Friction-Induced Wellbore Instability Due to Drill String

Abstract

In this chapter, we study numerically friction-inducedInduced wellboreWellbore instability due to frictionalFrictional interaction between drill string and rock materials using torsionalTorsional pendulum systemSystem. The classical Amontons--CoulombAmontons-Coulomb (AC) friction laws are widely used for explaining the variety of slidingSliding- and rotationRotation-related phenomena, yet the AC laws fail to explain stiffnessStiffness dependence of stick-slipStick-slip motionSlip motion. In recent times, the rate and state friction (RSF) model has found widespread applications for understanding the phenomena related to sliding of rock surfaces. The RSF modelRSF model, which is basically modified form of the aforementioned AC laws, has not yet got any attention for studying the friction-induced wellbore instability. The RSF laws state that friction of hard surfaces such as rocks and metals at high ({\textasciitilde}MPa) normal stress depends on current slip velocityVelocity as well as nature of the sliding surfaces. The literature review reveals that rotation of drill string causes stick-slip vibrationVibration, thus potentialPotential initiation of the failure process in surrounding mediumMedium. We use linearLinear and nonlinearNonlinear stability results to discuss a critical stiffness above stick-slip behaviour of the rotating system disappears. It is also demonstrated in the numericalNumerical simulationsSimulation that stick-slip motion could also be eliminated by increasing rotationalRotational velocityVibration of the drill string.