Torque and drag applications for deviated and horizontal wells: a case study

Çağlayan, Burak Kağan
One of the most critical limitations during hydrocarbon exploration, especially during directional drilling, is torque and drag generated by the contacts between the drill string and the borehole or casing. Therefore, torque and drag analysis and calculations are very important for well design to prevent equipment and economical losses. Proper modeling is highly important to predict and prevent downhole problems related to drill string and borehole, beforehand commencing to the activities if not during the course of the drilling campaign. In order to emphasize the importance of torque and drag in drilling activities, many studies were conducted and different models are already developed in literature. In this study, a synopsis of the important literature on torque and drag studies is demonstrated. An easy to use torque and drag calculation model based on Soft String Theory is constructed to be used in field drilling case applications for deviated and horizontal wells. The torque magnitude on the torque sensor while drilling is the cumulative torque measured which is the result of frictional and rotational torque values. Only the magnitude of frictional torque can be calculated by Soft String Theory. In order to construct a torque and drag model based on this theory, several parameters such as drill string components and drill string weight, casing depths, friction factors, drilling fluid density, well inclination and azimuth are considered and employed in the model. Histograms are generated for error comparison with the actual well data and an overall of 85% of data are observed to be calculated with less than 20% of error margin. For model validation purposes, the actual rotational torque values while drilling are back calculated; together with the pick-up (up move) drag in the scope of this study. It is expected that the oilfield personnel are going to be using the proposed methodology of torque and drag calculations while drilling deviated wells.