Cement sheath integrity is important to maintain zonal isolation, as the annular cement sheath is considered to be one of the most important well barrier elements in the well, both during production and after well abandonment. It is however well known that cement sheaths degrad over time, e.g. from repeated temperature variations during production, but the link between the actual leakage rate and the degradation of cement sheaths have not yet been established.

In this paper, we have mapped actual leak paths of degraded cement sheaths, created by thermal cycling experiments, by X-Ray Computer Tomography (CT). The resulting leak path was imported into a Computational Fluid Dynamics (CFD) simulation software, making it possible to determine flow rates of various fluids through actual degraded cement sheaths. The pressure drop over the cement sheath was used as boundary condition of the system. Pressure driven flow through two degraded cement shetats was studied using methane gas as model fluid. The degree of degradation of the cement sheaths varied from systematically connected cracks to real microannuli. The flow through a system of connected cracks compared to a flow through true micro annuli was found to differ by orders of magnitude.

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