9.1 Introduction

Hydraulic-powered downhole pumps are powered by a stream of highpressure power fluid (water or oil) supplied by a power fluid (PF) pump at the surface and sent to a downhole pump or pump engine.

Hydraulic pumps are basically of two types:

1. Piston downhole pumps that are similar to beam down-hole pumps

2. Jet downhole pumps that reduce the pressure on the formation by high-speed power fluid flow through the throat of a venturi or jet pump nozzle-diffuser combination

The surface PF pump can be either a piston type or a centrifugal highpressure pump with sufficient capacity to transmit a pressurized power fluid to the downhole pump. Power is supplied to the PF surface pump by either an electricor gas-powered prime mover.

Figure 9-1 shows an approximate depth-rate application chart for jet and reciprocating hydraulic systems application.

Figure 9-1: Approximate depth-rate envelope for jet and reciprocating hydraulic pumping systems

Figure 9-2 shows a typical skid-mounted, electric-powered triplex PF pump. Ordinarily the PF pump is either a split-case centrifugal pump, a horizontal electric pump (ESP) unit, or a triplex piston pump. Centrifugal PF pumps tolerate solids better but are less efficient than triplex positive displacement pumps.

Figure 9-2: Hydraulic pumping system. (Courtesy Weatherford.)

The power fluid transfers the power necessary to lift liquids from the surface to the bottomhole pump. The power fluid can be oil or water. Generally, two types of power fluid systems are used with hydraulic pumps: One where the power fluid is kept isolated from the production...