Crystallinity in Cements under Wellbore Conditions

Cement is a commonly used material for completing well applications due to its ability to be placed as a liquid and then converted to a solid during curing. The cement product created is designed to stabilize the wellbore environment while not allowing fluid to migrate through the cement. The ability for the cement to perform is directly tied to the final chemistry of the cement which is in turn linked to the temperature the cement was exposed to during curing. Silica and other materials are commonly added to stabilize the cement chemistry at elevated temperatures by promoting the development of certain cement phases, such as tobermorite and xonotlite, in order to avoid strength retrogression in the cement. These phases are crystalline which makes analysis of the cement sheath amenable to using X-ray diffraction (XRD) techniques. This presentation will discuss the analysis of cements subjected to downhole temperatures as it pertains to the phase stability of the resultant cement sheath.