Subsea processing technology applications have increased rapidly in recent years. This paper gives a general overview of subsea processing applications and maturity. In particular, subsea oil pressure boosting is often profitable for subsea deepwater oil developments. This paper describes the currently available subsea processing and boosting solutions, global portfolio needs for subsea oil boosting, and the limitations of existing technologies in meeting these needs.
Subsea processing is generally considered to include the following existing or developmental functional capabilities:
Oil systems
Subsea oil pressure boosting systems
Subsea oil processing
Bulk water separation
Sales quality oil polishing
Subsea raw seawater injection for reservoir pressure support
Subsea gas compression
Subsea Gas dewpointing/dehydration
For flow assurance
For sales quality
Subsea processing applications have increased significantly in recent years (see Figure 1).
Subsea processing applications and technical maturity.
Subsea oil pressure boosting can provide the following benefits:
Enables ultradeep light oil production
Enables deep heavy oil production
Increases ultimate recovery for deep light oil and may be used reduce flow assurance costs
In all cases, subsea boosting reduces or eliminates the backpressure on the wells from the riser hydrostatic head and riser and flowline viscous pressure drop. Although most reservoirs have sufficient pressure to produce to the seafloor without the use of downhole artificial lift, many ultradeep light oil and deep heavy oil reservoirs are near hydrostatic pressure and cannot produce to the sea surface under their own pressure for more than a short period of time.
Moderate-depth light oil wells are frequently economic without artificial lift. However, as pressure declines in late life, reducing backpressure on the wells can add significantly to ultimate recovery eonomically, even when water injection is present.
Subsea oil pressure boosting is broadly applicable to deepwater subsea oil projects. Ten applications are in place and an additional five have been announced. Subsea oil boosting is proven in moderate water depths to roughly 3000 feet, depending on desired boost pressure, gas content and viscosity. Significant cost or technical challenges remain for deeper light and heavy oil.
Bulk subsea water separation can be used to debottleneck water processing capacity where topside debottlenecking cannot be accomplished, enabling additional production to an existing host. Because topside debottlenecking is possible for many hosts, subsea water separation has selected applicability, with one system in place.
Bulk subsea water separation is proven without solids handling for relatively shallow water depths and easily separated oils. Solids handling components have been tested onshore and will be incorporated into an announced project. Water depth can most likely be extended somewhat by moderate changes in separator vessel design. Electrostatic coalescers are under testing in topside facilities to increase separation efficiency for difficult oils. Separators for deep water remain a technical challenge.
Sales quality oil processing technology is immature and future availability is uncertain.
Subsea raw seawater injection can be used to debottleneck topside facilities where additional topside injection capacity cannot be accommodated.
