SUBMERSIBLE HYDRAULIC PISTON PUMP

FOR TEST PUMPING FROM HYDROGEOLOGICAL WELLS

V. P. ROZHKOV, V. G. KHRAMENKOV

(Presented by the scientific seminar of the Department of Exploration Technology)

For carrying out test hydrogeological pumping from wells, various means are used, depending on the discharge and the water level. Most often air lifts and bailers are used; less often—water-jet pumps. With a sufficiently high dynamic level, piston pumps and horizontal centrifugal pumps are used.

Of the installations listed, the simplest in design and easiest to operate is the widely used air-lift installation, whose main advantage lies in its lack of sensitivity to the quality of the water being pumped. It also permits pumping from small-diameter wells, although its efficiency and capacity are thereby considerably reduced and a need arises for compressors with high discharge pressure.

The principal disadvantages of the air lift are: low efficiency (usually 0.1–0.15; for well-designed production air lifts—up to 0.25–0.30) and the need for costly pneumatic equipment. The latter entails a number of operational difficulties, namely:

1. The compressor installations used require qualified maintenance during operation and frequent repair.

2. In organizations that drill water wells on a large scale, it is not possible to assign compressors to individual crews. This leads to the depersonalization of the compressor fleet and, as a consequence, to careless, negligent treatment during the operation of compressor installations.

3. Cases often arise in which it is necessary to pump simultaneously from several wells. This leads to organizational difficulties and sometimes to downtime.

4. When work sites are widely scattered, the costs of transporting compressors increase considerably.

The use of sucker-rod pumps for preliminary pumping is expedient only at small well discharges; moreover, the water being pumped must not contain sand or silt, otherwise the pump quickly fails because of wear of the cups.

A water-jet pump has a somewhat higher capacity than a sucker-rod pump; its operating principle consists in the ejection of a jet of working fluid. A water-jet pump can operate on contaminated water and permits simple and

quickly, without stopping the pumping process, adjust the depth of its immersion below the dynamic level; it is simple in design, simple to manufacture and operate. Despite these positive qualities, its practical application is limited by the following features: the height of water lifting must not exceed 30–45 m, since at lower levels the power consumption increases sharply; the pump efficiency is low and is approximately 0.20.

Already from the brief analysis given above of the units used in production, it may be concluded that all of them have a number of substantial shortcomings, the principal one being their low efficiency. In addition, at present there is no unit that would make it possible to carry out test pumping most effectively from wells with low dynamic levels.

Therefore, it is a very urgent necessity to create a small-size, high-capacity pump meeting the following requirements:

1. The pump must be capable of carrying out pumping from wells with low dynamic levels.
2. It must have a sufficiently high efficiency.
3. It must permit operation in polluted water.
4. It must have small dimensions (especially in cross section).
5. It must allow capacity regulation from the surface during the pumping process.
6. It must be simple to operate, install, and dismantle.
7. It must permit operation in combination with the equipment available at the drilling site and, if possible, not require additional special equipment.

Such a pumping unit can be created, for example, by using the basic idea of hydraulic piston pumps employed in the operation of oil fields [1].

Units with hydraulic piston pumps have a high efficiency (60–70%), small dimensions and weight, are capable of lifting liquid (oil mixed with water, gas, and partly with sand) from very great depths, allow capacity regulation from the surface by regulating the number of double strokes (within the range 10–90), and are simple to install and dismantle.

Hydraulic-piston pumping units intended for the operation of oil fields are completely unsuitable for pumping water from wells. However, with certain changes in the general scheme and with a specially developed submersible pump, the idea of using the liquid injected into the well as an energy source for this pump proves extremely useful in the present case. Below is given one of the possible schemes of a hydraulic-piston unit for test pumping from hydrogeological wells (Fig. 1).

A unit with a submersible hydraulic-piston pump consists of five main parts: the submersible hydraulic-piston pump, water-pressure pipes, water-lifting pipes, wellhead equipment, and a mud drilling pump located on the surface.

Installation of such a unit is as follows. A water-lifting string is lowered into the well to the design depth, ending in the adapter shown in Fig. 2. Then the submersible pump is lowered on the water-supply pipes. During lowering, the pump passes with its lower, water-intake part through the opening in the adapter shoe and seats with its annular collar on a rubber gasket, thereby ...

Fig. 1. Schematic diagram of an installation with a hydraulic-piston pump: 1 — hydraulic-piston pump; 2 — water-pressure pipes; 3 — water-lifting pipes; 4 — receiving tank; 5 — drilling mud pump; a — adapter shoe of the water-lifting column.

Fig. 2. Adapter shoe of the water-lifting column: 1 — adapter body; 2 — rubber gasket; 3 — opening for passage of the water-intake part of the pump.

isolates the annular space from the borehole space.

Drill pipes used in drilling (73, 63, or 50 mm) may be used as water-pressure pipes.

