Cement design based on cement mechanical response

The disappearance of cement bond log response as a result of variations of downhole conditions has been observed in numerous wells. This observation h as led to concern about the loss of proper zonal isolation. Stresses induce d in the cement, through deformation of the cemented casing resulting from the variation of downhole conditions, are the cause of this damage. We present an analysis of the mechanical response of set cement in a cased wellbore to quantify this damage and determine the key controlling paramete rs. The results show that the thermo-elastic properties of the casing, ceme nt, and formation play a significant role. The type of failure, either ceme nt debonding or cement cracking, is a function of the nature of the downhol e condition variations. This analysis allows us to propose appropriate ceme nt mechanical properties to avoid cement failure and debonding. We show tha t the use of high compressive strength cement is not always the best soluti on and, in some cases, flexible cements are preferred.