During the life span of a well, the cement sheath may fail to provide zonal isolation and micro-annuli may develop between the cement-casing and cement-rock interfaces. Multiple factors during well construction and injection processes may have individual or combined influence on the micro-annuli formation. This paper presents a staged finite element modeling approach to simulate the well construction processes and injection cycle. Loads from the in-situ stress field, mud/slurry pressure, and periodic temperature changes are incorporated in the model. A “realistic” bottom-hole state of stress is generated in the model and microannuli generation is simulated by the tensile debonding of the cement-formation interface. The simulation results indicate the generation of micro-annuli is highly affected by the temperature difference between injection fluid and formation and the time span of the fluid injection cycle. Resulting debonding apertures in the models are in the order of 10-5m which corresponds with previous studies. The modeling results of this study indictates once debonding occurs, the debonding aperture increases quickly and may exceed the ranges considered hazardeous.

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