Design and Performance of Annular Pressure Build-Up APB Mitigation Techniques

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.

Study on Casing Safety Evaluation in High-Temperature Wells with Annular Pressure Buildup

“…• String materials: casing covered with compressible material [26]; optimization of casing size and steel grade [27]; vacuum insulated tubing [23]; • Equipment: rupture disk [28]; unidirectional pressure control tool; • Technological measures: injecting N 2 or compressible liquid into annuli [29]; adopting foam spacer.…”

Study on annular pressure buildup phenomenon in subsea wells considering the effect of cement

“…10,12,13,15,16 However, the presence of cement has a nonignorable effect on casing deformation and affects APB indirectly, including the influence on annular temperature and casing pressure. Moreover, some wells with APB adopt a wellbore structure that makes the TOC below the previous casing shoe, 8,19,28 which is called "cement shortfall." An open-hole section of the formation is exposed in this structure to reduce fluid mass for relieving APB.…”