Influence of Thermal Cycling on Cement Sheath Integrity in Permafrost Conditions

Cementing wellbore intervals in permafrost environments presents significant challenges due to cyclic freeze-thaw conditions, which induce microstructural degradation in the cement sheath, compromising zonal isolation and long-term well integrity. While existing studies have addressed thermal effects on cement properties, the interplay between alternating temperatures, unhydrated fluid behavior, and stress evolution in the pore space remains poorly understood. This study introduces an integrated methodology to systematically investigate the impact of cyclic thermal loads on cement sheath microstructure and mechanical performance under simulated permafrost conditions. A combination of advanced laboratory techniques – including X-ray microtomography, strain gauge monitoring, and controlled thermal cycling – was employed to analyze pore redistribution, microcrack propagation, and stress dynamics. Key findings reveal that unhydrated mixing fluid, trapped in the pore space, undergoes phase transitions during freeze-thaw cycles, generating internal stresses that exceed the cement’s tensile strength, leading to irreversible structural damage. To mitigate these effects, we proposed the use of a synthetic polyacrylamide-based polymer (PAM) as a multifunctional additive. Experimental results demonstrate that PAM reduces fluid loss by 54.76%, enhances compressive strength by 20%, and maintains Young’s modulus (13.1 GPa) after three freeze-thaw cycles. These improvements can be attributed to PAM’s ability to delay fluid loss, redistribute pore stress, and stabilize the cement matrix through enhanced coagulation and gelation mechanisms. The study’s scientific contribution lies in its holistic framework for evaluating cement degradation mechanisms in permafrost, coupled with actionable solutions for optimizing slurry design. This work advances the practical application of polymer-modified cements in Arctic well construction, offering a pathway to improve durability and reduce environmental risks in extreme cold environments.