Temperature Field Model and Casing Failure Mechanisms in Steam Huff-and-Puff Wells

This study addresses the high failure rate of casing in heavy oil thermal recovery wells by proposing a thermo-mechanical coupled damage theory, overcoming the limitations of traditional casing failure mechanisms. A fully-coupled wellbore-formation temperature/stress field model was established for entire thermal cycling, incorporating radial one-dimensional steady-state heat transfer in the wellbore and transient heat transfer in the formation. An innovative iterative algorithm was introduced to calculate the total heat transfer coefficient, achieving precise simulation of temperature fields during steam injection processes. Three-dimensional finite element analysis using ANSYS revealed that thermal insulation degradation (apparent thermal conductivity increased from 0.002 to 0.12 W/m·K) significantly elevates casing inner wall temperature (63.9 °C → 190.0 °C) and intensifies heat loss. Cementing voids induce non-uniform external collapse loads, with peak casing stress reaching 578 MPa (76% of yield strength at 150 °C) at 90° void angle. Analysis of thermal cycling shows casing temperature evolution follows “rapid rise → stabilization → sharp decline” pattern within 40-day injection cycles, with 780 m depth identified as the critical temperature transition point. Simulations confirm gradual expansion of thermal influence radius before stabilizing over production years. Experimental results demonstrate TP110H casing yield strength reduction to 701 MPa at 150 °C (8–10% decrease) and 20% reduction at 350 °C, significantly compromising collapse resistance. This research provides critical theoretical foundation and engineering decision-making basis for safety design and longevity enhancement of steam injection well casings.