Strain Design of Casing for Heavy Oil Thermal Recovery Wells

In the steam stimulation process of heavy oil thermal recovery wells, casings are highly susceptible to damage due to complex thermal stresses and high-temperature creep. Existing casing strength design theories fail to fully prevent the degradation of casing performance. To address this issue, this paper proposes a strain-based design method for casings. First, a series of high-temperature tensile and creep tests were conducted on typical thermal recovery casing materials to determine key parameters such as uniform elongation and steady-state creep rate. Subsequently, based on the parameters of directional thermal recovery wells and the newly established casing strain design criteria, a complete strain-based casing design framework and procedure were developed. The experimental results indicate that material properties degrade significantly under high-temperature environments. Non-thermal recovery steel grade casings exhibit high creep sensitivity and are unsuitable for long-term high-temperature service. This study establishes a novel method for casing design in thermal recovery wells. Safety evaluations using the proposed method demonstrate compliance with operational requirements, contributing to enhanced safety and reliability in heavy oil thermal recovery operations.