Enhancing Productivity of Gas Storage Wells Using Underbalanced Coiled Tubing Drilling (UBCTD) - A Success Story in Sharjah

Abstract In 2024, a highly specialized three well project utilizing Underbalanced Coiled Tubing Drilling (UBCTD) was successfully executed, marking a significant milestone in the evolution of the Moveyeid field into a strategic gas storage reservoir for Sharjah National Oil Corporation (SNOC). The project objectives were to enhance the existing wells' year-round production and injection capabilities and deliver peak gas demands at the lowest possible cushion gas pressure to improve the project's economics and maximize storage efficiency. Feasibility studies highlighted UBCTD as the best solution for well enhancement to allow utilizing the existing wells as conventional drilling was problematic in depleted fields. Detailed engineering was conducted based on the updated subsurface model, geomechanics, biostratigraphy, tubing forces modeling and multiphase hydraulics. The strategy adopted for this campaign was to drill multilaterals (four 1,500 ft laterals per well) within the most productive biozones and intercept the maximum number of fractures. A state-of-the-art AI/ML workflow using data from the landmark 2003-2007 Sajaa UBCTD project was used to determine best subsurface targets, address risks and augment drilling decisions. During UBCTD operations, gas was produced and exported to the Sajaa gas plant minimizing flaring at the wellsite, and costs were kept low by conducting the operations in the existing 4 ½″ completions without killing the wells and preserving the original perforations. The project exceeded all expectations by effectively achieving more than double the productivity per well, drilling additional 50% footage while saving 20% drilling cost within the stipulated time. Challenges were overcome during operations, and well trajectories were optimized on the fly to achieve longer contact length and more than the desired number of laterals from the singular casing exit. The successful deployment of this mature field enhancement project has helped to reduce the reservoir cushion gas requirement by a staggering 15%, along with gaining the ability to provide higher instantaneous production during periods of short-term peak demand. This paper elaborates on the overall project success, detailing the economics, schedule, HSE, drilling, and subsurface risks and challenges, along with the solutions adopted by the Operator. Extensive uncertainty mapping workflows and risk-based decision matrices were developed exclusively for this project, keeping the project NPT below 15%, a revered benchmark for a three-well underbalanced drilling campaign. The project is an accomplishment by all measures and was deployed in a highly efficient manner, overcoming challenges and delivering a successful well performance enhancement solution. Reservoir contact was increased from an initial 200 ft of flowing perforations to approximately 20,000 ft of openhole. This comprehensive approach demonstrates how integrating subsurface expertise with effective and efficient drilling strategies can optimize highly strategic underground gas storage projects and reutilize mature fields for resilient energy management solutions.