Study to Evaluate the Effect of Using Expansion Materials with Cement Slurry for High-Pressure/High-Temperature Wells

Abstract

Oil and gas operators are facing more challenges than ever before to sustain production and to effectively minimize workover cost associated with remedial cementing. Previously, achieving the initial hydraulic seal with a good cement bond log was considered the only indicator of complete and durable zonal isolation throughout the lifetime of the well. However, in a well drilled in a stressful environment, the initial zonal isolation can be jeopardized because of the changes in downhole conditions, primarily temperatures and pressures. Such cyclic changes in downhole pressures and temperatures generate radial cracks in cement and can cause the development of microannulus at casing/cement and cement/formation interfaces. Extensive studies have been conducted in the past to understand the technical challenges to designing cement slurries with enhanced mechanical properties regulating the flexibility of set cement to withstand the stressful environment at downhole conditions. However, limited work has been done to evaluate the structural changes and impact on the set cement durability due to the requirement of expansion in set cement to eliminate the risk of microannulus. A new methodology called industrial computed tomography is introduced to investigate the structural changes or cracks in set cement cured with various concentration of expansive additives. The novelty of this new methodology is that it represents a step change in defining the linear expansion requirement for given well conditions without jeopardizing the wellbore integrity.