Quantification of Casing Expansion-Induced Cracking in Oilwell Cement Sheaths

Abstract

Summary Cracking in the cement sheath of oil and gas wells is a major concern because it compromises well integrity and can lead to uncontrolled leaks of hydrocarbons, affecting both well safety and the environment. Among several reasons that might induce cracking, in the present study, we focus on the radial expansion of the steel casing resulting from pressure changes as one specific cause of damage. A test setup was designed to mechanically expand the steel casing while cameras monitored the cement to detect and measure cracking using digital image correlation (DIC) techniques. Six full-size replicas of 9-5/8-in. oilwell cross-sections were tested, and cracks in the cement ranging from 10 µm to 500 µm in width were quantified. Although each specimen exhibited a unique cracking pattern without a clear trend in the measured crack widths, analysis of the crack areas revealed a distinct pattern. Across all specimens, the cracked area showed (i) rapid growth at casing radial expansions between 0 µm and 100 µm, reaching cracked area values around 15 mm²; (ii) a gradually slower increase at casing radial expansions between 100 µm and 250 µm, reaching cracked areas up to 25 mm²; and (iii) a relatively constant cracked area stabilizing at approximately 25 mm² beyond radial expansions of 250 µm.