fax 01-972-952-9435. AbstractFrictional load losses during the tubular running into a wellbore are strongly associated with the well design. In complex architecture wells design, the drill string drag force is one of the most important analysis parameter. However, casing and liners drag forces are not proper considered, although differences between these types of pipes and the drill string can lead to significant changes in drag load levels.In this work, the influence of drag forces over casing and liner strings used in complex architecture wells is demonstrated. The study shows a numerical treatment of the problem and its validation through a model which calculates drag forces over the casing during running. In this way the prevalence of casing and liner drag forces as design parameter to be considered in conventional methodologies is demonstrated. The model involves stress and displacement calculations, using a recursive method, wich considers pipe discretization, stiffness of each pipe's element, and centralizer effects.The validation of the developed model was carried out with three wells located in the Santa Rosa field, Venezuela. The obtained calculations agreed with the actual values of hook loads, even in cases where the pipe got stuck, showing the model advantages for the design and analysis of complex architecture wells.