Dynamic buckling with friction inside directional wells

Abstract

The construction of deep and directional offshore wells brought the necessity to understand the behavior of columns on such conditions. Completely understanding their behavior means to be able to design and operate them while avoiding any problems. In the present work, we studied the differences observed on the measurements of the friction force during operations of tripping in and tripping out a tubing, one of the problems associated to columns inside directional wells. It is worth noting that this problem can occur in various operations, such as lowering a sand screen curled on a pipe inside an open hole segment, lowering a tubing string inside a casing string, or lowering a coiled tubing inside a tubing string. Generally, the projects – and even commercial software – consider only the associated static problem, which proved itself as not being able to justify the measurement differences obtained on field. Therefore, the present work introduces a dynamic model in opposition to the static model to explain the mentioned phenomenon. The main hypothesis is that the column buckling inside the well would cause it to vibrate differently during tripping in and tripping out. During tripping in, the column is under compression and thus suffers buckling, displacing itself angularly inside the well to either form a sinusoid or a helix; meanwhile, during tripping out, the column is under tension and thus there is no buckling, meaning that the column will remain in contact with the shortest portion of the well the whole time. Using the models developed to characterize the column during tripping in and out, it was observed that, in fact, the friction force is different on both cases, thus proving the hypothesis that buckling is the responsible for the observed differences on hook load during operations of tripping in and out a column.