Side Force and Directional Tendency of BHA with Eccentric Components
In directional drilling, both the side force and the tilt angle influence the dog leg severity (DLS) of the wellbore. The side force and the tilt angle of the drill bit also influence each other. It is imperative to calculate the two factors to predict the drilling direction. Three new analytical models are developed based on force analysis in this project in order to calculate the side force and DLS for Push-The-Bit BHA and Point-The-Bit BHA. In the models, the BHAs are assumed to be a continuous beam supported by the drill bit, the pivot pad and the stabilizer. The side force and tilt angle can be calculated when the BHA is in static force balance status. The DLS of the wellbore can be calculated with the side force and the tilt angle. Two models, one model with rigid drill pipe assumption and one model with elastic drill pipe, are used to analyze Push-The-Bit. The models show that the side force is the main factor to influence the walk direction of the drill bit for Push-The-Bit. The stronger the drill pipe, the higher the efficiency of directional drilling. One model is used to calculate the Point-The-Bit. The Point-The-Bit model shows that the tilt angle is the main factor that controls the walk direction for the Point-The-Bit. The models in this project uncover the interaction between the side force and the tilt angle. They also provide a way for drillers to estimate the drilling direction during operation that is a great advantage in controlling the drilling direction.