Caesar-Tonga Project Steel Lazy-Wave Riser Design
Authors: Lahey Edmund , Burke Roger W. , Balch Erin R. , Beattie Michael 
Published: May 2013

The Caesar-Tonga development in the Green Canyon Area in the Gulf of Mexico was the first application of steel lazy wave risers in the Gulf of Mexico, and it was the first such application tied back to a spar platform. Anadarko and co-owners completed the project on an aggressive schedule in which detailed design, procurement and preparation of the installation program progressed concurrently. Anadarko contracted Technip to perform the analysis and detailed design of these riser systems and, in light of the procurement schedule, the design team was required to refine the riser configuration and sizing early in the design program. This paper describes the strategy and methods employed in this successful riser design.

The utilization of the steel lazy wave riser configuration was an enabling technology for tie-back of a high pressure subsea development to an existing host facility with vertical I-tubes rather than pull tubes. The design optimization process required due consideration for internal pressure, extreme storm, currents, wave fatigue, clashing, and installation loads. The complex configuration required several design iterations to satisfy the competing design requirements.

A collaborative team environment was established with closely managed interfaces to progress the detailed design, procurement, fabrication and installation elements of this technologically challenging project. This technology may be used to enable tie-back of other high pressure subsea systems to deepwater floating hosts in the Gulf of Mexico.

Introduction

The Caesar-Tonga field development consists of four subsea wells tied back to the Constitution platform in the Green Canyon area. A dual flowline system links two drill centers to the host processing facility. The platform riser arrival configuration, combined with the high pressure requirements for the flowlines, created a major technical challenge for the project team. The team utilized steel lazy wave risers to bring the well contents from the seafloor to the host facility. This paper provides an overview of the design parameters, procurement program, and the installation campaign for the Caesar-Tonga riser systems.

The Anadarko-operated Caesar project is a partnership among Anadarko, Shell, Statoil and Chevron for the development and production of reserves in the Caesar Unit. This unit was formed to combine the Caesar and the Tonga discoveries and includes Green Canyon Area Blocks 683, 726, 727, and 770.

The Caesar-Tonga development is a unit formed to exploit several Miocene horizons. The initial discovery, Caesar, was made in Green Canyon Block 683 in 2006. The Tonga discovery occurred the following year in Block 726. The owners estimate that the field holds from 200 to 400 million barrels of oil equivalent. The project was sanctioned in 2009 and first production was achieved in March of 2012.

These reserves will be produced through a subsea system that ties back to the Constitution spar. The dual flowlines are rated for a pressure of 12,700 psi. A pipe-in-pipe design was used to meet flow assurance requirements. Anadarko utilized their standard 15K trees and controls in this project. A depiction of the Caesar-Tonga Development is shown in Figure 1.