Technologies for the collection and recycling of associated petroleum gas, in particular, a hydraulic jet technology for transportation of the product of wells from a measuring group unit along a single pipe [1,2] realized on a hydraulic jet unit, are being introduced to reduce losses of the gas in the course of recovery and transportation of petroleum to oil and gas enterprises. The product of the wells is ejected by means of an ejector pump that uses as active liquid a mixture of stratal water and petroleum delivered by an electrocentrifugal pump mounted in a pit. The active liquid at the outlet of the jet pump is separated from the gas–liquid mixture in a pipe separator and returned to the entrance of the electrocentrifugal pump.

By comparison with multiphase pump stations based on double-screw pumps, hydraulic jet units are distinguished by simplicity of design and operation and low capital and operating costs. However, the low efficiency of a hydraulic jet pump (not more than 30%) [3] leads to an increase in the energy cost of pumping the product of wells, particularly with a high gas and petroleum content (more than 150 m3/ton). A design has been developed to increase the efficiency of a hydraulic jet pump in which the working liquid is fed to an annular nozzle while the pumped product of the wells, after first being separated, is fed according to the following scheme: gas into a central pipe forming the inner diameter of the annular nozzle, while the liquid (petroleum and water) is fed into the gap between the nozzle and the mixing chamber (Fig. 1). The results of experimental studies (Fig. 2) on a laboratory test bench confirmed the efficiency of separate delivery of gas and liquid with the use of an annular nozzle, which yields an increase in the delivery of the pumped gas–liquid mixture.

Fig. 1
figure 1

Design of hydraulic jet pump: 1) nozzle; 2) mixing chamber.

Fig. 2
figure 2

Graphs illustrating dependence of flow rate Q on velocity of active liquid v in hydraulic jet pump: 1) flow rate of liquid and gas in separate delivery; 2) flow rate of gas without liquid; 3) flow rate of liquid and gas in joint delivery; 4) flow rate of liquid without gas.

A system for automatic maintenance of constant pressure in the gas–liquid mixture at the entrance to the hydraulic jet unit through regulation of the productivity of the electrocentrifugal pump (flow rate of active liquid) has been developed. A pressure sensor the signal from which is fed to a frequency converter that controls the rotation speed of the shaft of the submersible electric motor of the electrocentrifugal pump, is installed in the hydraulic jet pump to implement the design in the pipeline.

The automated hydraulic jet unit functions in the following way. As the pressure of the gas–liquid mixture at the entrance to the hydraulic jet unit rises (falls) relative to a given value, the signal from the sensor enters the controller of the control post of the electrocentrifugal pump, the rotational speed of the shaft of the submersible electric motor of the electrocentrifugal pump is increased (respectively, decreased) by the frequency converter, and the flow rate and pressure of the active liquid entering the nozzle of the jet pump correspondingly increase (decrease). The coefficient of ejection of the jet pump and volume of the pumped-out gas–liquid mixture increase and the pressure of the gas–liquid mixture at the entrance to the hydraulic jet unit decreases (increases).

The increase in the pressure of the gas–liquid mixture at the entrance to the hydraulic jet unit with constant cross-sectional area of the nozzle of the hydraulic jet pump leads to an increase in the power of the submersible electric motor of the electrocentrifugal pump (increase in power consumption), hence a mechanism for automatic regulation of the cross-sectional area of the nozzle as a function of the pressure of the active liquid at the entrance to the nozzle has been developed.

In the initial position of the mechanism (Fig. 3a ), the collar 1 is held in the leftmost position by the spring 2, in which case the cross-sectional area of the annular nozzle is minimal. As the pressure of the active liquid increases, the spring 2 is compressed, the collar 1 shifts to the right, and the cross-sectional area of the annular nozzle increases due to the increase in the annular gap between the gas pipe 3 and the internal shaped surface of the collar 1 (cf. Fig. 3b ). As the cross-sectional area of the nozzle increases, the flow rate of the active liquid and the rate of delivery of the pumped-out gas–liquid mixture both increase; the pressure at the entrance to the hydraulic gas unit and power of the submersible electric motor of the electrocentrifugal pump then fall, the pressure of the active liquid at the entrance to the hydraulic jet pump falls, and the collar 1 returns to its initial position under the influence of the spring 2.

Fig. 3
figure 3

Mechanism of automated regulation of cross-sectional area of nozzle: a) initial position; b) final position.

An increase in the operating efficiency of the hydraulic jet unit was achieved in the course of pilot-unit tests at one of the facilities of Lukoil-Perm company. The total reduction in power consumption in the operation of the pilot-unit automated unit (by comparison with a unit without automatic and frequency regulation) amounted to ~39%.

Thus, the use of a jet pump with annular nozzle and separate delivery of pumped-out gas and petroleum and partial regulation of the productivity of a pump used to pump out active liquid with automechanical regulation of the cross-sectional area of an annular nozzle yields a decrease in power consumption when the unit is in operation.