Experimental Measurements of mechanical parameters of Class G cement

Abstract

The new quest of unconventional resources is the achievement of well integrity which is highlighted by the inadequacy of conventional cementing procedures to provide zonal isolation. High temperatures and pressures or even post-cementing stresses imposed on the cement sheath as a result of casing pressure testing and formation integrity tests set in motion events which could compromise the long term integrity of the cement sheath due to fatigue. Knowledge of the mechanism of fatigue in cement and factors that affect it such as the magnitude of the load, strength and composition of the cement, mechanical properties of the cement and pattern of load cycles are important to achieve a realistic design of a cement system that will be subjected to fatigue loading. Such a design will go a long way to ensure the long term integrity of a well operating under downhole conditions. Finite element investigations help engineers to assess the stress magnitude and evolution for a given well configuration, but when structural calculations for casing-cement system are required, missing input parameters reduce the quality of the results. In order to have reliable data we performed an extensive experimental work using Class G cement in order to measure the principal parameters for mechanical structural calculations: compressive and tensile strength, Young modulus, Poison Ratio. The data was measured under room conditions and elevated temperature and pressure. The results were also extrapolated for a time period for more than 300 days. The paper will provide an excellent data inventory for class G cement that can be used when mechanical studies on cement, like finite element studies, are required.

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

“…This mechanism occurs in a vertical well that is subjected to reservoir compaction; the well compresses in the reservoir layer and elongates in the overburden layer. Although the compressive deformation could lead to severe well failure such as buckling, the tensile deformation is also critical as the well cement is damaged more easily in tension than in compression (i.e., cement tensile strength is approximately one tenth of the compressive strength (Teodoriu et al, 2012)). Also, the tensile failure could propagate upward along the well with the progress of reservoir compaction, inducing loss of zonal isolation.…”

Water absorption and shrinkage behaviour of early-age cement in wellbore annulus

“…The incremental form of constitutive equation for the cement skeleton is also employed in Hua et al (1995) and Zhen & Xiong (2013) to calculate the volumetric shrinkage strain. Experimental observations (Maharidge et al 2016;Teodoriu et al 2012) indicate that the stiffness of early-age cement increases significantly with time. In this study, the incremental linear isotropic elasticity with time-varying stiffness is employed to model the observed cement shrinkage behaviour.…”

HPHT 101 - What Every Engineer or Geoscientist Should Know about High Pressure High Temperature Wells

“…Figure19 shows how a crack can develop in the cement sheath esp. at HPHT condition Teodoriu et al 2012;YuanAl-yami et al 2012;YuanSchubert et al 2012). As the depth of well increases, the increased hydrostatic head causes an increase in ECD due to compression and increase in temperature causes a decrease in ECD due to thermal expansion.…”