This paper describes the world's first true coiled tubing under balanced casing exit using a Nitrogen (N2) gas mist as the milling fluid, which allowed a well in Sharjah's Sajaa field to remain live throughout the casing exit, ensuring uninterrupted gas production. Previous attempts to mill a window using a N2 gas mist with conventional milling technology proved unsuccessful. This was largely due to the lack of cooling and lubricity of the milling fluid resulting in a rapid deterioration of the window mills. Subsequent windows were milled using water only which resulted in massive fluid losses to the formation, due to the low reservoir pressures within the field, and more importantly caused interruptions to existing gas production.

The technology described in this paper allowed gas production to be maintained throughout the window milling operation and resulted in a dramatic reduction in fluid losses to the formation and a reduction in overall casing exit time. Following the casing exit, the build and lateral drilling assemblies were deployed through the window at the first attempt, allowing uninterrupted progression to the under balanced drilling phase. This technology has helped to extend the life of the Sajaa field and secure the future of the Sharjah Coiled Tubing Drilling (CTD) project.

You can access this article if you purchase or spend a download.