Summary
Typical seawater depths for deep-water oil fields range from 1000m to 4000m. For these deep-water oil fields, the most popular and cost-effective technologies for increased oil recovery are water injection and subsea boosting with a multiphase helico-axial pump on the seabed. By installing a pump on the seabed, the well head pressure and thus the bottom hole pressure can be reduced, which will result in an increased well lifetime and thus an increased oil recovery. This contributes to a reduction in CAPEX per produced barrel and hence make the field development economically more interesting.
Viscous multiphase production fluids occur in case of a viscous oil or in case of water-oil emulsions with a high apparent viscosity close to the inversion point. It is known that for viscous fluids the required power and size of the pump are significantly larger than for water-like products, such as low viscous oils. On top of this, due to the poor accuracy of the existing performance prediction models available in literature for viscous conditions, the pumps and the corresponding utility systems have to be significantly over-dimensioned to compensate for the uncertainties. This has a large negative impact on the CAPEX requirements for such field developments up to the point that it becomes economically unattractive to develop the field.
For this reason, TotalEnergies (Operator), Sulzer (OEM) and TechnipFMC (EPC contractor) have launched real-size pump test campaigns in 2012 and 2014 with viscosities up to 3,000 cP in hot fluid and 10,000 cP in cold start-up conditions.
The data obtained from those measurement campaigns have been used to develop a performance prediction model, which allows for accurate sizing of the pumps and corresponding topside utility system.
This model allows for a reduction of the uncertainties and risks related to subsea boosting for viscous deep-water field developments and related to this the overall CAPEX requirements. This enables subsea boosting as a viable solution for increased oil recovery for deep-water fields with viscous multiphase fluids.
This paper presents the test campaign and acquired measurement data. It explains how the effect of viscosity is modeled. It illustrates the match between the pump performance prediction model and the viscous multiphase test data. This allows for a reduction of the uncertainties and thus a more accurate pump selection.