Reliability Analysis of the Dynamics of a Horizontal Drill-String

Nowadays directional drilling, such as horizontal drilling, is very common. This chapter deals with the reliability analysis of a horizontal drill-string dynamics. A stochastic probabilistic computational model is considered, where a bar model (tension/compression) is used for the drill-string, and the system is discretized by means of the finite element method. The frictional forces between the column and the borehole are uncertain and relevant to the dynamic behavior of the structure. Therefore, a stochastic model is used for the frictional coefficient: a random field with exponential autocorrelation function. Because a probabilistic approach is employed, the reliability is measured in terms of the probability of the system not perform as it should, i.e., exceed stress limit, start a crack, or do not achieve a target efficiency. For the computation of the failure probability, importance sampling is applied to avoid too many stochastic simulations, and the stochastic system is analyzed for different scenarios.