A completion system and method adapted for use in wells having long lateral boreholes includes a mast assembly, a pipe handling mechanism, a pipe arm, a pipe tub, a pump/pit combination skid, a rig carrier, and a control system. The mast assembly can extend in a generally vertical direction, e.g., perpendicular to the rig carrier and/or the earth's surface, such that the rig can be placed directly adjacent to a wellbore, and the top drive or a similar drive system can be engaged with and move along the mast while remaining above the wellbore.