Downhole device for reducing intensity of axial vibrations in electric submersible pumps

Abstract

FIELD: oil producing industry.SUBSTANCE: invention can be used to increase the service life of electric submersible pump units (ESP) by reducing the intensity of axial vibrations that occur during the operation of oil producing wells using ESPs. A downhole device for reducing the intensity of axial vibrations in electrically driven centrifugal pumps includes a submersible portion of the electrically driven submersible pump installation, a tubing string, and a shank placed under the pump unit, and is characterized in that the shank has a length equal to one-quarter of the length of a longitudinal elastic wave propagating along the assembly of the electrically driven centrifugal pump and the tubing string with a frequency equal to the frequency of axial vibrations in the operating pump unit, at which the amplitude of these vibrations is maximum.EFFECT: increased operating time and efficiency of the ESP and reduced likelihood of emergency situations during their operation.1 cl, 3 dwg

Description

[0001] The invention relates to the oil production industry and can be used to increase the service life of electric centrifugal pump (ECP) units by reducing the intensity of axial vibrations that occur during the operation of oil producing wells using ESP.

[0002] One of the main problems arising when using ESP is pump vibration, caused by both the presence of rotating pump elements and pulsations of the hydrodynamic pressure of the liquid pumped out of the wellbore. Pump vibrations lead to a decrease in its efficiency, accelerated wear and to the occurrence of emergency situations (Smirnov N.I., Drozdov A.N., Smirnov N.N. Tribodynamic aspects of the resource of electric submersible vane pumps for oil production / / Notes of the Mining Institute. - 2023. - Vol. 264. - Pp. 962-970; Takacs G. Electrical Submersible Pumps Manual: Design, Operations, and Maintenance. Second Edition. Houston: Gulf Professional Publishing, 2018. - 574 p.).

[0003] Damping devices of various designs, including elastic elements (spring, rubber, etc.) are used as vibration dampers during the operation of the ESP (Dumler E.B. Study of a pneumatic spring compensator of pressure fluctuations with quasi-zero stiffness for a submersible electric centrifugal pump: dis. for a PhD in engineering: 05.02.13, Ufa, 2018; Sabitov R.V., Kirpichnikova I.M., Gorshkov K.E. Application of a submersible compensating device in oil production / / Bulletin of the Kazan State Power Engineering University. - 2023. - v.15. - No. 2 (58). - pp. 128-139; Gabdrakhimov M.S., Galeev A.S., Bikbulatova G.I., Sabanov S.L., Fakhrieva K.R. Reducing vibrations of a submersible electric centrifugal pump by installing a dynamic damper / / News of higher educational institutions. Oil and Gas. - 2016. - No. 4 (118). - pp. 18-23; Russian Federation Patent No. 2681563 "Compensator for reducing vibration in an electric centrifugal pump installation"; Russian Federation Patent No. 129545 "Damping unit").At the same time, the efficiency of the devices used, despite their relatively high cost, is not very high, and the problem of combating vibrations when using ESPs in oil production remains relevant.

[0004] At the same time, there is a fairly simple device for reducing the intensity of longitudinal (axial) vibrations in an oscillating system represented by a composite steel rod. This rod (from the standpoint of the mechanics of elastic wave propagation) is an assembly consisting of a tubing string and a pumping unit (pump, electric motor, etc.), with the inclusion of an additional element in this assembly that influences the nature of elastic wave propagation within it. This additional element is a liner, that is, a steel pipe string placed under the pumping unit and having an optimal length to most effectively neutralize the pumping unit's longitudinal vibrations.

[0005] It is well known that liners are widely used in ESP applications, for example, to provide hydrodynamic connection between the pump and the wellbore's subpacker space or the bottomhole zone of deviated or highly curved wells, when lowering the tubing string with the pump unit to the required depth is difficult. Liners are also used to improve water removal from the wellbore of an oil producing well. This improvement is due to the fact that the internal diameter of the tubing liners is significantly smaller than the internal diameter of the casing pipes, therefore the speed of vertical movement of the two-phase oil-water medium along the liners is higher than along the casing pipes (Urazakov K.R., Alimetov Sh.A., Tugunov P.M. Study of the efficiency of removing water and mechanical impurities from the bottom of oil wells / / Bulletin of Tomsk Polytechnic University. Engineering of Georesources. - 2021. - Vol. 332. - No. 10. - pp. 77-85).The disadvantage of the device described in the specified work, which is the closest to the claimed device, is that the length of the shank and its diameter are selected only based on the condition of the most effective removal of water from the wellbore, and the influence of the shank on the wave processes developing in the assembly and, accordingly, on the intensity of longitudinal vibrations in the pumping unit is not taken into account.

[0006] The technical problem solved by the proposed invention is a significant, 2-3 times, reduction in the intensity of elastic longitudinal vibrations developing in a composite rod system, which is an assembly of tubing and a pump unit, caused by the operation of the ESP, which makes it possible to increase their service life and reduce the likelihood of emergency situations occurring during their use.

