Effect of curing conditions on the mechanical properties of cement class G with the application to wellbore integrity

Abstract

Wellbore integrity is highly dependent on the integrity of the cement sheath which plays an essential role in preventing any communication between the formation fluids and the surrounding environment. Mechanical failure of the cement sheath within a wellbore is influenced and governed by many factors including cement mechanical properties. However, the paucity of cement class G mechanical parameters including lack of experimental data under different confining pressure, tensile properties, and the effect of curing temperatures on the long-term cement mechanical properties are impediments to the numerical simulations in wellbore integrity assessments. Therefore, this study expands the cement class G mechanical properties inventory. This paper investigates the mechanical behaviour of cement class G at two different curing temperatures (30°C and 70°C) at the age of 28 days. The effect of both the curing regime and confining pressures (15 MPa and 30 MPa) on the strength and post-peak response of the cement under compression are examined. The measurement of tensile capacity and fracture energy performing indirect three-point bending tests along with the challenges involved with measuring fracture energy and modifications incorporated to the three-point bending test set-up, are explored. The obtained experimental were interpreted and subsequently utilised as input data for a constitutive model specifically formulated for modelling geo-materials such as cementitious materials and validated by numerical analysis.