Fundamental Investigation of Mechanical Properties of Additives and Class H Cement Under Downhole Conditions

Abstract

Abstract The foremost function of primary cementing is to achieve zonal isolation and ensure long-term cement integrity during the lifetime of the well. Current advanced drilling and cementing technologies enable the production of oil and gas in more complex and challenging conditions such as deep wells and unconventional wells either onshore or offshore. Understanding the mechanical performance of cement sheath under downhole conditions, therefore, is crucial for successful cementing operations. Unfortunately, most published mechanical data were still limited to the compressive and tensile strengths determined at ambient condition as well as Young's modulus. The result for tensile strength varies greatly due to the lack of API standard tensile strength testing. The purpose of this study is to evaluate the additive-additive interaction on cement mechanical properties. Individual additives and their combinations were mixed with class H cement at a density of 16 ppg and cured under elevated temperature and pressure. The mechanical properties tested at ambient and curing conditions include compressive, tensile and yield strength, Young's modulus, and Poisson's ratio. The cement mechanical performances measured at curing conditions, especially the tensile strength, were different from the results obtained at ambient conditions. The elasticity of cement was improved by fiber and polymeric additives tested in this work. This study provides comprehensive experimental data on how the slurry formulation, chemical characteristics of the additives, and additive-additive interactions can affect cement mechanical properties. This study also gives insights into the correlations among various mechanical properties, and the key parameters that could determine cement elasticity. The results can be used as direct guidance for future field applications.