The word swivel probably doesn’t conjure up an image in your head of something amazing or all that interesting, however for those that work on, or operate ship-shaped floating production vessels, swivels take on a whole new meaning.
As the wind and current change, a ship-shaped production vessel such as an FPSO weathervanes around a buoy all-the-while producing hydrocarbons from a fixed point in the ocean and sending fluids, gas and electro-hydraulic umbilicals back down to the architecture on the seafloor via a system of risers. Doing so requires a stack of swivels that connect the weathervaning vessel to the fixed assembly hooked up to the buoy.
For production vessels in shallow water, dealing with the operating pressures within the swivel has been an issue sorted out years ago, however as these FPSOs move into ultra deep waters such as the Gulf of Mexico and tap into the ultra high pressure high temperature (HPHT) Lower Tertiary reservoirs located some 8,000 to 10,000 meters below sea level, the pressures needed to re-inject water or gas into the formation far surpass the rated capacity of today’s swivels.
Monaco-based offshore engineering firm, SBM Offshore describes the Lower Tertiary:
The reservoirs are typically found under very thick salt or tar sediment layers, and may have uneven porosity and permeability, so presenting multiple exploration and field development challenges.
Lower Tertiary fields also typically carry a low gas to oil ratio, making these reservoirs relatively low energy. This, along with the poor reservoir properties, may lead to an estimated oil recovery factor of only 10% using conventional techniques, or double this amount using state of the art EOR methods, compared to industry best practice of 60% or more.
OTC Houston awarded the Spotlight on New Technology Award to SBM Offshore this week after they introduced a toroidal swivel made of steel three meters thick with pre-pressurized seals in order to enable operating pressures to hit 830 bar, or 12,000 psi. According to Andrew Newport, Proposal & Technology Development Director at SBM Offshore, this provides 60 percent higher operating pressure than any other swivels currently available.
This new technology is targeted for turret-moored ultra deepwater fpsos that will be installed for full field development.
FPSOs such as Petrobras’ BW Pioneer, for comparison, are designed and equipped for early stage field development.
Here’s how it works: