Floating Production Storage and Offloading vessels, or FPSOs, are offshore production facilities that house both processing equipment and storage for produced hydrocarbons. The basic design of most FPSOs encompasses a ship-shaped vessel, with processing equipment, or topsides, aboard the vessel’s deck and hydrocarbon storage below in the double hull. After processing, an FPSO stores oil or gas before offloading periodically to shuttle tankers or transmitting processed petroleum via pipelines.
Moored in place by various mooring systems, FPSOs are effective development solutions for both deepwater and ultra-deepwater fields. A central mooring system allows the vessel to rotate freely to best respond to weather conditions, or weathervane, while spread-mooring systems anchor the vessel from various locations on the seafloor.
Usually tied to multiple subsea wells, FPSOs gather hydrocarbons from subsea production wells through a series of in-field pipelines. Once tapped by subsea wells, hydrocarbons are transmitted through flowlines to risers, which transport the oil and gas from the seafloor to the vessel’s turret and then to the FPSO on the water’s surface.
The processing equipment aboard the FPSO is similar to what would be found atop a production platform. Usually built in modules, FPSO production equipment can consist of water separation, gas treatment, oil processing, water injection and gas compression, among others. Hydrocarbons are then transferred to the vessel’s double-hull for storage.
Crude oil that is stored onboard is frequently transferred to shuttle tankers or ocean barges going ashore, via a loading hose. Loading oil from the stern of the FPSO to the bow of the shuttle tanker is known as tandem loading. While gas is many times transferred to shore via pipeline or re-injected into the field to boost production.
Permanently moored, FPSOs are viable development solutions for a number of different offshore field situations. Because FPSOs can be disconnected from their moorings, these offshore production vessels are optimal for areas that experience adverse weather conditions, such as cyclones and hurricanes.
Additionally, because FPSOs can be moved, they are a more economical solution for more marginal fields, in that the vessel can be moved to another development and redeployed once the original field has been depleted. Also, FPSOs are an optimal choice for development when there are no existing pipelines or infrastructure to transfer production to shore. Adding to the economic advantages of FPSOs, existing tankers are frequently converted into FPSOs.
Used in offshore production since the 1970s, FPSOs have been historically utilized in the North Sea, offshore Brazil, Asia Pacific, the Mediterranean Sea and offshore West Africa.