Design optimization of bottom-hole assembly to reduce drilling vibration

Drilling vibration has been considered as one of the major undesirable drill-string dynamics. This paper establishes a framework to optimize the design of the bottom hole assembly (BHA) such that the BHA structure is resilient against vibration. Firstly, a high-fidelity BHA model is established using the finite element method (FEM), which considers the buckling effects caused by the weight on bit (WOB) and the contact between stabilizers and wellbore. Then, vibration indices, such as the BHA strain energy and the stabilizer side force, are derived using the FEM model to evaluate BHA vibration. The stabilizer positions can determine the indices through influencing the boundary conditions; therefore, designing stabilizer positions to reduce drilling vibration can be formulated as an optimization problem to minimize the BHA vibration indices over the operational range. The cost function is non-convex within feasible domain and cannot be expressed explicitly in terms of stabilizer positions. The derivative-free genetic algorithm (GA) is selected to solve the non-convex problem, where parallel computation is implemented to expedite the computational process. For model verification, the finite element analysis of a BHA is conducted and compared against analytical solutions and existing literature and shows a good agreement. A production BHA is optimized following the proposed method. GA can optimize the stabilizer positions with high accuracy and low computational cost. The strain energy and stabilizer side force of the redesigned BHA are significantly reduced compared with the original design, which results in a much better BHA dynamic performance and less drilling vibration.