Pressure Transient Analysis in Advanced Wells Completed with Flow Control Devices

Abstract

Inflow Control Devices (ICDs) modify the inflow profile of a multi-zone well completion. Their imposition of an extra pressure drop at the sandface has proven to be particularly effective at delaying the breakthrough of (unwanted) water or gas in wells with long completion lengths. It is widely accepted that an ICD completion improves the field's economics; but the question of whether and why an ICD completion affects the accuracy of standard Pressure Transient Analysis (PTA) workflows has not been addressed. A typical ICD completion is designed to create an extra pressure drop of a similar magnitude to the well's expected reservoir drawdown when producing at its target rate. This paper shows why this extra pressure drop cannot always be treated as an additional skin value during PTA. This is because the ICD's pressure drop is a time dependent variable, varying with both fluid's viscosity and flowrate through the device. A nonlinear pressure loss can, sometimes, distort the pressure response and render conventional PTA methods inaccurate. The study presented in this paper uses an integrated, dynamically coupled, wellbore and reservoir model to define the limits within which treating the ICD pressure drop as an additional skin is a valid assumption and when its nonlinear nature will result in an inaccurately estimated value of skin and reservoir permeability. A general workflow for the analysis of PTA data measured in liquid producing wells completed with ICDs is proposed for the derivation of realistic values of the formation damage skin. The workflow has also been adapted for routine monitoring of wells completed with ICDs. The value of this study is illustrated by its application to two data sets from the North Sea's Golden Eagle field. This is an ideal field to test the validity of our theoretical analysis due to well completions with multiple levels of inflow control together with "state-of-the-art", downhole sensors. The results of this work allows Reservoir and Production Engineers to differentiate between deteriorating well performance due to increasing watercut and that due to an increasing formation damage skin.