Cement failure modeling for high pressure high temperature wells: Case studies

Well cementing is an important operation during drilling and completion of oil wells. The cement sheath must maintain well integrity behind the casing and provide long-term zonal isolation to ensure safety and prevent environmental problems. Some of the uses of cement sheath include providing support for casing, sealing off of annulus and protection of the casing from any corrosive formation fluids that may be in the casing well. Perforation and fracturing operations could damage the integrity of the system of casing-cement-formation during production which could eventually lead to failure. The problems of well cementing still persists despite advancements in technological development of cement and concrete materials. Moreover, changes in temperature and pressure during the life cycle of the well can give rise to several mechanisms of failure that could pose threat to the set cement sealing integrity. Therefore, crucial models are important to understand the behavior of cements at different conditions and hazardous outcomes of cementing failure. The objective of this paper is to review the available failure models for cement and illustrate the main causes of cement failure for actual field cases. This review provides an overview of the five cement failure models including analytical, finite element, probability, thermo-poro-elasto-plastic and buoyancy-driven models. The theory and applications of these models are discussed. Probable solutions to cement failure were also reviewed. This review will help to have proper understanding of the vulnerability of mechanisms of cement sheath failure to changes in important properties of a casing-cement-formation well section when subjected to different well operation conditions. The novelty of this work is the deep investigation of the failure mechanics of different cement slurries in addition to supporting the main conclusion of this work by actual case studies.