Analysis Method for Contact Forces Between Drillstring-Well-Riser

Abstract

Abstract This paper proposes a methodology to estimate the contact forces generated by the drill string against the wellbore and the marine drilling riser system. A new procedure for overall analysis of the drill string behavior inside the riser and wellbore is described. This is important in the safety analysis of the wellhead equipment and also in planning drilling operations. The results also suggest that the forces should be used in the dynamic analysis of marine riser system. Introduction The offshore exploration has faced many problems searching for oil in ever increasing depth. Those operation are made using floating vessels to drill and complete the wells. Along with the increasing depth, the riser strings are getting longer and the top tension settings higher. The forces generated by the drill string against the riser / wellhead in those situations can build into values that can damage the riser joints, the BOP and the casing-hangers while drilling. Reports have been already made by operators worldwide stating these problems. The knowledge of the magnitude of the contact forces are also very important in the prediction of the wear rate expected in the wellhead equipments and inside the casing. Many models have been used to predict the forces inside the wellbore, but those approaches are no longer valid inside the riser due to the bigger annular. These models generally use the formulation of Johansic et al. This work proposes a methodology for estimation of the contact forces between the drill string against the riser / wellhead I well-bore using a finite element model with a non linear, 2D, quasi-static approach. An example of application is shown using the data of a well drilled by a dynamic positioning drillship in a 550 m (1745.5 ft) water-depth in the Brazilian coast. P. 531^