A latent-heat-coupled wellbore heat-transfer model with phase-change materials

Deep and ultra-deep resource development is increasingly constrained by extreme downhole temperatures, which compromise drilling safety, tool integrity, and drilling-fluid performance. Conventional cooling measures—including drilling-parameter optimization, adjustment of drilling-fluid properties, surface cooling, and improved drillstring insulation—have achieved partial success; however, under deep/ultra-deep conditions, they often yield limited temperature reductions at high cost and with restricted adaptability. Phase-change materials (PCMs) offer an alternative approach by moderating wellbore-fluid temperature through heat absorption during melting and heat release during solidification. Nevertheless, prior studies have emphasized PCM development, whereas wellbore-scale heat-transfer modeling and the associated latent-heat coupling mechanisms remain insufficiently studied. To address this gap, a latent-heat-coupled wellbore heat-transfer model is developed by incorporating an enthalpy–temperature relation obtained from single-particle PCM simulations as a latent-heat source term. The model is validated against measurements from a self-built drilling-fluid circulation test rig, achieving an average prediction error below 5%. A case study for an 8000 m ultra-deep well indicates that adding 15% erythritol reduces the bottom-hole temperature by 16.6 °C. The proposed model establishes a sound theoretical basis for cooling design and evaluation using PCMs during drilling.