Novel Workflow to Optimise Annular Flow Isolation in Advanced Wells
Authors: MoradiDowlatabad Mojtaba , Muradov Khafiz Mikhailovich , Davies David 
Published: March 2015

Abstract
Advanced well completion with multiple, downhole flow control devices such as Inflow Control Devices (ICDs), are a proven and effective solution to mitigate water/gas breakthrough and coning problems in horizontal and multilateral wells. An important parameter adversely affecting the ICD completion's performance is the annular flow. Such annular flow can be minimised or eliminated by segmenting the wellbore into a number of compartments by installing Annular Flow Isolation (AFI). Installation of sufficient AFI at the optimum locations is a key step in achieving the desired well performance. This number of AFI devices is itself constrained by both costs and risks associated with installing the completion string in a long wellbore of complex geometry. Previous AFI design workflows were based on either a single well parameter or a static well-reservoir model that do not consider the total lifetime benefits of the technology. A new AFI design methodology that accounts for the well's lifetime performance has been developed to ensure optimal AFI design in terms of the location and number of AFI installed along the length of the completion.
This novel workflow is based on the concept of, to a degree, mimicking the inflow performance of an "ideal" completion (i.e. the completion where AFI is installed between every 12 m completion joint) with a reduced, realistic number of AFIs. The great advantage of this workflow to optimise the AFI design is that it is based on the well's lifetime production performance while at the same time limiting the computation to a single reservoir simulation run for each number of AFIs. The workflow achieves this by ranking the AFI locations based on a criterion related to the annular pressures. A significant recovery increase can be achieved for wells designed with this new workflow when compared to previously proposed AFI design protocols. The learnings from this study can thus be employed by well engineers to optimally design advanced well completions.

1. Introduction
The (Autonomous)ICD [(A)ICD] completion has proved to be an effective solution to delay water and gas breakthrough due to reservoir heterogeneity or coning/cusping (Al-Khelaiwi et al., 2010). Annular flow is one of the many parameters affecting the (A)ICD completion's performance that need to be taken into account when designing an (A)ICD completion. Segmenting the wellbore into a number of compartments by installing AFI (e.g. packers) will minimise or eliminate annular flow and its adverse effects on the completion's performance.
AFI was not installed in the first ICD completions in Norway in 1997 (Madsen, 1997) due, at least partly, to the homogeneity of the Troll reservoir. However, AFI quickly became an integral component of ICD completions once their use was extended to heterogeneous reservoirs (Al-Qudaihy et al., 2006, Henriksen et al., 2005). The significance of AFI in ensuring the success of ICD completions was addressed by (Gavioli et al., 2010, Henriksen et al., 2006, McIntyre et al., 2006, Sunbul et al., 2007). It is now generally accepted that AFI is a crucial component in an (A)ICD completion's design and installation.
However, despite this acceptance of the importance of AFI, there is not a single, generally accepted, "fit-for-purpose" AFI design methodology. Previous AFI designs methodologies include:
a) Installing AFI with a constant spacing regardless of reservoir heterogeneity (Sunbul et al., 2008, Raffn et al., 2008).
b) Separating the completion into compartments of significantly different reservoir properties based on the near-wellbore permeability profile and/or other log data (Al-Qudaihy et al., 2006, Ratterman et al., 2005, Halvorsen et al., 2012). These analyses did not provide a quantitative cut-off, but used engineering judgement to determine AFI placement, e.g. as an arbitrary permeability ratio criterion of 0.01 between adjacent compartments (Al-Khelaiwi, 2013).