Summary This paper presents a new friction model for application in petroleum wells. Although very simple, it applies for all wellbore shapes such as straight sections, drop-off bends, build-up bends, side bends or a combination of these. The drillstring is modelled as a soft string. In high tension the string weight is negligible as compared to the tension. This leads to simplified equations where the friction caused by the weight is negligible. For this case the friction in a bend is formulated in terms of the 3D dogleg. The same model therefore applies for 2D and 3D wellbores. The entire well can be modelled by two sets of equations, one for straight wellbore sections and one for curved wellbores. The latter is based on the absolute directional change, or the dogleg of the wellbore. Three worked examples are given in the paper: a 2D well, a 3D well and combined hoisting and rotation in the 3D well. One main purpose of this paper is to provide a simple explicit tool to model and to study friction throughout the well by separating gravitational and tensional friction effects.

The calculation and analysis of torque and drag play an important role in drilling and well design. Different models (soft, stiffness, mixed and finite element) have been used to calculate the torque and drag. This paper introduces a practical FEA (Finite Element Analysis) model of the drill string which can reflect working behavior, including interaction between the drillstring and borehole wall, computational model of torque and drag, and verification with examples. The sensitivity analysis to some key input and output parameters has been conducted. The calculated hook load shows a good match to the rig recorded values. The drillstring displacements calculated by the FEA model matches those from an analytical method. The program developed and discussed in this paper can be used for torque and drag analysis, dynamic behavior analysis, and friction coefficient back-calculation. The FEA program of the drillstring presented herein will benefit in preplanning and real-time simulation of oil and gas well drilling operations.

Wellbore friction modeling is considered as an important assessment to aid realtime drilling analysis. It predicts and prevents drilling troubles such as tight holes, cutting bed accumulations, differential sticking, etc.

This paper presents a new wellbore friction model for drilling horizontal and extended reach wells. This model can be easily applied for all wellbore shapes such as straight, curved and also combination of different curved sections. The model has the capability of torque and drag calculations for different drilling modes such as rotating, tripping and also combination of modes such as reaming and back reaming operations.

For improving the model, different effects such as contact surface and hydrodynamic viscous force were included in the model, and their impacts on the results were investigated. To show the application of model, a field case study was used and deviations of modeling results from field data were analyzed precisely.

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Wellbore friction modeling is considered as an important assessment to aid real-time drilling analysis and predict drilling troubles such as tight holes, poor hole cleaning, onset of pipe sticking etc. The torque and drag are typically the limiting factors facing the drilling industry to go beyond a certain measured depth in extended reach drilling. In extended reach drilling, surface measurement of weight on the bit and torque differ from downhole measurement due to the friction between the drill string and the wellbore. This friction force can be used to estimate an overall friction coefficient. The overall friction coefficient value versus measured depth while drilling can be used as an indicator during different drilling operations.