Effect of bit-rock interaction uncertainties on the torsional stability regions of an oil-well drilling system

Marcelo A. Trindade¹; Hugo L.S. Monteiro¹

¹ University of São Paulo, São Carlos School of Engineering

doi:10.20906/CPS/USM-2016-0050

Resumo

Torsional vibrations due to stick-slip phenomena may lead to large variations in the drilling angular velocity which in turn may cause to a large number of failures in the drilling process such as damage in drill pipes, due to large torsional deformation, and in drill bits, due to large angular velocities. Previous works have dealt with the search for stable drilling regions, in terms of the oscillation of the drill-bit angular velocities. It has been shown that standard linear proportional-integral (PI) control laws, in which the control torque is proportional to the deviation of the drive table angular velocity and displacement from the reference/target ones (constant angular velocity), may lead to an oscillating angular velocity at the drill-bit due to stick-slip phenomena. This effect can be reduced using properly designed control parameters (control gains). Stability regions were defined for a given set of control parameters, and for a given drilling condition, using as a criteria the average deviation from the expected/target angular velocity. This was done using a finite element model for the drilling system combined with a dry friction model for the interaction between drill-bit and rock formation. However, in reality, the latter is much more complex and, thus, quite hard to predict using such a simple dry friction model. In order to provide robustness for the analysis, one possible approach is to consider uncertain parameters for the dry friction model. This can be done using a stochastic model for the bit-rock interaction torque which then leads to stochastic results for the angular velocity response, when subject to a linear PI control, and, thus, for the angular velocity deviation stability regions. In this work, confidence intervals for the stability regions are presented. This is done using a Monte Carlo simulation using the previously developed finite element model and considering parametric uncertainties for a dry friction model, intended to represent the interaction between drill-bit and rock for

Palavras-chave: oil-well drilling; stick-slip phenomena; vibration control