Influence of cuttings on the mechanical extension limit of extended reach well

The drilling operation of extended reach well is of great difficulty and it requires highly in hole cleaning operation, so the influence of cuttings accumulation on the torque and drag shall not be neglected. In this paper, the coupling model of hole cleaning and torque and drag was established by modifying the soft string model which is commonly used to calculate the torque and drag. Then, the model for predicting the mechanical extension limit of extended reach well was established under the constraint of drilling rig, string and bit. Finally, a case study was performed on a real extended reach well with horizontal/vertical ratio of 5 by taking the influence of cuttings on the torque and drag into consideration. The torque and drag under different working conditions was calculated, the mechanical extension limit of horizontal section was predicted, and influence of the height of cuttings bed on the mechanical extension limit of extended reach well was analyzed. It is indicated that the mechanical extension limit of extended reach well predicted by the coupling model is more effective and true than the calculation result of the common soft string model. In addition, as cuttings bed accumulates, the influence of cuttings on the mechanical extension limit of extended reach well increases. The research results provide scientific basis for risk prediction, design and construction of extended reach wells.