Breakthrough in Ultra-Deep Wellbore Enlargement: Dual Profile Expandable Reamer and 3D Cutter Technology for High-Pressure Junggar Basin

Abstract

As the discovery of new oil and gas reserves slows, the industry is turning to ultra-deep drilling, where complex formations present significant engineering and tool design challenges. In China's Junggar Basin, high-pressure water zones at 8,000 meters necessitated increased mud weights (2.28 sg), heightening the risk of formation leakage. To address this, borehole enlargement was used to enable contingency casing, but the high unconfined compressive strength (up to 30 ksi) and interbedded abrasive lithologies complicated cutting structure durability and performance. This study presents an integrated wellbore and tool design solution—combining advanced casing strategies with a new 3D cutter block, dual profile reamer, and optimized bit technology. Using advanced 4D transient drilling dynamics modeling and iterative field validation from 2022 to 2025, the system was tailored for lateral vibration, torque, and lithology-specific bottom-hole assembly (BHA) requirements. The innovative ridge-shaped cutters and stinger conical diamond elements improved both shearing and impact resistance, while gauge pad diamond protection enhanced durability. Field deployment in Q1 2025 resulted in the first successful application in China of a dual profile expandable reamer cutting block: a 9.25-inch tool completed single-run borehole enlargement in an 8,000-meter ultra-deep well. The approach delivered a 20% increase in rate of penetration, a 20% improvement in drilled footage, and saved 14 rig days versus prior runs. The secondary gauge functioned as a robust backup, enabling continued drilling after primary wear and eliminating extra under-reaming. These achievements mark a breakthrough for deep well enlargement in China, setting new benchmarks for operational efficiency, technical resilience, and cost reduction in high-pressure, ultra-deep drilling environments.