Abstract
<jats:title>Abstract</jats:title> <jats:p>This paper presents an engineering approach for executing an extended reach cement milling operation using coiled tubing (CT) in a highly deviated offshore gas well in the Mahakam Field, Indonesia. The operation involved removal of approximately 3,747 m of cement inside a 3-1/2 in tubing string with well inclination reaching up to 70.36°, significantly exceeding conventional CT milling application limits.</jats:p> <jats:p>A comprehensive pre-job engineering workflow was implemented, integrating force modeling, hydraulic simulation, and fatigue analysis to define safe operational envelopes. Bottom hole assembly (BHA) configuration, milling tool selection, and fluid system design were optimized to improve penetration performance and mitigate risks related to frictional drag, CT buckling, and fatigue accumulation.</jats:p> <jats:p>Field execution was conducted through multiple milling runs with adaptive parameter optimization. The application of friction reducer fluids and optimized pump rate successfully reduced circulation pressure and improved cuttings transport efficiency. The operation achieved complete cement removal across the target interval without major operational failure, with penetration rates significantly improving during final runs using optimized bit selection.</jats:p> <jats:p>The results demonstrate that long interval CT cement milling in highly deviated wells is technically feasible when supported by integrated mechanical–hydraulic engineering design and real-time operational adaptation. This study provides a practical and scalable engineering framework for extending CT milling application limits in mature offshore developments.</jats:p>