Summary A fundamental understanding of the mechanical properties of zonal isolation materials is important for predicting well integrity during well operation conditions. Conventionally, the mechanical properties of zonal isolation materials are tested at ambient temperature using uniaxial testing. This study examined the mechanical properties of alternative zonal isolation materials such as rock-based geopolymer, thermosetting resin, and an industrial class expansive cement under realistic well conditions by triaxial testing. Mechanical properties such as Young’s modulus, Poisson’s ratio, cohesive strength, friction angle, and compressive strength of these materials at 30 and 90°C were compared. The effect of confining pressure on the mechanical properties of the materials was also examined. The findings of this study show that all selected materials possess compressive strength at 30 and 90°C and that the compressive strength of all the selected materials is strongly impacted by temperature and confining pressure. The Young’s modulus of all the selected materials was unaffected by confining pressure, while only the Young’s modulus of thermosetting resin was sensitive to temperature. The influence of temperature on the Poisson’s ratio varied from one material to another. In addition, when the test temperature increased, the friction angle of neat Class G and geopolymer decreased.
Formation of microannuli at the interface of cement-casing can create well integrity issues. X-ray CT and Optical microscopy are technological trends that may have potential for direct visualization of microannuli. CT has an advantage of providing non-destructive visualization of microannuli, but its resolution suffers with increase in casing thickness. Conversely, Optical microscopy has the potential of providing higher resolution needed to detect smaller sized microannuli; however, information about microannuli is limited to only a few sections where samples have been sliced. The objective of the current article is to describe a methodology to examine the interface of cement-casing. Experimental work was combined with literature review. This includes both direct visualization methods, evaluation of current trends to better understand the characteristics and geometric variation of relevant leakage paths. We generate test specimens consisting of cement plugs, various steel casing thickness and nano-coated aluminium casings. Hydraulic sealability tests were conducted by injecting water at the cement-casing interface. Flow rates are then interpreted in terms of microannuli aperture and direct visualization of the cement plug-casing interface by CT and Optical microscopy was implemented. The experimental findings of this article will form a basis for studying geometry and size of microannuli as well as modelling of fluid migration.
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