BHA Behavior-Prediction Model Offers Potential for Automated Analysis
Authors: Carpenter Chris 
Published: November 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191780-18ERM-MS, “Field Validation of a New BHA Model and Practical Case Studies in Unconventional Shale Plays, With a Framework for Automated Analysis for Operations Support,” by J.K. Wilson, Scientific Drilling International, prepared for the 2018 SPE/AAPG Eastern Regional Meeting, Pittsburgh, Pennsylvania, USA, 7–11 October. The paper has not been peer reviewed.

A new 3D drillstring model determines the static and dynamic behavior of bottomhole assemblies (BHAs) in realistic wellbores. The modeling approach provides a prediction of the BHA’s mechanical and dynamic behavior and can be used as a planning tool for BHA design, an investigative tool for root-cause analysis, or, potentially, as a real-time optimization tool for avoiding harmful operating conditions.

Introduction

When using any model, engineers cannot forget the limits of calculation. However, they can settle for “good enough” as long as they adhere to the following two rules:

The results capture the general behavior of the system with respect to the parameters of interest.

The engineer using the results fully understands the limits of the model used to obtain them.

These rules are particularly important when considering highly nonlinear systems, such as the 3D behavior of BHAs. Nonlinearity arises in these systems from the large, coupled deflection that occurs in the downhole components as they move within the wellbore, and the frictional contact that results from the borehole wall restraining that movement. These inherent complexities have been a driving factor for continued research on the subject of BHA modeling for years. On the basis of the author’s own investigative studies and working experience, there appear to be three primary areas of focus within the study of BHA mechanics and dynamics:

The mechanical loading on the downhole components

The directional performance of various drilling assemblies

The dynamic response of BHAs

The purpose of the current project was to develop a BHA model that could analyze each of these topics in an efficient manner while maintaining a reasonable level of accuracy. Such a model could then be leveraged routinely to design more-robust tools and provide a reliable approach to engineering support for drilling operations.

BHA Simulation Model

As a response to the need to estimate downhole performance better, a mathematical model has been developed for estimating the mechanical and dynamic behavior of BHAs in realistic wellbores. It is based on a nonlinear finite-beam element and accounts for various intricacies of the downhole environment. Modeling a drilling assembly using this approach allows for the complexities of the BHA components to be easily represented as a series of beams with varying mechanical properties. The model was initially developed to analyze the behavior of vibration- inducing devices in unconventional horizontal wells, but has since been expanded to examine a multitude of different drilling•scenarios.