Electric Submersible Pump Technology
Most producing oil fields utilize an electrically driven downhole pumping system to bring oil to the surface. The pump typically comprises several staged centrifugal pump sections that can be specifically configured to suit the production and wellbore characteristics of a given application.
ESP systems are a common artificial-lift method, providing flexibility over a range of sizes and output flow capacities. ESPs are typically used in older reservoirs on wells with high water cuts (percentage of water to oil).
ESPs provide cost effective production by boosting fluid production from these less efficient, older reservoirs. ESP completions are an alternative means of obtaining artificial lift in wells having low bottom hole pressures. ESP completions are the most efficient choice for high volume capable wells. Production rates up to 90,000 barrels (14,500-m3) of fluid per day have been obtained using large ESPs.
The ESP system consists of a number of components that turn a staged series of centrifugal pumps to increase the pressure of the well fluid and push it to the surface. The energy to turn the pump comes from a high-voltage (3-kV to 5-kV) alternating-current source to drive a special motor that can work at high temperatures of up to 300-deg F (150-deg C) and high pressures of up to 5,000-lb/in² (34-MPa), from deep wells of up to 12,000-ft (3.7-km) deep with high energy requirements of up to about 1,000-hp (750-kW).
The ESP uses a centrifugal pump (see Figure 2) which is attached to an electric motor and operates while submersed in the well fluid. The sealed electric motor spins a series of impellers. Each impeller in the series forces fluid through a diffuser into the eye of the one above it.
In a typical 4-in submersible pump, each impeller will add an approximately 9-psi (60-KPa) of pressure. For example, a typical 10-stage pump will develop a pressure of about 90-psi (600-KPa) at its outlet (i.e. 10 impellers x 9-psi). The lift and capacity of the pump is related to impeller diameter and the width of the impeller vanes. The pump pressure is a function of the number of impellers.
For example, a ½-hp 7-stage pump may deliver a high volume of water at a low pressure while a ½-hp 14-stage pump will deliver a lower volume, but at a greater pressure. Like all other centrifugal pumps, an increase in well depth or discharge pressure will reduce the capacity.