Abstract

Subsea wells use Annular Pressure Build-up (APB) mitigation devices to ensure well integrity. Type I mitigation techniques control APB by reducing radial heat loss from the production tubing to the wellbore. Type II techniques work by controlling the stiffness (psi/°F) of an annulus by modifying its contents and boundaries.

Though 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 due to lack of a unified approach to analyze mitigation strategies, and partly due to 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, i.e., 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. Based on an extensive survey of published literature and patents, we also review APB mitigation techniques that have been used less frequently or awaiting proof of concept/field trial.

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