Hydraulic pumping

Hydraulic pumping is a proven artificial lift method that has been used since the early 1930s. It offers several different systems for handling a variety of well conditions. Successful applications have included setting depths ranging from 500 to 19,000 ft and production rates varying from less than 100 to 20,000 B/D. Surface packages are available using multiplex pumps ranging from 15 to 625 hp. The systems are flexible because the downhole-pumping rate can be regulated over a wide range with fluid controls on the surface. Chemicals to control corrosion, paraffin, and emulsions can be injected downhole with the power fluid, while fresh water can also be injected to dissolve salt deposits. When pumping heavy crudes, the power fluid can serve as an effective diluent to reduce the viscosity of the produced fluids. The power fluid also can be heated for handling heavy or low-pour-point crudes. Hydraulic pumping systems are suitable for wells with deviated or crooked holes that can cause problems for other types of artificial lift. The surface facilities can have a low profile and may be clustered into a central battery to service numerous wells. This can be advantageous in urban sites, offshore locations, areas requiring watering systems (sprinkle systems), and environmentally sensitive areas

Basic operation

Hydraulic pumping systems transmit power downhole by means of pressurized power fluid that flows in wellbore tubulars. Hydraulic transmission of power downhole can be accomplished with reasonably good efficiency using a reciprocating piston pump. With 30°API oil at 2,500 psi in 2 ⁷/₈-in. tubing, 100 surface hydraulic horsepower can be transmitted to a depth of 8,000 ft with a flow rate of 2,350 B/D and a frictional pressure drop of less than 200 psi. Even higher efficiencies can be achieved with water as the hydraulic medium because of its lower viscosity.

The downhole pump acts a transformer to convert the energy into pressure in the produced fluids. A common form of a hydraulic downhole pump consists of a set of coupled reciprocating pistons, one driven by the power fluid and the other pumping the well fluids. Another form of a hydraulic downhole pump that has become more popular is the jet pump, which converts the pressurized power fluid to a high-velocity jet that mixes directly with the well fluids. In the turbulent mixing, momentum and energy from the power fluid are added to the produced fluids. The operating pressures in hydraulic pumping systems usually range from 2,000 to 4,000 psi. The most common pump used to generate this pressure on the surface is a multiplex positive displacement pump driven by an electric motor or multicylinder gas or diesel engine. Multistage centrifugal pumps and horizontal electrical submersible pumps (ESPs) have been used, and some systems have been operated with the excess capacity in water-injection systems. The hydraulic fluid usually comes from the well and can be either produced oil or water. A fluid reservoir at the surface provides surge capacity and is usually part of the cleaning system used to condition the well fluids for use as power fluid. Appropriate control valves and piping complete the system. A schematic of a typical hydraulic pumping system is shown in Fig. 1.

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  Fig. 1-Schematic of a single-well hydraulic pumping system.

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Types of hydraulic pump systems

There are two primary kinds of hydraulic pumps:

• Jet pumps
• Reciprocating positive-displacement pumps

Fig. 2 shows a jet pump arrangement. For jet pumps, high-pressure power fluid is directed down the tubing to the nozzle where the pressure energy is converted to velocity head (kinetic energy). The high-velocity, low-pressure power fluid entrains the production fluid in the throat of the pump. A diffuser then reduces the velocity and increases the pressure to allow the commingled fluids to flow to the surface.

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  Fig. 2—Schematic of a hydraulic jet pump. (Courtesy of Weatherford.)

The positive-displacement pump consists of a reciprocating hydraulic engine directly coupled to a pump piston or pump plunger. Fig. 3 shows a reciprocating hydraulically powered pump. Power fluid (oil or water) is directed down the tubing string to operate the engine. The pump piston or plunger draws fluid from the wellbore through a standing valve. Exhausted power fluid and production can be returned up a separate tubing string or up the casing.

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  Fig. 3—Schematic of a reciprocating hydraulic pump. (Courtesy of Weatherford.)

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When the power fluid and the production are combined, the system is an open power-fluid system. For a vented open power-fluid system, the production and power fluid typically are returned separately in a parallel tubing string with gas normally vented through the casing annulus to the surface. A nonvented casing installation requires a pump to handle the gas and production. The power fluid plus all reservoir fluids are produced up the annulus. Both completion types are used with positive-displacement pumps and with jet pumps. In fact, many bottomhole assemblies (BHAs) can accommodate jet or positive-displacement pumps interchangeably.

In a closed power-fluid arrangement, the power fluid is returned to the surface separately from produced fluids, requiring a separate tubing string. The use of a closed power fluid system is limited as a result of the added initial costs and clearance problems in small casing. Because the jet pump must commingle the power fluid and production, it cannot operate as a closed power-fluid pump.

The most outstanding feature of hydraulic pumps is the “free pump” system. Fig. 4 shows a schematic of a free hydraulic pump. Fig. 4a shows a standing valve at the bottom of the tubing, and the tubing is filled with fluid. In Fig. 4b, a pump has been inserted in the tubing and power fluid is being circulated to the bottom. In Fig. 4c, the pump is on bottom and pumping. When the pump is in need of repair, fluid is circulated to the surface as shown in Fig. 4d. The positive-displacement pump, the jet pump, and the closed power-fluid system previously shown are all free pumps.

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  Fig. 4—Schematic showing the operation of a “free” hydraulic pump installation. (Courtesy of Weatherford.)

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Surface facilities require a power-fluid storage and cleaning system and a pump. The most common cleaning systems are settling tanks located at the tank battery. Cyclone desanders sometimes are used in addition to settling tanks. In the last 40 years, wellsite power plants, which are separators located at the well with cyclone desanders to remove solids from the power fluid, have become popular.

