Design of High Toughness Cement for Effective Long Lasting Well Isolations

Abstract

Abstract During the well service life the cement isolation is exposed to extreme conditions that can cause its premature failure. Certain well completion operation as perforating and hydraulic fracturing, the changes in temperature and pressure during secondary recovery or the mechanical stress originated by formation displacements may cause severe damage to the cement isolation. The mechanical properties (compressive and tensile strength, toughness, Young modulus and Poisson ratio) of different cements were evaluated in order to establish their best service performance. Typical slurry designs were tested focusing the attention on the effect of certain additives such as latex, fibers and other polymers used as fluid loss control or dispersants. The cement mechanical properties were determined according to ASTM and API standard test methods. The cement toughness was evaluated following the API RP 43 standard for testing well perforators. The experimental results show that the mechanical properties of cement are strongly dependant on the particular additives used when preparing the slurry. Even when cement with no admixtures presents high compressive strength it also shows a fragile behavior with limited strain and low toughness. The use of latex improves the cement elastic behavior although it does not better its impact resistance. On the other hand, the addition of polymer fibers improves the cement toughness and its elastic behavior. As it was demonstrated by well testing profiles run before and after perforating, the addition of fibers improves the cement performance when exposed to the different events that may damage the isolation during the well service life.