A New Bottomhole Assembly Analysis Program for the Prediction of the Borehole Path Based on a Sophisticated Static Algorithm

Abstract

Abstract The theoretical bottomhole analysis of drillstring assemblies and the prediction of wellbore trajectories play an important role for directional drilling. Time play an important role for directional drilling. Time constraints, cost efficiency and accuracy require computer aided planning of the drilling process. As such a program should be user friendly and, at the same time, accurate, a program was developed for personal computers, combining simplicity even for less experienced users with complexity as regards the sophisticated computation of the directional drilling behaviour of a variety of bottomhole assemblies. The program is based on a newly developed three dimensional static drillstring analysis model for arbitrarily shaped boreholes. For any string assembly the wall contact problem is solved using a non-linear wall potential equation. The program allows sophisticated potential equation. The program allows sophisticated wellbore prediction calculations using an improved version of Ho's formula. The numerical results could be verified by field data; even the walk tendency is well predicted. Introduction Well operators face the problem of borehole deviation on nearly every well; either in vertical wells, where deflection should be minimal, or in directional wells where the bit course has to be controlled at all times. The key problem is to build the bottomhole assembly (BHA) by selecting the components for an optimum directional behaviour. This problem is generally approached in reverse by finding ways to predict the inclination and azimuth changes of the drillstring. The solution depends on different factors, such as BHA tool description, drilling parameters, especially weight on bit, well data including parameters, especially weight on bit, well data including surveys and hole size, and formation characteristics such as anisotropy and dip. Many mathematical models of bottomhole assemblies have been developed since the pioneer works on this subject by Lubinski and Woods. These models help to calculate the static parameters such as side forces and deflections along the drillstring and on bit. These parameters are responsible for the directional behaviour parameters are responsible for the directional behaviour of BHAs. There are different models such as static or dynamic calculations, 2D or 3D descriptions, and solution approaches for analytical or finite element formulations. FINITE ELEMENT METHOD Matrix methods of structural analysis based on the discipline of finite element techniques are used to determine the structural response characteristics of bottom hole assembly configurations. The most widely used form of the technique is the linear and nonlinear matrix-displacement method. The basic philosophy of the finite element method is a stepwise approximation. P. 449