ABSTRACT:

The state of stress in the cement of a completed well's annulus is a critical parameter in evaluating well integrity. This state of stress controls opening of permeable micro-annuli between the cement, formation rock, and/or casing as a result of the varying conditions of the well caused by fluid injection, production, thermal, and chemical changes. This state of stress also controls failure of the casing, such as by externally driven crushing or internally driven rupture. The first step in determining this state of stress is to estimate the effective stress exerted by the cement immediately after it cures, when it has transitioned from a liquid to a solid. This point in time, represents the initial condition for all failure and leakage analyses. In this work, we evaluate tensile annulus opening in a cemented wellbore by high-pressure fluid injection as an example illustrating the importance of considering the initial state of stress. We also present a work flow in Abaqus that allows for modelling the expected initial stress condition in a cemented wellbore.

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