New Expansion Additive Gives Good Results With Low C3A Cements

Expanding cements have been credited with improving cement bonding to casing and formation, and for providing better Zonal isolation. Historically however, results have been inconsistent apparentiy due to misapplication and lack of meaningful job analyses. This paper discusses ditterent types of expansive cements, the mechanism of chemical expansion, and relates cement transition volume changes to the need for expansive cements. Most expansive additives depend on the presence of tricalcium aluminate (C3A) in the cement to complete the expansion reaction.' High C3A cements, due to their inherently lower quality control and erratic retarder response, generally are not preferred for most casing cementing operations. A new expansive additive has been developed which does not depend on cement to supply C3A. It can be used with any API class of cement or pozzolan-cement blend. The performance of this new additive is summarized and its limitations discussed. Case histories of selected field jobs are given, complete with cement bond logs and fracture treatment entry point evaluation surveys.