A Laboratory Study of Factors Affecting Primary Cement Sheath Strength

Abstract

An investigation of factors affecting cement sheath strength has been carried out.. This study performed on hardened (cured for seven days) cement specimens. These specimens were prepared by mixing 35% fresh water by weight of dry Portland cement (class A according to API classification or C 150 type I according to ASTM classification) plus various percentages of Thumama sand (5-40% by weight of dry cement). The relationship between cement tensile and compressive strengths as well as cement direct and indirect tensile strenghs have been established. Factors affecting cement-casing and cement-formation shear bond strength were studied. Cement compressive and tensile strength were correlated to each other as well as to the cement shear bond strength. It was found that casing surface roughness, casing surface cleaning and casing centralization have enhanced the strength of cement-casing shear bond, whereas the deposition of mud cake on the wall of the simulated borehole has reduced the strength of cement-formation shear bond.