Investigation of Pressure Profiles of Reservoirs with Wells under Transient, Unstable Flow

Abstract

In this work, to the knowledge of the authors, it is the first time that an analytical solution demonstrates how the pressure profile changes with frequency and when this change takes place. Case studies are also presented to analyze the impact of different pressure profiles on well deliverability. Reservoir pressure profiles associated with steady-state, pseudosteady-state, and transient flow for a constant pressure drawdown were derived decades ago. These profiles, however, may not be applicable near the end-life of a well due to the unstable nature of fluid flow in the wellbore (e.g., liquid loading, slugging), and could explain why certain wells stop flowing before predicted. This paper shows how the flow instability changes the reservoir pressure profile and what consequences that change might bring to well production. Previous publications have shown numerical and experimental evidences that not only the pressure profile in the reservoir changes when there is an increase in the frequency of oscillation in the bottomhole pressure, but also that understanding this phenomenon is fundamental to reliably predict the time-dependent deliverability of wells.