Compliant vertical access riser assessment: DOE analysis and dynamic response optimization

As a contribution to the deepwater oil and gas industry, this paper addresses the use of optimization techniques together with a design of experiments (DOE) assessment, as a way of automating the design of compliant vertical access risers (CVARs) while also leading to an optimal riser configuration based on some desired efficiency parameters. The CVAR is a new riser concept that can improve the structural performance of the production system and also provide several operational benefits. The DOE is a statistical technique that provides an objective measure of how design parameters are correlated and the effective contribution of each one at the riser performance. Based on such a study some general conclusive remarks on the global behavior of CVAR will be presented. Such results also play an important role for the optimization process, as it can highlight significant design parameters, enabling design simplifications and efficiency improvement. For optimization assessment, geometric parameters are taken as the design variables and the design constraints consider both structural integrity and operational criteria. A multi-objective approach is considered taking into account the structural performance and geometric criteria. Optimal solution is obtained by NSGA-II method. Extreme and operational environmental conditions of a Brazilian offshore field are used as the base case.

▸DOE analysis followed by an optimization process is applied for CVAR design. ▸Design variables have different significance for each response parameter. ▸ Most significant variables: outer diameter, floater volume, well offset, overlength. ▸ Found less significant variables: stress-joints length and upper slick pipe length. ▸ Optimization gain: 35% for the stress utilization factor; 46% for the volume factor.