Prediction of Wellbore Trajectory Considering Bottomhole Assembly and Drill-Bit Dynamics

Summary This paper presents a numerical dynamic model to predict wellbore trajectory in both the vertical and horizontal planes. The model is three-dimensional (3D) and consists of the idealization of the bottomhole assembly (BHA) into a number of finite elements. Inertia properties are included to predict the transient dynamic behavior of the assembly during drilling. To ensure the correct boundary condition at the bit/rock interface, two rock/bit interaction models, one for a roller-cone bit and one for a polycrystalline-diamond-compact (PDC) bit, are developed. The time average of the rock/bit interaction force components is used to obtain an indication about the directional tendencies of the BHA. Examples of the rock/bit interaction forces for roller-cone and PDC bits and examples of the motion of a holding assembly for both bit types are given. The effects of hole inclination, weight on bit (WOB), rotary speed, and bit/stabilizer clearance are presented for an example of a building, holding, and dropping assembly. The deviation tendencies, as predicted by the model for several building and holding assemblies, are compared with field case data.