Optimized Well Design and Tailored Cementing Solutions to Mitigate Loss Zones in Re-Entry Wells: A Case Study on Combining Cement Support Tools and High Dog-Leg Severity Trajectories

Repurposing aging vertical wells (older than 20 years) by sidetracking the original hole and extending a medium-length horizontal section (4,000–5,000 ft) can significantly enhance production index, boost added value and extend well life by at least 10 years. This approach maximizes return on investment while revitalizing mature assets. However, sidetracking these wells poses significant challenges, particularly when penetrating troublesome formations associated with total mud losses. These formations often require extensive remediation efforts, consuming 5–7 days to cure, thereby increasing well control risks and cost implications. This case study highlights a successful horizontal re-entry operation where the casing design was modified to kick off the sidetrack below the problematic formation. Advanced trajectory design and cementing techniques were applied to drill the horizontal hole and cement the 4.5-inch off-bottom liner, efficiently achieving well objectives. To avoid the loss zone, the sidetrack was initiated deeper, necessitating a kick-off point below the existing 7-inch liner top, resulting in a double-cased sidetrack. This required working within a constrained vertical section to effectively land the well. The Dog-Leg Severity (DLS) was increased to 10°/30m—significantly higher than the conventional range of 4–5°—enabling successful trajectory design. A 6-inch horizontal hole was drilled to a total depth of 14,100 ft, planned for barefoot completion to produce from the open hole. To ensure proper zonal isolation, the penetrated reservoirs and formations above the target reservoir required isolation without compromising the exposed open-hole reservoir. A cement support tool (CST) was deployed 10 ft below the planned 4.5-inch off-bottom liner depth at 10,200 ft. The CST served as a mechanical fluid separator, providing a cement base that facilitated effective cementation of the 4.5-inch liner and enhanced wellbore stability during cement placement. The intervention successfully achieved its objectives, as validated by post-operation evaluations, including cement bond logs and pressure tests. The innovative integration of advanced trajectory design and tailored cementing solutions enabled the repurposing of the old well and ensured effective zonal isolation. Fluid losses were completely avoided, and the quality of the cement bond was significantly improved. These results addressed long-standing challenges in re-entry wells, delivering cost savings and operational efficiencies while achieving long-term well integrity. This study presents a novel methodology for mitigating complex loss zones in re-entry wells. By combining optimized well design with innovative cementing tools, such as the CST, this approach achieved precise zonal isolation and maintained wellbore stability. The framework offers practical solutions for similar challenges in depleted reservoirs, particularly in mature fields. This case study underscores the replicability of the strategy in high-risk well environments, demonstrating its potential to improve operational efficiency, reduce costs, and enhance reliability in challenging conditions.