Technical And Economic Evaluation Of Ship-Shaped Floating Production And Storage Systems For The Canadian East Coast Offshore

Abstract

Abstract This paper discusses the evaluation and technical feasibility of Ship-shaped oil production systems for the Nova Scotia, Grand Banks and Central Labrador areas. A general analysis of vessel dynamic response to wind wave action, current and ice is presented, on the basis of which two preferred designs are outlined: a fully dynamically-positioned ship, and a single point-moored vessel with a counterweight and a turret. The production downtimes due to the shuffle lanker oil export system are also studied using a wave hindcast computer model. An estimate of the economic threshold values for resources and well productivity is presented. The potential for early production systems and reservoir testing is highlighted. Introduction There are many systems available to the operator for development of offshore oilfields. These include floating production systems, fixed structures (concrete and steel), compliant structures, surface wellheads, subsea wellheads, subsea manifolds, glory holes to avoid iceberg scour, flowlines, pipelines, tankers, trenches, storage, offshore offloading systems and any combination of these. All have advantages and disadvantages. In shallow waters (less than 300 m water depth) and in ice-free environments, the fixed structure systems with export by pipelines appear the most popular and economic for elatively large fields. Where the size of the field is not large enough to support long pipelines and large production structures, floating production facilities with shuttle tanker export systems, together with subsea production systems, must be considered. A vast area of the Canadian east coast has ice-infestedaters. Large fixed structures, designed to withstand the impact of ice and icebergs are probably too expensive for the size of the majority of oil fields to be discovered. Floating facilities, on the other hand can be moved away if ice conditions are too severe. Consequently, based on existingworld-wide technology, this paper discusses ship-shaped floating production, storage and offloading systems (FPSO). The ship-shape system has a number of attractions compared with a semi-submersible floating production vessel; namely:The motion characteristics of a large ship are as good as a semi-submersible as shown in Figure 1.The ship can be more heavily ice-strengthened than a semi-submersible. Also, if a large bergy bit does puncture the ship (see Fig. 2), a ship can, in general, withstand a greater degree of structural damage and flooding.The ship can store up to 150 000 tonnes of oil which will reduce downtime for shuttle tanker loading during bad weather.The ship provides a large deck area for production equipment compared with the restrictions placed on semi-submersibles.For dynamically-positioned and internal-turret moored systems the ship will protect risers and moorings from pack ice and bergy bits. The turret area is large enough to install equipment to overcome problems of high-pressure swivels.Due to its relatively low costs, the FPSO could also be used as one step in the over-all development of a large oil field as well as for marginal field developments.