Cascade and Chinook Subsea Development: A Challenging and Successful Case History

Abstract

This paper is based on the subsea work performed during the design, implementation and operation of the Cascade and Chinook Field Development Project in ultra-deep waters of the U.S. Gulf of Mexico (USGoM). It describes the engineering, procurement, construction, installation, operation and integrity management phases of the subsea production system. This project required several innovative technologies and solutions that resulted in several " firsts" and records for the industry: first of a kind and deepest subsea boosting system with ESP-Electric submerged pumps installed on the seabed at 8800 ft, non-conventional power umbilicals utilizing carbon fiber rods as the principal tensile strength elements, first subsea pull-in of umbilicals utilizing a submerged winch, deepest and highest pressure rated Free Standing Hybrid Risers (FSHRs), deepest pipe-in pipe flowline and deepest gas export pipeline. This case history paper also describes the procurement strategies employed and the project management systems adopted to mitigate technical, time and cost risks. Introduction The C&C fields are located in the Walker Ridge Outer Continental Shelf (OCS) leasing area of the central USGoM. Both fields are situated near the base of the Sigsbee Escarpment on the abyssal plain of the USGoM in ultra deep water. Cascade is located about 160 miles south of the Louisiana coast in 8,200 ft water depth and Chinook is about 15 miles due south of Cascade in 8,800 ft water depth. The Cascade discovery was made in 2002 and Chinook was discovered in 2003. The C&C reservoirs are in the Lower Tertiary (Wilcox) Ultra-Deepwater trend. After appraisal work the C&C was sanctioned in late 2007 based on a phased development concept. The initial project phase, the subject of this paper, is an early production scenario based on a limited number of wells and subsea infrastructure and the purpose of this initial phase is to gain reservoir information in order to optimize future development phases. The initial phase utilizes a leased, disconnectable, floating, production, storage and offloading (FPSO) vessel located between the fields. Produced oil is transported from the field in shuttle vessels and gas is exported through an export pipeline. The main reason for selecting the FPSO was safety, primarily with respect to hurricanes. The detachable turret mooring buoy provides a mooring point for the FPSO and during the approach of a hurricane the buoy enables the FPSO to disconnect in a short period of time in order to depart the area. Future phases increase the amount of producing wells and subsea infrastructure and a definitive optimized permanent production facility is to be installed in the last phase. Decisions on the type of and design basis of a definitive facility and number of wells will be finalized in 2013 and 2014.

Floating, Production, Storage, and Offloading Unit: A Contingency Operating Mode Using Variable Frequency Drives

“…VFDs are commonly applied to FPSO units in Brazilian pre-salt oil wells, as shown in [27], [32]- [34]. Around the world, other similar applications are shown in [35]- [39]. Active and passive VFDs have been applied to the FPSO power electrical system for multiple purposes, such as:…”