composite wellbore system consisting of a heat source, alloy layer, and surrounding multilayer structures, and introduces an idealized moving heat flux function to simulate heat source propagation. The evolution of the temperature field and the progression of the phase interface are systematically analyzed. Results indicate that alloy melting exhibits pronounced non-uniform propagation characteristics and undergoes a staged evolution process from thermal initiation to quasi-steady phase transition and finally to a slowing completion stage. The study elucidates the fundamental heat transfer mechanisms governing alloy melting under moving heat source conditions and provides a theoretical basis for the design and optimization of thermal plugging parameters.