3D Rock-Bit Model for Drill Bit Design, and Performance in Challenging Field Applications
Authors: Huang Xu , Hanafy Ahmed , Ameri Taleb , Bomidi John 
Published: February 2025

Drill bit modeling is essential to bit design, bit selection, and bit drilling performance. The drill model bits are often developed from cutter-level cutting testing and atmospheric drilling environments, which limits their accuracy and field applications. In this study, a 3D bit model is developed combining cutter to bit level stepwise full-scale lab calibration and lab-to-field model transfer. The model accurately simulates drilling responses with different cutter shapes and designs, and predicts torsional stability such as stick-slip and HFTO at both sharp and worn states.

The interaction between the bit cutting structure and the rock is modeled using 3D Boolean operations on polygonal meshes. To accurately capture the cutting behavior of shaped cutters and worn cutters, penetration and cutting faces are differentiated and calculated using a physics-based unified force model. The model has rate dependent effects to capture torsional stability. A novel stepwise model calibration approach is developed to reliably determine model parameters from sharp state to worn state, and final progressive wear state, using hundreds of full-scale laboratory downhole simulator tests. Further calibration is successfully applied from lab to field applications to overcome field data limitations. To further improve simulation speed for real-time application, a 3D point-array drilling model is developed and validated.

The bit drilling model is first evaluated using cutting forces from single cutter lab tests. While the cutter-rock interaction is modeled correctly, the model over-predicts WOB and torque by more than 80% at given ROPs. After applying stepwise calibration on full-bit laboratory dataset, the WOB/torque error is reduced to 18% for both sharp and worn states, which is within strength variance of rock samples. The bit model is further validated to predict drilling responses of new cutter shapes and bit designs not in the calibration dataset, without loss in accuracy. The model-predicted HFTO excitability with different cutter shapes and bit designs matches with the measured vibrations in the full-scale laboratory drilling tests. By lab-to-field learning transfer, the drilling model successfully predicts the drilling response and bit dull in the target field application with very limited offset data. The 3D-array model captures the drilling response and cutter wear distribution in the field with a significant simulation speed improvement.

The present study shows that full-bit scale laboratory tests in relevant formation and real downhole drilling environment are necessary and important for high-fidelity drilling model calibration and development. The stepwise calibration process from sharp to worn state, and final progressive wear significantly improves model reliability and accuracy. The lab-to-field model learning is critical for the field application of the drilling model to overcome field data limitations. With rate-dependent calibrations, the drill bit model can predict torsional stability such as stick-slip and HFTO vibration tendency reliably. Application and design engineers can employ this robust model to enhance bit design and performance in challenging field applications such as interbedded hard sandstone and limestone.