Mustafa Azeez, "Torque and drag analysis", Master Thesis, School of Mineral Resources Engineering, Technical University of Crete, Chania, Greece, 2019
https://doi.org/10.26233/heallink.tuc.81213
Drilling through the subsurface is a complex operation and problems are almost guaranteed to occur. Therefore, understanding and anticipating drilling problems, understanding their causes and planning solutions are necessary for successfully reaching the target. The most prevalent drilling problems include pipe sticking, lost circulation, hole deviation, pipe failures, borehole instability, mud contamination, formation damage, hole cleaning. Torque and drag modeling is very important to analyze the mechanical behavior of the drill string and the wellbore condition, hence, to predict and prevent downhole problems. There have been a number of different approaches to the way that torque and drag has been modeled in the well drilling industry. These include the soft string and stiff string approaches. This thesis will study the torque and drag in the wellbore and will give a general overview of the sources, effects and challenges of torque, drag and buckling in the wellbore. Furthermore, it will study and simulate the soft string model to calculate torque and drag along a drill string in a 12 1/4” vertical section wellbore as well as provide calculations of hook-loads and frictional torque for specific bit depths. Additionally, it will provide a simulation of the section with the PayZone drilling simulator to calculate the torque on bit while drilling. Both the model and the PayZone values are summed up together to get the cumulative torque which is the torque observed at the surface while drilling.