Concept Design of Two Permanently Coupled Floaters for Production and Storage of Oil and LNG

Abstract

The combination of oil, LNG and LPG present at offshore fields may require a multi purpose production and storage facility that can produce the different hydrocarbons. In order to achieve feasibility, the required vessel size to handle multiple hydrocarbons is significant. HSE, technical and economical considerations led to the investigating of using two floaters to split the LNG / LPG storage from the production vessel. This paper deals with the intention to deploy two vessels in tandem: One producing unit that has storage capacity for produced oil and one barge that stores the LNG and LPG. Challenges to be met in the design of the tandem moored vessels relate to relative motions between the vessels: The relative motion is restricted by the transfer lines for products and the flexibility of a gangway that enables safe passage between the vessels. The mechanism that connects the two vessels should be capable of withstanding the forces to keep the vessels at the intended distance without growing into enormous proportions itself. This paper provides the technical background and the feasibility of the concept to connect two large barges in benign conditions. The concept has been developed based on existing tower mooring principles that is combined with a spread moored mooring arrangement. Additionally the paper discusses the sensitivity of the connector and mooring design on the overall performance.