Step Change in Under-Reaming Efficiency: Novel Architecture Engineered for Stability and Durability

Expandable reamers enlarge a wellbore, often below a restriction, by removing rock using diamond cutting elements. The inherent dynamic instability of the reamer and abrasive lithologies can rapidly degrade the diamond cutting elements and jeopardize the successful enlargement of the planned wellbore section. This paper presents a holistic design methodology and provides field verification for innovative cutting structures that enhance stability and wear resistance of expandable reamers in demanding applications. The first goal was to reduce the lateral excitation of the reamer. This was achieved by introducing: (1) a stabilized body and sleeve to limit the eccentric movement of the reamer; (2) refining the aspect ratio of the profile to reduce static imbalance forces; (3) optimizing the cutter rake configuration to limit dynamic excitation generated during cutter-rock interaction; and (4) introducing a lateral displacement control feature to dampen excessive shock peaks. The second goal was to improve wear resistance of the reamer by introducing a second profile that acts as a full-gauge backup and effectively doubles the diamond volume of the first profile. The novel designs were verified using 4D transient drilling dynamics modeling. The design of experiments considered different BHA types, well plans, operating parameters, and rock types. Key observations included reduced lateral vibrations in all test cases and reduced stick-slip in 79% of test cases. Simulations were further validated on a test rig in an under-reaming-only configuration. The previous baseline experienced five incidents of 12 g or greater lateral acceleration, whereas the novel concept experienced no such incidents. Field validation was conducted in deepwater North America wells where previous reamers had failed to enlarge the planned section. The novel designs successfully opened the holes in single runs, demonstrating significant reductions in both lateral and torsional vibration severity. This paper provides an example of state-of-the-art advanced cutting structure design based on forensic examination, concept development, and advanced computer modeling, along with full-scale experimentation and field validation. The resulting, novel cutting structures have established new stability and durability benchmarks in North America.