Sirena Dotada truss spar design for East Central Gulf of Mexico

A student team at Texas A&M University has designed a truss spar for producing oil and gas in East Central Gulf of Mexico for a 4000 ft (1219.2 m) water depth. The Spar was designed to withstand a 100 year storm. American Bureau of Shipping (ABS) rules and American Petroleum Institute (API) guidelines were used in the design. The Truss Spar, known as " Sirena Dotada", is located 176 miles southwest of Clearwater, FL. This area is located just off the continental shelf in an area known as "The Elbow". The reservoir is estimated to contain 300 million barrels of oil and have a field life of approximately 20 years. The total length of the Spar hull, from the top of the hard tank to the bottom of the soft tank, is 646 ft (196.9 m) and the diameter of the hard tank is 120 ft (36.6 m). There are three heave plates that are spaced 85 ft (25.9 m) apart. Full workover capabilities are implemented into the production facilities. The topsides have a three deck system with 30 ft (9.14 m) of spacing between the decks. Each deck is 170 ft (51.8 m)by 215 ft (65.5 m). There is a 55 ft (16.8) air gap between the first deck and the waterline to allow for large waves from extreme weather conditions. Since the Spar is located at a 4000 ft (1219.2 m) water depth, there are several options that need to be considered when designing the mooring system using Orcina\´s mooring software "Orcaflex". Either a set of nine chain-polyester-chain or a chain-wire-chain mooring line can be used in this application, and a full analysis was performed to determine which is the better option. The chain-wire-chain mooring line provided the best results and was chosen to be used. The stability analysis was performed with the program Stab CAD. In this program, a model was created that accurately portrayed the overall shape of the Spar, to include a hard tank, topsides facilities, trusses, heave plates, and a soft tank. The model was analyzed for intact and damage stability. A structural analysis was us- ed to analyze several key structural points during certain "high-stress" scenarios. The major critical joints include the topside to the hard tank, hard tank to the truss section, and the truss section to the soft tank. These areas are analyzed during hull self floating period, hull upending at 15 degrees, and the topsides and hull during a 100-year storm at the maximum inclination angle of 11 degrees. The maximum bending moments are used to determine the type of steel and connection needed. Also, a cost analysis showed how much individual components contributed to the total cost of 1.46 billion US dollars. The above topics are discussed and explained in further detail throughout the report.