The benefits of introducing subsea processing in a field development could be:
- Reduced total CAPEX, by reducing the topside processing and/or pipeline CAPEX;
- Accelerated and/or increased production and/or recovery;
- Enabling marginal field developments, especially fields at deepwater/ultra-deepwater depths and with long tie-backs;
- Extended production from existing fields;
- Enabling tie-in of satellite developments into existing infrastructure by removing fluid;
- Handling constraints;
- Improved flow management;
- Reduced impact on the environment.
Subsea boosting, as explained in an earlier section, is one means of increasing the energy of the system. Subsea separation can be based either on two- or three-phase separation:
- Two-phase separators are used for separation of any gas–liquid system such as gas–oil, gas–water, and gas–condensate systems.
- Three-phase separators are used to separate the gas from liquid phase and water from oil.
The technology and products required for subsea boosting and water removal are available and in operation, while three-phase separation and subsea gas compression still require some qualification before being put into operation. Thus, a three-phase separator is useful for the crude consisting of all three phases, namely, oil, water, and gas, whereas a two-phase separator is used for the system consisting of two phases such as gas–oil, gas–water, or gas condensate. Further, subsea separation could have a positive effect on flow assurance, including the risk related to hydrate formation and internal corrosion protection derived from the presence of the produced water in combination with gas. As opposed to the traditional methods of processing reservoir fluids at a process station, subsea processing holds great promise in that all of the processing to the point where the product is final salable crude is done at the seabed itself. This offers cost benefits and also improves recovery factors from the reservoir. Other advantages include a lesser susceptibility to hydrate formation and lower operating expenditures.
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