Investigating the Correlation Between Compressive and Tensile Strength of Well Cement During the Curing Process

Abstract Wellbore integrity is significantly dependent on the integrity of well cement which plays a vital role in providing zonal isolation and structural support. Mechanical failure of the well cement is influenced by many factors, including cement characteristics and its strength and stiffness. While several studies have explored Young’s modulus and compressive strength of the well cement at early ages, the evolution of tensile strength of the cement over the curing process has rarely been investigated, despite its critical role in crack and debonding formation. Although the American Petroleum Institute (API) has recommended methods for assessing the compressive strengths of oil well cement, there are currently no equivalent standards for evaluating the tensile strength. It has been generally reported that the tensile strength of well cement ranges between 8–17% of its compressive strength, though this is more of a rule of thumb. The relationship between these mechanical characteristics under different curing conditions still remains unclear. This lack of a consistent correlation highlights the need for further assessment to understand how these mechanical properties correlate under different curing conditions, such as curing age and temperature. This study investigates the correlation between tensile and compressive strength of well cement, emphasizing the effects of curing age and temperature on the correlation. Experimental results from splitting tensile and unconfined compression tests have been conducted to assess the correlation and determine how varying curing conditions influence it. A new power law equation is proposed for the first time to relate tensile strength of “well cement” to its compressive strength accordingly. The findings offer valuable insights into the evolution of mechanical strengths of well cements under different curing conditions.