Modelos de trajetória e de torque e arraste aplicados à análise de desgaste em revestimentos de poços

Abstract

In the drilling stage of oil and gas wells, the drilling column can come into contact with the casing strings, generating lateral forces that, associated to the rotation of the drillstring, cause the removal of material from the inner wall of the tubulars. High casing wear values induce a reduction in mechanical strength of casing string and may compromise the well integrity. This work deals to the implementation and comparative analysis between methodologies for casing wear evaluation, comprising models for trajectory planning, lateral forces calculation and wear volume estimate. Torque and drag models are employed to quantify the lateral forces, using the soft-string and stiff-string approaches. The latter differs from the soft-string model by taking into account effects related to the drillstring stiffness, besides inserting the contact angle into the formulation. The stiff-string model depends on directional parameters as torsion and curvature, for which a model based on cubic splines is applied. The spline-based model is then compared with the minimum curvature method, widely employed by industry. The results show that the model based on splines provides smooth curvature and non-zero torsion. The influence of spacing between the survey stations on the accuracy of the trajectory models is also analyzed. Finally, a complete case study is developed, allowing to conclude that the use of stiff-string model can reduce the predicted wear on the casing string, due to its distribution as a function of the contact angle.