Effect of Internal Pressure and Cement Strength on the Resistance of Concentric Casing Strings

Abstract

ABSTRACT Some solutions have been suggested to avoid failure of casing particularly opposite massive salt bodies.The most effective of these solutions has been the use of multiple cemented casing strings. It has been found that dual cemented-casing strings have a collapse resistance superior to the sum of the collapse resistances of the casing strings composing this system. But, these results do not include the effect of the internal pressure. This paper discusses the influence of a high internal pressure (alone, or combined with external pressure) and the cement properties on the collapse resistance of cemented concentric strings. The resistance of the system depends on the quality of the cement. A low quality cement will continue to creep after setting and will not contribute much to the system under combined pressure loads. The application of an internal pressure that corresponds to normal pressure gradients reduces the tangential stress and increases the collapse resistance of the system by 25% over the same system without internal pressure.