The First Worldwide Dynamic Solution for Iron Sulfide Removal Using Coiled Tubing

Abstract Iron Sulfide (FeS) scale accumulation presents a significant challenge in hydrocarbon wells, impacting well intervention, production efficiency, and safety. Descaling methods have evolved with time to the point where scale removal operations can be done in flowing conditions. This paper explores the design process of the world's first underbalanced descaling system with an enclosed solid handling system using Coiled Tubing (CT) in flowing well conditions. The paper will also discuss the design techniques and optimization based on documented experiences of descaling operations. Mechanical scale removal in flowing conditions using CT combined with real-time downhole measurement enhances descaling operation. The design consists of multiple key components such as using customized bottom-hole assembly (BHA) which can overcome harsh well conditions, using the right fluid systems to remove and transport scale back to the surface, controlling scale loading in the annulus, controlling rate penetration, ECD (Equivalent Circulating Density) while removing residual scale sticking to the completion walls among other considerations. The job design consists of two main runs; the first is the mechanical descaling incorporating a combination of a high-speed rotating tool (Turbine) in combination with a custom mill to create a pilot hole, and the second part is the rotary high-pressure jetting tool run which can withstand abrasive material, different combination of fluids like acids, solvents, gels and pure nitrogen. Unlike conventional descaling operations in overbalanced conditions, this design prioritizes maintaining the well in underbalanced and flowing conditions throughout the entire process. This approach aims to minimize injected fluids into the formation, reducing the risk of induced formation damage. Integration of real-time downhole telemetry sensors enhances job execution by detecting stalls, assessing downhole tool efficiency, and monitoring critical parameters. The successful implementation of this system demonstrated a significant advancement in scale removal operations. This pioneering design emphasizes safety, enhances control of hydrostatic pressure by limiting scale loading in the annulus, and ensures sufficient annular velocity of scale particles, presenting an evolution in gas well scale removal practices. This paper provides an overview of best practices in designing the world's first underbalanced CT descaling with an enclosed solid handling system, emphasizing the deployment of real-time downhole telemetry systems. The findings offer valuable insights, especially for harsh environment wells with limited reservoir pressure, and present recommendations for the seamless execution of novel underbalanced CT descaling operations, particularly for sour gas producers.