Benefits and Shortcomings
In many field applications, jet pumps provide a variety of operational advantages, including versatility, over other forms of lift. When the size of the nozzle and throat are changed, a jet pump can produce wells ranging in depth from 300 m [1,000 ft] to 5,500 m [18,000 ft] and production of less than 8 m3/d [50 bbl/d] to more than 3,200 m3/d [20,000 bbl/d].
Because jet pumps have no moving parts to generate mechanical wear, they can operate for several years at a low risk of failure and with minimal maintenance requirements. They also tend to be more rugged and tolerant of corrosive and abrasive well fluids than other types of downhole lift systems. As a precautionary measure, production chemicals can be mixed with the injected power fluid to help control downhole corrosion, paraffin and emulsion problems. Jet pumps can handle significant volumes of free gas in the production stream. Operators install jet pumps via wireline or by using pressurized power fluid to transport the pump downhole. By redirecting the flow of the power fluid, technicians can bring the jet pump back to the surface for repair or replacement without incurring the expense of a workover or pulling unit that is commonly required to retrieve a downhole pump. To optimize pump efficiency as well conditions change, pump nozzles and throats can be quickly changed at the rig site and the pump redeployed downhole.
Jet pumps are prone to some design drawbacks, including the risk of cavitation—the formation of vapor cavities—at the entrance of the throat section caused by the rapid acceleration of the production fluids as they enter the pump body. As the fluid's velocity increases quickly, fluid pressure can decline to its vapor pressure. Vapor cavities form at this low pressure, resulting in restricted flow into the throat. These vapor cavities may col-lapse as pressure rises in the pump, causing cavitation damage—erosion of internal pump parts. Field experience has shown that cavitation-induced erosion rates are low in most oil wells, but the rate could increase in high water-cut wells in which little gas is present.
The choice of oil as the power fluid can prove problematic. Not only does oil introduce a fire hazard to the well site, but the large oil inventories required for such an operation also lower the profitability of the well.
Because they are essentially high-velocity mixing devices, jet pumps are prone to significant internal turbulence and friction, which drops horse-power efficiency—the percentage of the total power supplied that goes into lifting fluids out of the well—to approximately 35%. Although this is lower than the efficiencies typically achieved by using positive displacement pumps, the operational benefits of jet pumps combine to make them a more dependable and economic solution for many wells.
Diverse Applications and Well Conditions
Jet pumps are flexible enough to boost production in a variety of scenarios but are commonly deployed in wells that are difficult to produce because of challenging geometries and fluid compositions. The pump's compact size and rig-free installation make it well suited for use in horizontal and highly deviated wells. A jet pump can be deployed through wellbore turns of up to 24° per 30 m [100 ft], and have demonstrated equally reliable operation in both deviated and straight holes.
Because the pump is able to handle high volume, high gas and high solids, it is a good fit for early well production applications. The jet pump can reliably operate in high-volume production wells by raising the horsepower of the surface pump to increase the power fluid flow rate.
Jet pumps are manufactured with high-strength, corrosion-resistant alloys for deployment in wells that have highly corrosive produced fluids and high solids production. By incorporating high-temperature elastomers for its sealing elements, a jet pump can operate reliably in high-temperature production environments. Heated power fluid can be pumped through the jet pump to dilute viscous crudes and enable consistent flow in heavy-oil production.
Jet pumps have been successfully deployed in marginal offshore wells in which high intervention costs make the use of ESPs prohibitive. The pumps have also been used to dewater gas, coalbed methane and shale wells. In flowback operations following hydraulic stimulation, jet pumps deliver quick and cost-effective recovery of fluid and proppant at rates of 300 m3/d [2,000 bbl/d] or more.
Jet pump suppliers continue to evolve pump designs to help oil and gas operators increase production at minimal operating expense. Current trends in well placement include positioning multiple wells on one site, which creates logistics and footprint problems for some conventional lift systems. A jet pump can be configured through a manifold system to run multiple wells, which serves to reduce lease operating expenses by limiting the amount of equipment on location.
Although earlier versions of the jet pump had a reputation for high energy consumption and raising operational costs, new technologies are allowing the surface pump to be powered with gas coming directly from the well. Integrated control systems precalibrated for the particular engine model help to optimize the engine's performance during fluctuations in gas flow rate or in BTU levels while ensuring that the field operation maintains emission compliance by flaring less gas to the atmosphere.
As design innovations continue, jet pumps seem well positioned to address the industry need for cost-effective and reliable lifting solutions for all manner of marginal production scenarios.
Oilfield Review 2016.
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