Data Analytics and Physics-Based Simulation Enable Bit, Motor, and BHA Combination
Authors: Carpenter Chris 
Published: January 2021

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 29875, “Combined Data Analytics and Physics-Based Simulation for Optimal Bit, Motor, and Bottomhole Assembly Combination,” by Samba Ba, SPE, Dmitry Belov, SPE, and Daniel Nobre, SPE, Schlumberger, et al., prepared for the 2019 Offshore Technology Conference Brasil, Rio de Janeiro, 29-31 October. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission.
Today, drill bits and mud motor issues can account for more than half of the reasons for pulling out of hole before total depth (TD) on directional drilling wells. The complete paper presents a methodology designed for optimally matching drill bits, mud motors, and bottomhole-assembly (BHA) components for reduced failure risks and improved drilling performance.
Work Flow
The overall work flow includes detailed modeling of each sophisticated component and an algorithm to combine them efficiently at the system level without losing their specific nature.
Drilling-Bit Simulation. The drill-bit model is created in 4D - 3D space modeling plus the transient behavior with time. In 4D finite-element modeling, both polycrystalline-diamond-compact (PDC) and reverse-circulation bits can be modeled. The detailed cutting structure model may include specifying the number of cutters and how to place them in a 3D cutter space. The bit cutter and rock interaction must be modeled correctly to simulate the real scenario. This interaction is characterized by laboratory testing for almost all types of rocks interacting with the cutters.
Motor Simulation. The mud motor consists of multiple subassemblies. The power section assembly is where the transformation of hydraulic power into mechanical power occurs; this consists of a rotor/stator pair. The rotor is the moving part and the stationary stator is a metal tube with rubber bonded inside.
The authors developed a motor- optimization modeling work flow for evaluating the mud motor’s performance and durability for any defined drilling conditions. This model includes performance, fatigue, and hysteresis heating simulation capabilities. Within the framework of the developed work flow, the authors use three types of simulation (mechanical, thermal, and fatigue), with mutual correlations between the results.
Drillstring Simulation. A proper drill-string simulation is critical for the successful evaluation of drilling performance and equipment reliability. In this study, the drillstring and BHA analysis consists of a comprehensive full-scale finite-element model that also includes a proper transient analysis of the drilling process in a 4D analysis. This finite- element model uses 3D beam elements with six degrees of freedom for each finite-element node.
The described complex finite-element model incorporates all components from drill bit to surface. This model considers factors affecting the dynamic performance of the drillstring and can predict the transient response in the time domain. Detailed working mechanisms and geometries of downhole drive tools were implemented in the model to study the dynamic characteristics and directional performance of these tools.