This paper summarizes the concept development work aimed at designing a safe, practical, and economically feasible DualGradient Drilling (DGD) riser system for deployment in ultra-deepwater environments. Three (3) concept alternatives wereshortlisted for evaluation after an initial screening of more than twenty (20) potential solutions. The benefits and the risks ofthe three alternatives are identified, and the anticipated functional constraints associated with each alternative are highlighted.The paper reviews several technical issues on the basis of which the concepts were evaluated and scored, and discusses thetechnological developmental efforts required to address these issues. A methodology is developed to rank the alternativesbased on the results of the technical analyses, comparison of costs, benefits, and risks, and the determination of potentialfunctional constraints. The effort documented here is a testament to the fact that even the most challenging design issues canbe successfully addressed by efficient team work and comprehensive engineering.
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