Jet Pump

Key Takeaways

• Jet pump operating principles are governed by the continuity equation and Bernoulli's theorem for the high-velocity power fluid jet, and by the conservation of momentum for the mixing of the power fluid and formation fluid streams in the throat: the nozzle converts power fluid pressure energy into velocity (P_1/rho + v_1^2/2 = P_2/rho + v_2^2/2 from Bernoulli, with most pressure dropped to accelerate the fluid from near-zero velocity to 20 to 80 m/s through the nozzle); the jet exits the nozzle at high velocity and low pressure (the static pressure at the nozzle exit is below the power fluid supply pressure by the dynamic pressure term rho*v^2/2), with the local pressure at the nozzle exit potentially below the formation fluid pressure, causing reservoir fluid to be drawn into the throat; in the throat, the two streams mix (the power fluid decelerates, the formation fluid accelerates) and momentum is transferred from the fast power fluid to the slow formation fluid, creating a mixed stream at intermediate velocity; the diffuser then converts this velocity back to pressure, raising the discharge pressure above the intake pressure at the formation perforations, providing the net lift pressure needed to move the mixed fluid to the surface against the hydrostatic head and friction losses in the return conduit; jet pump efficiency (ratio of useful work done on the formation fluid to total work input from the power fluid) is typically 20 to 35 percent, substantially lower than ESP efficiency (50 to 70 percent) or sucker rod pump efficiency (50 to 65 percent), with the lower efficiency offset by the absence of downhole mechanical components and the ability to pump high-solids and high-gas-content fluids without mechanical failure.
• Nozzle and throat sizing for jet pump design determines the operating point on the pump's performance curve and must be matched to the well's inflow performance relationship (IPR) and the power fluid system capacity: the nozzle size (cross-sectional area, commonly expressed as a nozzle code from 1 to 12 in increasing area increments) controls the power fluid flow rate for a given surface injection pressure (by the nozzle flow equation Q_nozzle = Cd*A*sqrt(2*deltaP/rho), where Cd is the discharge coefficient approximately 0.96); the throat size controls the total flow capacity of the pump (nozzle plus formation fluid) and the efficiency of momentum transfer; the ratio of nozzle to throat area is the primary design variable for a given operating condition (power fluid pressure, formation fluid pressure, and desired production rate), with smaller ratios providing higher pressure boost at lower efficiency and larger ratios providing higher flow rate at lower pressure boost; jet pump manufacturers (SPX, Guiberson/National, TRW Mission, Wood Group) provide sizing charts that allow the optimum nozzle-throat combination to be selected for a given set of well conditions (wellbore pressure at pump depth, required discharge pressure, desired production rate, power fluid properties) without iterative hand calculation; the pump is changed (by retrieving the pump insert by wireline or by circulating it out of the well with increased power fluid pressure in pump-through installations) when well conditions change sufficiently to require a different nozzle-throat combination.
• Power fluid systems for jet pump installations require a dedicated surface injection pump (typically a triplex plunger pump or centrifugal multistage pump), a power fluid treating facility (to remove sand and gas that would cause erosion or cavitation in the nozzle), a power fluid storage tank (to hold the volume required for continuous injection), and a return fluid treating system (since the power fluid mixes with the production fluid in the downhole jet pump and arrives at the surface as a mixed stream that must be separated into power fluid and produced fluids): open power fluid systems (where the produced oil or water is treated and recycled as power fluid) are the most common configuration, requiring only that the produced fluid is compatible with the injection pump and that adequate treatment (sand removal, deaeration, dehydration) is available to provide clean, gas-free power fluid; closed power fluid systems (using fresh water or treated brine as the power fluid that is recycled separately from the produced oil) avoid contamination of the produced oil by mixing with power fluid but require more complex surface facilities (separate power fluid and produced fluid separation, compatible corrosion inhibition for both the power fluid and the produced fluid chemistry); for offshore platform installations, jet pump power fluid systems can use the platform's existing produced water treating system as the power fluid supply, minimizing the incremental surface equipment required for jet pump artificial lift.
• Gas handling capability is the most distinctive operational advantage of jet pumps over other artificial lift systems in high-GOR wells: gas entrained in the formation fluid entering the jet pump throat is simply mixed into the combined fluid stream and carried to the surface with the liquid, without causing the cavitation and vibration that degrades ESP performance or the fluid pound that causes rod pump damage; jet pump performance is affected by gas (which reduces the density of the mixed fluid stream and hence the hydrostatic pressure available to lift the fluid, requiring higher power fluid injection pressure to compensate), but the pump continues to operate and produce without mechanical damage even at gas-to-liquid ratios (GLR) that would require a gas separator or flow controller to protect an ESP or rod pump; in coal seam gas wells (where high initial water production and variable gas-to-water ratios require a flexible artificial lift system), in tight gas condensate wells (where liquid condensate loading reduces bottomhole pressure and requires assisted unloading), and in wells undergoing gas-assisted lift without a dedicated gas lift system, jet pumps provide continuous, damage-free operation across the range of gas-to-liquid ratios encountered during the well's production life.
• Retrievable and fixed jet pump installation configurations determine the ease of pump replacement and the operational flexibility of the artificial lift system: retrievable jet pump installations use a sliding sleeve or standing valve housing in the production tubing (similar to a gas lift mandrel) into which the jet pump insert can be pumped down or pulled by wireline, allowing pump size changes without pulling the production tubing; pump-in, pump-out capability (where the pump insert is pumped down to the landing sub by pressurizing the power fluid line and retrieved by reversing circulation or by applying a wireline pulling force) allows the pump to be changed in a few hours with a wireline unit and no workover rig, at a cost of $20,000 to $50,000 versus $300,000 to $1,000,000 for a full workover; fixed (or tubing-conveyed) jet pump installations require the production tubing to be pulled to change the pump, but provide a larger flow area and higher efficiency because the pump can be sized to the full tubing bore rather than a smaller insert; for deep wells (below 3,000 m), the power fluid injection pressure required to operate the jet pump is high (typically 100 to 300 bar surface injection pressure for wells at 3,000 to 5,000 m depth), approaching the rated working pressure of the surface injection equipment and surface flowlines, which may limit the jet pump's applicability in very deep wells where the power fluid pressure requirement exceeds available surface equipment ratings.