Cascade and Chinook Subsea Development: the World

Abstract Located in 8,200 feet water depth, the Cascade & Chinook subsea development risers are the deepest production risers in the world. These are also the first offset free-standing hybrid risers to be installed in the Gulf of Mexico, and the world's first use of hybrid risers in combination with a disconnectable turret-moored FPSO. This paper presents the unique benefits and challenges associated with using hybrid riser tower technology in the deepwater Gulf of Mexico, based on the experience gained by both client and contractor in executing the Cascade & Chinook riser project. The authors review the history of the Cascade & Chinook riser system, from concept selection through engineering, procurement, construction, installation and pre-commissioning. The most significant challenges and the key project management decisions are highlighted, covering: field layout considerations; strength and fatigue performance; design verification; interfaces with the production facility and subsea infrastructure; procurement and fabrication logistics, and spare materials philosophy; installation engineering and execution; safety and quality management; and regulatory compliance. The project management strategy, and the relationship between client and contractor through the project life cycle, are presented and critically assessed. The paper concludes with an evaluation of the delivery time, cost and project execution risks associated with the hybrid riser concept, and compares this with more traditional deepwater riser solutions, in the context of a deepwater Gulf of Mexico development. Introduction Cascade and Chinook are two separate fields located in the Walker Ridge Outer Continental Shelf leasing area of the central Gulf of Mexico, in the United States. They are situated near the Sigsbee Escarpment on the abyssal plain, in ultra deep water. Cascade is 160 miles south of the Louisiana coast in 8,200 feet water depth and Chinook is 16 miles south of Cascade in 8,800 feet water depth. Each field is being independently developed but they share a floating production, storage, and offloading (FPSO) unit, located between the two fields, and export infrastructure including two shuttle tankers and a gas export pipeline (Figure 1). The Cascade & Chinook project was sanctioned in late 2007 based on a phased development strategy. Phase I is an early production program. Reservoir and well productivity information obtained during Phase I will form the basis of later field development phases. The Phase I development required five risers: one pair of production risers for each of the Cascade and Chinook fields; and, one shared gas export riser. These risers are the subject of this paper. More details on the overall subsea development are discussed by Porciuncula, Ribeiro and Cassity1. The Cascade & Chinook risers are the first offset free-standing hybrid risers installed in the Gulf of Mexico. The Placid Green Canyon 29 and Enserch Garden Banks 388 developments of the 1980's and 90's used free-standing hybrid risers located directly beneath the floating production facility2. BP's Macondo emergency response riser was installed after the Cascade & Chinook risers, although its short period of operation occurred prior to arrival of the Cascade & Chinook FPSO, BW Pioneer.