A Comparative Evaluation of Active Cooling and Passive Insulation Technologies for Thaw Mitigation During Permafrost Drilling

Permafrost thawing induced by heat transfer from circulating drilling fluid poses a significant threat to wellbore integrity and drilling safety in Arctic hydrocarbon exploration. The absence of clear application boundaries for the two primary mitigation strategies, passive insulation and active cooling, impedes the cost-effective selection of engineering measures. This study presents a comparative numerical evaluation of insulated-casing technology and refrigerant-fluid circulation technology using a coupled hydrothermal heat transfer model solved via the finite difference method. Passive insulation reduces thawed volume by increasing radial thermal resistance, with performance improving sharply as apparent thermal conductivity declines below 0.02 W/(m·K). At an optimal conductivity of 0.006 W/(m·K), insulated casing achieves a thawed volume of 2.3 m3 after 7 days, comparable to aggressive active cooling at −15 °C and 20 L/s, demonstrating its viability as an energy-free alternative. Active cooling offers superior operational controllability, yet its effectiveness hinges critically on inlet temperature; lowering this temperature exerts a dominant influence on thaw suppression, whereas increasing flow rate yields diminishing returns beyond 12.5 to 15.0 L/s. A critical caveat is that operating at 0 °C and 5 L/s paradoxically reverses the cooling effect and exacerbates thawing. Sensitivity analyses reveal that refrigerant-fluid circulation technology excels in permafrost layers up to 500 m, reducing thaw volume by a factor of two to three compared with high-performance insulation. This advantage diminishes for thicknesses exceeding 600 m, where insulated casing provides robust, thickness-independent protection. These findings establish a quantitative framework for context-specific technology selection, enabling engineers to balance thermal performance, operational controllability, and energy efficiency in permafrost drilling operations.