Directional Steering System (DSS) has been established for well drilling in the oilfield in order to accomplish high reservoir productivity and to improve accessibility of oil reservoirs in complex locations. Rotary Steerable System (RSS) is the current state of the art in directional drilling. In this work, we address the problem of real time control of RSS with unknown formation friction and rock strength. The work presents an online control scheme for real time optimization of drilling parameters to (1) maximize rate of penetration, (2) minimize the deviation from the planned well bore trajectory, and (3) assess the degree of bit wear. Nonlinear model for the drilling operation was developed using energy balance equation, where rock specific energy is used to calculate the minimum power required for a given rate of penetration. The bit wear is mathematically represented using Bourgoyne model. Detailed mathematical formulation and computer simulation were used for evaluation of the performance of the proposed technique, based on real well data. The obtained results showed excellent ability to accommodate the changes in the formation properties. In addition, the rate of bit wear has been optimized.

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