Identifying Important Features to Minimize Hole Deviation in Percussive Drilling

Sammanfattning: Hole deviation is one of the most significant problems in drilling applications. Deviated holes result in inefficient blasting and have severe economic impacts due to increased equipment consumption. Conversely, straighter holes help in increasing production scales and reduce operational costs. The reason for hole deviations could range from anisotropic behavior of the rocks being drilled to the behavior of the drill string under the action of imposed forces. Deviations caused due to rock anisotropy are complex in nature and non-controllable to some extent but deviations due to mechanics of drill strings can be controlled as they lie in the operator’s area of influence. In this thesis, a 2D mathematical model is constructed which predicts the bending behavior of the drill rod and the model is further extended to predict the buckled profile of the entire drill string. Two bit state parameters are defined which help in better characterization of hole deviation and understanding of deflected state of the drill bit. Epiroc’s drilling data is inserted in the model developed and the buckled profile of the drill string is studied. The developed model is used to further understand the effect of various drilling parameters like bit thrust, angle of inclination, hole length, etc. on hole deviation. Through the results it was concluded that the bending stiffness of the drill rods is the most critical parameter influencing hole deviation for Epiroc’s drilling data and drill string setup. Finally, potential improvements and techniques to validate results obtained from the mathematical model are proposed.