Simplifying Complex Design: Achieving Stable Production in Dual-String Gas Lift Utilizing Injection Pressure Operated (IPO) Valves – Handil Case Study

Abstract Handil Field, an oilfield in East Kalimantan, heavily depends on gas lift as its main artificial lift system. As of 2024, around 447 wells have been drilled. However, only 35% of the wells were active. Nearly 50% of the inactive wells were dual-string completions, mainly due to aging infrastructure, tubing integrity issues, cannibalized surface facilities, high water cuts, and operational challenges like unstable flow dynamics and difficulty restarting production. Many of these problems were caused by gas lift robbing and multi-injection phenomena, especially in dual-string completions with shared annulus injection and Injection Pressure Operated (IPO) valve utilization. The difficulty of designing dual-string gas lift systems was a major concern. Also, finding gas lift problems in flowing wells was limited by time-consuming and costly methods like FGS (flowing gradient survey) or CO2 tracer. Meanwhile, existing steady-state production simulators have limitations when used to evaluate dual-string wells. To tackle these challenges, three major innovations were introduced: Optimizing the number of valves: Historically, gas lift designs used three unloader valves and one orifice per string. The updated method adjusted the valve count based on updated reservoir data, including productivity index, reservoir pressure, and water cut. The new design required only one unloader and one orifice valve per string at most. This reduced complexity and decreased the risk of injection instability.Specifying valve size based on design sensitivity: Instead of using generic valve sizes, each valve was sized according to choke flow correlation and inflow performance relationship (IPR) conformance.Developing a custom dual string simulation tool: A new in-house simulation model was developed using network modeling principles to simulate dual string performance. The tool matched surface parameters such as wellhead pressure, temperature, and gas injection pressure to accurately estimate gas lift allocation per string without requiring dynamic simulations or tracer operation. These strategies successfully brought seven idle dual-string wells back online with stable production. Peak production hit 450 BOPD, and over 177 MBO cumulative oil has been produced since early 2024. The new evaluation tool outperformed standard software in accurately simulating gas lift distribution. The study also highlights the need to consider tubing leak history, water cut uncertainty, and injection pressure fluctuations when choosing valve sizes and injection depths. In a novel case, a dual-string well was redesigned and simulated to produce from a single reservoir using both strings, resulting in a 44% increase in production. By simplifying dual-string gas lift design through optimized valve configurations, customized orifice sizing, and the use of purpose-built simulation tools, this case study demonstrates how operational constraints can be effectively overcome and previously idle wells can be brought back online for production.