Underreaming While Drilling Excellence: A Success Story of Asia’s Longest Two Consecutive Hole Opening Sections in a Deviated Well with Single Run Strategy

Abstract Back in 2020, a High-Pressure High-Temperature (HPHT) and high CO2/H2S carbonate appraisal well was drilled to remove subsurface uncertainties and to support the future development drilling campaign. The well architecture necessitated the inclusion of two consecutive hole opening sections to ensure optimum casing shoe placements. Along with the demand for long section intervals, the presence of problematic interbedded formation compounded by thick hard stringers added to the challenge for the underreaming operations where cutters durability need to be preserved. High shocks and vibration, Measurement While Drilling (MWD) lost signal, low Rate of Penetration (ROP), and Bottom Hole Assembly (BHA) twist-off were among the challenges and risks that were encountered and led to significant Non-Productive Time (NPT). A final appraisal well for this block was drilled in 2023 which is more challenging due to the deviated well profile. Re-evaluating the lessons learnt from the previous experience, the engineering team from multiple drilling disciplines among the operator and contractor worked closely together to investigate and identify all potential weak points in the planning stage. The aim is to reach Total Depth (TD) for both hole opening sections in a single-run strategy. A physics-based finite element modeling was conducted to study the drilling dynamics of the drilling operation involving bit selections, BHA design optimization, and drilling parameter sensitivity. A much wider range of worst-case scenario modeling was conducted in terms of lithology exposure, and several key technical recommendations were examined and prepared thoroughly to ensure all drilling objectives can be achieved. This extensive collaboration resulted in a comprehensive road map for offshore team to follow through including the contingency scenarios with the close support from engineering team in town. As a result, both 18-1/8in × 19-1/2in and 14-3/4in × 16-1/2in hole opening sections were drilled successfully with an impressive multiple rig-days saving against planned duration collectively. The combined 2,213m depth interval from the two consecutive sections puts this remarkable achievement in the record book as the longest hole opening operations in Asia. This paper will share the experience of the complete engineering cycle from the pre-job well construction planning, drilling dynamics modeling and analysis, drilling parameters execution, also capturing key lessons learnt from the operation and recommendations for similar hole opening application in the future.