Bit Technology and Bottomhole Assemblies

Topics: Drilling

Drilling-efficiency improvements, needed to ensure continuous reductions in project cycle time, require holistic drilling-system evaluations. Bottomhole assemblies (BHAs), as part of the drilling system, have dominating effects on the functionality and effectiveness of other system components. BHA design, usage, and monitoring must promote drilling-system compatibility, efficiency, and reliability.

BHA design must provide or contribute to the creation of operational conditions that ensure efficient failure and removal of rocks. Additionally, it must enable the use of appropriate drilling parameters as needed by specific applications without compromising efficiencies of other drilling-system components. Research continues to investigate rock-failure mechanisms and the implications the processes have on drilling performance. Through this effort, it has been identified that different drilling parameters are needed for dissimilar rock types, even when rock hardness, hole sizes, well profiles, and hydraulic considerations are the same. In most cases, these findings dictate the need for different BHAs to accommodate appropriate parameter ranges and sweet spots.

BHA usage must not create conditions that initiate or promote dynamic dysfunctions. Such a condition, while compromising the functional efficiencies of other drilling-system components, also promotes premature downhole-tool failures. The contributions of microdoglegs to dynamic dysfunctions, excessive torque and drag, poor weight-on-bit transfer, and other issues have been known for a long time. Research into this area is providing a deeper understanding, together with findings that are bound to improve drilling-parameter management and overall drilling efficiency.

Appropriate parameter ranges, and improved BHA compliance with regard to vibrations, improve drilling efficiency. These conditions, though beneficial, are not sufficient to ensure BHA reliability. Considering the effect that BHA failures (e.g., twistoff) have on project cycle time and operational costs, investigators have taken a deeper dive into this issue. With the “whys” and “hows” of BHA failures identified, work flows have been developed to address these reliability issues.

Ensuring BHA efficiency and reliability is critical for drilling performance. These requirements must thread through BHA design, usage, and monitoring. Yes, the industry has the tools and know-how, and it can be done.

This Month's Technical Papers

How To Design a Bottomhole-Assembly Rotary-Speed Sweet Spot

Continuous Inclination Measurements and BHA Modeling Help Detect Microdoglegs

Development of Work Flow To Manage Fatigue of Bottomhole Assemblies

Recommended Additional Reading

SPE 183870 A Modified Three-Point-Contact Approach for Dogleg-Severity Modeling by Hossam Gharib, Halliburton, et al.

SPE 183037 Testing and Characterization of Shock and Vibration Loads To Enhance Drilling-Tool Reliability and Efficiency by Dennis Heinisch, Baker Hughes, a GE company, et al.

OTC 27575 Applying Real-Time Data Analytics To Detect Underreamer Failure Early During Hole Enlargement While Drilling in Deepwater Gulf of Mexico by Xianping Wu, Shell, et al.

Graham Mensa-Wilmot, SPE, is a senior adviser for drilling engineering at Chevron Energy Technology Company. He is the MAXDRILL (performance drilling) project leader and has more than 29 years of experience in drilling-applications research, downhole-tool development, drilling mechanics, drilling-­vibrations identification and remediation, and performance-­drilling improvement. Mensa-Wilmot serves on the SPE/IADC Drilling Conference Program Committee and the SPE Drilling and Completions Committee. He served as an SPE Distinguished Lecturer in 2016–2017 and previously served as a drilling-dynamics and performance-drilling instructor for the Petroleum Network Educational Courses series.  Mensa-Wilmot serves on the technical board of the SPE Gulf Coast Section and is a member of the JPT Editorial Committee. He holds an MS degree in drilling engineering from Romania’s Petroleum-Gas University of Ploiesti. Mensa-Wilmot can be reached at

Bit Technology and Bottomhole Assemblies

Graham Mensa-Wilmot, SPE, Drilling Engineering Senior Adviser, Chevron

01 December 2017

Volume: 69 | Issue: 12