Simulation of directional drilling by dynamic finite element method

Directional drilling in gas wells is expensive and time-consuming. Therefore, the most ideal drilling method is to drill along the target trajectory as fast as possible without trip-out. In this study, a dynamic drilling simulation model was developed that can virtually apply the WOB and drill bit rotation speed necessary for tracking the target trajectory without trip-out to the BHA equipped with a fixed-angle bent sub. Most of the models that calculate the expected trajectory of the drill so far are based on the static model, so the calculation is fast, but there is a disadvantage in that the vibration of the drill string accompanying drilling cannot be implemented. In real drilling sites, continuous exposure to the stick-slip phenomenon causes breakage and deformation of the drill bit, so a tripping out is required. The dynamic FEM model proposed in this study can predict failures caused by stick-slips and the drill trajectory according to operating conditions. The drilling trajectory prediction by this model was in good agreement with the results of commercial software performed under the same conditions. The proposed model simulates the stick-slip phenomenon well under operating conditions where stick-slip can occur. According to the results, when stick-slip occurs in the simulated bedrock condition, about 3.2 times the rotational torque is required than in the case of the normal operation condition. The proposed model can simulate the ROP during the stick-slip period, and according to the results, the normal operation when the drilling speed is 30 RPM improved the ROP by about 21 % compared to the stick-slip period. In conclusion, the presented model can be used as a means for virtual construction of a given target trajectory under optimal operating conditions when performing directional drilling with a BHA equipped with a fixed angle bent sub.