  This work intends to analyze the nonlinear stochastic dynamics of
drillstrings in horizontal configuration. For this purpose, it considers a beam
theory, with effects of rotatory inertia and shear deformation, which is
capable of reproducing the large displacements that the beam undergoes. The
friction and shock effects, due to beam/borehole wall transversal impacts, as
well as the force and torque induced by bit-rock interaction, are also
considered in the model. Uncertainties of bit-rock interaction model are taken
into account using a parametric probabilistic approach. Numerical simulations
have shown that the mechanical system of interest has a very rich nonlinear
stochastic dynamics, which generate phenomena such as bit-bounce, stick-slip,
and transverse impacts. A study aiming to maximize the drilling process
efficiency, varying drillstring velocities of translation and rotation is
presented. Also, the work presents the definition and solution of two
optimizations problems, one deterministic and one robust, where the objective
is to maximize drillstring rate of penetration into the soil respecting its
structural limits.
