Future of Directional Casing Drilling with the New Block Type High Ratio Underreamer Technology to Further Optimize the well Engineering Design and Reduce Carbon Foot Print
Authors: Baharudin Alif Shamir , Chai Beng Seow , Nik Mohd Najmi Nik Fahusnaza , Bayking Elias Jr. , Ravendrnathan Khabilashini 
Published: August 2022

Abstract
With more wells planned in the future to be drilled in challenging formations, directional casing while drilling technology need to be on par with the demand. In Malaysia, there is a need to utilize directional casing while drilling to mitigate the risk of losses from the offset wells and when there is wellbore stability which will affect the drilling operation, especially when we drill deeper near the hydrocarbon zone.
The main challenge in this field is the abrasive formation with interbedded stringer. To further optimize the well engineering by eliminating one casing design, the plan is to drill with directional casing while drilling with long 12-1/4" hole interval for the well design. Thus, there is a need to have a robust underreamer design to meet the well design’s objective, which is the new block type high ratio underreamer technology. With anti-collision issue, the Directional Casing Drilling Bottom Hole Assembly was planned to be run with motor. This will be the first assembly run globally. Thus, the pre-job planning is essential in order to deliver flawless execution.
As part of the method to make this operation a success, the main challenges were identified and solved. The main challenge is the technology maturity for the underreamer from arm type high ratio underreamer to block type high ratio underreamer with more cutter density that can enlarge the hole with higher durability, and the cutting structure technology that can withstand both impact damage (from interbedded formation) and wear (from abrasive formation) with long interval of drilling footage. With the offset data obtained, the deep leech technology was applied to the cutting structure which increase the impact and wear resistance.
The Cutter density per arm of block type high ratio underreamer is 200% more than the arm type high ratio underreamer, which provide more durability in drilling challenging formation. The compatibility of the block type high ratio underreamer with the motor assembly was studied for risk assessment and mitigation plan. The drilling parameter road map have been studied with the previous track record of Directional Casing Drilling as a baseline to minimize the damage to the cutting structure.
With the careful planning for the first block type high ratio underreamer, the longest interval for 9-5/8" Directional Casing Drilling have been performed back-to-back for two wells in East Malaysia with challenging formation. The well design successfully eliminates 1 string by having 13-3/8" casing only as a conduit, which save approximately USD 400,000 and 48 hours in the flat time per well compared with the conventional well design cost from the offset well.
The introduction of block type high ratio underreamer expand the directional casing drilling application into more challenging formation with longer interval. This will greatly change the well engineering design and reduce the carbon footprint by eliminating surface casing requirement.