Coiled Tubing Intervention in Extreme Sour Wells (H2S 40%) to Prevent Sulfide Stress Cracking: Best Practices

The need to maximize hydrocarbon extraction from complex reservoirs is a key driver for the coiled tubing (CT) market, which offers efficient rigless well intervention solutions. A significant challenge lies in performing acid stimulation in severely sour wells with high temperatures, while simultaneously protecting the coiled tubing from corrosion and sulphide stress cracking (SSC). This study presents guidelines for the successful execution of CT interventions in extreme conditions containing up to 40% H2S and 11% CO2, under reservoir pressures of 6,000 psi and bottomhole temperatures near 300°F, all while mitigating risks associated with aci d and H2S corrosion. To address these conditions, an integrated approach was developed combining tailored pipe integrity management, recommended CT practices in sour services (API RP 5C7) and chemical protection strategies. This method establishes a comprehensive framework for operating CT in aggressive sour environments while extending its service life. The pipe management system continuously updates the CT's operational limits, monitors wall thickness, and characterizes deformations. It also evaluates pipe condition by detecting anomalies—such as pitting, mechanical damage, and corrosion—in accordance with API RP 5C8. By analysing extensive integrity data in real time, the system supports proactive decision-making, tracks the evolution of defects, and dynamically adjusts operating parameters. Chemical protection, incorporating specialized scavengers and fatigue derating, is used to inhibit corrosion in conjunction with engineered pipe management. This paper highlights how improved practices and continuous monitoring of defect progression throughout the string's lifespan enhance reliability and allow for on-the-fly adjustments to the operating window, reducing the risk of tubing failure. Case studies are included to illustrate key practices and provide lessons for the design and execution of CT interventions in similarly demanding conditions.