Analysis of mooring and steel catenary risers system in ultra deepwater

Abstract

With the gradual depletion of oil and gas resources onshore as well as shallow offshore waters, oil exploration is gradually moving deeper into the seas. One of the major means of oil exploration at such locations is by way of Floating Production Storage and offloading (FPSO) system. Because of the ever increasing depths of exploration and the prevailing harsh environmental conditions, there is a need to constantly re-evaluate or develop new methods for mooring system and riser analyses. There are several methods available which are well tested for the analysis of systems operating in shallow to deepwater using catenary or finite element approach in both frequency and time domain. These have been reviewed and the method considered to be most relevant for the purpose of this research has been identified for further development. Based on this a methodology a quasi-static and dynamic analyses of single and multicomponent mooring and steel catenary risers system in ultra deepwater has been developed. The dynamic equations of motion were formulated based on the modified Lagrange’s equation and solved using the fourth order Runge-Kutta method. Because of the dearth of experimental data at such water depth, the developed methodology for line dynamics has been validated using relevant published data for finite water depth. These techniques are then applied to the analysis of a mooring and steel catenary risers system of an FPSO unit in 2500m of water offshore Nigeria and also the Gulf of Mexico both in the frequency and time domain. The results were found to be practical and compare reasonably very well between the two approaches.