Characterization of annulus well cement quality to estimate the leakage potential in cement well barriers

Abstract

Cement is nowadays the most used material that is placed inside of wells as a barrier element to ensure zonal isolation and avoid migration of fluids between the reservoir and surface. Sometimes the well integrity can be compromised due to the presence of imperfections called leakage paths. Some of those paths can be the result of defects during the well construction or can be the consequence of mechanical, chemical and physical processes during the well life that induce alteration and degradation in the barriers. Annular cement barriers are the object of study of this thesis. Full-size test sections have been constructed to investigate barrier quality and their correlation with single phase gas and water leakage rates. A durability study of oil well cement 30+ years old is also presented analyzing the variation of mechanical, petrophysical and compositional properties in connection with the overall cell permeability behavior. Finally, the research conducted to construct a facility for the testing of logging technologies of annular well barriers is presented. Results show that migration paths correlate well with the logging interpretation and fit well with the variations of hydraulic properties measured on the cells.