Cement is an important barrier element that provides pressure isolation between formation(s) and a well. Failure in the cement sheath can compromise well integrity and potentially lead to severe environmental, health, safety, and business impacts.

This work aims to assess fitness-for-service of cement sheath specifically in the context of shallow depth liner-casing overlaps in offshore wells. Primary objective of this paper is to investigate influence of pressure loads, material properties, and sheath dimensions on structural integrity of cement. The ultimate objective is to perform risk assessment and identify likely modes of failure. This work is based on a three-dimensional finite element model of cement sheath validated by analytical calculations. Sensitivity analysis was performed to evaluate and rank the influence of various operating and design parameters on mechanical stresses in a cement sheath.

Results indicate that cement material properties (Young’s modulus, Poisson’s ratio, expansion) and wellbore pressure are the major factors influencing cement’s structural integrity. Risk assessment suggests that interfacial bond failure, radial cracking, and cement top failure are likely modes of structural failure for a cement sheath in shallow-depth liner-casing overlap. Flexible and expanding cement are likely to be more robust to structural failure than brittle and non-expanding cement. Although annulus pressure has negligible influence on stress distribution within bulk of a cement sheath, it can potentially cause failure near the top of the cement column.

Sensitivity curves generated in this work will help engineers understand performance of cement sheath under different conditions. Regulators and industry will be able to strengthen the guidelines for assessment and qualification of cement as a barrier.

水泥是重要的屏障元素，可在地层和井之间提供压力隔离。水泥护套的故障会损害井的完整性，并可能导致严重的环境，健康，安全和业务影响。

这项工作旨在评估水泥护套的适用性，特别是在海上钻井中浅层衬管与套管重叠的情况下。本文的主要目的是研究压力载荷，材料特性和护套尺寸对水泥结构完整性的影响。最终目标是执行风险评估并确定可能的故障模式。这项工作基于通过分析计算验证的水泥鞘三维有限元模型。进行了敏感性分析，以评估和排序各种操作和设计参数对水泥护套中机械应力的影响。

结果表明，水泥材料的性能（杨氏模量，泊松比，膨胀率）和井筒压力是影响水泥结构完整性的主要因素。风险评估表明，浅层衬管与套管重叠时，界面粘结破坏，径向裂缝和水泥顶部破坏可能是水泥护套结构破坏的方式。柔性和膨胀水泥比脆性和非膨胀水泥对结构破坏的抵抗力更强。尽管环空压力对水泥护套内部应力分布的影响可忽略不计，但它可能会导致水泥柱顶部附近的破坏。

这项工作中生成的灵敏度曲线将帮助工程师了解水泥在不同条件下的性能。监管机构和行业将能够加强水泥的评估和鉴定准则，将其作为障碍。