Reliable toolface calculation is essential for achieving robust automatic steering control with rotary steerable systems (RSS). For RSS with fully rotating sensor packages, this task becomes particularly challenging under extreme conditions, where signal-to-noise ratio (SNR) of measurements from one or more sensors reduce significantly (e.g., while drilling near-vertical wells, along dip, towards magnetic north, in the vicinity of casing and/or under severe vibration and stick-slip). To ensure robust toolface control for fully rotating RSS under these conditions, this paper proposes a novel dynamic toolface calculation method.
The proposed dynamic toolface calculation method of the new-generation fully rotating RSS overcomes the challenge of achieving robust toolface control despite extreme drilling conditions, by bringing together real-time health monitoring, online sensor calibration and novel sensor fusion techniques. Considering that robust toolface control is the heart of any drilling automation architecture with RSS, this technology is key to enable advanced drilling control strategies in the future.
Surface-based damping mechanisms are the most commonly used method to mitigate stick-slip vibration in drilling systems, and their parameters are typically chosen based on low-order models of the drilling system. Field experience indicates that these low-order models do not capture all deformation mechanisms, and there is a need to include higher-order modes of deformation in the model. As a result, it is also imperative to delineate the effect of the surface damping mechanism on the higher-order modes of deformation, and vice versa. This work investigates this interplay using a combination of analytical methods, numerical simulations, and field data analysis.
The effect of surface-based damping mechanisms, in principle, is similar to that of vibration absorbers used to quench self-excited oscillations in nonlinear systems. Therefore, to determine the stability of the drilling system as a function of the surface damper parameters, a torsional model of the drillstring with a negative damping boundary condition at the bit is considered. For this system, the stability chart determining the rate of growth of amplitude of the natural modes as a function of the surface damper parameters is shown to depend on the operational parameters and on the configuration of the drillstring. These analytical observations are then evaluated using transient numerical simulations of a coupled axial-torsional model of the drillstring, with a realistic bit-rock interaction law. Finally, the efficacy of the analytical and numerical model in reproducing field results is demonstrated by analyzing downhole rotational speeds of the bit acquired using high-frequency data acquisition sensors.
The results described in this paper provide a mechanism to determine the effect of the surface damper parameters on the higher-order dynamics of the drilling systems, and provide a rationale to determine consistent damping parameters that do not adversely affect the higher-order dynamics of drilling systems.
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