Excessive torque and drag can be critical limitation during drilling highly deviated oil wells. Using the modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. Identify which problems lead to excessive torque and drag to prevent cost losses and equipment damage. Proper modeling data is highly important for knowing and prediction hole problems may occur due to torque and drag and select the best method to avoid these problems related to well bore and drill string. In this study, Torque and drag well plan program from landmark worldwide programming group (Halliburton Company) used to identify hole problems.one deviated well in Zubair oil fields named, ZB-250 selected for analyses the effect of friction factor on torque and effective `tension of the drill string along well depth, moreover the effect of well bore problems such as; mud losses, accumulation of cutting bed in the well bore, stuck pipe, caving, sloughing, high torque and drag values on drill string components and well trajectory. Wells data which include hole section size, mud properties, well profile survey, casing string depth, rig specification, drill string components, drilling parameters like weight on bit, rotary speed and flow rate were used to compare between planning and drilling stages for these wells and identify the reasons of difference between these stages. The results showed a difference for the drilling phase and increasable in effective tension, torque, pick up and slack off drag, measured string weight, and possibility to occur the buckling if compare with planning phase. Wellbore instability, high friction factor, high tortuosity, high flow rate ,stuck pipe , excessive drag spot, partial to total losses, increase of drilling parameters, hard formations and bad hole cleaning, all these factors yield to this difference between planning and actual phases. When drilling hole section 8.5", the main causes of varying were drilling fluid losses, high value of friction factor, stuck pipe and friction forces when the maximum torque was (16 to 20 klb-ft) and pick up weight (20-40 klb)

The benefits from doing this analytical study in order to be able to measure and predict the frictional forces affecting a drill string and wellbore (Torque and drag) by construct model of well plan software, hence; the high deviated and directional wells must be planned to keep the torque and drag forces at a minimum and allowable limit. Also, knowledge of the drill string phenomena can give us an opportunity to choose drill string components that consider these extra forces involved in the operations "high torque and drag values" in directional sections. In addition to knowledge of influence torque and drag on planned well trajectory can give us a good idea and lesson learned to consider this challenges in the next planned well profile. As a result of well path design one of the best ways to reduce torque and drag forces. One deviated well in Zubair oil field named, ZB-348 have been selected for analyses torque and drag problems and study the effect of (friction factor, well profile and drill string design) on the mentioned problem. Well data include hole section size, fluid properties, well profile survey, rig specification, drill string details and drilling parameters were used in well plan software from landmark worldwide programming group to make a comparison between actual and planning status. The results show a difference between planning and actual case when drilling 12.25" hole and found the root causes for this difference are high flow rate, tortuosity, well bore instability and complete losses.  The maximum torque about (20 klb-ft) and drag value approximately (30 klb).