Breaking New Ground: Sidetrack Operations in Un-Cemented Liners

The objective of this paper is to summarize the strategy and operation sequence for the project. These strategies enabled the successful opening of a window in the un-cemented 11.7/8″ contingency liner. As a result, the team was able to reach the top of the objective and deploy the 9.5/8″ liner, in alignment with the original well plan. The paper provides details on the following: The comprehensive evaluation process Risk identification and mitigation measures Preparatory steps Whipstock deployment Milling operations The drill-ahead strategy Each phase is outlined to highlight both the technical execution and the lessons learned. These insights are valuable for future applications in similar well environments. After encountering severe hole stability issues and repeated stuck pipe events while drilling the 12 1/4″ section, the main branch was abandoned, and the 11 7/8″ liner contingency was deployed. However, the liner became stuck, preventing any cementing operations. Consequently, a decision was made to abandon the bottom of the hole and open a window in the uncemented liner. A peer review identified several critical risks associated with performing the sidetrack operation in uncemented casing, and mitigations were planned accordingly. This included a cleanout run with a scraper BHA, and a bridge plug set & pressure tested accordingly. A hydraulic whipstock was successfully deployed and a window in the 11.7/8″ liner was milled achieving stable parameters through controlled milling. Several control runs were performed to ensure the stability of the window and the wellbore, with successful results. The operation successfully executed a cased hole sidetrack in an uncemented liner. This practice is not commonly employed, however, it is often necessary in this region because of recurrent hole instability, casings or liners set off bottom, and poor cement jobs. The operation allowed saving 750m drilled and an additional 11.7/8″ liner contingency deployment (if the sidetrack was performed in the 14″ CSG). This operation highlights the critical role of adaptive strategies and innovative technologies in addressing complex drilling challenges. The successful execution of a cased hole sidetrack in an uncemented liner offers valuable lessons for future well interventions, particularly in technically demanding environments. This paper presents the first such operation conducted by the Drilling & Wells team, detailing the key challenges encountered, the solutions implemented, and the operational outcomes—underscoring its significance for future drilling campaigns.