Oil prospecting uses an equipment called drillstring to drill the soil until the reservoir level. This equipment is a long column under rotation, composed by a sequence of connected drill-pipes and auxiliary equipment. The dynamics of this column is very complex because, under normal operational conditions, it is subjected to longitudinal, lateral, and torsional vibrations, which presents a nonlinear coupling. Also, this structure is subjected to friction and shocks effects due to the mechanical contacts between the pairs drill-bit/soil and drill-pipes/borehole. This work presents a mechanical-mathematical model to analyze a drillstring in horizontal configuration. This model uses a beam theory which accounts rotatory inertia, shear deformation, and the nonlinear coupling between three mechanisms of vibration. The model equations are discretized using the finite element method. The uncertainties in bit-rock interaction model parameters are taken into account through a parametric probabilistic approach, and the random parameters probability distributions are constructed by means of maximum entropy principle. Numerical simulations are conducted in order to characterize the nonlinear dynamic behavior of the structure, specially, the drill-bit. Dynamical phenomena inherently nonlinear, such as slick-slip and bit-bounce, are observed in the simulations, as well as shocks. A spectral analysis shows, surprisingly, that slick-slip and bit-bounce phenomena result from the lateral vibration mechanism, and that shock phenomena comes from the torsional vibration. Seeking to increase the efficiency of the drilling process, an optimization problem that aims to maximize the rate of penetration of the column into the soil, respecting its structural limits, is proposed and solved.