Abstract
This paper investigates the effects of a down-hole anti-stall tool (AST) in deviated wells on the drilling performance of a rotary drilling system. Deviated wells typically induce frictional contact between the drill-string and the borehole, which affects the drill-string dynamics. In order to study the influence of such frictional effects on the effectiveness of the AST in improving the rate-of-penetration and drilling efficiency, a model-based approach is proposed. A dynamic model with coupled axial and torsional dynamics of a drilling system including the down-hole tool in an inclined well is constructed. Furthermore, the frictional contact between the drill-string and the borehole is modelled by a set-valued spatial Coulomb friction law affecting both the axial and torsional dynamics. These dynamics are described by state-dependent delay differential inclusions. Numerical analysis of this model shows that the rate-of-penetration and drilling efficiency increases by inclusion of the AST, both in the case with and without spatial Coulomb friction. Furthermore, a parametric design study of the AST in different inclined drilling scenarios is performed. This study reveals a design for the AST, which gives optimal drilling efficiency, robustly over a broad range of inclined drilling scenarios.
Highlights
Drilling is used for the exploration of oil, gas, minerals and increasingly for geothermal energy
A comparison between the ROP and drilling efficiency obtained with the benchmark model and with the model including anti-stall tool (AST) shows that incorporating the AST significantly improves the ROP and the drilling efficiency for a broad range of spatial friction levels
The effect of a passive down-hole anti-stall tool on the drilling performance of rotary drilling systems has been investigated for deviated well scenarios
Summary
Drilling is used for the exploration of oil, gas, minerals and increasingly for geothermal energy. This paper focuses on the modelling and analysis of the coupling of axial and torsional vibrations in drill-string dynamics, and studies how a down-hole tool, called the anti-stall tool (AST) [31], affects the drilling performance (in terms of ROP) in a deviated borehole. In highly deviated wells the effects of this friction becomes more prominent, because the drill-string is resting under its own weight on the borehole wall In these models no vibrational dynamics and down-hole tooling have been taken into account, while it has been shown that the functioning of the AST is intrinsically related to the drill-string dynamics [37]. – Secondly, a model-based analysis of the effect of frictional contact between BHA and borehole wall on the drilling performance (in terms of ROP and drilling efficiency) is performed;.
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