Recent Developments in Drilling Riser Disconnect and Recoil Analysis for Deepwater Applications

With exploration and development of hydrocarbon resources moving into ever deeper waters, there is significantly increased demand for drilling vessels capable of drilling in water depths of up to 10,000 ft and beyond. One of the main challenges associated with drilling in these water depths is control of the recoil behavior of the drilling riser after an emergency disconnect. This is required from time to time in the event of loss of the vessel’s station-keeping capability, either in extreme weather or through a failure of the dynamic positioning system. In these scenarios, the riser must be quickly disconnected below the Lower Marine Riser Package (LMRP) to avoid damage to the riser or well structure. Once disconnected, the LMRP should lift sufficiently clear of the Blow-Out Preventer (BOP) to avoid subsequent contact between the LMRP and the BOP, while at the same time the upward movement of the riser must be arrested in time to prevent collapse of the telescopic joint (which could cause impact loads on the drillfloor) or compression in the tensioning lines. These conflicting requirements become more severe in deepwater, where the ratio between the wet weight and inertia of the riser is reduced. This highlights the requirement for an accurate recoil analysis capability in order to determine the optimum riser stack-up and operability limits for deepwater operations. This paper describes the development of a disconnect and recoil analysis software tool that for the first time has been integrated with a 3D finite element (FE) structural model of the drilling riser system. The tool incorporates a detailed model of the riser tensioning system, including the ability to model the behavior of each tensioning cylinder independently and the ability to model the behavior of the anti-recoil control system. The tool also incorporates an advanced fluid flow model, implemented by means of a finite volume numerical model, that models the flow of drilling mud out of the riser immediately after disconnect. The details of the tensioner system and fluid flow models are discussed, along with the approach taken to integrate these into the existing FE structural analysis code. A number of case studies are presented to illustrate the application of the tool to deepwater riser recoil analysis and to examine the effect of key parameters (including vessel offset) on the recoil behavior of the riser system.Copyright © 2009 by ASME