This chapter presents a comprehensive analysis of the mechanisms responsible for the degradation and failure of cement sheaths in oil, gas, and carbon storage wells. Serving as a primary barrier for zonal isolation and casing support, the cement sheath is critical for maintaining long-term well integrity. However, it is subject to a variety of mechanical, thermal, chemical, and geomechanical stresses throughout the well’s lifecycle, all of which can compromise its performance. This chapter begins by examining mechanical failure modes such as debonding, radial and shear cracking, and micro-annulus formation—conditions often exacerbated by poor mud removal, casing expansion, thermal cycling, or insufficient cement properties. The chapter also explores the cumulative effects of operational stresses like pressure and temperature fluctuations, which drive fatigue damage in the cement matrix and casing interfaces over time. In addition to mechanical degradation, the chapter delves into chemical attack mechanisms including carbonation, sulfate attack, acid leaching, and magnesium infiltration—each of which alters the microstructure of the cement and increases permeability. These reactions are particularly relevant in CO₂-rich and aggressive saline environments typical of carbon storage and geothermal wells. Advanced topics include long-term performance strategies such as the incorporation of flexible or fiber-reinforced cement, elastomeric and pozzolanic additives, and self-healing formulations. Emphasis is placed on understanding time-dependent degradation under coupled thermal, mechanical, and chemical (TMC) conditions, with modeling and laboratory simulations guiding cement system design for extended durability. The influence of geomechanical stresses—due to formation movement, reservoir compaction, salt creep, and fault reactivation—is also explored, highlighting the necessity of stress-informed cement design. Finally, the chapter outlines mitigation and remediation approaches, including cement squeezes, polymer gels, and section milling, while also referencing key industry standards (API, ISO, NORSOK) for cement performance verification. Through a multidisciplinary lens, this chapter underscores the importance of robust cement design, predictive modeling, and proactive remediation in preventing barrier failure and ensuring long-term subsurface containment in a variety of well applications, including permanent abandonment (P&A), CO₂ storage, and thermal recovery operations.

Cement Sheath Failure Mechanisms and Degradation

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发表日期：

2026年

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Ahmed Alsubaih,
Kamy Sepehrnoori

摘要

This chapter presents a comprehensive analysis of the mechanisms responsible for the degradation and failure of cement sheaths in oil, gas, and carbon storage wells. Serving as a primary barrier for zonal isolation and casing support, the cement sheath is critical for maintaining long-term well integrity. However, it is subject to a variety of mechanical, thermal, chemical, and geomechanical stresses throughout the well’s lifecycle, all of which can compromise its performance. This chapter begins by examining mechanical failure modes such as debonding, radial and shear cracking, and micro-annulus formation—conditions often exacerbated by poor mud removal, casing expansion, thermal cycling, or insufficient cement properties. The chapter also explores the cumulative effects of operational stresses like pressure and temperature fluctuations, which drive fatigue damage in the cement matrix and casing interfaces over time. In addition to mechanical degradation, the chapter delves into chemical attack mechanisms including carbonation, sulfate attack, acid leaching, and magnesium infiltration—each of which alters the microstructure of the cement and increases permeability. These reactions are particularly relevant in CO₂-rich and aggressive saline environments typical of carbon storage and geothermal wells. Advanced topics include long-term performance strategies such as the incorporation of flexible or fiber-reinforced cement, elastomeric and pozzolanic additives, and self-healing formulations. Emphasis is placed on understanding time-dependent degradation under coupled thermal, mechanical, and chemical (TMC) conditions, with modeling and laboratory simulations guiding cement system design for extended durability. The influence of geomechanical stresses—due to formation movement, reservoir compaction, salt creep, and fault reactivation—is also explored, highlighting the necessity of stress-informed cement design. Finally, the chapter outlines mitigation and remediation approaches, including cement squeezes, polymer gels, and section milling, while also referencing key industry standards (API, ISO, NORSOK) for cement performance verification. Through a multidisciplinary lens, this chapter underscores the importance of robust cement design, predictive modeling, and proactive remediation in preventing barrier failure and ensuring long-term subsurface containment in a variety of well applications, including permanent abandonment (P&A), CO₂ storage, and thermal recovery operations.