Subsea wells use annular-pressure-buildup (APB) mitigation devices to ensure well integrity. We define mitigation techniques that control APB by reducing lateral heat loss from the production tubing to the wellbore as Type I techniques. Mitigation techniques that control the stiffness (psi/°F) of an annulus by modifying its contents and boundaries are defined as Type II techniques.
Although the physics of APB mitigation is well-understood, the reliability of a mitigation strategy or its interaction with other parts of the wellbore is not always quantifiable. This is partly because of the lack of a unified approach to analyze mitigation strategies, and partly because of the lack of downhole data after well completion. Simply stated, the engineer is hard-pressed to find computational-predictive methods to assess alternative scenarios and strategies within the framework of the design basis during the life of the well. In this light, our paper presents a quantitative approach to design the currently used APB mitigation strategies: rupture disks, syntactic foams, nitrified spacers, and vacuum-insulated tubing (VIT). In each case, the design is linked to the notion of “allowable APB” in an annulus, which in turn is tied to the design of the casing strings, and thus to wellbore integrity. We also review APB mitigation techniques that have been used less frequently or are awaiting proof of concept/field trial.