Prediction of Drilling Trajectory in Directional Wells Via a New Rock-Bit Interaction Model

Abstract

ABSTRACT This paper presents the basic concepts and methodologies of a new general rock-bit interaction model useful in predicting drilling trajectories in directional (and deep vertical) wells. This model is a generalization of existing similar models. It accounts for the anisotropic drilling characteristics of both the formation and the bit. The model is developed in a 3-D geometry. Therefore, it is capable of predicting the walk tendency and the build/drop tendency of a given BHA (bottomhole assembly) under any drilling condition. The model can be used as follows: in the forward mode to predict the drilling direction; in the inverse mode to generate the rock and bit anisot ropy indices; in the log-generation mode to generate drilling logs, such as a drilling dip log. Examples of the first two uses are shown. The drilling directions predicted using various practices and theories are compared to those using this general theory in parametric form. Significant differences can be seen, not only in the predicted walk tendency, which is often missed, but also in the predicted build/drop tendency of the BHA. This paper also shows why a 3-D analysis is essential to properly predict the drilling direction. A 2-D analysis not only completely ignores the walk tendency of the BHA, it also incorrectly predicts the build/drop tendency.