Surface pumps are most commonly triplex plunger pumps. Other types are quintiplex plunger pumps, multistage centrifugal pumps, and “canned” ESPs. The surface pressure required is usually in the 1,500 to 4,000 psi range. It is important to specify 100% continuous duty for the power-fluid pump at the required rate and pressure. Low volume (< 10,000 B/D), high-pressure installations (> 2,500 psi) typically use plunger-type pumps.

Table 1 shows approximate maximum capacities and lift capabilities for positive-displacement pumps. In some cases, two pumps have been installed in one tubing string. Seal collars in the BHA hydraulically connect the pumps in parallel; thus, maximum displacement values are doubled.

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  Table 1

A relationship between capacity and lift is not practical for jet pumps because of the many variables and the complex relationships among them. To keep fluid velocities below 50 ft/sec in suction and discharge passages, the maximum production rates vs. tubing size for jet-free pumps are approximated in Table 2.

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  Table 2

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Fixed-type jet pumps (those too large to fit inside the tubing) have been made with capacities of 17,000 B/D, and even larger pumps are possible. Maximum lifting depth for jet pumps is approximately 8,000 to 9,000 ft if surface power-fluid pressure is limited to approximately 3,500 psi for water power fluid and approximately 4,000 psi with oil power fluid, considering the operating life of a triplex pump. The maximum capacities can be obtained only to approximately 5,000 to 6,000 ft. These jet pump figures are only guidelines. The maximum capacities listed are for high-volume jet pumps that require BHAs that are incapable of accommodating piston pumps.

Advantages

Hydraulic pumping has the following advantages.

• Being able to circulate the pump in and out of the well is the most obvious and significant feature of hydraulic pumps. It is especially attractive on offshore platforms, remote locations, and populated and agricultural areas.
• Positive-displacement pumps are capable of pumping depths to 17,000 ft and deeper. Working fluid levels for jet pumps are limited to approximately 9,000 ft.
• By changing the power-fluid rate to the pumps, production can be varied from 10 to 100% of pump capacity. The optimum speed range is 20 to 85% of rated speed. Operating life will be significantly reduced if the pump is operated above the maximum-rated speed.
• Deviated wells typically present few problems to hydraulic free pumps. Jet pumps can even be used in through flowline installations.
• Jet pumps, with hardened nozzle throats, can produce sand and other solids.
• There are methods in which positive-displacement pumps can handle viscous oils very well. The power fluid can be heated, or it can have diluents added to further aid lifting the oil to the surface.
• Corrosion inhibitors can be injected into the power fluid for corrosion control. Added fresh water can solve salt-buildup problems.

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Disadvantages

Hydraulic pumping has the following disadvantages.

• Removing solids from the power fluid is very important for positive-displacement pumps. Solids in the power fluid also affect surface-plunger pumps. Jet pumps, on the other hand, are very tolerant of poor power-fluid quality.
• Positive-displacement pumps, on average, have a shorter time between repairs than jet, sucker rod, and ESPs. Mostly, this is a function of the quality of power fluid but, on average, the positive-displacement pumps are operating from greater depths and at higher strokes per minute than for a beam pump system. Jet pumps, on the other hand, have a very long pump life between repairs without solids or if not subjected to cavitation. Jet pumps typically have lower efficiency and higher energy costs.
• Positive-displacement pumps can pump from a low BHP (< 100 psi) in the absence of gas interference and other problems. Jet pumps cannot pump from such low intake pressures, especially when less than the cavitation pressure. Jet pumps require approximately 1,000 psi BHP when set at 10,000 ft and approximately 500 psi when set at 5,000 ft.
• Positive-displacement pumps generally require more maintenance than jet pumps and other types of artificial lift because pump speed must be monitored daily and not allowed to become excessive. Power-fluid-cleaning systems require frequent checking to keep them operating at their optimum effectiveness. Also, well testing is more difficult.

Applications for hydraulic pumping

Hydraulic systems are normally is used in areas where other types of artificial lift have failed or, because of well conditions, have been eliminated because of their shortcomings. Hydraulic pumping systems have been labeled expensive, but they may have application where other artificial lift methods may not be feasible. These include, but are not limited to, the following:

• Using hydraulic free pumps in remote areas where the rig costs are unusually high or the availability of workover rigs is limited
• Crooked or deviated wells
• Use of hydraulic systems in relatively deep, hot, high-volume wells (Note: Hydraulic pumps can go through tubing with as much as a 24° buildup per 100 ft.)
• The use of jet pumps in sandy corrosive wells
• The use of reciprocating pumps in deep wells with low bottomhole producing pressure
• Wells with rapidly changing producing volumes
• The use of jet pumping systems in wells producing with gas/liquid ratios less than 750:1 but producing under a packer where free gas must be pumped
• Using hydraulic free pumps in wells with high-paraffin contents
• Using hydraulic open power fluid systems in low-API-gravity wells.

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References

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Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

Noteworthy books

Bradley, H. B., & Gipson, F. W. (1992). Petroleum engineering handbook. Richardson, TX, U.S.A: Society of Petroleum Engineers. WorldCat

Coberly, C. J. (1961). Theory and application of hydraulic oil well pumps. Huntington Park, Calif: Kobe, Inc. WorldCat

Frick, T. C., & Taylor, R. W. (1962). Petroleum production handbook. Dallas, Tex: Society of Petroleum Engineers of AIME. WorldCat

iBooks

Pugh, Toby. 2014. Overview of Hydraulic Pumping. Weatherford. iBook.

External links

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro

See also

Downhole hydraulic pump installations

Downhole hydraulic pump types

Hydraulic pumping surface equipment

Hydraulic pumping systems for single wells

Hydraulic pumping system design

PEH:Hydraulic_Pumping_in_Oil_Wells

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Page champions

Toby Pugh P.E.