Investigation of thermal-hydro characteristics in seepage channels of stratified porous media: A mesoscopic approach

A hybrid thermal lattice Boltzmann model based on the immersed boundary method was proposed to address pore-scale thermal-flow coupling. The model incorporates the multiple-relaxation-time collision operator to enhance numerical stability. A fourth-order Runge–Kutta algorithm was introduced to solve the energy equation. The framework enabled precise capture of transient microscopic temperature gradients. Gravity-driven seepage in stratified porous media with lateral porosity variations was systematically investigated. The results revealed a flow-thermal separation mechanism induced by structural heterogeneity. Preferential flow channels in high-porosity zones accelerated fluid penetration. However, the shortened residence time hindered local thermal equilibrium. Consequently, steady-state temperatures in high-porosity zones remained lower than those in low-porosity zones. The temperature-flow coupling was clarified. High temperatures reduced surface tension and viscosity. These reductions weakened capillary effects in narrow pores and triggered a transition from fingering flow to piston-like displacement. Particle gradation analysis demonstrated that introducing coarse aggregates reduced fluid tortuosity and eliminated stagnant zones. These effects effectively enhanced thermal penetration efficiency. The study validates the hybrid framework for heat transfer and provides mesoscopic insights into transport within heterogeneous geological structures.