The hydraulic piston pump is actuated by a stream of liquid pumped by a surface mud pump through the water-pressure pipes. Ordinary mud pumps used on drilling rigs for flushing boreholes may be used as the surface mud pump. The water-pressure string and the discharge line of the mud pump are connected by means of a hose. The suction hose of the mud pump is lowered into a receiving tank with water; the hose connected to the water-lifting string is also lowered into the same tank.

As is clear from the description, test pumping with such an installation can be carried out, as needed, during borehole drilling without any dismantling of the drilling equipment. In this case the equipment of the drilling rig is used: the winch—for lowering and raising the pipes of the submersible pump; the mud pump—for delivering the working liquid to the submersible pump; and ordinary casing pipes may be used as the water-lifting pipes.

The hydraulic piston pump itself consists of three main units: a mud piston pump, a reciprocating hydraulic motor, and a spool-valve device. The hydraulic piston pump operates as follows. When the working liquid is supplied, the spool-valve device directs it into the corresponding chamber of the hydraulic motor; under the pressure of the liquid the piston is set in motion and actuates the submersible pump. The pump draws the liquid to be pumped from the borehole and delivers it into the annular space between the water-pressure and water-lifting strings, through which it rises to the surface and is discharged into the receiving tank. Part of the water from the tank is again supplied by the mud pump to the submersible hydraulic motor, while the remaining part goes to discharge. The discharged portion constitutes the yield of the borehole (or the capacity of the pump). By its operating principle, the submersible pump may be either single-acting or double-acting.

Fig. 3. Schematic diagram of a hydraulic piston pump: 1—filter for coarse cleaning; 2—suction branch pipe; 3—pump piston; 4—rod; 5—motor piston; 6—distributing rod; 7—spool-valve device.

The hydraulic motor is a power cylinder with reciprocating motion of the piston; therefore the requirements imposed on it are the same as those for the submersible pump.

The reciprocating motion of the piston of the hydraulic motor is achieved by the automatic operation of the spool-valve device. For this device to operate, motion of the spool is necessary (reciprocating, rotary, or a combination of the two), which can be obtained in various ways: by using a magnet or an electric motor, and also by various use-

…of mechanical or hydraulic energy supplied from the surface. Obviously, it is most expedient to use hydraulic energy supplied to the submersible motor, which makes it possible to avoid additional units.

In this case, according to the linkages by means of which the spool is brought directly into action, all spool devices may be divided into hydraulic and mechanical ones. In devices of the first group, the hydraulic energy of the working fluid is converted into mechanical energy directly in the device itself (Fig. 4). In mechanical spool devices, mechanical energy is supplied from outside, i.e., from other units or mechanisms.

Fig. 4. Schematic diagram of a hydraulic spool device: 1 — stroke of the distributing rod (or of the motor piston),

Labels in the figure: “network”; “to drain”; “to the pump.”

An automatic hydraulic-type spool device consists of the spool proper 1 and the distributing rod 2. The working fluid pumped from the surface passes through channel C (the network) and enters the spool box, from which it passes through channel 3 into the lower chamber of the motor cylinder; the motor piston rises upward under the pressure of the fluid. The distributing rod 2 is rigidly connected with the motor piston and also moves upward. Having reached the uppermost position, the distributing rod connects channel 4 with channel 5. The working fluid will pass through channel 4, the annular groove in the distributing rod, and channel 5, and will move the spool to its lowermost position. At this time, the fluid located in the lower chamber of the spool box is forced through channel 6 to drain.

The movement of the spool to its lowermost position entails a change in the direction of motion of the working-fluid flow. Now the injected fluid, after passing through channel C, the annular groove of the spool, and channel 7, enters the lower chamber of the motor and, consequently, causes the piston to move downward. The distributing rod will also move downward. The movement of the distributing rod will cause the fluid in the upper chamber of the spool box to be clamped, which will fix the spool in this position until the piston approaches its lowermost position. The fluid, …

displaced from the lower chamber will pass through channel 8, the spool’s groove, channel 9, and then to the drain.

At the moment when the moving system reaches its extreme lower position, the fluid from channel 4 will enter channel 6 and move spool 1 to its extreme upper position, while the fluid displaced from the space above the spool will pass through channel 5 and enter the cavity of the distributor rod, and then go to the drain. The flow of working fluid will pass through channel C, the annular groove of spool 1, channel 8, and enter the lower chamber of the cylinder. The piston will begin to move upward, while the fluid displaced from the upper chamber will pass through channel 7, the annular groove of the spool, channel 9, and then to the drain.

The group of mechanical-type spool devices is apparently the most varied both in its principle of operation and in its design. Therefore, it is not yet possible to give a description of the most typical device.

Taking into account the desire to obtain a pump that is simple in design and, if possible, simpler in operation, it is highly desirable to avoid including additional units in the pump circuit; that is, the spool device should be driven directly by the moving parts of the engine or pump.

REFERENCES

1. A. S. Kazak, Submersible Rodless Piston Pumps with Hydraulic Drive. Gostoptekhizdat, 1961.