Presently, offshore fields can be developed following two possible conventional routes. Either they can be ‘stand-alones’, when the hydrocarbons are separated into gases and liquids and exported separately, or ‘satellites’ using only the reservoir energy to transfer the unstabilized well fluids to the terminal. The firs; option allows the wellhead back-pressure to be minimized and is not limited in transfer distance, but it faces the expense of an investment in full process facilities, hydrocarbon transfer station, and a large offshore support structure to locate these facilities The second option is attractive because of minimized capital and operating expenditure, but in many cases will be penalized by a reduced production rate owing to back-pressures on the wellheads, especially for long flowlines.
This latter route may be enhanced in the form of a multiphase boosted satellite, which means that the unstabilized well fluids are boosted in pressure, thereby cumulating the advantages of the two above-described conventional options by featuring cost-effectiveness, maximized production and enhanced safety. The SMUBS project (Shell Multiphase Underwater Booster Station) was started with this objective in mind and this contribution reports on the progress of this development effort aiming at bringing multiphase boosting technology to the required level of maturity to be considered for subsea field development.
Other approaches, like subsea separation, can also be considered, this implying that the field is not developed as a satellite but instead as a ‘standalone’ These are not addressed in this paper.
Basically, three discrete approaches can be considered to transfer unstabilized well fluids (Fig. 1). Two would consist of locating equipment in the well itself. (Fig. 1 is available in full paper)
The downhole pump, single phase or multiphase: an efficient technology for which reliability expectations are often low. Furthermore, equipment redundancy is not normally feasible
Gas lifting, a well established technology but inefficient for export over long distances.
Both these options have the advantage of concurrently providing vertical lift in the tubing and horizontal transfer in the flowline. The drawback, however, is that their maintenance has to be done through costly well re-entry.
The third approach would be to use a surface multiphase pump located at any point between the Christmas tree and the terminal facilities. It features the advantage of being maintainable directly without well re-entry, which is attractive from both the cost-effectiveness and the safety aspects. It may also be installed retroactively on existing fields at minimal costs, typically to enhance the recovery performance of satellites Moreover, the reliability of a pumping station can be enhanced by straightforward provision of equipment redundancy. The main limitation of surface multiphase pumping is the requirement for the well fluids to reach the pump inlet. However, it has to be noted that gas lift can be used concurrently with multiphase pumping.