[0007] The technical problem is solved by a downhole device for reducing the intensity of these longitudinal vibrations during pump operation. It comprises a submersible section of an ESP, tubing, and a tubing liner installed beneath the pump unit with optimally selected parameters. The novel feature is that the optimal liner length is determined by the condition that it is equal to one-quarter of the wavelength of a longitudinal wave propagating in a steel rod at the longitudinal vibration frequency (axial vibration), at which the amplitude of the vibrations developing during pump operation is maximum. The essence of the invention is as follows.

[0008] The submersible part of the ESP, schematically shown in Fig. 1, where the number 1 marks the casing pipes of the production well, the number 2 marks the tubing string, and the number 3 marks the pumping unit, from the standpoint of the mechanics of the process of propagation of elastic waves, is a composite elastic steel rod, the wave process in which is initiated by the operation of the pump. The characteristic frequencies of the waves excited in this case are mainly in the range of ~10-50 Hz (Smirnov N.I., Drozdov A.N., Smirnov N.N. Tribodynamic aspects of the resource of electric submersible vane pumps for oil production / / Notes of the Mining Institute. - 2023. - Vol. 264. - Pp. 962-970; Takacs G. Electrical Submersible Pumps Manual: Design, Operations, and Maintenance. Second Edition. Houston: Gulf Professional Publishing, 2018. - 574 p.).If a tailpiece 4, positioned beneath pump unit 3, is added to the described vibration system, then, given certain tailpiece parameters, the wave process throughout the entire assembly may change significantly, and, accordingly, the parameters of the axial vibrations developing in the pump unit during its operation will also change. As will be shown below, if the tailpiece length is equal to (or close to) one-quarter of the wavelength with maximum amplitude in the frequency range specified above, the vibration velocity in the pump unit, which characterizes the intensity of the vibration process, will decrease significantly.

[0009] For a numerical analysis of the possibilities of using liners to reduce the intensity of elastic longitudinal vibrations of a pumping unit, provided that the interaction of the pipe string with the wellbore walls has an insignificant effect on the wave processes in the string, that is, for vertical or near-vertical wells, a one-dimensional wave equation of the form (Rabotnov Yu.N. Mechanics of a Deformable Solid Body. Moscow: Nauka, 1979. - 744 p.) was used.

[0010] w ττ =c0 2 ⋅w zz ,

[0011] describing the process of propagation of longitudinal elastic waves along the assembly shown in Fig. 1. Here, the parameter w [m] denotes the displacement of the assembly along the vertical coordinate z [m] at each point, the parameter τ [s] is time, the parameter c0 [m / s] is the speed of sound in steel, which in further estimates was taken to be equal to 5100 m / s. When modeling the wave process in the assembly, it was assumed that in the section of the assembly corresponding to the position of pumping unit 3, from the moment of time t = 0, sources of harmonic oscillations with a frequency of ω [s] begin to act uniformly distributed along the length of this unit. -1]. The boundary conditions that best correspond to the actual conditions in a production well were the condition of securing the tubing string to the wellhead and the absence of stress at the end of the liner or, in the absence of a liner, the absence of stress in the lower part of pumping unit 3. At the junctions of the pumping unit and the tubing, the condition of equality of displacements and loads integrated over the corresponding cross-sectional areas on opposite sides of the connection points was set. It was assumed that the cross-sectional area of ​​the massive pumping unit 3, averaged over its length, is 3 times greater than the cross-sectional area of ​​the main tubing string 2, located above the pumping unit.

[0012] Fig. 2a shows the results of the numerical calculation of the described problem at a harmonic oscillation frequency of 50 Hz (ω=2⋅π⋅50≈314.16 s -1), for the case of lowering a pumping unit with a total length of 30 m to a depth of 1 km. This figure shows the dependences of the dimensionless, in arbitrary units, vibration velocity u of the pumping unit on the dimensionless time t = ω⋅τ in the interval from 500 to 800 units of time t, when the wave process in the assembly reaches a quasi-stationary regime after starting the pump at t = 0.

[0013] Number 1 in Fig. 2a represents the u(t) dependence for the case of a liner-less assembly. Number 2 represents the u(t) dependence in the case of a liner at the bottom of the assembly with a cross-sectional area twice that of the main tubing string, i.e., in the case of using massive pipes as the liner. Number 3 in Fig. 2a represents the u(t) dependence in the case of using lightweight pipes with a cross-sectional area half that of the main tubing string.

[0014] In both cases, the length of the shank was taken to be 25.5 m, that is, equal to one quarter of the length of a longitudinal wave in a steel rod with a frequency of 50 Hz (102 m = 5100 m : 50).

