Modeling and Analysis of Axial and Torsional Vibrations of Drillstrings with Drag Bits

Abstract

Rotary oil-well drilling systems supplied with drag bits are used to drill deep boreholes for the exploration and the production of oil and natural gas. Drilling systems usually suffer from severe vibrations, which occur as axial, lateral and torsional oscillations. These vibrations mostly cause failures of drill-strings, abrasive wear of tubulars, damage of the bit, reduction of the rate of penetration (ROP), and incur high costs. Despite extensive research in this area, there is still a need to develop a consistent model that adequately captures all relevant phenomena such as nonlinear cutting and friction forces at the bit/formation interface, drive system characteristics and coupling between various models of vibrations. This study presents a physically consistent nonlinear lumped-parameter model for the coupled axial and torsional motions of a rotating drill string equipped with a drag bit. An innovative cutting and contact model is used to model rock/bit interaction. The dynamics of rotary and axial drive systems including hoisting system are also considered. The equations of motion are solved numerically to carry out parametric studies. The effects of various operational parameters are investigated for achieving a smooth and efficient drilling. The proposed model appears to capture stick-slip and bit-bounce as the simulation results qualitatively agree well with field observations and published theoretical results. The rotational and axial motions of the bit are obtained as a result of the overall dynamic behavior rather than prescribed functions or constants. The results show that with a proper choice of operational parameters it is possible to minimize the effects of stick-slip and bit-bounce and to increase the ROP. Therefore, it is anticipated that the results will help reduce the time spent in drilling process and costs incurred due to severe vibrations and consequent damage to equipment.

Research on vibration and deflection for drilling tools of coal auger

“…Drilling tools are acted by a complex contribution of their own weight, propelling resistance, drilling torque, impact contact force with hole wall and frictional resistance from coal during the process of coal auger drilling. The article focuses on drilling tools and puts forward following basic assumptions [30,31]:…”

Vibration and Deflection Behavior of a Coal Auger Working Mechanism

“…A nonlinear model of axial and torsional coupled vibration of the rotary drill-rod was established. It suggests that adjusting the processing parameter properly contributes to reduce the drill-rod stick-slip vibration and bit bouncing [21]. The stress distribution of the drill-rod worked in soft coal seam was simulated, which shows that the drill-rod joint causes stress concentration [22].…”

A multibody dynamics model of contact between the drillstring and the wellbore and the rock penetration process

“…This approach uses the absolute nodal coordinate formulation (ANCF) beam to model the flexible drillstring. 6,7 This method enables modeling and simulation of the large deformation, large displacement, and rotation of the drillstring with complex stochastic contact boundaries and slenderness ratio up to 10 3 . The full-hole multibody dynamics drillstring model is thus developed and the simulation results greatly promote engineering understanding of the drilling process dynamics.…”

“…In the past decades, there have been numerous theoretical and simulation investigations of the drilling process on predicting the wellbore and analyzing the drillstring's motion and deformation. [1][2][3][4][5] Conventional methods include the finite element method (FEM), the differential equation method, and other analytical solutions. Among them, analytical solutions are concise but have over-simplified the stochastic collision between the drillstring and the wellbore; FEM, although playing an important role in drilling process analysis, is not competent to modeling and simulating large deformation, large displacement, and rotation of the drillstring, and the large number of modeling elements greatly impairs the calculation speed.…”