Relatively few field installations of a dual-electric submersiblepump (DESP) completion have been reported. In general, the purpose of the second pump was either to increase the pumping capacity, or to act as a backup to improve the reliability of the pumping system. However, DESPs potentially can address a much wider range of reservoir management challenges. This paper will analyze the performance of a DESP in a range of reservoir scenarios. It will show how DESP performance can be modeled by use of commercially available, coupled, well-performance and reservoir-simulation tools.Four DESP applications were analyzed. Where possible, the robustness of the numerical-modeling results will be compared with analytical predictions. DESPs gave improved oil production and recovery in reservoirs with strong aquifer support and became progressively more attractive in a layered-reservoir scenario as the pressure difference between the production zones increased. However, while DESPs had no significant advantages in a long, horizontal well placed in a homogeneous reservoir, they can increase recovery in a tilted, layered reservoir. A slim, deepwater well completed with a lower-capacity downhole pump and a larger (multiwell) seabed booster pump was shown to be a potentially attractive solution for some reservoir developments.This work provides a comparison of the drivers for the choice of a single electric submersible pump (SESP) and a DESP in the scenarios studied. It illustrates a modeling methodology and provides DESP-selection guidelines, thus aiding the increased application of this technology. MethodologyThe studies were carried out with the help of a two-phase (oil and water) simulation of a 3D reservoir model using the Eclipse TM 100 package. Wellflo TM was used to model the vertical-lift performance for the produced fluids through the wellbore and the pump performance under the various reservoir conditions. The results obtained were transferred to the Eclipse TM models in the form of vertical-flow-performance (VFP) tables. A detailed description of the model used as input for comparison of the Eclipse TM , the Wellflo TM and the analytical solutions is listed in Tables 1 and 2. Simulation results using the Eclipse TM and Wellflo TM programs were compared with appropriate analytical solutions where possible (see Appendix).

Field installation of a dual Electric Submersible Pump (dESP) completion has been reported. The purpose of the second pump was to increase the pumping capacity and to act as a back-up to improve the reliability of the pumping system. However, dESPs can potentially address a much wider range of reservoir management challenges. This paper will analyse the performance of a dESP in a range of reservoir scenarios. It will show how dESP performance can be modelled using commercially available, coupled, well performance and reservoir simulation tools. Four dESP applications were analysed. Where possible, the robustness of the numerical modelling results will be compared with analytical predictions. dESPs gave improved oil production and recovery in reservoirs with strong aquifer support and became progressively more attractive in a layered reservoir scenario as the pressure difference between the production zones increased. However, while dESPs had no significant advantages in a long, horizontal well placed in a homogenuous resevoir, they can increase recovery in a tilted, layered resevoir. Preliminary results on a deep-sea well example where the combination of deep-set single ESP (sESP) and a second pump placed at the seabed are discussed. This work provides a comparison of the drivers for the choice of a sESP and a dESP in the scenarios studied. It illustrates a modelling methodology and provides dESP selection guidelines, thus aiding the increased application of this technology. 1. INTRODUCTION Artificial lift methods, including Electric Submersible Pumps (ESPs), are required when a well ceases to flow naturally or when the production rate is too low to be economical. ESPs boost the pressure of the produced fluid, allowing an increase in the well drawdown and providing the additional energy required for the reservoir fluids to flow. For the purposes of this papaer, we will assume that ESPs are the preferred form of artificial lift. The typical ESP installation employs a single multi-stage pump driven by an electric motor {called a single ESP (sESP) in this paper}. Now-a-days it is technically possible to employ more than one pump/motor set in the tubing string. E.g. references 1 and 2 report the application of dual ESPs (dESP) where the second pump increases the pumping capacity and acts as a back-up to improve the reliability of the pumping system. Realistic economic analysis of ESP application has to account for the longevity or failure frequency of the ESP. This frequency will depend on the correctness of the choices made during the ESP selection process, the severity of the operational conditions, the skill of the wellsite installation staff and of the production operators. An independent, back-up pump would be justified if frequent ESP failure were expected since it would allow the longest period of uninterrupted production from the reservoir. This paper will explore the potential for dESP application for a range of reservoir performance scenarios where the use of a sESP results in a lack of "pressure-balance" along the wellbore. One such wellknown example is the effect of friction and pressure drop along a horizontal well. There are several reported field examples where "flattening" the pressure profile using one or more downhole flow restrictions installed across the completion interval had shown accelerated production and increased recovery. At its most basic, an ESP increases the well drawdown and provides additional energy to lift the well fluid to the surface. In principle, installation of a sensitively controlled dESP across the completion interval is also, capable of modifying the drawdown profile in a similar manner. This realisation leads us to examine whether they can be used to improve well performance, particularly from a reservoir performance point of view. Four different possible applications of dESPs will be analysed in this paper:Commingling production from zones with different pressure regimesControl of water coning by producing from both oil and water zones in bottom water drive reservoirsControl of water cresting in long horizontal wells by using dESPs at heel and toeInstallation of a reduced-power downhole pump at the production zone supplemented by a higher capacity pump at the seabed for production from deep water oil reservoirs