Real Time Torque and Drag Analysis during Directional Drilling
Creators: name: Fazaelizadeh, Mohammad
Publisher: name: Graduate Studies
Year: 2013
Subjects: subject: Engineering--Industrial
subject: Engineering--Petroleum
subject: Drilling
subject: Directional
subject: Real-time
subject: Analysis

description: The oil industry is generally producing oil and gas using the most cost-effective solutions. Directional drilling technology plays an important role especially because the horizontal wells have increased oil production more than twofold during recent years. The wellbore friction, torque and drag, between drill string and the wellbore wall is the most critical issue which limits the drilling industry to go beyond a certain measured depth. Surface torque is defined as the moment required rotating the entire drill string and the bit on the bottom of the hole. This moment is used to overcome the rotational friction against the wellbore, viscous force between pipe string and drilling fluid as well as bit torque. Also, the drag is the parasitic force acting against drill string movement to pull or lower the drill string through the hole. The drill string friction modeling is considered an important assessment to aid real time drilling analysis for mitigating drilling troubles such as tight holes, poor hole conditions, onset of pipe sticking, etc. In directional drilling operations, the surface measurement of weight on bit and torque differs from downhole bit measurement due to friction between the drill string and wellbore. This difference between surface and downhole measurements can be used to compute rotating and sliding friction coefficients from torque and hook load values respectively. These friction coefficients are used as indicators for real time drilling analysis. To do this analysis, analytical and finite element approaches were used to develop practical models for torque and drag calculations for any well geometry. The reason why two different approaches were used to develop torque and drag models is that the drill string was assumed to be soft string in the analytical approach which has full contact with the wellbore. In the finite element approach, the effect of drill string stiffness was included in the model and the drill string does not have full contact with the wellbore. Also, a new method for effective weight on the bit estimation was developed using wellbore friction model. The new method only utilizes the available surface measurements such as hook load, stand pipe pressure and surface rotation. Using the new method will eliminate the cost of downhole measurements tools and increase drilling rate of penetration by applying sufficient weight on the bit. In this research, different effects which have great contributions on torque and drag values were investigated precisely. These effects include buoyancy, contact surface due to curve surface area, hydrodynamic viscous force, buckling, hydraulic vibrations, adjusted unit weight and sheave efficiency. Finally, some field examples from offshore and onshore wells were selected for model validation and verification. The field data include hook load and surface torque for different operations such as drilling, tripping in/out and reaming/back reaming.