Manatee is located approximately 160 miles southwest of New Orleans in Green Canyon Block 155 of the Gulf of Mexico. It operated by Shell Exploration and Production Company (SEPCo) with a 52% interest. Devon Energy holds the remaining 48% interest in the field. The leases were acquired for approximately $1,324,800 in OCS Lease Sale 157 in April 1996.
The field is developed as a subsea production system located in 1,940ft of water. It has been designated as a two-well development. These wells are tied back five miles to Shell’s Angus subsea manifold in Green Canyon 113. This in turn carries production 17 miles to Shell’s Bullwinkle platform in Green Canyon 65 for processing.
The subsea controls extend from Bullwinkle through the Angus umbilical termination structure and the five mile umbilical from the Angus hydraulic distribution manifold.
Manatee is the fourth subsea production system using Bullwinkle as its processing hub. Previous field tiebacks to Bullwinkle include Rocky in 1996, Troika in 1997 and Angus in 1999.
Manatee is expected to recover in excess of 12 million barrels of oil equivalent, with peak production rates potentially reaching up to 25,000 barrels of oil per day.
DRILLING THE DISCOVERY WELL
The discovery well was drilled in April of 1998 by Shell using Diamond’s Ocean Concord semi-submersible rig. The original well was subsequently sidetracked three times, once in June 1998 and twice in May of 2000.
The target reserves are in turbidite sands at depths ranging from approximately 16,800ft to 17,100ft subsea. The average net thickness is approximately 100ft in two reservoirs.
The reserves are primarily oil. API gravity is approximately 33° with sulphur content put at approximately 1.12% wt.
ANGUS UMBILICAL TERMINATION STRUCTURE
The subsea system consists of three wells connected to an adjacent eight-slot manifold and tied back to the Bullwinkle platform via two 8in buried, multiphase flowlines configured in a piggable loop. The subsea manifold is located on Green Canyon Block 113. Initial development will target reserves in Green Canyon Blocks 112 and 113.
The Bullwinkle platform consists of topsides sitting on a one-piece jacket, which was designed and engineered by Shell Oil Company. It is the world’s tallest pile-supported, fixed steel platform. Gulf Marine Fabricators was awarded the contract for fabrication, transportation and installation of the jacket. Heerema Marine Contractors was selected by Gulf Marine Fabricators for the transportation and installation of the jacket. Petro-Marine Engineering designed the original production modules.
Total height of the structure is 1,736ft, from the sea bottom to the top of the flare boom. The platform has 60 well slots. Total structural weight is over 77,000t. The jacket weighs 49,375t, the deck initially weighed 2,033t, the piles weigh 10,500t and the conductors weigh 12,760t. Initial processing capacity at the platform was 59,000 barrels of oil per day and 100 million cubic feet of gas per day.
McDermott installed a 7.5 mile oil pipeline connecting the Bullwinkle platform to the Boxer platform in Green Canyon 19 where initial production from the Bullwinkle field was processed. After the facilities were set, the platform produced oil into a 12in line that connected to the Boxer system and the gas flowed into a separate 12in line that tied into what is now the Manta Ray system.
Major contractors participating in the Manatee development were:
- FMC: subsea trees
- Duco: umbilical fabrication
- FMC-KOS: controls
- US Steel and CPW America: flowlines
- Shell Deepwater Services: detailed engineering
- Global Industries: flowline installation
- Halliburton Subsea: umbilical installation
Total development costs are less than $80 million, excluding lease costs.