Pre-commissioning Gas Lift Design Optimisation and Stability Analysis: Application to a High Water-cut Brownfield Well

Abstract

Gas lift remains essential for sustaining oil production in mature fields. Yet, despite its widespread deployment, instability‑related losses from heading, cyclic downtime, and compressor-trip shutdowns are often overlooked at the design stage, leading to deferred production. This study addresses this gap by presenting an integrated pre-commissioning workflow that combines nodal analysis, gas lift optimisation, and flow stability criteria, applied to ATIRI-W001T, a well in Atiri Field, Nigeria that quit production at 60% water cut due to vertical lift insufficiency rather than reservoir depletion (pressure depletion < 10% of initial). As part of an uptime improvement campaign, nodal analysis was implemented and identified an optimal gas injection rate of 1.8 MMscf/d within an operating envelope of 0.8 – 2.5 MMscf/d, yielding a predicted oil rate of 828 STB/d. Sensitivity analysis revealed a 94% decline in net oil rate (828 to 46 STB/d) as water cut increased from 60% to 90% BS&W, while the Gas Utilisation Factor (GUF) deteriorated from 2,174 to 65,217 scf/STB, underscoring the economic impact of rising water cut under limited lift gas supply. Flow stability evaluation using Asheim's two-criterion framework returned F₁ = 0.809 and F₂ = 1.028. the study provides a structured workflow for identifying instability‑prone wells and highlights the significance of pre‑commissioning stability verification in gas lift candidate screening and selection.