A New Buckling Model Successfully Validated with Full-Scale Buckling Tests
Résumé
Buckling of tubulars inside wellbores has been the subject of many researches and articles in the past. An increasing number of observations in the field suggest that existing buckling theories have to be challenged, as they fail to predict the buckling phenomenon, such as lockup. Indeed, existing buckling theories assume generally that the wellbore is idealistically perfect without any dog legs. Recent advancements in drillstring mechanics modelling have demonstrated that dog legs, friction and rotation greatly affect the buckling phenomenon. For the first time, this paper compares results of full-scale buckling tests with a new buckling model that takes into account the actual tortuosity of the wellbore. Full-scale buckling tests have been performed in a 2000 m depth well in testing two (2) different drill string configurations. Various weights on bit have been applied for buckling drill pipe in the wellbore, and then a high accuracy continuous gyroscope has been run into the drill pipe to estimate its deformed geometry. This paper shows for each drill string and weight on bit experimental and theoretical results in terms of weight transfer (lockup prediction) and buckling state (sinusoidal or helical). Although existing models failed to predict observed buckling behaviour, the new buckling model has given excellent predictions for each full-scale buckling test performed, not only in terms of deformed buckling shape, but also in terms of weight transfer. This paper shows for the first time to the drilling industry that a new buckling model has been derived and successfully validated in the field. This model has proved its ability to realistically predict the onset and severity of buckling in any kind of 3D trajectory.