[0015] As can be seen from the comparison of the values ​​of the conditional dimensionless vibration velocities u(t), corresponding to curves 1, 2 and 3, the presence of the shank reduces the intensity of the longitudinal vibrations of the pump unit by 2-3 times, and the diameter of the shank does not significantly affect the effect of reducing the intensity of vibrations.

[0016] Figure 2b shows similar dependences of the vibration velocity u(t) at an oscillation frequency of 10 Hz, in the absence of a liner in the assembly (curve 1) and in the presence of a liner made of heavy tubing (curve 2) and light tubing (curve 3). The liner length in both cases was taken to be 127.5 m, that is, also equal to one-quarter of the wavelength with a frequency of 10 Hz (510 m = 5100 m : 10). As can be seen from the comparison of vibration velocities in Figure 2b, in this case too, the presence of a liner significantly reduces the intensity of longitudinal vibrations in the pumping unit.

[0017] It should be noted that, as numerical calculations show, a similar reduction in longitudinal vibration intensity also occurs with a liner length equal to three-quarters of the longitudinal wave, etc. This indicates that this reduction in longitudinal vibration intensity is due to a local antiresonance effect, i.e., the reflection of the longitudinal wave in the liner from the lower portion of the more massive pump unit, which leads to significant neutralization of its axial vibrations. It is obvious that the greatest practical interest lies in the use of shorter liner lengths, i.e., liner lengths equal to one-quarter of the longitudinal wave length. Note that the liner assembly can include a filter, installed either at the top or bottom.

[0018] It is important to emphasize that, as numerical calculations have shown, when using liners with a wavelength multiple of half the longitudinal wavelength, a local resonance effect opposite to that described above occurs when the wave is reflected in the liner from the bottom of a massive pump unit, resulting in a slight increase (up to 10-15%) in the intensity of its oscillations. Therefore, it can be concluded that selecting a liner length equal to or close to one-quarter the wavelength with the maximum oscillation amplitude, despite a possible, but significantly smaller, increase in the intensity of longitudinal oscillations at other frequencies, will generally lead to a decrease in the overall oscillation intensity. The frequency of longitudinal oscillations with maximum amplitude during pump unit operation should be determined based on the results of bench or field studies of the amplitude-frequency characteristics of axial vibrations developing during the operation of this unit.

[0019] It should be noted that the results of the conducted studies cannot be directly applied to describing the propagation characteristics of shear waves in the assembly. This is because this process is mathematically described by differential equations of a higher order than the wave equation presented above. As shown in the monograph (Rabotnov Yu.N. Mechanics of a Deformable Solid Body. Moscow: Nauka, 1979. - 744 p.), the velocity of a traveling shear wave in rods or hollow cylinders depends both on the frequency of this wave and on their cross-sectional area, which, for an assembly consisting of a pump unit and tubing of different diameters, is a parameter that varies significantly along the assembly. It follows that, in the case of shear waves, determining the optimal liner length with an accuracy acceptable for quantitative assessments for actually used assemblies is practically impossible.At the same time, it can be expected that the tailpiece placed under the pumping unit will provide a certain resistance to the displacement of the pumping unit in the transverse direction, that is, reduce the intensity of its transverse vibrations.

[0020] Thus, based on the results of the studies conducted, the claimed downhole device can be described as follows.

[0021] A downhole device for reducing the intensity of axial vibrations in electric-driven centrifugal pumps, comprising a submersible portion of the electric-driven centrifugal pump unit, a tubing string and a shank placed under the pump unit, characterized in that the shank has a length equal to one-quarter of the length of a longitudinal elastic wave propagating along the assembly of the electric-driven centrifugal pump and the tubing string with a frequency equal to the frequency of axial vibrations in the operating pump unit, at which the amplitude of these vibrations is maximum.

[0022] Example of application of the claimed downhole device

[0023] Based on bench and field studies, it was established that the primary frequency of axial vibrations during ESP use in production wells at this field, leading to accelerated wear of the pumping equipment, is 50 Hz. This means that the corresponding longitudinal wave length in the assembly is 102 m (5100 m : 50). Therefore, the optimal length of the liner placed under the pumping unit is selected equal to one-quarter of the longitudinal wave length, or 25.5 m.

[0024] A 25.5-meter-long tubing liner of any diameter is installed in the submersible section of the ESP unit beneath the pump unit. This arrangement effectively reduces the intensity of axial vibrations that develop during pump operation.

[0025] The use of the claimed device will increase the service life of ESPs used in the operation of oil wells.

Claims

A downhole device for reducing the intensity of axial vibrations in electrically driven centrifugal pumps, comprising a submersible portion of the electrically driven centrifugal pump unit, a tubing string and a shank placed under the pump unit, characterized in that the shank has a length equal to one-quarter of the length of a longitudinal elastic wave propagating along the assembly of the electrically driven centrifugal pump and the tubing string with a frequency equal to the frequency of axial vibrations in the operating pump unit, at which the amplitude of these vibrations is maximum.

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