BHA-Design Approach Improves Drilling Performance and Wellbore Quality
Authors: Feder Judy 
Published: January 2021

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 199617, “Drilling Performance Evaluation Using Advanced BHA Modeling and Field Validation,” by Jeremy Greenwood, SPE, Julien Marck, SPE, and Vakkeyil Naveen Nair, Halliburton, et al., prepared for the 2020 IADC/SPE International Drilling Conference and Exhibition, Galveston, Texas, 3-5 March. The paper has not been peer reviewed.
Implementing a physics-based digital twin of a drilling system can enable the drilling team to leverage data at each stage of the engineering process to deliver more-consistent, repeatable drilling performance and improved borehole quality, which in turn enables drilling farther and faster while increasing downhole tool life. The complete paper discusses a new performance-evaluation methodology that combines bottomhole assembly (BHA) modeling with field data. BHA modeling simulates the drilling process accurately to establish key performance indicators (KPIs) to help optimize BHA designs to deliver improvements in drilling performance and wellbore quality. The model also can estimate quantities such as microtortuosity that are not directly measured by standard equipment.
Importance of Effective BHA Performance Evaluation
Determining the cumulative effect of BHA behavior during drilling on the quality of the wellbore and the subsequent impact on performance and life of the BHA is an important goal for improving overall drilling and well-delivery efficiencies. A higher-quality wellbore not only has a positive effect on reducing the time required for all drilling, casing, or completions running operations; in curved holes, it can also extend the life of the drilling equipment by reducing the rate of accumulation of fatigue and reducing the amount of work the bit is required to perform. This leads to longer runs because the system is more mechanically efficient and has a reduced equipment failure rate.
Developing an effective set of measurements allows for an objective comparison of different BHA designs and stabilization, bit selections, and downhole drive systems of rotary steerable tools, motors, or turbines. This quantification of BHA performance can be used to improve BHA designs in terms of component stiffness, amount and position of stabilization, type and configuration of the drive system, and bit-design features.
Defining terms to describe borehole quality at different scales is necessary to develop indices that are comparable across wells and that reflect any deviation of the wellbore from a perfectly smooth path. To fully quantify the mechanical effect of wellbore quality on the BHA, a wellbore-propagation model was developed to replicate the borehole and determine the accumulated stresses as the BHA passes through it. This approach overcomes the limitations of not having the required resolution of downhole measurements that accurately describe the wellbore trajectory on the smaller scale. The validation of the propagation model has been completed on multiple runs with examples presented in the complete paper.